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ABSTRACT: Sensitivity to corrugations defined by binocular disparity differs as a function of the modulation frequency. Such functions have proved to be useful descriptive and analytical tools in the study of the mechanisms involved in disparity processing. Indeed, given certain assumptions, these sensitivity functions can be used to predict certain perceptual outcomes. Given their importance, it is surprising that there is no comprehensive data set of disparity sensitivity functions (DSF) for a range of observers over a broad range of spatial frequencies and orientations. Here we report DSFs for six observers over an eight octave range of sinusoidal corrugations in disparity (0.0125-3.2 cpd). Multi-cycle, low frequency surfaces were used to assess the degree to which the fall-off in sensitivity at low corrugation frequencies is attributable to the decreasing number of cycles displayed. The data was found to form a continuous function despite the different number of cycles displayed. We conclude that the fall off in sensitivity is due to the spatial interactions in disparity processing. We also determined DSFs for the same observers to both vertically and horizontally oriented sinusoidal disparity corrugations in order to characterise the extent of the stereoscopic anisotropy. In general, the best thresholds for detecting vertically oriented disparity corrugations were higher (approximately 4 arc sec) than for horizontally oriented corrugations (approximately 2 arc sec). Moreover, the functions were shifted toward the high spatial frequency end of the spectrum.
Vision Research 10/1999; 39(18):3049-56. · 2.41 Impact Factor
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ABSTRACT: When the corresponding horizontal meridia of the two eyes are aligned, the corresponding vertical meridia are tilted outwards in a temporal direction, a phenomenon first described by Helmholtz. However, it is not known if this effect is confined to the principal meridia or whether the same relationship exists between corresponding horizontal and corresponding vertical meridia at eccentric retinal locations. We sought to address this issue by exploiting the technique of Nakayama (1977 Proceedings of the Society of Photo-Optical Instrument Engineers 120 2-9) in which the positions of alternating dichoptic images that produce minimal apparent motion were used to measure the relative tilt of corresponding meridia at a range of eccentricities up to +/- 16 deg away from the fovea. Stimuli were composed of dichoptic images, one containing a blank field and the other a pair of dots, which alternated at a rate of 0.63 Hz and the relative tilt (binocular orientation difference) between the pairs of dots presented to the two eyes was varied between +/- 11 degrees. Nonius lines were used to maintain vergence angle, which was varied between 28 cm and infinity. Subjects judged which pair of alternating images produced the smallest amount of apparent motion (position change). It was found that at all eccentricities examined the corresponding horizontal meridia were generally aligned but the corresponding vertical meridia were consistently offset (extorted) by about +/- 2 degrees. The tilts of corresponding principal meridia were typically unaffected when vergence angle was varied, indicating that little or no cyclovergence accompanied changes in horizontal vergence. The results suggest that the binocular correspondence system appears to be mapped by a horizontal shear distortion that extends to retinal locations at least as far as 16 deg away from the foveae. The invariant extortion of corresponding principal vertical meridia with vergence state is consistent with previous suggestions that the empirical vertical horopter becomes progressively inclined with respect to the vertical as viewing distance increases.
Perception 01/1999; 28(2):143-53. · 1.31 Impact Factor
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ABSTRACT: Frisby et al (1993 Perception 22 Supplement, 115) proposed that the visual system might make cyclovergent eye movements in order to minimise the overall pattern of both vertical and horizontal disparities when an observer views an inclined stereoscopic surface. Their measurements of cyclovergence, which used vertically oriented nonius lines, were found to be consistent with that proposal. In our experiment 1, we measured torsional eye movements objectively, using scleral coils, and found no evidence of a cyclovergent response to either a real inclined surface or to a simulated inclined surface in which the two stereoscopic images were related by a horizontal shear transformation. These results are inconsistent with the disparity minimisation hypothesis. In order to account for the discrepant findings of the two studies, we propose that vertically oriented nonius lines may not be a valid method for assessing cyclovergence because the lines can be seen as lying 'within' the inclined surface. In experiment 2, we tested the predictions of the cyclovergence hypothesis of Frisby et al against our own 'within surface' explanation, using both horizontally and vertically oriented nonius lines and dichoptic images related by either a horizontal or a vertical shear. If cyclovergence were the cause of the misalignment, both horizontal and vertical nonius lines should appear misaligned to the same extent. This was not found to be the case. We conclude that vertical nonius lines may not be a valid technique for measuring cyclovergence when the lines are seen against a background of an inclined surface.
Perception 01/1999; 28(2):127-41. · 1.31 Impact Factor
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ABSTRACT: Disparity discrimination thresholds are known to increase with both retinal eccentricity and distance from the horopter. However, little is known about how the detectability of cyclopean gratings varies with retinal position. Thresholds for disparity corrugations were measured as a function of corrugation frequency for different visual eccentricities. Subjects viewed annular displays of random dot stereograms, and judged in which of two intervals a circumferential disparity modulation was present. For any given eccentricity, visual sensitivity to disparity corrugations was bandpass. As eccentricity increased from 3.5 to 21.0 degrees, peak-to-trough thresholds were found to increase, the optimal corrugation frequency for detection decreased, and the upper cutoff corrugation frequency also decreased. The M-Scaling functions of Rovamo and Virsu were used to replot the data in terms of cycles per unit cortical distance. Peak detection frequency was constant at 0.8 cycles per mm of cortex after this rescaling, demonstrating that acuity for disparity modulations is approximately M-scaled beyond the fovea.
Vision Research 10/1998; 38(17):2533-7. · 2.41 Impact Factor
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ABSTRACT: A veridical estimate of viewing distance is required in order to determine the metric structure of objects from binocular stereopsis. One example of a judgment of metric structure, which we used in our experiment, is the apparently circular cylinder task (E B Johnston, 1991 Vision Research 31 1351-1360). Most studies report underconstancy in this task when the stimulus is defined purely by binocular disparities. We examined the effect of two factors on performance: (i) the richness of the cues to viewing distance (using either a naturalistic setting with many cues to viewing distance or a condition in which the room and the monitors were obscured from view), and (ii) the range of stimulus disparities (cylinder depths) presented during an experimental run. We tested both experienced subjects (who had performed the task many times before under full-cue conditions) and naïve subjects. Depth constancy was reduced for the naïve subjects (from 62% to 46%) when the position of the monitors was obscured. Under similar conditions, the experienced subjects showed no reduction in constancy. In a second experiment, using a forced-choice method of constant stimuli, we found that depth constancy was reduced from 64% to 23% in naïve subjects and from 77% to 55% in experienced subjects when the same set of images was presented at all viewing distances rather than using a set of stimulus disparities proportional to the correct setting. One possible explanation of these results is that, under reduced-cue conditions, the range of disparities presented is used by the visual system as a cue to viewing distance.
Perception 02/1998; 27(11):1357-65. · 1.31 Impact Factor
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ABSTRACT: Yang and Blake (1991 Vision Research 31 1177-1189) investigated depth detection in stereograms containing spatially narrow-band signal and noise energies. The resulting masking functions led them to conclude that stereo vision was subserved by only two channels peaking at 3 and 5 cycles deg-1. Glennerster and Parker (1997 Vision Research 37 2143-2152) re-analysed these data, taking into account the relative attenuation of low- and high-frequency noise masks as a consequence of the modulation transfer function (MTF) of the early visual system. They transformed the data using an estimated MTF and found that peak masking was always at the signal frequency across a 2.8 octave range. Here we determine the MTF of the early visual system for individual subjects by measuring contrast thresholds in a 2AFC orientation-discrimination task (horizontal vs vertical) using band-limited stimuli presented in a 7 deg x 7 deg window at 4 deg eccentricity. The filtered stimuli had a bandwidth of 1.5 octaves in frequency and 15 degrees in orientation at half-height. In the subsequent stereo experiment, the same (vertical) filters were used to generate both signal and noise bands. The noise was binocularly uncorrelated and scaled by each subject's MTF. Subjects performed a 2AFC depth-discrimination task (crossed vs uncrossed disparity) to determine threshold signal contrast as a function of signal and mask frequency. The resulting functions showed that peak masking was at the signal frequency over the three octave range tested (0.4-3.2 cycles deg-1). Comparison with simple luminance-masking data from experiments with similar stimuli shows that bandwidths for stereo masking are considerably larger. These data suggest that there are multiple bandpass channels feeding into stereopsis but that their characteristics differ from luminance channels in pattern vision.
Perception 02/1998; 27(11):1345-55. · 1.31 Impact Factor
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ABSTRACT: Two-frame random-dot kinematograms (RDKs) of different dot density, area and contrast were used to study the spatial properties of the human visual motion system. It was found that the maximum spatial displacement at which observers could reliably discriminate the direction of motion (dmax) increased gradually by a factor of up to 6.4 as dot density was decreased from 50 to 0.025% for high Michelson contrast (0.997) stimuli. As stimulus area was reduced from 645 deg2, this trend gradually disappeared so that by a stimulus area of 2.56 deg2, there was no effect of density upon dmax. A further experiment investigated the effects of reducing Michelson contrast from 0.77 to 0.2 on dmax over this same range of dot densities. It was found that at the highest densities, dmax declined as contrast was reduced. Furthermore, for contrasts at and below 0.4, dmax was invariant of density over the range 50-5%. These results can be accounted for by the fact that both reducing contrast, while keeping density fixed, and reducing density, while maintaining a fixed high contrast, reduce the stimulus mean luminance. For all contrasts, decreasing density below 5% led to an increase in dmax. However, the rate of this increase was slower for the lower contrast stimuli. A two-stage model based on bandpass filtering followed by an informationally limited motion detection stage is proposed and shown to provide a good account of these data.
Vision Research 09/1997; 37(15):2091-102. · 2.41 Impact Factor
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ABSTRACT: Under identical viewing conditions, observers made two types of judgement about the shape of stereoscopically defined surfaces: one required an estimate of viewing distance for correct performance (e.g. setting the depth of a hemi-cylinder to equal its half-height or a dihedral angle to 90 deg), the other did not (matching the depth of, for example, sinusoidal corrugations or hemi-cylinders presented at two distances). Depth constancy for the two types of task was about 75% and 100%, respectively. We argue that observers may use a simple "direct" strategy to perform the depth matching task rather than constructing and comparing a metric representation of each surface.
Vision Research 12/1996; 36(21):3441-56. · 2.41 Impact Factor
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ABSTRACT: Depth from binocular disparity and motion parallax has traditionally been assumed to be the product of separate and independent processes. We report two experiments which used classical psychophysical paradigms to test this assumption. The first tested whether there was an elevation in the thresholds for detecting the 3D structure of corrugated surfaces defined by either binocular disparity or motion parallax following prolonged viewing (adaptation) of supra-threshold surfaces defined by either the same or different cue (threshold elevation). The second experiment tested whether the depth detection thresholds for a compound stimulus, containing both binocular disparity and motion parallax, were lower than the thresholds determined for each of the components separately (sub-threshold summation). Experiment 1 showed a substantial amount of within- and between-cue threshold elevation and experiment 2 revealed the presence of sub-threshold summation. Together, these results support the view that the combination of binocular disparity and motion parallax information is not limited to a linear, weighted addition of their individual depth estimates but that the cues can interact non-linearly in the computation of depth.
Vision Research 12/1996; 36(21):3457-68. · 2.41 Impact Factor
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ABSTRACT: The present study compared the relative effectiveness of differential perspective and vergence angle manipulations in scaling depth from horizontal disparities. When differential perspective and vergence angle were manipulated together (to simulate a range of different viewing distances from 28 cm to infinity), approximately 35% of the scaling required for complete depth constancy was obtained. When manipulated separately the relative influence of each cue depended crucially on the size of the visual display. Differential perspective was only effective when the display size was sufficiently large (i.e., greater than 20 deg) whereas the influence of vergence angle, although evident at each display size, was greatest in the smaller displays. For each display size the independent effects of the two cues were approximately additive. Perceived size (and two-dimensional spacing of elements) was also affected by manipulations of differential perspective and vergence. These results confirm that both differential perspective and vergence are effective in scaling the perceived two-dimensional size of elements and the perceived depth from horizontal disparities. They also show that the effect of the two cues in combination is approximately equal to the sum of their individual effects.
Vision Research 06/1996; 36(9):1255-64. · 2.41 Impact Factor
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ABSTRACT: Two-frame random-element kinematograms were used to study the matching algorithm employed by the visual system to keep track of moving elements. Previous data have shown that the maximum spatial displacement detectable (dmax) for random-dot kinematogram stimuli increases both with increasing dot size and with decreasing centre frequency for spatially band-pass kinematograms. Both of these findings could be explained by either (i) a matching algorithm sensitive to the number of false targets in the display (informational limit) or (ii) spatial-frequency tuned sensors hardwired for detecting displacements of a constant proportion of their preferred frequency (phase-based limit). The present experiment was designed to differentiate between these alternative explanations. The stimuli were band-pass filtered (difference-of-Gaussian) random-dot patterns. The combination of six dot densities and three filter sizes produced 18 experimental conditions and allowed independent control of the spectral content and filtered-element density of the stimuli. When the dot density was high, dmax was larger for the coarse-filtered stimuli, as predicted by both theories. There was also a critical dot density for each filter size, above which dmax was constant but below which dmax rose sharply. This critical density was higher for fine-filtered stimuli such that at the lowest dot density of 0.025%, dmax was constant for all filter sizes. In support of the informational limit model, dmax was found to be directly proportional to the two-dimensional spacing of filtered elements. In contrast, dmax varied from 0.6 to 8.5 cycles of the stimulus peak frequency, suggesting that a phase-based model of motion detection cannot account for the results.
Vision Research 03/1996; 36(4):545-58. · 2.41 Impact Factor
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ABSTRACT: Naive observers of random-dot stereograms depicting complex surfaces often find that they require several tens of seconds before the impression of depth emerges. With practice, however, perception times often decrease markedly: perceptual learning occurs. Current explanations of these effects were assessed in two experiments. In the first experiment the perception times of naive observers for random-dot stereograms which depicted the same complex shape but contained different ranges of disparity were measured. In the second experiment the minimum times required by experienced observers to perceive a given complex shape in stereograms that contained different ranges of disparity were determined. Perception times for the naive observers were all very fast (<3 s) and showed no evidence of perceptual learning. There was no effect of disparity range on perception times in either experiment. It was found that very large-disparity (80 min arc) complex stereograms could be perceived quickly, even by naive observers. It is concluded that the long initial latencies previously reported are not due to surface complexity nor to the range of disparities present. Other factors. such as dot size, dot density, and the correlation of the stereo images, appear to be important determinants of efficient stereoscopic performance when viewing complex random-dot stereograms.
Perception 02/1995; 24(7):749-59. · 1.31 Impact Factor
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ABSTRACT: Binocular disparity can be defined in a variety of ways and its measurement depends upon the particular coordinate framework chosen. As a result of the inverse square law, binocular disparities need to be scaled by some estimate of absolute distance if they are to be interpreted correctly. The experiments described in this paper investigated the extent to which (i) the vergence angle and (ii) the horizontal gradient of vertical disparities or 'differential perspective' provide the necessary information for judging that a stereoscopic surface is flat and frontoparallel. For small displays (< 20 deg) vergence is more effective than differential perspective in scaling frontoparallel surfaces but for larger displays (> 30 deg), differential perspective plays the major role. When both cues together specify the viewing distance, the constancy of frontoparallel-surface scaling is close to perfect for all sizes of display up to 80 deg. Analysis of the geometry of stereoscopic images shows that when a surface patch lies in a frontal plane, the binocular horizontal size ratio of any surface feature is equal to the square of its binocular vertical size ratio, whatever its distance from the observer.
Perception 02/1995; 24(2):155-79. · 1.31 Impact Factor
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ABSTRACT: It is demonstrated that when the two halves of the Müller-Lyer illusion are shown separately to the two eyes this can result in a perception of the binocularly viewed shaft as slanted in depth. For short fin lengths, the magnitude of this slant can be predicted by the extent of the ordinary two-dimensional illusion. This result is discussed in relation to Julesz's claim that stereoscopic matching of the images in the two eyes must precede whatever process is responsible for the Müller-Lyer illusion (whereas the reported illusion seems to imply the reverse). The cyclopean Müller-Lyer demonstration on which Julesz's argument is based is reexamined. It is suggested that the matching of coarse-scale features in the images in the two eyes may help to explain both the cyclopean and the reported three-dimensional Müller-Lyer illusion.
Perception 02/1993; 22(6):691-704. · 1.31 Impact Factor
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B J Rogers
Reviews of oculomotor research 02/1993; 5:119-37.
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ABSTRACT: To calculate the depth difference between a pair of points on a three-dimensional surface from binocular disparities, it is necessary to know the absolute distance to the surface. Traditionally, it has been assumed that this information is derived from non-visual sources such as the vergence angle of the eyes. It has been shown that the horizontal gradient of vertical disparity between the images in the two eyes also contains information about the fixation distance. Recent results, however indicated that manipulations of the vertical disparity gradient have no effect on either the perceived shape or the perceived depth of surfaces defined by horizontal disparities. Following the reasoning of Longuet-Higgins and Tyler, we suggest that vertical disparities are best understood as a consequence of perspective viewing from two different vantage points and the results we report here show that the human visual system is able to exploit vertical disparities and use them to scale the perceived depth and size of stereoscopic surfaces, if the field of view is sufficiently large.
Nature 02/1993; 361(6409):253-5. · 36.28 Impact Factor
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ABSTRACT: Motion parallax has been shown to be an effective and unambiguous source of information about the structure of three-dimensional (3-D) surfaces, both when an observer makes lateral movements with respect to a stationary surface and when the surface translates with respect to a stationary observer (Rogers & Graham, 1979). When the same pattern of relative motions among parts of the simulated surface is presented to a stationary observer on an unmoving monitor, the perceived corrugations are unstable with respect to the direction of the peaks and troughs. The lack of ambiguity in the original demonstrations could be due to the presence of (1) non-visual information (proprioceptive and vestibular signals) produced when the observer moves or tracks a moving surface, and/or (2) additional optic flow information available in the whole array. To distinguish between these two possibilities, we measured perceived ambiguity in simulated 3-D surfaces in situations where either nonvisual information or one of four kinds of visual information was present. Both visual and nonvisual information were effective in disambiguating the direction of depth within the simulated surface. Real perspective shape transformations affecting the elements of the display were most effective in disambiguating the display.
Perception & Psychophysics 10/1992; 52(4):446-52. · 1.37 Impact Factor
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ABSTRACT: Under identical viewing conditions, observers made two types of judgement about the shape of stereoscopically defined surfaces: one required an estimate of viewing distance for correct performance (e.g. setting the depth of a hemi-cylinder to equal its half-height or a dihedral angle to 90 deg), the other did not (matching the depth of, for example, sinusoidal corrugations or hemi-cylinders presented at two distances). Depth constancy for the two types of task was about 75% and 100%, respectively. We argue that observers may use a simple “direct” strategy to perform the depth matching task rather than constructing and comparing a metric representation of each surface. Copyright © 1996 Elsevier Science Ltd.
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