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A covariance structure analysis of flicker sensitivity
Abstract
We tested whether linear structural models of the mechanisms underlying flicker sensitivity could reproduce the variance-covariance matrix of temporal contrast sensitivity data. Monocular sensitivities to frequencies between 2.5 and 45 Hz were measured for 124 subjects, ages 18-88 yr. Exploratory factor analyses revealed that both a two-mechanism and a three-mechanism model could adequately account for the data. Furthermore, confirmatory factor analyses and full structural equation models, using age as an explanatory variable, supported both models, with the three-factor model giving a somewhat better representation of the data. Parsimony favors the two-mechanism model. But patterns of loss associated with pre-exudative age-related maculopathy are more easily understood in terms of three underlying mechanisms.
... Methodology from psychometrics and mathematical psychology, like factor analysis and structural modeling (Bentler 1980;Gorsuch 1983;Harris 1985;Rindskopf 1981), was adopted by vision researchers to probe the number and tuning of psychophysical channels or physiological mechanism active under particular conditions. Often this yielded intriguing results (e.g., Sekuler et al. 1984;Peterzell andTeller 1996, 2000;Peterzell et al. 1993Peterzell et al. , 1995Mayer et al. 1995;Scialfa et al. 2002;Dobkins et al. 2000;Guth and Lodge 1973;Dobkins 2002, 2003;Romney et al. 2005;Webster and MacLeod 1988;Webster et al. 2000aWebster et al. , b, 2002Young 1986;Emery et al. 2016); for a brief overview, see the Appendix. However, this review is not about such successful studies of individual variation. ...
... More recently, the discovery of multiple parallel visual channels raised the possibility that information about the underlying mechanisms might be encoded in the variance/covariance structure of human vision measured under conditions that differentially tap these channels. Thus, several studies attempt to infer the number and tuning of spatial and temporal frequency channels from contrast sensitivity data in many observers (Sekuler et al. 1983;Peterzell and Kelly 1997;Peterzell andTeller 1996, 2000;Peterzell et al. 1993Peterzell et al. , 1995Mayer et al. 1995;Simpson and McFadden 2005). For an example of such data, see Table 2 (from Billock and Harding 1996). ...
... For large numbers of observers, structural modeling and factor analysis can be used to create sensible multichannel models of visual modalities (e.g., Sekular et al. 1984;Peterzell 2016;Peterzell et al. 1993Peterzell et al. , 1995Mayer et al. 1995;Scialfa et al. 2002). Similarly, several studies of individual variation in color vision or chromatic neural response yielded useful results (Bosten et al. 2014;Dobkins et al. 2000;Emery et al. 2016;Guth and Lodge 1973;Dobkins 2002, 2003;Read et al. 2016;Romney et al. 2005;Webster and MacLeod 1988;Webster et al. 2000aWebster et al. , b, 2002Young 1986). ...
In both theory and practice, individual behavioral differences can reveal details of underlying neural mechanisms, and this has been widely exploited in experimental psychology. However, under some circumstances, individual differences are conspicuous by their absence. Three illuminating examples are treated in this theoretical review: (1) In color vision, there is a surprising lack of variation in red–green color opponency, especially as studied using unique hues, given the huge variation of L:M-cone ratios in normal observers. (2) Conversely, in achromatic vision, individual differences in L:M-cone ratios can be studied by measuring spectral sensitivity (luminance efficiency) functions. However, contrary to reasonable expectations, parvo and magno mechanisms can give rise to indistinguishable spectral sensitivity functions, so individual variations in parvo and magno activation often cannot be studied via spectral sensitivity. (3) Similar convergences occur in neuroscience: in simulated and actual neuronal networks and in electrophysiological/functional imaging studies of intact animals/humans. Neuronal systems trained or developed to do the same tasks need not wind up with the same wiring or the exact same behavior. However, under some circumstances, their behaviors can become functionally similar. Markedly different neural mechanisms somehow yield similar behaviors, a result found in systems as different as motor behaviors in crustaceans and sensory behaviors in humans. Theoretically, similar neural mechanisms can result from different neural combinations, a response convergence which limits our ability to infer the origins of some perceptual channels. When expected individual differences do not manifest, this is a clue that something interesting is happening and a goad to further investigation.
... When testing multiple observers, there are often identifiable patterns of systematic variation that arise from differences regarding optical, neural, and cognitive processes (Mollon et al., 2017;Peterzell, 2016). This individual differences approach has been used to study the temporal mechanisms underlying the first-order system (Billock & Harding, 1996;Dobkins et al., 2000;Mayer et al., 1995;Peterzell et al., 1997). In general, those individual differences studies suggest the existence of two to three temporal mechanisms, in agreement with previous psychophysical evidence (Hess & Snowden, 1992;Mandler & Makous, 1984;Waugh & Hess, 1994). ...
... This study aimed to test the existence of different temporal frequency mechanisms underlying frontoparallel stereomotion. This individual differences approach has been used to study the temporal mechanisms underlying the first-order system suggesting the existence of two to three temporal mechanisms (Billock & Harding, 1996;Dobkins et al., 2000;Mayer et al., 1995;Peterzell et al., 1997), in agreement with previous psychophysical evidence (Hess & Snowden, 1992;Mandler & Makous, 1984;Waugh & Hess, 1994). This approach has also been used to study the spatial-frequency selectivity in stereovision Reynaud & Hess, 2017) suggesting the existence of at least two spatial-frequency mechanisms in agreement with masking experiments and detection/discrimination experiments (Serrano-Pedraza et al., 2013;Witz & Hess, 2013). ...
Masking experiments, using vertical and horizontal sinusoidal depth corrugations, have suggested the existence of more than two spatial‐frequency disparity mechanisms. This result was confirmed through an individual differences approach. Here, using factor analytic techniques, we want to investigate the existence of independent temporal mechanisms in frontoparallel stereoscopic (cyclopean) motion. To construct stereomotion, we used sinusoidal depth corrugations obtained with dynamic random‐dot stereograms. Thus, no luminance motion was present monocularly. We measured disparity thresholds for drifting vertical (up‐down) and horizontal (left‐right) sinusoidal corrugations of 0.4 cyc/deg at 0.25, 0.5, 1, 2, 4, 6, and 8 Hz. In total, we tested 34 participants. Results showed a small orientation anisotropy with lower thresholds for horizontal corrugations. Disparity thresholds as a function of temporal frequency were almost constant from 0.25 up to 1 Hz, and then they increased monotonically. Principal component analysis uncovered two significant factors for vertical and two for horizontal corrugations. Varimax rotation showed that one factor loaded from 0.25 to 1–2 Hz and a second factor from 2 to 4 to 8 Hz. Direct Oblimin rotation indicated a moderate intercorrelation of both factors. Our results suggest the possible existence of two somewhat interdependent temporal mechanisms involved in frontoparallel stereomotion.
... When it comes to the study of spatiotemporal frequency tuned mechanisms, a structure of mechanisms tuned in spatial and temporal frequency has been able to be discerned (Billock & Harding, 1996. See also Strasburger, Murray, & Remky, 1993;Mayer, Dougherty, & Hu, 1995;Peterzell, Dougherty, & Mayer, 1997;Dobkins, Gunther, & Peterzell, 2000 for temporal mechanisms. See Peterzell, 2016 for a review). ...
... indices of neural processing) for the 2 Hz and 8 Hz data in Fig. 9, and further, by the high cross-condition correlations seen in this experiment. In this line, it is relevant to note that other authors employing an individual differences approach found that temporal sensitivity functions had two and even three factors, one of them operating at all temporal frequencies below 8-12 Hz and the rest operating at frequencies above (Mayer et al., 1995;Peterzell et al., 1997;Dobkins et al., 2000). This may explain the high cross-condition correlations seen between 2 Hz and 8 Hz (both probably included within the same temporal mechanism or both being activated by two very broad temporal mechanisms, Anderson & Burr, 1985). ...
The study of motion perception through classical psychophysical methods has suggested that independent spatiotemporal filters acting over specific locations in retinal images carry out early motion processing. On the other hand, individual differences approaches have been able to identify a structure of spatiotemporal filters too. In this same fashion—through an individual differences approach—the present study aims to uncover a structure of spatiotemporal frequency selective motion mechanisms. This is done, for the first time, using supra-threshold contrast stimuli in a motion direction discrimination task. Two experiments were performed measuring duration thresholds for drifting 2D Gabor gratings of 0.25, 0.5, 0.75, 1, 1.5, 2, 3 and 6 c/deg. They moved with a speed of 2 deg/sec, with Michelson contrasts of 0.1 or 0.9 (Experiment 1) or had a contrast of 0.9 drifting with a temporal frequency of 2 Hz or 8 Hz (Experiment 2). Principal component analyses uncover three factors in each of four conditions. When Varimax-rotated, these are seen to be selective to spatial frequencies lower than 0.5 c/deg, intermediate ones from 0.5 to 1–1.5 c/deg, and frequencies greater than 1–1.5 c/deg. Direct Oblimin rotations indicate that factors are moderately correlated. Further analyses show very slight differences in the correlational structures between contrast conditions (0.1 vs. 0.9), and no differences between temporal frequency conditions (2 Hz vs. 8 Hz). To conclude, the idea of a three-factor structure in motion processing for low, intermediate, and high spatial frequencies is supported.
... In the χ 2 distribution, the null hypothesis, that "the composed path diagram is correct" was rejected. Although these results rejected the null hypothesis, we recommend that the model fitness be not judged based on the χ 2 value, which is sensitive to the number of data (Toyoda, 2014). This investigation included 220 counts of data. ...
... and AGFI = .828, both of which were lower than the recommended .9. GFI, AGFI, and CFI > .9 are considered a satisfactory fit (even >.95 for CFI), RMSEA <.5 is considered a good fit, and ≥.1 is considered a poor fit (Toyoda, 2014). However, it was considered to be within the acceptable range considering that CFI was <.95 but ≥.9, and RMSEA was not >.1, which would be considered a poor fit. ...
Aim:
The purpose of this study was to develop a scale to assess daily time management capabilities among working patients with diabetes and to test this scale's reliability and validity.
Methods:
A self-administered questionnaire survey was conducted among 277 diabetes outpatients, and data from 220 participants (mean age = 54.3 ± 10.2 years, 76.8% male) were analyzed. Questionnaire items were selected through exploratory factor analysis. During the process of developing the questionnaire, opinions were solicited from experts on education for patients with diabetes, and Cronbach's α was calculated as a coefficient of reliability. Correlations with the Instrument of Diabetes Self-Care Agency (IDSCA) were examined and confirmatory factor analysis was performed to check for validity.
Results:
Adequacy of a 4-factor, 16-item scale was confirmed. Cronbach's α coefficient was ≥.7 for the entire scale and for the subscale items. There was a significant correlation between total IDSCA scores and various factors (r = .280-.469). However, there was no correlation between the "adjustment of life rhythms" and parts of the IDSCA subscale.
Conclusion:
Although some aspects warrant further investigation, the developed scale provides a reliable and valid means of assessing daily time management capabilities among working patients with diabetes, and can thus be applied to help diabetes patients to manage their daily lives.
... The correlation is obtained from the covariance. When two data sets X, Y are given as (X, Y ) = (x 1 , y 1 ), (x 2 , y 2 ), ..., (x n , y n ), the covariance can be calculated in Eq. (1) [12]. ...
... R represents a correlation matrix between explanatory variables. For more detail on how to calculate, refer to [2], [12], [13]. ...
... where f i indicates the value of latent factor. By definition [16], the variance of f i is assumed to be 1, and the average of f i is Fig. 2. Evaluation of the model adaptability to be 0. a i represents the regression coefficient which indicates the degree of correlation. e i is an independent constant value that is regarded as an error. ...
... according to Eq. (1), which is the same formula with the variance of f i [16]. Therefore, we can obtain simultaneous equations as follows. ...
... This result is a bit surprising because contrast sensitivity has been shown to worsen with age (e.g. Tyler, 1989; Mayer, Dougherty & Hu, 1995; Knoblauch, Barbur & Vital-Durand, 1995, and see Werner et al., 1990 for a review). In summary, the results from our analysis of age show moderate effects on performance, with the strongest (and least surprising) effects of age seen for G/R-EQUIL data. ...
... With respect to temporal channels for luminance detection, results from masking, summation and temporal frequency discrimination paradigms point to the existence of two to four temporal-frequency-tuned channels (King-Smith & Kulikowski, 1975; Tyler, 1975; Mandler & Makous, 1984; Moulden, Renshaw & Mather, 1984; Anderson & Burr, 1985; Lehky, 1985; Tyler, 1989; Hammett & Smith, 1992; Hess & Snowden, 1992; Metha & Mullen, 1996). In addition, results from previous studies employing factor analyses on luminance contrast sensitivity data also suggest the existence of two to three temporal channels (Mayer et al., 1995; Billock & Harding, 1996; Peterzell, Dougherty & Billock, 1996a; Peterzell, Kelly, Chang, Gordon, Omaljev & Teller, 1996b; Peterzell, Chang, Kelly, Hartzler & Teller, 1997a; Peterzell, Dougherty & Mayer, 1997b). In the present study, our factor analyses revealed two temporal factors underlying luminance contrast detection (one loading onto 2–8 Hz, the other loading onto 8–16 Hz, seeFig. ...
In order to investigate the mechanisms underlying green/red equiluminance matches in human observers and their relationship to mechanisms subserving luminance and/or chromatic (green/red) contrast sensitivity, we tested 21 human subjects along these dimensions at 16 different spatial and temporal frequencies (spatial frequency, 0.25-2 c/deg; temporal frequency, 2-16 Hz) and applied factor analysis to extract mechanisms underlying the data set. The results from our factor analysis revealed separate sources of variability for green/red equiluminance, luminance sensitivity and chromatic sensitivity, thus suggesting separate mechanisms underlying each of the three main conditions. When factor analysis was applied separately to green/red equiluminance data, two temporally-tuned factors were revealed (factor 1, 2-4 Hz; factor 2, 8-16 Hz), suggesting the existence of separate mechanisms underlying equiluminance settings at low versus high temporal frequencies. In addition, although the three main conditions remained separate in our factor analysis of the entire data set, our correlation matrix nonetheless revealed systematic correlations between equiluminance settings and luminance sensitivity at high temporal frequencies, and between equiluminance settings and chromatic sensitivity at low temporal frequencies. Taken together, these data suggest that the high temporal frequency factor underlying green/red equiluminance is governed predominantly by luminance mechanisms, while the low temporal frequency factor receives contribution from chromatic mechanisms.
... 14,15 An individual's visibility threshold for flicker measured by the critical flicker frequency (CFF) has been used in the study of the stroboscopic effect as a physiological measure of visual fatigue to analyse visual performance during tasks, although it varied with individual differences and certain external conditions. 16 In summary, workers who are suffering from physiological discomfort (visual fatigue, musculoskeletal disorders and stress) spend most of their working hours in offices today. 8 There are already several studies showing that physical symptoms are related to the luminous environment of offices. ...
... 14,15 An individual's visibility threshold for flicker measured by the critical flicker frequency (CFF) has been used in the study of the stroboscopic effect as a physiological measure of visual fatigue to analyse visual performance during tasks, although it varied with individual differences and certain external conditions. 16 In summary, workers who are suffering from physiological discomfort (visual fatigue, musculoskeletal disorders and stress) spend most of their working hours in offices today. 8 There are already several studies showing that physical symptoms are related to the luminous environment of offices. ...
The stroboscopic effect from LED light sources can become considerable in working environments. Therefore, this study aims to explore the short-term health effect of a temporal light artefact. The experiment was carried out featuring 10 university students. Three frequencies and three modulation depths were assessed. Psychological reaction was evaluated through subjective scales, while physiological parameters were also collected for mutual validation and analysis. It was found that when the conditions are in the high-risk zone defined by IEEE Standard 1789-2015, subjects considered these conditions to be unacceptable and reported discrete spatial movement and higher visual fatigue levels. Supported by psychological and physiological evidence, it is suggested that such fatigue is caused by a higher chance of flicker. Invisible flicker also significantly affected alpha and beta wave power density, suggesting that a strobe of low frequency could potentially decrease drowsiness and increase cortical arousal. Some limitations to the work performance of this study are also discussed.
... The factor analytic approach has been used in previous studies to elucidate temporal processes in data (Billock & Harding, 1996;Dobkins, Gunther, & Peterzell, 2000;Peterzell, 1993;Peterzell, Dougherty, & Mayer, 1997;Strasburger, Murray, & Remky, 1993), and chromatic processes in data (Burt, 1940(Burt, , 1946Dobkins et al., 2000;Emery, Volbrecht, Peterzell, & Webster, 2017a, 2017b, 2017cGunther & Dobkins, 2003;Hamer, et al., 2016;Jones & Jones, 1950;Mayer, Dougherty & Hu, 1995;Peterzell, 2011;Peterzell, Chang, & Teller, 2000;Peterzell, Chang, Kelly, Hartzler & Teller, 1997;Peterzell et al., , 2016Pickford, 1951;. (See also Bosten & Mollon, 2010). ...
In classic simultaneous color contrast and simultaneous brightness contrast, the color or brightness of a stimulus appears to shift toward the complementary (opposite) color or brightness of its surrounding region. Kaneko and colleagues proposed that simultaneous contrast involves separate “fast” and “slow” mechanisms, with stronger induction effects for fast than slow. Support for the model came from a diverse series of experiments showing that induction by surrounds varying in luminance or color was stronger for brief than long presentation times (10–40 vs. 80–640 ms). Here, to further examine possible underlying processes, we reanalyzed 12 separate small data sets from these studies using correlational and factor analytic techniques. For each analysis, a principal component analysis of induction strength revealed two factors, with one Varimax-rotated factor accounting for brief and one for long durations. In simultaneous brightness experiments, separate factor pairs were obtained for luminance increments and decrements. Despite being based on small sample sizes, the two-factor consistency among 12 analyses would not be expected by chance. The results are consistent with separate fast and slow processes mediating simultaneous contrast for brief and long flashes.
... The rationale is that the correlation in detection thresholds for pairs of stimuli should be higher for stimuli detected by the same mechanism than for stimuli detected by different mechanisms (Owsley et al., 1983;Sekuler et al., 1984;Billock and Harding, 1996). Hence by looking at the inter-correlations between individuals' sensitivity at neighboring frequencies, one is able to determine the presence of frequency channels (Mayer et al., 1995;Billock and Harding, 1996;Peterzell and Teller, 2000;Simpson and McFadden, 2005;Rosli et al., 2009). Therefore, a factor analysis of the dataset consisting of a principal component analysis (PCA) and a rotation of the factors in order to determine a simple structure can characterize the tuning curves of the channels (Simpson and McFadden, 2005). ...
It has been suggested that at least two mechanisms mediate disparity processing, one for coarse and one for fine disparities. Here we analyze individual differences in our previously measured normative dataset on the disparity sensitivity as a function of spatial frequency of 61 observers to assess the tuning of the spatial frequency channels underlying disparity sensitivity for oblique corrugations (Reynaud et al., 2015). Inter-correlations and factor analysis of the population data revealed two spatial frequency channels for disparity sensitivity: one tuned to high spatial frequencies and one tuned to low spatial frequencies. Our results confirm that disparity is encoded by spatial frequency channels of different sensitivities tuned to different ranges of corrugation frequencies.
... In summary, common factors play a crucial role in science and everyday life. Previously it was shown that there is little evidence for common factors in healthy vision (Bosten & Mollon, 2010;Cappe et al., 2014;Coren & Girgus, 1972;Mayer, Dougherty, & Hu, 1995;Peterzell, Werner, & Kaplan, 1993Peterzell & Teller, 1996. Here, we have shown that there is very little evidence for common factors for visual illusions. ...
In cognition, audition, and somatosensation, performance strongly correlates between different paradigms, which suggests the existence of common factors. In contrast, visual performance in seemingly very similar tasks, such as visual and bisection acuity, are hardly related, i.e., pairwise correlations between performance levels are low even though test-retest reliability is high. Here we show similar results for visual illusions. Consistent with previous findings, we found significant correlations between the illusion magnitude of the Ebbinghaus and Ponzo illusions, but this relationship was the only significant correlation out of 15 further comparisons. Similarly, we found a significant link for the Ponzo illusion with both mental imagery and cognitive disorganization. However, most other correlations between illusions and personality were not significant. The findings suggest that vision is highly specific, i.e., there is no common factor. While this proposal does not exclude strong and stable associations between certain illusions and between certain illusions and personality traits, these associations seem to be the exception rather than the rule.
... For each SEM, we fitted with robust maximum likelihood method using the R package lavaan (Rosseel 2012). The goodness fit of each model was evaluated with the chi-square test, and the comparative fit index (CFI): chi-square values higher than 0.05, and CFI higher than 0.90 indicate a good fit between the SEM model and observed data (Grace et al. 2012, Toyoda 2014. We deleted each path to examine its effect on the model fit, and paths were retained if their deletion caused lack-of-fit. ...
Increased ungulate browsing has altered the composition of plant communities and food webs of forest ecosystems in many regions around the world. To evaluate the cascading impact of deer browsing on pollination and plant reproduction is critical to understand the roles of species interactions in maintaining plant populations and for conservation management. In this study, we investigated the relationships among floral resources of understory herbaceous plants, pollinator visitation, and fruit set of shrub species based on data accumulation over three years in six temperate deciduous forests with deer and without deer.We found that in deer browsed sites, the visitation rate of bumblebees had decreased due to severe reduction in the coverage of autumn-flowering herbaceous plants, while the effect varied between bumblebee species. On the other hand, other insect taxa showed no dependence on variation in autumn floral resources. The two genera of bumblebee-pollinated shrubs showed reduced fruit set due to severe decline in autumn-flowering herbaceous plants and bumblebee visitation (Weigela: 18.5% and Rhododendron: 21.9%). In contrast, the fruit set of shrubs pollinated by insects that did not show dependence on autumn floral resources were not negatively affected by deer browsing. Our results suggest that deer browsing have not only caused negative effects on herbaceous plants, but in addition have negative indirect effects on reproduction of woody plants through cascading effects of pollination linkages.
... Classical evidence for the existence of spatial channels comes from a variety of psychophysical paradigms, primarily masking, adaptation and summation at threshold (Graham, 1989). More recently, co6ariance structure analysis, a technique based on the analysis of individual differences, has been used to estimate the properties of spatiotemporal channels for the detection of luminance-modulated stimuli (Sekuler, Wilson & Owsley, 1984;Peterzell, Werner & Kaplan, 1991, 1993Strasburger, Murray & Remky, 1993;Mayer, Dougherty & Hu, 1995;Peterzell, Werner & Kaplan, 1995;Billock & Harding, 1996;Peterzell, Kelly, Chang, Gordon, Omaljev & Teller, 1996;Gunther, Peterzell & Dobkins, 1997;Peterzell, Chang, Kelly, Hartzler & Teller, 1997;Peterzell, Dougherty & Mayer, 1997;Gunther, Peterzell & Dobkins, 1998;see Peterzell & Teller, 1996 for a simple introduction). The term co6ariance channels will be used to describe the spatial channels estimated from the use of covariance structure analysis. ...
Purpose. The experiment investigated the spatial channels underlying chromatic CSFs, and their relationships to luminance CSFs, in adults and infants. Method. CSFs were measured in adults and in 2, 3.5, 5 and 8 month old infants, using luminance-modulated and isoluminant red-green gratings. At each age, 25 to 40 subjects provided complete data. Thresholds were estimated using swept-contrast VEP methodS (Kelly et al. ARVO 1995; Norcia et al. 1986). Subjects viewed sinewave gratings (0.3 to 8 c/deg) on a 20 deg field presented on a CRT. Gratings were counterphased at 12 reversals/sec (6 Hz). The 2 nd harmonic response was used to estimate thresholds. Results. We computed statistical "sources" of individual variability (or factors), then calculated the number, nature (discrete vs. continuous) and frequency tuning of factor-channels (see Peterzell et al. 1995). Color and luminance CSFs from adults each contained 3 spatial-frequency-tuned factor-channels, consistent with comparable psychophysical results. These factor-channels shifted upward in spatial frequency with age, with the largest shifts occurring between 2-3.5 months. Although the tuning of color and luminance channels differed, preliminary analyses indicate that both channel types shift at similar rates with age. Conclusions. The results provide new information about chromatic spatial channels and their development, and the relationships between chromatic and luminance spatial channels. Scale changes coincide with, and are probably determined by, developmental cone migration into the fovea and growth in eye size.
... This limen is however shown to fluctuate (a threshold shift) with age-related functional changes in human vision (Eisner, Fleming, Klein, & Mauldin, 1987;Mayer, Dougherty, & Hu, 1995). Given this, critical flicker fusion threshold has been used to measure age-related visual impairments (Vianya-Estopa, Douthwaite, Pesudovs, Noble & Elliott, 2004) and CNS alertness (Curran, 1990;Curran, Hindmarch, Wattis, & Shillingford, 1990), as well as sensory sensitivity (Clark, 1966) or response bias (Clark, Brown, & Rutschmann, 1967) in psychiatric patients. ...
This study renews the classical concept of subliminal perception (Peirce & Jastrow, 1884) by investigating the impact of subliminal flicker from fluorescent lighting on affect and cognitive performance. It was predicted that low compared to high frequency lighting (latter compared to former emits non-flickering light) would evoke larger changes in affective states and also impair cognitive performance. Subjects reported high rather than low frequency lighting to be more pleasant, which, in turn, enhanced their problem solving performance. This suggests that sensory processing can take place outside of conscious awareness resulting in conscious emotional consequences; indicating a role of affect in subliminal/implicit perception, and that positive affect may facilitate cognitive task performance.
... The statistical technique used by Peterzell and colleagues to characterize their results is factor analysis. Several other researchers have used latent variable modeling techniques to isolate contrast sensitivity mechanisms (Dobkins et al, 2000; Billock & Harding, 1996; Mayer et al., 1995; Sekuler et al, 1984). Such methods have also contributed to our knowledge of the functional organization of color vision (Bimler, Kirkland & Jameson, 2004; Gunther & Dobkins, 2003; Burt, 1949; Jones, 1948) and motion perception (Morrone et al, 1999). ...
This paper is a call for greater use of individual differences in the basic science of visual perception. Individual differences yield insights into visual perception's functional organization, underlying biological/environmental mechanisms, and utility. I first explain the general approach advocated and where it comes from. Second, I describe five principles central to learning about the nature of visual perception through individual differences. Third, I elaborate on the use of individual differences to gain insights into the three areas mentioned above (function, biology/environment, utility), in each case describing the approach advocated, presenting model examples from the literature, and laying out illustrative research proposals for the case of stereopsis.
... It is also possible that the method could be used in place of, or as a supplement to, traditional confirmatory factor analysis techniques. Factor analysis of sensory data has proven useful (Sekuler et al. 1984;Webster & MacLeod, 1988;Peterzell et al. 1993;Mayer, Dougherty & Hu, 1995), however, to achieve stable results, factor analysis generally requires many observers, because the accuracy of each correlation coefficient is important to the analysis. By examining the overall structure of the correlation matrix, rather than each correlation coefficient, conclusions may be drawn from fewer observers. ...
1. The statistical correlation of detection thresholds for pairs of stimuli should be higher for stimuli detected by the same mechanism than for stimuli detected by different mechanisms--a property that can be used to probe the visual mechanisms that underlie detection. 2. Correlation of contrast sensitivities for pairs of spatiotemporal stimuli is approximately a linear function of spatial or temporal frequency separation in octaves. Using the slope of this function as an index of neural processing gave results consistent with: more spatial mechanisms than temporal; more spatial mechanisms at low temporal frequencies than at high; and at least two temporal mechanisms active at spatial frequencies up to 22.6 cycles deg-1. 3. This method of analysing sensitivity data is insensitive to experimental conditions and applicable to any sensory detection task mediated by tuned channels. In addition to being applicable to psychophysical sensitivity measurements, it may also be useful in analysing some kinds of electrophysiological measurements that pool the responses from many active mechanisms (such as evoked potentials).
... lens and macular pigment density; rod intrusion), quantified relative contributions to color matching, and estimated cone absorption spectra ( ). It has also provided estimates of the spatiotemporal channels underlying the detection of luminance contrast, and of the tuning of spatial and temporal frequency channels in adults and infants (Sekuler et al., 1984; Peterzell, Werner & Kaplan, 1991; Strasburger, Murray & Remky, 1993; Peterzell et al., 1993 Peterzell et al., , 1995 Mayer, Dougherty & Hu, 1995; Billock & Harding, 1996; Peterzell, Kelly, Chang, Gordon, Omaljev & Teller, 1996; Peterzell, Dougherty & Mayer, 1997; Peterzell & Kelly, 1997; Gunther, Peterzell & Dobkins, 1997 Dobkins, Gunther & Peterzell, 2000). The visual channels derived using individual differences have, until now, generally appeared to be similar to those obtained using other methods. ...
This study concerns the spatial-frequency-tuned channels underlying infants' contrast sensitivity functions (CSFs) for red-green chromatic stimuli, and their relationship to the channels underlying infants' CSFs for luminance-modulated stimuli. Behavioral (forced-choice preferential-looking) techniques and stationary stimuli were used. In experiment 1. contrast thresholds were measured in 4- and 6-month-olds, using isoluminant red-green gratings with spatial frequencies ranging from 0.27 to 1.53 c deg. In experiment 2. contrast thresholds were measured in 4-month-olds. using both red-green and luminance-modulated gratings in the same low spatial frequency range. Covariance analyses of individual differences were performed. Experiment 1 revealed one dominant covariance channel for the detection of red-green gratings, with a second channel contributing to detection of the highest spatial frequencies used. Experiment 2 revealed two to three channels serving color and luminance: but surprisingly these channels were not statistically separable for luminance versus chromatic stimuli. Thus, covariance channels for color and luminance that are independent for adults [Peterzell & Teller (2000). Spatial frequency tuned covariance channels for red-green and luminance-modulated gratings: psychophysical data from human adults. Vision Research, 40, 417-430] are apparently interdependent in infants. These data suggest that for infants, detection thresholds for chromatic and luminance-modulated stimuli may be limited by common mechanisms.
... In order to maximize the number of zero or near zero factor loadings, the orthogonal factors resulting from the PCA were rotated to Ôsimple structureÕ using the Varimax criterion (Kaiser, 1958 ), and then further rotated obliquely. Note that the oblique rotation (commonly used in studies of this sort, e.g., Mayer, Dougherty, & Hu, 1995; Dobkins et al., 2000; Peterzell & Teller, 2000 ) allows for some degree of intercorrelation between factors, which may arise from (1) variation in subjectsÕ overall performance due to cognitive factors (such as attention or motivation) or (2) actual intercorrelation between neural mechanisms underlying the separate factors (e.g., postreceptoral mechanisms could be correlated because they share cone inputs). Either way, the important point is that the factors pulled out in our analyses are meant to reveal regions of color space that are least correlated with (i.e., most independent of) one another. ...
Many previous studies employing paradigms such as adaptation, masking and summation-near-threshold have demonstrated the existence of separate mechanisms underlying the detection of the three cardinal axes of color space: L+M, L-M and S-(L+M). In addition, some studies have demonstrated the existence of higher-order mechanisms tuned to non-cardinal axes (which are made up of combinations of the cardinal axes). In order to address the issue of separate and independent color mechanisms further, here we applied factor analysis to contrast threshold data obtained from 41 subjects for nine different axes in color space (the three cardinal axes and the six non-cardinal axes midway between). In line with previous studies, the results of a three-factor analysis performed on contrast thresholds for the cardinal axes revealed independence across the three. However, in some of our factor analyses (for example, when a two-factor analysis was performed on the cardinal axes), intercorrelation was observed between L-M and S-(L+M) stimuli. With regard to higher-order mechanisms, our factor analyses revealed mechanisms selective for non-cardinal axes within the (L-M)/(L+M) and (S-(L+M))/(L+M) color planes, but not the (L-M)/(S-(L+M)) color plane. To ensure that the intercorrelation observed between L-M and S-(L+M) cardinal axes was not due to the particular stimulus parameters or testing measures employed, in three of our subjects we performed a "summation-near-threshold" experiment using experimental conditions nearly identical to those in the factor analysis experiments. In accordance with previous findings [Vision Research 39 (1999) 733], L-M and S-(L+M) stimuli were found to be separable in this analysis. This seeming discrepancy between the results of our factor analysis and those obtained from paradigms such as summation-near-threshold can be resolved by proposing that the mechanisms underlying detection of L-M and S-(L+M) stimuli are separable (as defined by the ability to isolate activity within each mechanism using select stimuli), yet nonetheless intercorrelated. Such intercorrelation could arise if these two mechanisms are limited by the same source of variability and/or subject to the same gain control.
The human visual system's sensitivity to flicker, and the processes underlying this sensitivity, are generally understood. The system's sensitivity to flicker is described by a bandbass function that varies with flicker rate (de Lange, 1958a, b). The processes underlying the de Lange function include narrowly tuned bandpass channels that combine to determine sensitivity.
The processes underlying the contrast senstivity functions (CSFs) of human adults are generally understood. Multiple spatial channels, selective for spatial frequency, have been found using sinewave gratings (Graham, 1989; De Valois & De Valois, 1988).
Virus infections remain a problem for the PC owner. Despite receiving instructions on how to fix the virus and warnings about the dangers of not doing so, there are many cases where owners are still not taking the required recovery action. Research on individual behavior and decision-making in a virus-infection situation is important for developing protection systems for information security. This paper describes a threat appeals model for information security based on collective protection motivation theory. The analytical results obtained using this model are also discussed. Our results show that the response efficacy for the Japanese Students is effective in persuading a person to initiate protection measures. And the results also indicate that a trustworthy source of media for providing the security information is necessary to realize a protection measure for Australia students.
This study concerns the spatial-frequency-tuned channels underlying:infants' contrast sensitivity functions (CSFs) for red-green chromatic stimuli, and their relationship to the channels underlying infants' CSFs for luminance-modulated stimuli. Behavioral (forced-choice preferential-looking) techniques and stationary stimuli were used. In experiment 1, contrast thresholds were measured in 4- and 6-month-olds, using isoluminant red-green gratings with spatial frequencies ranging from 0.27 to 1.53 c/deg. In experiment 2, contrast thresholds were measured in 4-month-olds, using both red-green and luminance-modulated gratings in the same low spatial frequency range. Covariance analyses of individual differences were performed. Experiment 1 revealed one dominant covariance channel for the detection of red-green gratings, with a second channel contributing to detection of the highest spatial frequencies used. Experiment 2 revealed two to three channels serving color and luminance; but surprisingly these channels:were not statistically separable for luminance versus chromatic stimuli. Thus, covariance channels for color and luminance that are independent for adults [Peterzell & Teller (2000). Spatial frequency tuned covariance channels for red-green and luminance-modulated gratings: psychophysical data from human adults. Vision Research, 40, 417-430] are apparently interdependent in infants. These data suggest that for infants, defection thresholds for chromatic and luminance-modulated stimuli may be limited by common mechanisms.
Abstract Structural equation modeling (SEM) is a modeling framework that encompasses many types of statistical models and can accommodate a variety of estimation and testing methods. SEM has been used primarily in social sciences but is increasingly used in epidemiology, public health, and the medical sciences. SEM provides many advantages for the analysis of survey and clinical data, including the ability to model latent constructs that may not be directly observable. Another major feature is simultaneous estimation of parameters in systems of equations that may include mediated relationships, correlated dependent variables, and in some instances feedback relationships. SEM allows for the specification of theoretically holistic models because multiple and varied relationships may be estimated together in the same model. SEM has recently expanded by adding generalized linear modeling capabilities that include the simultaneous estimation of parameters of different functional form for outcomes with different distributions in the same model. Therefore, mortality modeling and other relevant health outcomes may be evaluated. Random effects estimation using latent variables has been advanced in the SEM literature and software. In addition, SEM software has increased estimation options. Therefore, modern SEM is quite general and includes model types frequently used by health researchers, including generalized linear modeling, mixed effects linear modeling, and population average modeling. This article does not present any new information. It is meant as an introduction to SEM and its uses in ocular and other health research.
Age-related macular degeneration (AMD), the late stage of age-related maculopathy (ARM), is the leading cause of blind registration in developed countries. The visual loss in AMD occurs due to dysfunction and death of photoreceptors (rods and cones) secondary to an atrophic or a neovascular event. The psychophysical tests of vision, which depend on the functional status of the photoreceptors, may detect subtle alterations in the macula before morphological fundus changes are apparent ophthalmoscopically, and before traditional measures of visual acuity exhibit deterioration, and may be a useful tool for assessing and monitoring patients with ARM. Furthermore, worsening of these visual functions over time may reflect disease progression, and some of these, alone or in combination with other parameters, may act as a prognostic indicator for identifying eyes at risk for developing neovascular AMD. Lastly, psychophysical tests often correlate with subjective and relatively undefined symptoms in patients with early ARM, and may reflect limitation of daily activities for ARM patients. However, clinical studies investigating psychophysical function have largely been cross-sectional in nature, with small sample sizes, and lack consistency in terms of the grading and classification of ARM. This article aims to comprehensively review the literature germane to psychophysical tests in ARM, and to furnish the reader with an insight into this complex area of research.
The number and nature of spatial channels tuned to low spatial frequencies in photopic vision was examined by measuring individual differences in the contrast sensitivity functions (CSFs) of seven visually normal adults. Stationary, 51 cd/m2, low spatial frequency sinusoidal gratings between 0.27 and 2.16 c/deg were used as stimuli. Correlational and factor analyses revealed that the set of CSFs contained only one statistical source of individual variability at spatial frequencies below 1 c/deg (tuned to a peak of about 0.8 c/deg), and a second source above 1 c/deg (tuned to about 1.4 c/deg). The sources ("factor-channels") mapped well onto the two coarsest spatial frequency channels from some existing computational models. The analysis was applied also to earlier data from 4-, 6- and 8-month-old infants, in which two sources of variability have been found below 1 c/deg [Peterzell, D. H., Werner, J. S. & Kaplan, P. S. (1995). Vision Research, 35, 961-980]. The combined results are consistent with the hypothesis that in photopic vision of the neonate, there are two channels with peak sensitivities below 1 c/deg, and that these channels shift their tuning from lower to higher spatial frequencies by about a factor of four during development.
We investigated the spatial frequency tuned channels underlying the contrast sensitivity functions (CSFs) of adults and infants. CSFs were measured in adults and in 8-, 14-, 20-, and 32-week-old infants, using the swept-contrast visual evoked potential (sweep-VEP). At each age, 8 to 21 subjects provided complete data. Subjects viewed achromatic sine wave gratings (0.3 to 8 c/deg) on a 20 degrees field presented on a CRT. Gratings were counterphased at 12 reversals/s (6 Hz). The second harmonic response was used to interpolate thresholds. We computed statistical "sources" of individual variability (or factors) underlying CSFs, then calculated the number, nature (discrete vs. continuous) and frequency tuning of "covariance" channels. CSFs from adults each contained three spatial frequency tuned covariance channels, consistent with psychophysical results spanning a similar spatial frequency range. Covariance channels in infants shifted upward in spatial frequency with age, with rapid shifts occurring between 8 and 14 weeks. The change in scale coincided with, and was probably determined by, developmental cone migration into the fovea and growth in eye size.
In working environments all over the world, fluorescent tubes are by far the dominating light source. Still, there have been very few studies on the impact of the non-visible flicker from fluorescent tubes. The purpose of the study was to compare the impact on subjective well-being, performance and physiological arousal of fluorescent light powered by conventional and high-frequency ballasts. Thirty-seven healthy males and females were subjected to either condition in a laboratory office on two separate occasions with 1 week in between. Although the methodology was quite extensive, only a few general effects were observed. However, when the light was powered by the conventional ballasts, individuals with high critical flicker fusion frequency (CFF) responded with a pronounced attenuation of EEG alpha waves, and an increase in speed and decrease in accuracy of performance. These results may be understood in terms of heightened arousal in the central nervous system in response to the pronounced light modulation caused by the conventional ballasts. In order to alleviate this potential stress source, it is recommended that fluorescent lighting be powered by electronic high-frequency ballasts of good quality.
Visual detection and discrimination thresholds are often measured using adaptive staircases, and most studies use transformed (or weighted) up/down methods with fixed step sizes--in the spirit of Wetherill and Levitt (Br J Mathemat Statist Psychol 1965;18:1-10) or Kaernbach (Percept Psychophys 1991;49:227-229)--instead of changing step size at each trial in accordance with best-placement rules--in the spirit of Watson and Pelli (Percept Psychophys 1983;47:87-91). It is generally assumed that a fixed-step-size (FSS) staircase converges on the stimulus level at which a correct response occurs with the probabilities derived by Wetherill and Levitt or Kaernbach, but this has never been proved rigorously. This work used simulation techniques to determine the asymptotic and small-sample convergence of FSS staircases as a function of such parameters as the up/down rule, the size of the steps up or down, the starting stimulus level, or the spread of the psychometric function. The results showed that the asymptotic convergence of FSS staircases depends much more on the sizes of the steps than it does on the up/down rule. Yet, if the size delta+ of a step up differs from the size delta- of a step down in a way that the ratio delta-/delta+ is constant at a specific value that changes with up/down rule, then convergence percent-correct is unaffected by the absolute sizes of the steps. For use with the popular one-, two-, three- and four-down/one-up rules, these ratios must respectively be set at 0.2845, 0.5488, 0.7393 and 0.8415, rendering staircases that converge on the 77.85%-, 80.35%-, 83.15%- and 85.84%-correct points. Wetherill and Levitt's transformed up/down rules--which require delta-/delta+ = 1--and the general version of Kaernbach's weighted up/down rule--which allows any delta-/delta+ ratio--fail to reach their presumed targets. The small-sample study showed that, even with the optimal settings, short FSS staircases (up to 20 reversals in length) are subject to some bias, and their precision is less than reasonable, but their characteristics improve when the size delta+ of a step up is larger than half the spread of the psychometric function. Practical recommendations are given for the design of efficient and trustworthy FSS staircases.
Structural equation modeling was used to assess the utility of the sensorineural model of contrast sensitivity proposed by Sekuler et al. [Vision Res. 24, 689 (1984)] to account for spatial vision in adulthood. In Study 1, visual acuity and contrast sensitivity (1.5–18 c/deg) were measured in 84 people between the ages of 19 and 81 yr. No three-filter model fitted the data well. Although a two-filter model was associated with good fit indices, parameter estimates for both filters were inconsistent with physiological and behavioral data. In Study 2, acuity and contrast sensitivity (1.5–18 c/deg) were assessed in 95 observers between the ages of 23 and 73 yr. All measures were gathered once per month over a three-month period. The Sekuler et al. three-filter model did not fit the data from any time of measure, but a two-filter, bandpass model provided a consistent and excellent fit for all three waves. The model suggests that age-related change in the neural mechanisms underlying contrast sensitivity is minimal once acuity is controlled. Discrepancies between this conclusion and that reported by Sekuler et al. may be related to test type, psychophysical method, reliability, and sample selection.
Contrast sensitivity functions differ from observer to observer. We propose that these differences arise because each observer has unique weights for the outputs of the neural channels that underlie the contrast sensitivity function. By applying principal components analysis to individual contrast sensitivity functions of 297 observers, estimates of the channel tuning curves were found. We find evidence for three broadly tuned bandpass channels with peaks at 4, 8, and 16c/deg and bandwidth near 1.3 octaves. These channel tuning curves were reproduced in a cross-validation study of 56 observers.
Late age-related maculopathy (ARM) is responsible for the majority of blind registrations in the Western world among persons over 50 years of age. It has devastating effects on quality of life and independence and is becoming a major public health concern. Current treatment options are limited and most aim to slow progression rather than restore vision; therefore, early detection to identify those patients most suitable for these interventions is essential. In this work, we review the literature encompassing the investigation of visual function in ARM in order to highlight those visual function parameters which are affected very early in the disease process. We pay particular attention to measures of acuity, contrast sensitivity (CS), cone function, electrophysiology, visual adaptation, central visual field sensitivity and metamorphopsia. We also consider the impact of bilateral late ARM on visual function as well as the relationship between measures of vision function and self-reported visual functioning. Much interest has centred on the identification of functional changes which may predict progression to neovascular disease; therefore, we outline the longitudinal studies, which to date have reported dark-adaptation time, short-wavelength cone sensitivity, colour-match area effect, dark-adapted foveal sensitivity, foveal flicker sensitivity, slow recovery from glare and slower foveal electroretinogram implicit time as functional risk factors for the development of neovascular disease. Despite progress in this area, we emphasise the need for longitudinal studies designed in light of developments in disease classification and retinal imaging, which would ensure the correct classification of cases and controls, and provide increased understanding of the natural course and progression of the disease and further elucidate the structure-function relationships in this devastating disorder.
Covariance structure analysis uses χ–2 goodness-of-fit test statistics whose adequacy is not known. Scientific conclusions based on models may be distorted when researchers violate sample size, variate independence, and distributional assumptions. The behavior of 6 test statistics was evaluated with a Monte Carlo confirmatory factor analysis study. The tests performed dramatically differently under 7 distributional conditions at 6 sample sizes. Two normal-theory tests worked well under some conditions but completely broke down under other conditions. A test that permits homogeneous nonzero kurtoses performed variably. A test that permits heterogeneous marginal kurtoses performed better. A distribution-free test performed spectacularly badly in all conditions at all but the largest sample sizes. The Santorra-Bentler scaled test performed best overall. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
The flicker sensitivity of the human eye may be characterized by the De Lange curve (temporal modulation transfer function plot). In the curves of two out of eight observers, Kelly D. H. [ J. Opt. Soc. Am. 52, 940– 947 ( 1962)] found three peaks instead of one, as had been reported in previous publications, and suggested that they are related to the three mechanisms of color vision. Several investigations have been based on this suggestion, but there has been no confirmation of his observation. In this paper, a new measuring method was devised and the existence of the peaks was confirmed, but the hypothesis that they are related to color processes was questioned.
We have attempted to reconcile the results of several recent chromatic flicker studies. By adjusting the relative amplitudes of red and green sine-wave stimuli that were flickering in opposite phase, we obtained conditions varying from purely chromatic (red–green) stimulation, through each “silent-cone” condition, to purely luminous (homochromatic) stimulation. We also tested the effects of adapting backgrounds in each condition. Our results can be explained in terms of a low-frequency band that represents the opponent-color response, and a high-frequency band that represents the achromatic response. These two bands respond in various proportions, depending on the red–green stimulus ratio. Chromatic adaptation generally affects the low- and high-frequency bands differently and hence changes the shape of the flicker sensitivity curve. However, if the temporally varying waveform and the adapting background are both chosen to stimulate the same cone type, then the opponent-color and achromatic bands are both attenuated by the same amount. In this case, the shapes of the silent-red and silent-green flicker curves are preserved under chromatic adaptation. We conclude that none of these flicker curves are controlled by the temporal characteristics of independent cone types.
Flicker thresholds were measured in an automated paradigm at several temporal frequencies for the critical fusion frequency in more than 1000 observers of ages 5–75 years. The results can be described by two processes. The first process was a uniform increase in sensitivity at all frequencies, at a rate that would double sensitivity every 10 years, up to the age of 16 years. In the second process the data indicated that after the age of 16 years the visual response showed gradual slowing but little sensitivity decrease for the remainder of the life span.
Photopic temporal contrast sensitivity for healthy eyes of observers 65 years old and older is compared with retinal-illuminance-matched sensitivity of younger eyes. The older observers are significantly less sensitive for frequencies between 10 and 45 Hz. Although there is a slight shift to slower flicker rates in the mean contrast sensitivity function for older observers, this trend is not statistically significant, suggesting that there is relatively little loss of temporal resolving power of the visual system with healthy aging. These are preliminary results from an ongoing study of temporal contrast sensitivity in healthy aging eyes.
Temporal-frequency characteristics were measured as a function of retinal location, with test-field size scaled to provide equivalent sensitivity at each eccentricity. The results showed that the temporal-frequency limits increased uniformly by about a factor of 2 between the fovea and 45° eccentricity, corresponding to a decrease in the response-time constant from 70 to 35 msec. These data were compared with the change in inner- and outer-segment diameters of the cones across the same retinal range. The data conform to the hypothesis that visual time constant varies inversely with cone outer-segment diameter. A second hypothesis that visual sensitivity increases in proportion to cone outer-segment length in the central fovea was also supported.
Threshold elevations for spatially localized test stimuli were measured as a function of the temporal frequency of a sinusoidal mask grating. Ten of these temporal-masking curves were determined, each using a test stimulus of different temporal frequency. It was found that these data could be accounted for by four temporal-tuning curves: one low-pass curve with a corner frequency of 8.0 Hz and three bandpass curves with bandwidths of 2.0–2.5 octaves and peaks all within the region 4.0–8.0 Hz. In another set of experiments, a series of 1 spatial-masking curves was determined, each using a test stimulus of different spatial frequency. Measurement of the entire series was repeated using 1.0- and 8.0-Hz mask temporal modulations. Spatial-masking data collected under the two temporal conditions could both be accounted for by a single set of seven spatial-tuning curves, without changing the shape of any of these curves. The data are therefore compatible with spatiotemporal separability. Finally, a large set of contrast-response curves (threshold elevation as a function of mask contrast) was collected. These curves were found to follow a power law whose exponent varied with the spatiotemporal conditions of the experiment.
The existing literature on transmission of the human ocular media in the visible region is reviewed. Added is an ocular density curve derived from the CIE scotopic sensitivity function and the absorption curve of human rhodopsin. This ocular density curve fits the literature data very well and can serve as the transmission curve of a standard observer. The extent of individual differences in ocular density is calculated to be ±25 per cent of the average density values.RésuméOn passe en revue la littérature relative à la transmission des milieux oculaires de l'homme dans le visible. On ajoute une courbe de densité oculaire dérivée de la fonction de sensibilité scotopique CIE et de la courbe d'absorption de la rhodopsine humaine. Cette courbe de densité oculaire s'accorde très bien avec les données antérieures et peut servir de courbe de transmission de l'observateur de référence. La marge des différences individuelles de la densité oculaire est évaluée à ±25 pour cent des valeurs moyennes de densité.ZusammenfassungDie Literatur über die Transmission der Augenmedien im sichtbaren Spektralbereich wird zusammengefasst. Eine Extinktionskurve der Augenmedien, die aus der skotopischen Empfindungskurve abgeleitet wird und die Absorptionskurve von menschlichem Rhodopsin werden hinzugefügt. Die Extinktionskurve der Augenmedien stimmt mit den Literaturangaben gut überein und könnte als Transmissionskurve des standardbeobachters verwendet werden. Die individuellen Unterschiede in der Extinktion betragen etwa 25 Prozent der mittleren Dichtewerte.РефератДaeтcя oбзop cyщecтвyющeй литepaтypы o пpoпycкaнии глaзными oптичecкими cpeдaми чeлoвeкa paзличныч лyчeй видимoгo cпeктpa. Дoпoлнeны дaнныe oтнocитeльнo кpивoй oптичecкoй плoтнocти глaзныч cpeд. вывeдeннoй из фyнкции cкoтoпичecкoй чyвcтвитeльнocти CЛE и кpивoй пoглoщeния poдoпcинa чeлoвeкa. Этa кpивaя oптичecкoй плoтнocти oчeнь чopoшo coвпaдaeт c дaнными литepaтypы и мoзeт cлyзить в кaчecтвe кpивoй пpoпycкaния для cтaндapтнoгo нaблюдaтeля. Pacчитaны вeличины индивдyaльныч paзличий в oптичecкoй плoтнocти cpeд глaзa, кoтopыe oтклoняютcя oт ycpeднeнныч вeличин нa ±25%.
Foveal flicker contrast sensitivity was measured for healthy adults at temporal frequencies from 2.5 to 50 Hz. The first experiment compared two-interval forced-choice (2IFC) and yes-no detection (Y–N) testing procedures for younger (19–33-year-old) and older (67–73-year-old) observers. The 2IFC technique resulted in higher absolute estimates of sensitivity. However, within a method, relative differences were similar. Therefore the two methods gave similar estimates of temporal contrast-sensitivity change with age. Experiment 2 compared 89 observers from 18 through 77 years of age to explore the effect of the time course of aging on flicker sensitivity. The 2IFC procedure was used, and retinal illuminance changes with age were controlled. Significant overall losses in contrast sensitivity were found for the 45–54, 55–64, and 65–77-year-old age groups. Overall sensitivities for the 35–44-year-old group were comparable with or (not significantly) higher than those for the 18–24- and 25–34-year-old groups. The results suggested that (1) foveal temporal contrast sensitivity does not decline until after 44 years, (2) losses after 44 years are in amplitude but not in temporal resolution of the visual response, and (3) the mean rate of loss is ∼0.78 decilog per decade after 44 years. These results are consistent with the existence of three phases of development of temporal contrast sensitivity over the life span. The results also emphasize the importance of including healthy-eyed age-matched controls in studies of flicker sensitivity in visual dysfunctions that affect mainly older adults.
To evaluate whether foveal flicker sensitivity and fundus appearance are good predictors of exudative age-related maculopathy (ARM) when the effects of aging, retinal illuminance, and criterion differences are controlled.
Fellow eyes of monocular exudative ARM patients were tested at baseline. Seven of these eyes have now developed exudative ARM. Therefore, at baseline they were in pre-exudative stages of ARM. The foveal flicker sensitivity and fundus appearance of the pre-exudative and nonconverted eyes were compared with healthy, age-matched eyes. The flicker stimulus was a uniform, 2.8 deg circular field at 660 nm, modulated sinusoidally at frequencies from 2.5 to 50 Hz. Fundus photographs were evaluated using the Wisconsin ARM grading system.
Flicker modulation sensitivity at two frequencies discriminated pre-exudative from healthy older eyes with 100% accuracy. Using the same criterion, pre-exudative eyes also were discriminated from nonconverted eyes with 100% accuracy. Whereas an overall fundus ARM risk score discriminated pre-exudative from healthy older eyes with 100% accuracy, it did not discriminate pre-exudative from nonconverted eyes at better than chance levels.
There were functional changes in the retina preceding development of exudative ARM. Foveal flicker sensitivity at low- to mid-temporal frequencies seemed highly sensitive to these pre-exudative changes in this relatively small group of subjects. The authors hypothesize that foveal flicker sensitivity is a good predictor of exudative ARM and a sensitive monitor of retinal function in pre-exudative ARM. These predictions are being tested on a larger, independent sample.
To address the question of whether temporal-frequency information in the fovea and the periphery is processed in fundamentally different ways we measured temporal-frequency-discrimination thresholds for spatiotemporally narrow-band stimuli presented at suprathreshold contrast. Temporal-frequency-discrimination thresholds are similar (within a factor of 2) at the fovea and at 30° in the periphery. We use a line-element approach and three spatiotemporally separable temporal mechanisms to model foveal and peripheral data with the same degree of fidelity. These findings suggest that not only are the front-end temporal mechanisms in the fovea and periphery likely to be similar but also the way in which their outputs are combined at more central sites is the same.
In this paper it is shown that the well-known residual brightness flicker just above the color-flicker limit with heterochrome flicker photometery can be brought down to zero by introducing an external phase correction in one of two light beams sinusoidally modulated 100% in antiphase and simultaneously presented to the eye. The phase correction is found to be a function of luminance, color difference, and frequency.
From the attenuation characteristic of the color system it is found that the extra delay in color perception at 595 mμ is caused by a single integration process with a time constant of about 120 msec at high luminance; at low luminance a triple integration process occurs with the same time constant.
A generally known method for the dynamic investigation of any linear system is recalled to mind. Applied to the visual organ with sinusoidally modulated light, the dynamic nature of the system fovea→brightness perception is embodied in attenuation characteristics, by plotting the ratio output amplitude over input amplitude against frequency at constant mean luminance. This manner of investigation, first applied in previous papers with white light, is expanded over a greater part of the range of cone vision and is continued with colored light. The existing theories on flicker fusion provide no explanation for the shape of the attenuation characteristics obtained with the experiments and calculated from investigations of other authors.
This book introduces multiple-latent variable models by utilizing path diagrams to explain the underlying relationships in the models. This approach helps less mathematically inclined students grasp the underlying relationships between path analysis, factor analysis, and structural equation modeling more easily. A few sections of the book make use of elementary matrix algebra. An appendix on the topic is provided for those who need a review. The author maintains an informal style so as to increase the book's accessibility. Notes at the end of each chapter provide some of the more technical details. The book is not tied to a particular computer program, but special attention is paid to LISREL, EQS, AMOS, and Mx. New in the fourth edition of Latent Variable Models: * a data CD that features the correlation and covariance matrices used in the exercises; * new sections on missing data, non-normality, mediation, factorial invariance, and automating the construction of path diagrams; and * reorganization of chapters 3-7 to enhance the flow of the book and its flexibility for teaching. Intended for advanced students and researchers in the areas of social, educational, clinical, industrial, consumer, personality, and developmental psychology, sociology, political science, and marketing, some prior familiarity with correlation and regression is helpful. © 2004 by Lawrence Erlbaum Associates, Inc. All rights reserved.
consider the following issues: (a) the usefulness of the χ[superscript]2 statistic based on various estimation methods for model evaluation and selection; (b) the conceptual elaboration of and selection criteria for fit indexes; and (c) identifying some crucial factors that will affect the magnitude of χ[superscript]2 statistics and fit indexes / review previous research findings as well as report results of some new, unpublished research (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Analysis of Ordinal Categorical Data Alan Agresti Statistical Science Now has its first coordinated manual of methods for analyzing ordered categorical data. This book discusses specialized models that, unlike standard methods underlying nominal categorical data, efficiently use the information on ordering. It begins with an introduction to basic descriptive and inferential methods for categorical data, and then gives thorough coverage of the most current developments, such as loglinear and logit models for ordinal data. Special emphasis is placed on interpretation and application of methods and contains an integrated comparison of the available strategies for analyzing ordinal data. This is a case study work with illuminating examples taken from across the wide spectrum of ordinal categorical applications. 1984 (0 471-89055-3) 287 pp. Regression Diagnostics Identifying Influential Data and Sources of Collinearity David A. Belsley, Edwin Kuh and Roy E. Welsch This book provides the practicing statistician and econometrician with new tools for assessing the quality and reliability of regression estimates. Diagnostic techniques are developed that aid in the systematic location of data points that are either unusual or inordinately influential; measure the presence and intensity of collinear relations among the regression data and help to identify the variables involved in each; and pinpoint the estimated coefficients that are potentially most adversely affected. The primary emphasis of these contributions is on diagnostics, but suggestions for remedial action are given and illustrated. 1980 (0 471-05856-4) 292 pp. Applied Regression Analysis Second Edition Norman Draper and Harry Smith Featuring a significant expansion of material reflecting recent advances, here is a complete and up-to-date introduction to the fundamentals of regression analysis, focusing on understanding the latest concepts and applications of these methods. The authors thoroughly explore the fitting and checking of both linear and nonlinear regression models, using small or large data sets and pocket or high-speed computing equipment. Features added to this Second Edition include the practical implications of linear regression; the Durbin-Watson test for serial correlation; families of transformations; inverse, ridge, latent root and robust regression; and nonlinear growth models. Includes many new exercises and worked examples.
The assumptions underlying the science of colorimetry are examined in order to generalize the color-matching technique so that it may be used to study a wide range of sensory attributes. The simplest test of the generalized matching method allows the experimenter to estimate the number of 'channels' that sample a given sensory dimension. More elaborate experiments can then proceed to determine the form of these 'channels,' again using an extension of the color-matching method. System linearity is not required. Examples of the general matching technique are given for flicker and visual texture, and its application to auditory and tactile sensations is outlined.
Clinical and pathological examination was performed on 378 eyes from 216 patients aged 43 to 97 years. This series represented eyes in which the fundi were normal or showed various manifestations of senile macular degeneration. The eyes were divided into six groups according to the histological appearance of a linear deposit at the base of the retinal pigment cells. Groups I and II were considered to represent normal ageing, Groups III and IV the progressive development of senile macular degeneration, and Groups V and VI the end-results.
An analysis of human psychophysical flicker thresholds is developed from the increment threshold technique of Stiles (1939). Two independent detection components are required to account for all available modulation sensitivity data. These components are differentiated by properties corresponding to the difference between sustained and transient units in the cat retina.
Flicker contrast sensitivity was tested in the "good" eyes of 13 patients with monocular exudative age-related maculopathy (ARM). The stimulus was a foveal, long-wavelength, low spatial frequency 2.8 degrees circle in an equiluminant (photopic) surround. Two of these ARM-risk eyes have since developed exudative ARM. Compared to healthy age-matched eyes, the two eyes that developed exudative ARM had significantly lower sensitivity at 10-40 Hz up to 9 mo before exudative symptoms appeared. The implications of these results regarding the time-course of ARM and the predictive value of foveal contrast sensitivity testing are considered. Based upon data and theoretical considerations, the authors speculate that sensitivity loss between 10 and 40 Hz is a good predictor of which eyes will develop exudative ARM. This proposal will be tested by new data from current as well as new ARM-risk subjects.
The "good" eyes of 13 patients with monocular exudative ARM were compared with age-matched healthy eyes of 19 subjects. Membership in the two study groups was based upon careful clinical evaluation of the tested eye as well as upon status of the fellow eye. We asked whether temporal contrast sensitivity for a long-wavelength, low spatial frequency stimulus can be used to identify the group in which a given eye belongs. Using step-wise discriminant analysis, we found that the ARM-risk and healthy eyes could be classified with 78% accuracy on the basis of foveal flicker sensitivity at two temporal frequencies--14 and 10 Hz (in order of estimated weight.)
Temporal contrast sensitivity in eyes at risk for exudative age-related maculopathy (ARM) was compared to that in age-matched healthy older eyes. The test stimulus was a foveally viewed, flickering, long-wavelength 2.8 degrees diameter circle in an equiluminant (photopic) surround. Retinal illuminance and decision criterion differences were experimentally controlled. Eyes in the healthy and ARM-risk groups had 20/30 or better Snellen acuity and intraocular pressure of less than 22 mmHg. Nevertheless, the ARM-risk patients were less sensitive to flicker contrast, especially for mid-temporal frequencies. This suggests that flicker sensitivity may be useful in identifying patients at risk for exudative ARM. In addition, comparison with other research reveals a paradox: Mid-temporal frequency sensitivity losses may be attributable primarily to a "high temporal frequency" mechanism.
Covariance structure analysis uses chi 2 goodness-of-fit test statistics whose adequacy is not known. Scientific conclusions based on models may be distorted when researchers violate sample size, variate independence, and distributional assumptions. The behavior of 6 test statistics is evaluated with a Monte Carlo confirmatory factor analysis study. The tests performed dramatically differently under 7 distributional conditions at 6 sample sizes. Two normal-theory tests worked well under some conditions but completely broke down under other conditions. A test that permits homogeneous nonzero kurtoses performed variably. A test that permits heterogeneous marginal kurtoses performed better. A distribution-free test performed spectacularly badly in all conditions at all but the largest sample sizes. The Satorra-Bentler scaled test statistic performed best overall.
The temporal properties of the foveal visual filters were revealed using a method which is a variant on previously used noise masking paradigms. This enables the temporal properties of the mechanisms underlying threshold detection of a spatio-temporal probe to be measured. In accord with recent suggestions these results support the existence of three temporal mechanisms. The evidence for the third, higher temporal mechanism is only persuasive at low spatial frequencies. Furthermore, the results suggest that although there is some degree of spatio-temporal covariation in the filtering properties either of individual filters or across the filter population, the well known spatio-temporal covariation in human detection sensitivity is adequately explained by a sensitivity scaling of individual temporal filters with approximately invariant temporal properties.
Research studying robustness of maximum likelihood (ML) statistics in covariance structure analysis has concluded that test statistics and standard errors are biased under severe non-normality. An estimation procedure known as asymptotic distribution free (ADF), making no distributional assumption, has been suggested to avoid these biases. Corrections to the normal theory statistics to yield more adequate performance have also been proposed. This study compares the performance of a scaled test statistic and robust standard errors for two models under several non-normal conditions and also compares these with the results from ML and ADF methods. Both ML and ADF test statistics performed rather well in one model and considerably worse in the other. In general, the scaled test statistic seemed to behave better than the ML test statistic and the ADF statistic performed the worst. The robust and ADF standard errors yielded more appropriate estimates of sampling variability than the ML standard errors, which were usually downward biased, in both models under most of the non-normal conditions. ML test statistics and standard errors were found to be quite robust to the violation of the normality assumption when data had either symmetric and platykurtic distributions, or non-symmetric and zero kurtotic distributions.
Temporal frequency discrimination at and above the detection threshold has been studied using gratings of low (0.2 c/deg) and medium (2 c/deg) spatial frequencies. At 2 c/deg the results of previous investigators are confirmed: The results being consistent with the existence of two broadly tuned and directionally selective temporal mechanisms (up to 32 Hz). For the lower spatial frequency an additional temporal frequency discrimination at threshold can be made between 4 and 32 Hz and enhanced temporal frequency discrimination at suprathreshold levels occurs above 24 Hz. One interpretation of this result is the existence of one or more additional temporal mechanisms with restricted spatial acuity responding to higher temporal frequencies.
A linear structural model of mechanisms underlying spatial vision was generated from the variance-covariance matrix of contrast sensitivity data. The data had been collected on a large group of observers ranging in age from 19 to 87 yr, using gratings of 0.5-16 c/deg spatial frequency. Structural models incorporating various numbers of spatial frequency-tuned mechanisms were compared, with a three-mechanism model giving the best account of the data. The same analysis was applied to contrast sensitivity data simulated from Wilson and Bergen's (1979) model. When the stimulated data covered 0.5-16 c/deg, only three mechanisms were needed to give a satisfactory account of the data; when the simulated data covered 0.25-16 c/deg, four mechanisms were required. Peak sensitivities and bandwidths of the mechanisms extracted from the simulated data resembled those extracted from the real, population data. This reinforces the idea that at an early stage of human vision a small number of spatially-tuned mechanisms are operative. In addition, the outcome of analyses with both real and simulated data illustrate the potential value of linear structural models for vision research.
The human visual system contains a large number of narrowly-tuned spatial-frequency-specific channels. Does it contain an analogous set of channels tuned to a narrow range of temporal frequency? On the basis of data gathered with the use of a threshold elevation technique it is argued that human sensitivity to flicker can be accounted for by assuming the existence of just two filters, one a low-pass filter peaking gently at around 6 Hz and one a band-pass filter peaking at around 9 Hz. Similar data gathered from studies of interocular transfer suggest that at least some of the mechanisms involved are binocular, rather than being purely monocular as has previously been suggested.
This paper derives the constraints on a set of channels that would be consistent with the results of several experiments on the temporal properties of the visual system, and it describes a specific set of channels that meet these constraints. Data on simultaneous detection and discrimination require a minimum of three channels. Temporal frequency discrimination at and above threshold constrain the bandwidths and locations of the channels. The shape of the temporal modulation sensitivity function constrains their sensitivities. The functions that meet these constraints are similar to those derived from masking data, and they can account for data on flicker matching, notch losses in modulation sensitivity, and changes of perceived temporal frequency with changes of modulation depth.
We examined discriminations between small patches of grating that differed in either spatial or temporal frequency. The patches were presented at contrasts near to detection threshold. For certain pairs of stimuli, each was correctly identified as often as it was detected. To explain this result, we hypothesize that the detectors of these stimuli arelabelled, in the sense that the observer can distinguish the response of each detector from that of any other. Under this assumption, we find that the detectors form two non-overlapping sets in their selectivity for temporal frequency. In their selectivity for spatial frequency, the detectors of slowly varying stimuli can be partitioned into 7 distinct sets, but only 3 sets are evident among the detectors of rapidly modulated patterns.
SPSS for the Macintosh
- Spss Inc
SPSS Inc. (1990). SPSS for the Macintosh, version 4.0.
The vertebrate retina: Principles of structure and function
- R W Rodieck
Rodieck, R. W. (1973). The vertebrate retina: Principles of structure and
function (p. 345) San Francisco, Calif.: Freeman.