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PubMed1983

Effects of brightness, hue, and saturation on perceived depth between adjacent regions in the visual field.

The effects of brightness, hue, and saturation on perceived depth between adjacent regions have been examined. The stimulus consisted of two hemifields of different colors, and the subject was asked to state which appeared nearer and to judge the perceived depth between them. When both hemifields were achromatic, the perceived depth was found to increase with increasing brightness difference. Some subjects tended to judge the brighter side nearer, others the darker side nearer. With the achromatic-chromatic combination, there were no differences in perceived depth among three hue conditions, whilst with the chromatic-chromatic combination the perceived depth depended on hue combination. In terms of decreasing frequency of 'nearer' judgments the hue order was red, green, blue. When the two hemifields differed only in saturation, the perceived depth increased with increasing saturation difference, and whether the effects of brightness and saturation on perceived distance from the observer can be attributed to figure-ground differentiation between adjacent regions in the visual field; but this argument does not cover the effect of hue under achromatic background conditions.

Color Perception↗
PubMed1986

Chromostereopsis and chromatic dispersion.

Slits placed before the eyes measured the chromatic dispersion of the eyes as a function of the separation of the slits. Prisms in front of the eyes determined the separation of the visual and null axes. The product of these separate measurements predicted the apparent depth expected with full-pupil stereoscopy. Agreement was good suggesting that chromostereopsis depends primarily on dispersion. The pupils were important modulators; a term for the Stiles-Crawford effect was not needed. Theoretical calculations to predict the effects of dispersion by slits and prisms agreed with experiments.

Color Perception↗
PubMed1995

Depth release of illusory contour shape in the Ehrenstein grid.

In the Ehrenstein grid, bright illusory patches delineated by illusory contours are seen. In order to assess whether the illusory patches possess shape constancy, the Ehrenstein grid was viewed straight on and at various angles of slant with respect to the observer. Observers matched the apparent shape of the illusory patches with a circle or an ellipse defined by real lines in a reference stimulus. Results show that, when viewed at a slanted angle, the shape of the bright patches was deformed and became oval. Such deformation was much less when the illusory contours were replaced by real contours. We label this dissociation of shape perception from depth cues depth release to contrast it with the previously described phenomenon of depth capture in which depth cues displace the illusory patches in depth. As a common explanation for both effects, it is proposed that the illusory contours induced by line ends or line ends themselves provide only weak or ineffective depth signals.

Adult↗
PubMed2005

Gaze direction modulates visual aftereffects in depth and color.

Prior physiological studies indicate that gaze direction modulates the gain of neural responses to visual stimuli. Here, we test gaze modulation in the perceptual domain using color and depth aftereffects. After confirming retinotopy of the effects, we employed a balanced alternating adaptation paradigm (adaptation alternates between opponent stimuli) to demonstrate that opposite color and depth aftereffects can co-develop at the same retinal location for different gaze directions. The results provide strong evidence for (a) gaze modulation of aftereffects, (b) generality of gaze modulation across two visual attributes, and (c) perceptual correlates of the modulation of neural activity by gaze direction.

Color Perception↗
PubMed2005

Intermittent exotropia increasing with near fixation: a "soft" sign of neurological disease.

AIM: To examine the association of distance-near disparity with neurological disease in children with intermittent exotropia. METHODS: A retrospective analysis was performed of the medical records of all children with intermittent exotropia examined at the Arkansas Children's Hospital between 1989 and 2002. The study group consisted of children with intermittent exotropia who had a near deviation that exceeded the deviation at distance by at least 10 prism dioptres. The control group consisted of children with intermittent exotropia who had a distance deviation greater than or equal to the deviation at near. The main outcome measure was the prevalence of neurological abnormalities in the study and control groups. RESULTS: Among the 29 patients in the study group, 19 (66%) had a history of concurrent neurological abnormalities. Associated neurological conditions included developmental delay (10 patients), attention deficit disorder (four patients), cerebral palsy (four patients), history of intracranial haemorrhage (four patients), periventricular leucomalacia (three patients), seizures (two patients), cortical visual impairment (two patients), hydrocephalus (one patient), history of anoxic brain damage (one patient), history of encephalitis (one patient), and autism (one patient). Among the 37 patients in the control group, seven (19%) had a history of concurrent neurological abnormalities. The difference in the prevalence of neurological disease between the study group and the control group was significant (p=0.0002). CONCLUSION: Intermittent exotropia increasing with near fixation is associated with neurological disease in children.

Adolescent↗
PubMed1995

The contribution of color to depth perceived from motion parallax.

Perceived depth was measured in a colored stimulus while stimulus movement yoked to head displacement simulated a depth of 1 cm. Velocity judgments were also made for similar stimuli moving at the same average speed but without head movement. Both measures decreased to a minimum of about 30-40% of the veridical values when the stimuli were equiluminous. Perceived depth and speed also decreased for a monochromatic stimulus as a function of luminance contrast but much more abruptly than for the chromatic stimuli. The results indicate that equiluminous color stimuli contribute to the perception of depth from motion parallax and that the contribution is not mediated by residual luminance.

Color Perception↗
PubMed2005

Colour helps to solve the binocular matching problem.

The spatial differences between the two retinal images, called binocular disparities, can be used to recover the three-dimensional (3D) aspects of a scene. The computation of disparity depends upon the correct identification of corresponding features in the two images. Understanding what image features are used by the brain to solve this binocular matching problem is an important issue in research on stereoscopic vision. The role of colour in binocular vision is controversial and it has been argued that colour is ineffective in achieving binocular vision. In the current experiment subjects were required to indicate the amount of perceived depth. The stimulus consisted of an array of fronto-parallel bars uniformly distributed in a constant sized volume. We studied the perceived depth in those 3D stimuli by manipulating both colour (monochrome, trichrome) and luminance (congruent, incongruent). Our results demonstrate that the amount of perceived depth was influenced by colour, indicating that the visual system uses colour to achieve binocular matching. Physiological data have revealed cortical cells in macaque V2 that are tuned both to binocular disparity and to colour. We suggest that one of the functional roles of these cells may be to help solve the binocular matching problem.

Color↗
PubMed2002

Hearing visual motion in depth.

Auditory spatial perception is strongly affected by visual cues. For example, if auditory and visual stimuli are presented synchronously but from different positions, the auditory event is mislocated towards the locus of the visual stimulus-the ventriloquism effect. This 'visual capture' also occurs in motion perception in which a static auditory stimulus appears to move with the visual moving object. We investigated how the human perceptual system coordinates complementary inputs from auditory and visual senses. Here we show that an auditory aftereffect occurs from adaptation to visual motion in depth. After a few minutes of viewing a square moving in depth, a steady sound was perceived as changing loudness in the opposite direction. Adaptation to a combination of auditory and visual stimuli changing in a compatible direction increased the aftereffect and the effect of visual adaptation almost disappeared when the directions were opposite. On the other hand, listening to a sound changing in intensity did not affect the visual changing-size aftereffect. The results provide psychophysical evidence that, for processing of motion in depth, the auditory system responds to both auditory changing intensity and visual motion in depth.

Acoustic Stimulation↗
PubMed1990

A stereoscopic view of visual processing streams.

Recent anatomical and physiological studies of the visual pathway suggest the existence of at least three parallel processing streams in the lateral geniculate/primary cortex structure--a magno/interblob stream for motion and transient information; a parvo/interblob stream for high spatial frequency, static information; and a parvo/blob stream for chromatic and low spatial frequency information. How does this functional typology relate to the processing for stereoscopic depth? Human stereopsis may be viewed as consisting of three distinct types of disparity processing: coarse, local stereopsis suitable for stereomovement processing by the magno/interblob stream; fine, global stereopsis suitable for the processing of complex random-dot stereograms by the parvo/interblob stream; and simple, protostereopsis for processing size differences between the two eyes by the parvo/blob stream. Extensive psychophysical evidence supports the identification of these three disparity processes with the three processing streams.

Color Perception↗
PubMed2000

An early antecedent to modern random dot stereograms --'the secret stereoscopic writing' of Ramón y Cajal.

The use of computerized random dot stimuli in modern neuroscience was introduced by Julesz in the 1960s. This method made it possible to study exclusively cortical processing of binocular information by disparity-sensitive neurons, and it has attained widespread use among neuroscientists and psychologists. It is now largely forgotten that in the last century, the famous neuroanatomist Ramón y Cajal had worked on random dot stereograms as a means of encoding written information. A brief note was finally published in a Spanish journal on photography in 1901. We present a translation of this text and summarize the early ideas on random dot stereograms, and we also supply a brief historical account on stereoscopic perception.

Depth Perception↗
PubMed1996

Functional anatomy on perception of position and motion in depth.

To investigate the neural substrates for the perception of motion and of position in depth, we examined the changes in regional cerebral blood flow during positional and motion stereopsis in humans by positron emission tomography. During positional stereopsis, the right striate and peristriate cortices (areas V1/V2 and V3) and the inferior parietal lobule were significantly activated. During motion stereopsis, the right striate and peristriate cortices (V1/V2) and the ventrolateral occipital cortex (V5) were significantly activated. These results suggest that brain regions active during stereopsis may be dependent, despite their considerable overlap, on the properties of stereopsis, i.e. positional or motion stereopsis.

Adolescent↗
PubMed1992

Depth capture and transparency of regions bounded by illusory and chromatic contours.

Spillmann and Redies noted that when a transparent textured pattern is held above the Ehrenstein figure, the subjective surfaces appear to lie not in the plane of the figures but in the plane of the overlying texture. In Experiment 1, we tested this phenomenon with chromatic squares and found that the perceived depth of regions bounded by the chromatic contours was captured by overlying texture planes when the square was equiluminous with the background. We then tested this phenomenon with a variety of illusory contour stimuli and found that it only occurs with figures involving fine line terminators, and not, for example, with the solid Kanizsa triangle. These results suggest that chromatic contours and the illusory contours induced by line terminators provide only weak binocular disparity signals and that these signals are easily overwhelmed by the disparity signals from the overlying luminance texture.

Color Perception↗
PubMed2006

Scene and position specificity in visual memory for objects.

This study investigated whether and how visual representations of individual objects are bound in memory to scene context. Participants viewed a series of naturalistic scenes, and memory for the visual form of a target object in each scene was examined in a 2-alternative forced-choice test, with the distractor object either a different object token or the target object rotated in depth. In Experiments 1 and 2, object memory performance was more accurate when the test object alternatives were displayed within the original scene than when they were displayed in isolation, demonstrating object-to-scene binding. Experiment 3 tested the hypothesis that episodic scene representations are formed through the binding of object representations to scene locations. Consistent with this hypothesis, memory performance was more accurate when the test alternatives were displayed within the scene at the same position originally occupied by the target than when they were displayed at a different position.

Attention↗
PubMed2002

The Pulfrich phenomenon in a large population of young healthy subjects.

BACKGROUND: To determine whether the Pulfrich phenomenon, an optical illusion occurring in many ophthalmological diseases, is perceived equally in both eyes in a large group of healthy medical students. SUBJECTS AND METHODS: A pendulum bob swinging perpendicular to the direction of observation was observed with either the right or the left eye covered with neutral density filters (50, 80 or 90 % absorption) and the apparent elliptical pendulum movement measured in depth. Interocular time delay was calculated from depth. Data from 65 individuals were included based on having: completed all 7 determinations of depth, a visual acuity of >/= 20/20 on both eyes and an intact stereoscopic perception (Titmus stereotest, acuity of >/= 20/25). RESULTS: All subjects perceived the phenomenon. Depth perception was not significantly different (p > 0.05; MANOVA) between the two eyes (depth in [mm]; mean +/- sem): OD: 8.5 +/- 0.38, 23.7 +/- 0.53, 36.3 +/- 0.81; OS 9.4 +/- 0.50, 24.1 +/- 0.69, 35.6 +/- 0.92; for 50, 80 and 90 % absorption of the filter respectively. At 0 % absorption the pendulum was seen in average at positive values (0.9 +/- 0.23 mm; p > 0.05). Calculated interocular time delay (ms) was: OD: 8.0 +/- 0.18, 5.1 +/- 0.12, 1.8 +/- 0.08; OS: 7.46 +/- 0.15, 5.0 +/- 0.11, 1.9 +/- 0.10. The average depth perceived without filter corresponded to a time delay for the right eye of 0.2 +/- 0.05 ms. Correction for the depth perception perceived without filter did not alter statistical significance. CONCLUSIONS: The Pulfrich phenomenon is perceived equally in both eyes. Depth perception without filters was not significantly different from zero. The illusion has clinical utility, since in normal subjects reliability of measurements is good and size of the illusion (without filters) small.

Adult↗
PubMed1982

Measurement of interpupillary distance with chromostereopsis.

Chromostereopsis is a perceived depth difference between coplanar objects of different color and can be used for highly accurate measurement of interocular separation (PD). A survey of PD measurement with chromostereopsis and with the PD rule on 83 subjects shows that these methods on average result in the same PD, indicating that chromostereopsis is a valid technique for PD measurement. Repeated PD measures by these 83 individuals on the authors, using the PD rule and chromostereopsis, shows that the chromostereopsis result is far more repeatable than the PD rule. Suggestions are made for the use of the chromostereopsis technique in optometric practice.

Biometry↗
PubMed1990

Neural model of stereoacuity and depth interpolation based on a distributed representation of stereo disparity.

We have developed a model for the representation of stereo disparity by a population of neurons that is based on tuning curves similar in shape to those measured physiologically (Poggio and Fischer, 1977). Signal detection analysis was applied to the model to generate predictions of depth discrimination thresholds. Agreement between the model and human psychophysical data was possible in this model only when the population size representing disparity in a small patch of visual field was in the range of about 20-200 units. Interval encoding and rate encoding were found to be inconsistent with these data. Psychophysical data on stereo interpolation (Westheimer, 1986a) suggest that there are short-range excitatory and long-range inhibitory interactions between disparity-tuned units at nearby spatial locations. We extended our population model of disparity coding at a single spatial location to include such lateral interactions. When there was a small disparity gradient between stimuli at 2 locations, units in the intermediate, unstimulated position developed a pattern of activity corresponding to the average of the 2 lateral disparities. When there was a large disparity gradient, units at the intermediate position developed a pattern of activity corresponding to an independent superposition of the 2 lateral disparities, so that both disparities were represented simultaneously. This mixed population pattern may underlie the perception of depth discontinuities and transparent surfaces. Similar types of distributed representations may be applicable to other parameters, such as orientation, motion, stimulus size, and motor coordinates.

Depth Perception↗
PubMed1987

Segregation of form, color, and stereopsis in primate area 18.

Primate visual cortical area 18 (visual area 2), when stained for the enzyme cytochrome oxidase, shows a pattern of alternating dark and light stripes; in squirrel monkeys, the dark stripes are clearly of 2 alternating types, thick and thin. We have recorded from these 3 subdivisions in macaques and squirrel monkeys, and find that each has distinctive physiological properties: (1) Cells in one set of dark stripes, in squirrel monkeys the thin stripes, are not orientation-selective; a high proportion show color-opponency. (2) Cells in the other set of dark stripes (thick stripes) are orientation-selective; most of them are also selective for binocular disparity, suggesting that they are concerned with stereoscopic depth. (3) Cells in the pale stripes are also orientation-selective and more than half of them are end-stopped. Each of the 3 subdivisions receives a different input from area 17: the thin stripes from the blobs, the pale stripes from the interblobs, the thick stripes from layer 4B. The pale stripes are thus part of the parvocellular system, and the thick stripes part of the magnocellular system. The physiological properties of the cells in the thin and pale stripes reflect the properties of their antecedent cells in 17, but nevertheless exhibit differences that suggest the kinds of processing that might occur at this stage.

Animals↗
PubMed1985

Stereopsis with chromatic signals from the blue-sensitive mechanism.

Evidence is presented that the depth seen in dim violet targets superimposed on a bright yellow background is mediated solely by the blue-sensitive mechanism. In forced-choice experiments using these stimuli, observers could discriminate between crossed and uncrossed disparities when the targets were either figural or random dot stereograms. Stereo thresholds for a three bar target whose spatial parameters were adjusted for the B cone mechanism were on the order of 40 sec of arc, a value considerably smaller than the spacing between B cones. With the additional assumption that signals from the blue-sensitive mechanism do not contribute to luminance, these results confirm that purely chromatic signals have access to stereoscopic mechanisms.

Color Perception↗