[Show description][Hide description] DESCRIPTION: Categorization is common in a wide variety of human behaviors but the degree to which categories are the result of perception versus other factors (e.g., cognitive or linguistic) is less well understood. We investigated whether simple visual stimuli (sinusoidal grating mixtures) exhibit categorization. Previous investigators have found that 180 degree relative phase shifts in f + 2f gratings are discriminated when the sine or cosine contrast of the shift exceeds some criterion. Three observers performed traditional categorical perception tasks of classification and discrimination tasks with f + 2f gratings.
[Show abstract][Hide abstract] ABSTRACT: Previous work on spatial contextual interactions between shapes defined by radial frequency (RF) contours has demonstrated that such interactions depend on the rotational phase alignment between a mask and target stimulus (Habak et al., 2004; 2009). When the points of maximum curvature in target and masking RF contours are aligned (i.e., zero phase difference), thresholds for detecting deviations from circularity are significantly elevated relative to a baseline condition that contains no masking stimulus, and the strength of masking declines as the relative phase difference increases (Habak et al., 2004; 2009). The current study extended this previous work by examining the effect of RF number on the magnitude of threshold elevation observed across seven target-mask relative phases. We measured detection thresholds for five RF contours (RF3, 5, 6, 8, 11) in the presence of a surrounding mask of the same RF number as the target in seven target-mask relative phase combinations (0°, 30°, 60°, 90°, 120°, 150°, 180°). Although the amount of masking varied considerably across RF contours, we found that the magnitude of masking declined with increasing relative target-mask phase difference for all RF combinations. However, we also found a significant interaction between RF number and phase such that the rate at which masking declined with phase differed across RF contours. Overall, these results suggest significant differences exist in how the frequency of local curvature affects the interference observed as a function of the alignment between two shapes. The results of this study serve as a foundation for interpreting the effect of rotational phase alignment between spatially separated shapes.
[Show abstract][Hide abstract] ABSTRACT: Background / Purpose:
In order to examine the processing underlying figure/ground perception, we examined neural signals associated with convexity context effects (Peterson and Salvagio, 2008). During a convexity task with 2- and 8-region black and white stimuli that involved indicating which central region was perceived as figure, we recorded electroencephalography of the posterior region of the cortex that was time-locked to stimulus onset. One sample of observers was used to characterize the evoked response potential (ERP) profile and determine spatiotemporal location(s) sensitive to how the stimulus was perceived and a second sample was used to directly test those findings in a replication.
We observed a robust effect on mean amplitude of the ERP that was sensitive to how the stimulus is perceived (convex vs. concave as figure interpretations) in the medial parietal/occipital cortex between 160-180ms post stimulus onset. In combination with the other findings presented, these results are consistent with the idea that the early visual system is sensitive to figure/ground perception and highlight the importance of perceived, 3-dimensionality in the processing underlying it.
Vision Sciences Society Annual Meeting 2014; 06/2014
[Show abstract][Hide abstract] ABSTRACT: The standard model of early vision claims that orientation and spatial frequency are encoded with multiple, fixed-bandwidth, and approximately independent channels. The standard model was developed from observer data that used deterministic patterns such as Gabor patches and gratings used as stimuli, but detection data using noise as a stimulus suggests that the visual system may use adjustable, rather than fixed-bandwidth channels. In our previous work, we used classification images as a key piece of evidence against the adjustable channels hypothesis for spatial frequency. Here we tested the adjustable channels hypothesis for orientation with two-dimensional filtered noise that varied in orientation bandwidth presented in white noise. Unlike spatial frequency, our data were consistent with the predictions of an adjustable channel model; we found quarter-root law thresholds consistent with optimal summation, relatively high and constant absolute efficiency, and classification images that show an adjustment in channel bandwidth. Thus, for orientation summation, both detection thresholds and classification image results support the adjustable channels hypothesis. Classification images also reveal hallmarks of inhibition or suppression from uninformative spatial frequencies and/or orientations. This work highlights the limitations of the standard model of summation for orientation. The standard model of orientation summation and tuning was chiefly developed with narrow-band stimuli that were not presented in noise, stimuli that are arguably less naturalistic than than the variable bandwidth stimuli presented in noise used in our experiments. Finally, the disagreement between the results from our experiments on spatial frequency summation with the data presented in this paper suggests that orientation may be encoded differently, particularly with mechanisms with greater flexibility than spatial frequency channels.
Frontiers in Psychology 06/2014; 5:578. DOI:10.3389/fpsyg.2014.00578 · 2.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: THE: CURRENT EXPERIMENTS EXAMINED THE EFFECT OF HEALTHY AGING ON THE INTEGRATION OF ORIENTATION AND POSITION INFORMATION IN SHAPE PERCEPTION: FOLLOWING DAY AND LOFFLER 2009, CONFLICTING CONTOURS WERE CREATED BY SAMPLING THE ORIENTATIONS OF ONE SHAPE EG, A ROUNDED PENTAGON WITH GABORS, AND POSITIONING THEM ON THE CIRCUMFERENCE OF A DIFFERENT SHAPE EG, A CIRCLE IN EXPERIMENT 1, SUBJECTS JUDGED WHETHER THE CONFLICTING CONTOUR LOOKED MORE CIRCULAR THAN A ROUNDED PENTAGON OF VARYING AMPLITUDE, WHICH ALLOWED US TO ESTIMATE THE PERCEIVED SHAPE OF THE CONFLICTING CONTOUR THE RELATIVE AMOUNT OF POSITION AND ORIENTATION INFORMATION WAS MANIPULATED BY VARYING THE NUMBER OF GABORS COMPRISING THE TARGET CONTOUR ORIENTATION INFORMATION DOMINATED THE PERCEPT FOR CONTOURS SAMPLED WITH 15-40 ELEMENTS, PRODUCING A STRONG SHAPE ILLUSION, BUT POSITION INFORMATION DETERMINED THE SHAPE WITH DENSER SAMPLING THE MAGNITUDE OF THIS ORIENTATION DOMINANCE EFFECT WAS EQUAL IN YOUNGER AND OLDER SUBJECTS ACROSS ALL SAMPLING LEVELS IN EXPERIMENT 2, SUBJECTS DISCRIMINATED FIVE CONTOURS THAT DIFFERED IN ORIENTATION AND/OR POSITION INFORMATION BOTH GROUPS SHOWED POOR DISCRIMINATION BETWEEN CONFLICTING CONTOURS AND THEIR PERCEPTUALLY EQUIVALENT RADIAL FREQUENCY PATTERNS, CONFIRMING THE MAIN FINDING OF EXPERIMENT 1 IN ADDITION, OLDER SUBJECTS SHOWED WORSE DISCRIMINATION BETWEEN TWO NONCIRCULAR RADIAL FREQUENCY PATTERNS THAN YOUNGER SUBJECTS IN SUM, INTEGRATION OF ORIENTATION AND POSITION INFORMATION IN SHAPE PERCEPTION IS PRESERVED WITH AGING; HOWEVER, OLDER ADULTS ARE LESS ABLE TO MAKE FINE SHAPE DISCRIMINATIONS BETWEEN NONCIRCULAR SAMPLED CONTOURS:
Journal of Vision 05/2014; 14(5). DOI:10.1167/14.5.12 · 2.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Many sensory and cognitive changes accompany normal ageing, including changes to visual attention. Several studies have investigated age-related changes in the control of attention to specific locations (spatial orienting), but it is unknown whether control over the distribution or breadth of attention (spatial focus) also changes with age. In the present study, we employed a dual-stream attentional blink task and assessed changes to the spatial distribution of attention through the joint consequences of temporal lag and spatial separation on second-target accuracy. Experiment 1 compared the rate at which attention narrows in younger (mean age 22.6, SD 4.25) and older (mean age 66.8, SD 4.36) adults. The results showed that whereas young adults can narrow attention to one stream within 133 ms, older adults were unable to do the same within this time period. Experiment 2 showed that older adults can narrow their attention to one stream when given more time (266 ms). Experiment 3 confirmed that age-related changes in retinal illuminance did not account for delayed attentional narrowing in older adults. Considered together, these experiments demonstrate that older adults can narrow their attentional focus, but that they are delayed in initiating this process compared to younger adults. This finding adds to previously reported reductions in attentional dynamics, deficits in inhibitory processes, and reductions in posterior parietal cortex function that accompany normal ageing.
Psychological Research 12/2013; 79(1). DOI:10.1007/s00426-013-0528-2 · 2.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background / Purpose:
We aimed to discover when the human visual system detects faces.
The earliest ERP face sensitivity in a sample of 120 subjects (aged 18-81) was already visible at 87 ms [81, 94] post-stimulus.
European Conference of Visual Perception 2013; 10/2013
[Show abstract][Hide abstract] ABSTRACT: People with schizophrenia (SCZ) are impaired in several domains of visual processing, including the discrimination and detection of biological motion. However, the mechanisms underlying SCZ-related biological motion processing deficits are unknown. Moreover, whether these impairments are specific to biological motion or represent a more widespread visual motion processing deficit is unclear. In the current study, three experiments were conducted to investigate the contribution of global coherent motion processing to biological motion perception among patients with SCZ. In Experiments 1 and 2, participants with SCZ (n = 33) and healthy controls (n = 33) were asked to discriminate the direction of motion from upright and inverted point-light walkers in the presence and absence of a noise mask. Additionally, participants discriminated the direction of non-biological global coherent motion. In Experiment 3, participants discriminated the direction of motion from upright scrambled walkers (which contained only local motion information) and upright random position walkers (which contained only global form information). Consistent with previous research, results from Experiment 1 and 2 showed that people with SCZ exhibited deficits in the direction discrimination of point-light walkers; however, this impairment was accounted for by decreased performance in the coherent motion control task. Furthermore, results from Experiment 3 demonstrated similar performance in the discrimination of scrambled and random position point-light walkers.
Frontiers in Psychology 08/2013; 4:507. DOI:10.3389/fpsyg.2013.00507 · 2.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Practice in perceptual tasks over hundreds or thousands of trials often leads to long-lasting improvements in performance that generalize only partially to new stimuli. However, the time courses of the general and stimulus-specific aspects of learning are still debated. Some researchers argue that general aspects of the task are learned first in an initial rapid phase of learning and that stimulus-specificity emerges more slowly. In contrast, Hussain et al. (Front Psychol. 2012; 3:226) reported that 105 trials in a 10-AFC face identification task on Day 1 was sufficient to produce stimulus-specific learning in a test phase on Day 2, suggesting that stimulus-specific improvements can emerge rapidly. The current experiments extend these findings by examining 1) whether similar, rapid stimulus-specific learning occurs in a 10-AFC texture identification task; 2) if this rapid stimulus-specificity is long-lasting by increasing the interval between Days 1 and 2 from 24 hours to 1 week; and 3) the effects of reducing practice on Day 1 from 840 to just 21 trials. On Day 1, subjects performed a 10-AFC identification task with band-pass random textures embedded in three levels of external noise. The textures were presented at 7 contrasts that spanned the threshold range; hence the signal-to-noise ratio varied significantly across trials. On Day 2, subjects performed the task with the same or a novel set of textures. The dependent variable was response accuracy, and stimulus-specificity was measured by comparing performance with the same and novel textures on Day 2. We found stimulus-specific learning in subjects who received 840, 105, and 63 trials of practice, but not in subjects who received 21 trials of practice. Our results are consistent with the idea that stimulus-specific learning can emerge rapidly during practice and that this rapid learning is long lasting.Meeting abstract presented at VSS 2013
Journal of Vision 07/2013; 13(9-9):1090. DOI:10.1167/13.9.1090 · 2.73 Impact Factor