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Disparity-tuned channels of the human visual system.

Traditionally, it has been thought that the processing of binocular disparity for the perception of stereoscopic depth is accomplished via three types of disparity-selective channels--"near," "far," and "tuned." More recent evidence challenges this notion. We have derived disparity-tuning functions psychophysically using a subthreshold summation (i.e. low-level masking) technique. We measured correlation-detection thresholds for dynamic random-element stereograms containing either one or two surfaces in depth. The resulting disparity-tuning functions show an opponent-type profile, indicating the presence of inhibition between disparity-tuned units in the visual system. Moreover, there is clear inhibition between disparities of the same sign, obviating a strict adherence to near-far opponency. These results compare favorably with tuning functions derived psychophysically using an adaptation technique, and with the tuning profiles from published single-unit recordings. Our results suggests a continuum of overlapping disparity-tuned channels, which is consistent with recent physiological evidence as well as models based on other psychophysical data.

Depth Perception↗
PubMed1994

Visual directions of two stimuli in Panum's limiting case.

Visual directions of the two stimuli in Panum's limiting case with different interstimulus and convergence distances confirmed the predictions from the reformulated Wells-Hering's laws of visual direction. In experiment 1, six observers each converged on the midpoint of the interstimulus axis at 30, 60, and 90 cm from the eyes and adjusted a probe on the fixation plane to be in the same visual direction as that of each stimulus. Visual direction of the far stimulus was always nonveridical whereas that of the near stimulus was veridical only when its retinal disparity was small. In experiment 2, three observers each converged on the intersection of mid-sagittal plane and (a) the frontoparallel plane of the near stimulus, (b) that of the midpoint between the two stimuli, or (c) that of the far stimulus. The midpoint of the interstimulus axis was 60 cm from the eyes. Visual direction of the far stimulus was veridical only with convergence at the far plane. Visual direction of the near stimulus was veridical with convergence at the near plane, and also, only when its retinal disparity was small, with convergence at the two other planes.

Analysis of Variance↗
PubMed1994

Spatial displacement limits for cyclopean (stereoscopic) apparent-motion perception.

The range of spatial displacements over which cyclopean (stereoscopic) apparent motion is perceived was investigated. The cyclopean stimuli were created from retinal disparity embedded in dynamic random-dot stereograms. In one experiment, the displacement range for crossed-disparity cyclopean motion was compared with that for luminance-domain motion. The results showed that cyclopean motion was perceived over spatial displacements that were about two to three times larger than the displacements over which luminance motion was perceived. In a second experiment, the displacement range for crossed-disparity cyclopean motion was compared with that for uncrossed-disparity cyclopean motion. The results revealed that the displacement range was restricted (motion quality was poor) for uncrossed motion relative to crossed motion. It is inferred that cyclopean motion from crossed disparity is represented at a coarse spatial scale, relative to luminance motion, and that cyclopean motion from uncrossed disparity is suppressed due to occlusion cues present when uncrossed stimuli are seen behind a textured background.

Female↗
PubMed1995

Position dependency of rapidly induced saccade disconjugacy.

We tested the ability of normal subjects to alter the conjugacy of their saccades in a position-specific manner. Five subjects dichoptically viewed a stereogram produced by two random-dot patterns. They immediately perceived a three-dimensional wedge with its apex closer to them. They were asked to saccade for 15 min back and forth between the apex and two lateral dots of the wedge. For fixation sequences between centre-right-centre, saccades immediately became larger in the right eye. For sequences between centre-left-centre, saccades immediately became larger in the left eye. For two subjects this non-monotonic position-specific disconjugacy compensated for the disparity of the stereogram almost perfectly. The disconjugacy persisted even under monocular viewing of one of the random-dot patterns. It diminished or disappeared immediately, however, when the random-dot pattern was shifted on the screen. We suggest the existence of a fast learning mechanism capable of producing position-specific disconjugacy by associating saccades with disparity. Such a mechanism would use a visual reference rather than the position of the eyes in the orbit.

Adult↗
PubMed2001

Disparity tuning in macaque area V4.

Neural processing of stereoscopic depth is conventionally associated with the dorsal (spatial) pathway in primate visual cortex. The role of depth information in the ventral (object) pathway has been less certain. We found prominent tuning for stereoscopic disparity in area V4, an intermediate stage in the ventral pathway. Eighty percent of the cells in our sample exhibited significant disparity tuning over the -1.0 degree to 1.0 degree range, and the majority showed > 2:1 response differences. Tuning function shapes were similar to those reported previously in other visual areas. We observed a significant tuning bias towards crossed (near) disparities. This could reflect an emphasis in the ventral pathway on foreground objects or parts of objects projecting towards the viewer.

Animals↗
PubMed1998

Vergence eye movements elicited by stimuli without corresponding features.

We have observed quantitative depth perception with a dichoptic stimulus which possessed no contrast-defined binocular corresponding features (phantom stereogram). The depth perception can be the result of appreciation of a partial-occlusion situation depicted by the stimulus, or the result of activities of low-level disparity detectors which are capable of combining dissimilar local features in the stimulus. Although both mechanisms predict similar depth perception, they predict different vergence eye-movement outputs, especially in the vertical dimension. To identify the underlying mechanisms of the phantom stereopsis, we recorded vergence tracking eye movements to four types of dichoptic stimuli: (a) conventional stereogram with horizontal disparity (HD); (b) horizontal phantom stereogram (HP); (c) conventional stereogram with vertical disparity (VD); and (d) vertical phantom stereogram (VP). We found that HD, HP, and VD stimuli could elicit robust vergence tracking eye movements but VP stimulus could not. While the success of HP stimulus in eliciting vergence tracking may be explained by proximal vergence, the failure of VP stimulus in eliciting vergence tracking clearly indicates that phantom stereogram could not elicit coherent responses among low-level disparity detectors. Partial occlusion, therefore, has to play an important role in the depth perception from the phantom stereogram.

Data Interpretation, Statistical↗
PubMed2000

The effects of age upon the perception of depth and 3-D shape from differential motion and binocular disparity.

The ability of younger and older adults to perceive the 3-D shape, depth, and curvature of smooth surfaces defined by differential motion and binocular disparity was evaluated in six experiments. The number of points defining the surfaces and their spatial and temporal correspondences were manipulated. For stereoscopic sinusoidal surfaces, the spatial frequency of the corrugations was also varied. For surfaces defined by motion, the lifetimes of the individual points in the patterns were varied, and comparisons were made between the perception of surfaces defined by points and that of more ecologically valid textured surfaces. In all experiments, the older observers were less sensitive to the depths and curvatures of the surfaces, although the deficits were much larger for motion-defined surfaces. The results demonstrate that older adults can extract depth and shape from optical patterns containing only differential motion or binocular disparity, but these abilities are often manifested at reduced levels of performance.

Adult↗
PubMed2004

BOLD response in dorsal areas varies with relative disparity level.

Using fMRI, we explored cortical responses to dichoptically presented random-dot (RD) stimuli which formed a checkerboard by means of horizontal disparity (Julesz). Depth reversals occurred every 800 ms by appropriate horizontal shifting of a subset of the RD pattern. We compared cortical blood oxygen level dependent (BOLD) responses of five subjects under conditions with and without binocular disparity. The results indicate that only extrastriate, but not striate, areas responded more to the stimuli with binocular disparity. We further found that the BOLD signal increased with increasing disparity level only in dorsal areas of occipito-parietal and prefrontal cortex. These results suggest that the fMRI BOLD response can reflect the processing of relative binocular disparity in extrastriate cortex.

Brain Mapping↗
PubMed1988

Lens-induced fixation disparity curves.

Change in fixation disparity was measured as lens sphere power was changed at distance and near on a young adult population. The results were graphed to yield a lens-induced fixation disparity curve. The lens curves found were grouped into four basic types (A through D). Two types (A and B) had increasing eso fixation disparity with increasing minus lens power. Type C had little change in fixation disparity with any change in lens power, whereas type D had an initial increase and then no further change with increasing minus power. In addition, approximately 74% of the 38-subject sample had different curve types at distance and near. Possible clinical uses of the lens-induced fixation disparity curve include the prescribing of near additions for pre-presbyopes based on measures of the binocular vergence response to various lens sphere combinations.

Accommodation, Ocular↗
PubMed1992

Area 21a in the cat and the detection of binocular orientation disparity.

Visual response properties were examined in 115 cells, recorded in area 21a of the cerebral cortex of anaesthetized and paralysed adult cats. Cells were binocular and had receptive fields consisting of a single uniform discharge region which fired with composite ON/OFF responses to stationary flashing stimuli. Most cells were sharply tuned for orientation, but this was unaffected by changes in stimulus length. This result is consistent with a model in which the cells of area 21a receive their input from C cells of the striate cortex. Evidence for this was obtained by studying the decline in the responsiveness in area 21a that accompanied the cooling of areas 17 and 18. There was little indication that the cells of area 21a were effective detectors of spatial disparity, but their sharp monocular orientation tuning and differences in the preferred orientation of ipsilateral and contralateral eyes hinted at a role in the detection of binocular orientation disparity. Our results, however, showed that the recorded binocular disparity curves could be accounted for by summing the two monocular contributions and there was no apparent novel binocular component.

Animals↗
PubMed2005

All Pulfrich-like illusions can be explained without joint encoding of motion and disparity.

In the Pulfrich effect, an interocular time delay results in the perception of depth. Two modified versions, the stroboscopic Pulfrich effect and dynamic visual noise with a delay, are generally explained by postulating an early stage of space/time-inseparable filtering, encoding motion and disparity jointly. However, most disparity sensors in monkey V1 do not show joint motion/disparity encoding, and we recently showed that depth perception in the stroboscopic Pulfrich effect is equally compatible with space/time-separable filtering. Here, we demonstrate that this filtering can be implemented with a population of physiologically plausible energy model units. Similar results are obtained whether the neurons are pure disparity sensors (like most V1 neurons) or joint motion/disparity sensors (like MT). We also demonstrate that the dynamic noise stimulus produces correlations between the activity in pure disparity sensors, and in a separate population of pure motion sensors. These correlations are sufficient to explain the percept. Thus, joint encoding of motion and disparity is not required to explain depth perception in Pulfrich-like stimuli: a brain which encoded motion and disparity in entirely separate neuronal pathways could still experience all of these illusions.

Animals↗
PubMed2006

Motion aftereffects specific to surface depth order: beyond binocular disparity.

Despite evidence for concurrent processing of motion and stereopsis from psychophysics and neurophysiology, the detailed relationship between depth and motion processing is not yet clear. Using the contingent aftereffect paradigm, we investigated how the order of surfaces presented across depth influenced motion perception. After having observers adapt to two superimposed populations of dots moving in opposite directions at different binocular disparities, we assessed how much of the motion aftereffect (MAE) was specific to absolute disparity and how much was specific to the depth order of the surfaces. The test contained two planes of moving dots at several different pairs of disparities and asked observers to report the MAE direction at one of the planes (the target). In addition to the disparity-contingent MAE (Verstraten, Verlinde, Fredericksen, & van de Grind, 1994), we found MAEs dependent on surface order. When the target surface was in front of another surface, observers more often reported the MAE in the direction opposite to the front adapting surface than the back. This effect was observed despite differences in absolute and relative disparity between the adapted and test surfaces. The results suggest that some motion information is represented in terms of surface depth order.

Adult↗
PubMed1997

Artificial looming yields improved performance over lateral motion: implications for stereoscopic display techniques.

In the natural world, a number of visual cues indicate that an item is quickly approaching the perceiver. Binocular disparity is one cue for depth, and it has been demonstrated that abrupt changes in disparity, artificially unaccompanied by correlated depth cues, are capable of causing the perception of looming for the observer. An experiment involving 38 undergraduates, using a computer-controlled stereoscopic display, examined the ability of above-threshold changes in disparity (artificial looming) to facilitate response time and accuracy for observers engaged in an object-enumeration task within a cluttered display. Compared with performance using the same stimuli without disparity information (lateral motion), participants were more accurate regardless of the disparity level (9, 12, 24, or 48 minutes of arc) and faster at the two lowest levels of disparity. Participants showed the classic subitizing function, suggesting that target stimuli presented with motion information were segregated from otherwise identical distractor items. It is proposed that binocular disparity information can act as a valid location cuing method in stereoscopic computer displays in which form and color information are to be preserved.

Computer Graphics↗
PubMed2000

Disparity tuning as simulated by a neural net.

Previous research has suggested that the processing of binocular disparity in complex cells may be described with an energy formalism. The energy formalism allows for a representation of disparity by differences in the position or in the phase of monocular receptive subfields of binocular cells, or by combination of these two types. We studied the coding of disparities with an approach complementary to previous algorithmic investigations. Since realization of these representations is probably not genetically determined but learned during ontogeny, we used backpropagation networks to study which of these three possibilities were realized within neural nets. Three types of networks were trained with noise patterns in analogy to the three types of energy models. The networks learned the task and generalized to untrained correlated noise pattern input. Outputs were broadly tuned to spatial frequency and did not respond to anti-correlated noise patterns. Although the energy model was not explicitly implemented, we could analyze the outputs of the networks using predictions of the energy formalism. After learning was completed, the model neurons preferred position shifts over phase shifts in representing disparity. We discuss the general meaning of these findings and the correspondences and deviations between the energy model, V1 neurons, and our networks.

Computer Simulation↗
PubMed1992

The precision of size constancy.

The precision of objective size judgments, made when target disparity changed at random from trial-to-trial, was compared to the precision of angular size judgments made under the same condition. Subjects judged incremental changes in the vertical distance separating a pair of horizontal lines. For the objective judgments (in cm), the angle subtended by the target separation decreased with increasing depth consistent with the natural geometry of physical objects. For the angular judgments (in arc min), the angular separation did not change with disparity. For separations subtending an angle < 10 arc min, objective thresholds were considerably higher than angular thresholds, indicating that size constancy does not function well at small scales. At larger scales (> 20 arc min), the Weber fractions for angular and objective thresholds were nearly equal (approximately 6%) for two of the three subjects. These same two subjects also learned to judge "objective size" when angular subtense systematically increased with increasing depth in an exact inversion of the natural relationship. Although their "anti-constancy" judgments were less precise (approximately 9%) than their constancy judgments, the fact that subjects could learn this task with little practice suggests that constancy itself may be a learned response. Angular thresholds for targets presented only in the fixation plane were significantly lower than the angular thresholds measured with random changes in disparity, showing that observers with normal stereopsis do not have direct access to information about the angle subtended at the retina.

Depth Perception↗
PubMed2004

Stabilized structure from motion without disparity induces disparity adaptation.

3D structures can be perceived based on the patterns of 2D motion signals. With orthographic projection of a 3D stimulus onto a 2D plane, the kinetic information can give a vivid impression of depth, but the depth order is intrinsically ambiguous, resulting in bistable or even multistable interpretations. For example, an orthographic projection of dots on the surface of a rotating cylinder is perceived as a rotating cylinder with ambiguous direction of rotation. We show that the bistable rotation can be stabilized by adding information, not to the dots themselves, but to their spatial context. More interestingly, the stabilized bistable motion can generate consistent rotation aftereffects. The rotation aftereffect can only be observed when the adapting and test stimuli are presented at the same stereo depth and the same retinal location, and it is not due to attentional tracking. The observed rotation aftereffect is likely due to direction-contingent disparity adaptation, implying that stimuli with kinetic depth may have activated neurons sensitive to different disparities, even though the stimuli have zero relative disparity. Stereo depth and kinetic depth may be supported by a common neural mechanism at an early stage in the visual system.

Adaptation, Ocular↗
PubMed2000

Parietal neurons represent surface orientation from the gradient of binocular disparity.

In order to elucidate the neural mechanisms involved in the perception of the three-dimensional (3D) orientation of a surface, we trained monkeys to discriminate the 3D orientation of a surface from binocular disparity cues using a Go/No-go type delayed-matching-to-sample (DMTS) task and examined the properties of the surface-orientation-selective (SOS) neurons. We recorded 57 SOS neurons from the caudal part of the lateral bank of the intraparietal sulcus (area CIP) of three hemispheres of two Japanese monkeys (Macaca fuscata). We tested 29 of 57 SOS neurons using the square plate of a solid figure stereogram (SFS) and random-dot stereogram (RDS) without perspective cues; almost all of the tested neurons (28/29) showed surface orientation selectivity for the SFS and/or the RDS without perspective cues. Eight of these 28 neurons (28.6%) showed selectivity for both the RDS and SFS, 7 (25.0%) were dominantly selective for the RDS, and 13 (46.4%) were dominantly selective for the SFS. These results suggest that neurons that show surface orientation tuning for the RDS without perspective cues compute surface orientation from the gradient of the binocular disparity given by the random-dot across the surface. On the other hand, neurons that show surface orientation tuning for the SFS without perspective cues may represent surface orientation primarily from the gradient of the binocular disparity along the contours. In conclusion, the SOS neurons in the area CIP are likely to operate higher order processing of disparity signals for surface perception by integrating the input signals from many disparity-sensitive neurons with different disparity tuning.

Animals↗
PubMed2004

A study of relationship between multifocal VEF responses and binocular disparity.

Multifocal visual evoked magnetic field (mfVEF) is useful for shortening the measurement time and/or improving the signal-to-noise ratio of recording, in investigating cortical activities elicited by multiple stimulus patches across the visual field. To record the whole-head mfVEF, we previously developed custom software to deliver multifocal stimuli and to analyze the acquired data, and we applied it to investigation of stereopsis. In the present study, relationship between mfVEF responses and binocular disparity was investigated. Subjects were instructed to fixate a nonius line in the center of a screen, and they were presented with rapid alteration of random-dot (RD) patches. The experiments consisted of a luminance change condition (condition L) and seven binocular disparity conditions (condition BDs) ranging from a crossed disparity of 1 deg to an uncrossed disparity of 1 deg. Each response evoked by one of the RD patches was obtained with the multifocal technique. Although all subjects showed obvious responses in the condition L, only one of the subjects showed obvious responses in condition BDs. The sources of the responses recorded in condition BDs were mainly localized around calcarine sulci according to the known retinotopic cortical representation. The responses obtained in condition BDs showed dependence on binocular disparity in the magnitude and the latency. These results would be the basis for further analysis of brain magnetic responses related to stereopsis.

Adult↗