Modification of depth judgment following exposures to magnification of uniocular image: Are changes in perceived absolute distance and registered direction of gaze involved?

Two studies were designed to determine whether the perceptual learning that has been demonstrated to occur during exposure to uniocular image magnification can be explained by either a modification in the perception of egocentric distance or the direction of gaze. Experiment 1 was designed to determine whether exposure to uniocular image magnification produces changes in perceived absolute distance. Experiment 2 tested the possibility that exposure to uniocular image magnification modifies the registration of direction of gaze. The results showed that, despite the occurrence of adaptive shifts in perceived depth, no significant changes in perceived absolute distance or in registered direction of gaze occur. These findings bolster confidence in the hypothesis that adaptation to uniocular image magnification is the result of a recalibration of retinal disparity.     

Temporal aspects of slant and inclination perception.

Linear transformations (shear or scale transformations) of either horizontal or vertical disparity give rise to the percept of slant or inclination. It has been proposed that the percept of slant induced by vertical size disparity, known as Ogle's induced-size effect, and the analogous induced-shear effect, compensate for scale and shear distortions arising from aniseikonia, eccentric viewing, and cyclodisparity. We hypothesised that these linear transformations of vertical disparity are processed more slowly than equivalent transformations of horizontal disparity (horizontal shear and size disparity). We studied the temporal properties of the stereoscopic slant and inclination percepts that arose when subjects viewed stereograms with various combinations of horizontal and vertical size or shear disparities. We found no evidence to support our hypothesis. There were no clear differences in the build-up of percepts of slant or inclination induced by step changes in horizontal size or shear disparity and those induced by step changes in vertical size or shear disparity. Perceived slant and inclination decreased in a similar manner with increasing temporal frequency for modulations of transformations of both horizontal and vertical disparity. Considerable individual differences were found and several subjects experienced slant reversal, particularly with oscillating stimuli. An interesting finding was that perceived slant induced by modulations of dilation disparity was in the direction of the vertical component. This suggests the vertical size disparity mechanism has a higher temporal bandwidth than the horizontal size disparity mechanism. However, conflicting perspective information may play a dominant role in determining the temporal properties of perceived slant and inclination.     

Seeing versus imagining movement in depth

Subjects judged the quality of rigid motion between pairs of three-dimensional drawings that differed by a rotation in depth. The figures were aligned with, and rotated around, either the vertical axis or an axis that was oblique with respect to the XYZ co-ordinate system. Rated quality of motion decreased with increasing angular disparity between the figures and with decreasing stimulus duration, regardless of whether the figures were vertical or oblique. The same subjects then participated in a mental rotation task using the same stimuli and angular disparities. An effect of principal axis emerged, such that subjects took longer to make decisions about obliquely aligned stimuli than about vertically aligned stimuli, especially if they received the oblique stimuli first. These data imply that perceived versus imagined movement through the same trajectory involves different processes. Whereas the apparent motion system performs its computations relatively automatically, the processes involved in mental rotation are more strategic in nature.     

Visually perceived eye level with reversible pitch stimuli: implications for the great circle and implicit surface models

Visually perceived eye level (VPEL) and perceived pitch were measured while subjects viewed two sets of stimuli that were either upright or pitched top-toward or top-away from them. The first set of stimuli, a pair of vertical lines viewed at various angles of pitch, caused systematic changes in perceived pitch and upward and downward VPEL shifts for the top-toward and top-away pitches, respectively. Neither the perceived pitch nor the VPEL measures with these stimuli differed between monocular and binocular viewing. The second set of stimuli was constructed so that, when viewed at the appropriate pitch angle, the projected orientations of the lines in the retinal image of each stimulus were similar to those generated by a pair of vertical lines pitched by a lesser amount in the opposite direction. When viewed monocularly, these stimuli appeared pitched in the direction opposite their physical pitch, yet produced VPEL shifts consistent with the direction of their physical pitch. These results clearly demonstrate a dissociation between perceived pitch and VPEL. The same stimuli, when viewed binocularly, appeared pitched in the direction of their physical pitch and caused VPEL shifts indistinguishable from those obtained monocularly. The retinal image orientations of these stimuli, however, corresponded to those of vertical line stimuli pitched in the opposite direction. This finding is therefore consistent with the hypothesis that VPEL and perceived pitch are processed independently, but inconsistent with the specific version of this hypothesis which states that differences in VPEL are determined solely on the basis of the orientation of lines in the retinal image.     

Spatial variations of visual-auditory fusion areas

The tolerance to spatial disparity between two synchronous visual and auditory components of a bimodal stimulus has been investigated in order to assess their respective contributions to perceptual fusion. The visual and auditory systems each have specific information-processing mechanisms, and provide different cues for scene perception, with the respective dominance of space for vision and of time for hearing. A broadband noise burst and a spot of light, 500 ms in duration, have been simultaneously presented to participants who had to judge whether these cues referred to a single spatial event. We examined the influence of (i) the range and the direction of spatial disparity between the visual and auditory components of a stimulation and (ii) the eccentricity of the bimodal stimulus in the observer's perceptual field. Size and shape properties of visual-auditory fusion areas have been determined in two dimensions. The greater the eccentricity within the perceptual field, the greater the dimension of these areas; however, this increase in size also depends on whether the direction of the disparity is vertical or horizontal. Furthermore, the relative location of visual and auditory signals significantly modifies the perception of unity in the vertical plane. The shape of the fusion areas, their variation in the field, and the perceptual result associated with the relative location of the visual and auditory components of the stimulus, concur towards a strong contribution of audition to visual-auditory fusion. The spatial ambiguity of the localisation capabilities of the auditory system may play a more essential role than accurate visual resolution in determining fusion.     

An analysis of motor coordination components for various localization tasks

Localization abilities of subjects in three perceptual-motor tasks were considered before and after an exposure to a visual distortion. During this distortion the subject observed his hand ballistically point to an invisible but audible target while either receiving or not receiving knowledge of results (KR) concerning pointing accuracy. Also, subjects either received a 1- or a 4-sec rest period between each of 30 exposure ballistic pointing actions. The pre- and postexposure tasks involved the ability of a subject to accurately point to an occluded and stationary auditory target, to point to the straight-ahead position in space, and to indicate when a moving, auditory target was perceived as being in the straight-ahead position. For these tasks, the pre- vs. postexposure localization difference scores are referred to as the negative aftereffect, the proprioceptive shift, and the auditory shift, respectively. Wilkinson's (1971) two-component additive model (negative aftereffect = proprioceptive shift plus auditory shift) held when KR was given regardless of amount of rest between exposure pointing responses. With a 4-sec rest and no KR, the relationship between coordination components was nonadditive (negative aftereffect greater than proprioceptive shift plus auditory shift).     

An Analysis of Motor Coordination Components for Various Localization Tasks

Localization abilities of subjects in three perceptual-motor tasks were considered before and after an exposure to a visual distortion. During this distortion the subject observed his hand ballistically point to an invisible but audible target while either receiving or not receiving knowledge of results (KR) concerning pointing accuracy. Also, subjects either received a 1-or a 4-sec rest period between each of 30 exposure ballistic pointing actions. The pre-and postexposure tasks involved the ability of a subject to accurately point to an occluded and stationary auditory target, to point to the straight-ahead position in space, and to indicate when a moving, auditory target was perceived as being in the straight-ahead position. For these tasks, the pre-vs. postexposure localization difference scores are referred to as the negative aftereffect, the proprioceptive shift, and the auditory shift, respectively. Wilkinson’s (1971) two-component additive model (negative aftereffect= proprioceptive shift plus auditory shift) held when KR was given regardless of amount of rest between exposure pointing responses. With a 4-sec rest and no KR, the relationship between coordination components was nonadditive (negative aftereffect greater than proprioceptive shift plus auditory shift).     

The appearance of surfaces specified by motion parallax and binocular disparity

The experiments reported in this paper were designed to investigate how depth information from binocular disparity and motion parallax cues is integrated in the human visual system. Observers viewed simulated 3-D corrugated surfaces that translated to and fro across their line of sight. The depth of the corrugations was specified by either motion parallax, or binocular disparities, or some combination of the two. The amount of perceived depth in the corrugations was measured using a matching technique.

A monocularly viewed surface specified by parallax alone was seen as a rigid, corrugated surface translating along a fronto-parallel path. The perceived depth of the corrugations increased monotonically with the amount of parallax motion, just as if observers were viewing an equivalent real surface that produced the same parallax transformation. With binocular viewing and zero disparities between the images seen by the two eyes, the perceived depth was only about half of that predicted by the monocular cue. In addition, this binocularly viewed surface appeared to rotate about a vertical axis as it translated to and fro. With other combinations of motion parallax and binocular disparity, parallax only affected the perceived depth when the disparity gradients of the corrugations were shallow. The discrepancy between the parallax and disparity signals was typically resolved by an apparent rotation of the surface as it translated to and fro. The results are consistent with the idea that the visual system attempts to minimize the discrepancies between (1) the depth signalled by disparity and that required by a particular interpretation of the parallax transformation and (2) the amount of rotation required by that interpretation and the amount of rotation signalled by other cues in the display.     

Wheatstone—Panum limiting case: Occlusion, camouflage, and vergence-induced disparity cues

We examined effects of binocular occlusion, binocular camouflage, and vergence-induced disparity cues on the perceived depth between two objects when two stimuli are presented to one eye and a single stimulus to the other (Wheatstone—Panum limiting case). The perceived order and magnitude of the depth were examined in two experimental conditions: (1) The stimulus was presented on the temporal side (occlusion condition) and (2) the nasal side (camouflage condition) of the stimulus pair on one retina so as to fuse with the single stimulus on the other retina. In both conditions, the separation between the stimulus pair presented to one eye was systematically varied. Experiment 1, with 16 observers, showed that the fused object was seen in front of the nonfused object in the occlusion condition and was seen at the same distance as the nonfused object in the camouflage condition. The perceived depth between the two objects was constant and did not depend on the separation of the stimulus pair presented to one eye. Experiment 2, with 45 observers, showed that the disparity induced by vergence mainly determined the perceived depth, and the depth magnitude increased as the separation of the stimulus pair was made wider. The results suggest that (1) occlusion provides depth-order information but not depth-magnitude information, (2) camouflage provides neither depth-order nor depth-magnitude information, and (3) vergence-induced disparity provides both order and magnitude information.     

Wheatstone-Panum limiting case: occlusion, camouflage, and vergence-induced disparity cues.

We examined effects of binocular occlusion, binocular camouflage, and vergence-induced disparity cues on the perceived depth between two objects when two stimuli are presented to one eye and a single stimulus to the other (Wheatstone-Panum limiting case). The perceived order and magnitude of the depth were examined in two experimental conditions: (1) The stimulus was presented on the temporal side (occlusion condition) and (2) the nasal side (camouflage condition) of the stimulus pair on one retina so as to fuse with the single stimulus on the other retina. In both conditions, the separation between the stimulus pair presented to one eye was systematically varied. Experiment 1, with 16 observers, showed that the fused object was seen in front of the nonfused object in the occlusion condition and was seen at the same distance as the nonfused object in the camouflage condition. The perceived depth between the two objects was constant and did not depend on the separation of the stimulus pair presented to one eye. Experiment 2, with 45 observers, showed that the disparity induced by vergence mainly determined the perceived depth, and the depth magnitude increased as the separation of the stimulus pair was made wider. The results suggest that (1) occlusion provides depth-order information but not depth-magnitude information, (2) camouflage provides neither depth-order nor depth-magnitude information, and (3) vergence-induced disparity provides both order and magnitude information.     

Illusory temporal order for stimuli at different depth positions

We used four experiments to examine how the perceived temporal order of two visual stimuli depends on the depth position of the stimuli specified by a binocular disparity cue. When two stimuli were presented simultaneously at different depth positions in front of or around a fixation point, the observer perceived the more distant stimulus before the nearer stimulus (Experiments 1 and 2). This illusory temporal order was found only for sudden stimulus presentation (Experiment 3). These results suggest that a common processing, which is triggered by sudden luminance change, underlies this illusion. The strength of the illusion increased with the disparity gradient and the disparity size (Experiment 4). We propose that this illusion has a basis in the processing of motion in depth, which would alert the observer to a potential collision with an object that suddenly emerges in front of the observer.     

Interrelation of the effects of binocular disparity and perspective cues on judgments of depth and height

The effects of binocular disparity (aniseikonia) and perspective cues operating together on judgments of depth and height were studied, both when these stimulus variables operated in the same direction and when they were in conflict. Both depth cues were effective upon the perception of depth and height. The effects of binocular disparity and perspective cues upon perceived depth were found to be additive. The effects of these depth cues upon perceived height showed some interaction in the sense that, operating together, the effect of the perspective cue was stronger than the separate effect of the perspective cue, both when binocular disparity and perspective cues operated in the same direction and when they were in conflict. This interactive effect increased with increasing strength of the perspective cues. The size-distance invariance hypothesis was confirmed under the present experimental conditions. By a causal analysis of inference, this invariant relation could be explained in the following way: both the perceived depth and the perceived height of the sides of the patterns were directly determined by binocular disparity and perspective cues, but the perceived height was also indirectly determined through change of perceived depth. A direct causal relation between perceived depth and perceived height was found.     

Postfusional latency in stereoscopic slant perception and the primitives of stereopsis

Random dot stereograms of slanted surfaces were constructed, each representing one or two slanted surfaces in different relative arrangements and with different axes. Latency to fusion and from fusion to stereoscopic resolution was measured for each stimulus. It was found that latency to fusion was always very brief but that latency to stereoscopic resolution varied markedly, depending upon the orientation and arrangement of the stereoscopic surfaces. A gradient of discontinuities at a surface boundary produced an instant slant response for that surface, whereas a gradient of absolute disparities across the surface did not, except under conditions where vertical declination (a form of orientation disparity) was present. We conclude that stereopsis is not based on the primitives used in matching the images for fusion and that it is, at least initially, a response to disparity discontinuities which play no role in the fusion process. We also conclude that vertical declination is responded to globally as a slant around a horizontal axis but that other forms of orientation disparity are ineffective. The evidence from our experiments does not support the existence of a stereoscopic ability to respond globally to differences in magnification (or spatial frequency). It is suggested that stereoscopic perception of slant around a vertical axis is slow because it results from the integration of local processes.     

Conditioned changes in pain reactivity I: A discrete CS elicits hypoalgesia, not hyperalgesia, on the tail-flick test

Prior work suggests that a stimulus which has been paired with an aversive event may elicit either an increase or decrease in pain reactivity. In four experiments we attempted to isolate the variables which determine the direction of the conditioned response. In all experiments, one stimulus was paired with shock (the CS+) while another was nonreinforced (the CS−). Pain reactivity was assessed by measuring tail withdrawal from radiant heat (the tail-flick test). Experiment 1 tested whether the amount of training plays a critical role. We found that the CS+ elicits longer tail-flick latencies irrespective of whether subjects received 6 or 24 CS-US pairings. Although there was some evidence that subjects may exhibit a general hyperalgesia at 2 min after the presentation of the conditioned stimulus, the results of Experiment 2 revealed that this effect was an artifact caused by differences in the amount of time between test trials. The results of Experiment 2 also showed that the difference observed between the CS+ and CS− was not due to a CS− induced hyperalgesia. Rather, it reflects a CS+ induced hypoalgesia. Experiment 3 evaluated whether the time of day at which testing occurs is important. We found that subjects exhibit conditioned hypoalgesia when tested in either the light or dark portion of the light-dark cycle. In Experiment 4 we examined whether it matters if subjects are tested in the training context or a neutral context. We found that subjects exhibit conditioned hypoalgesia during the CS+ irrespective of where they are tested. The results suggest that a CS+ elicits hypoalgesia, not hyperalgesia, on the tail-flick test over a wide range of conditions.     

Compound self-motion perception induced by two kinds of optical motion

Two kinds of flow patterns consisting of random dots were presented simultaneously to subjects to investigate whether or not two kinds of vection occur simultaneously. One pattern induces vertical linear self-translation, whereas the other induces self-rotation around a vertical axis (when either pattern is presented alone). Three sets of conditions were tested. The first condition was one in which random dots moved in a summed direction of both flow vectors. In the second condition, both flow patterns were simply overlaid, whereas in the third condition, the two kinds of flow patterns were overlaid with a depth separation produced by binocular disparity. The subjects perceived both kinds of vection simultaneously in directions opposite to those of the corresponding flow components under the first condition, whereas either vection occurred mainly under the second condition. Under the third condition, both of the flows induced each kind of vection simultaneously, despite there being no physical vector summation of dot motion. The background flow induced vection in a direction opposite to the flow direction, whereas the foreground flow induced vection in the same direction as the flow direction. These results show that induced self-translation and induced self-rotation can occur simultaneously in two ways.     

The effects of duration and luminance on binocular depth mixture

Two stimuli in the same binocular direction, one in front and the other an equal disparity behind a fixation point, are perceived at one depth. This depth is between that corresponding to the two stimulus disparities and varies continuously from one stimulus to the other as a function of the ratio of their luminances. When either duration or absolute luminance is increased, perceived depth changes toward the midpoint of the two disparities.     

Perception of depth: Processing of simple positional disparity as a function of viewing distance

Dependency of perceived depth (relative to the fixation point) on disparity, viewing distance, and the type of the stereoscopic stimulus was investigated. Nearly complete constancy of depth, as required for a veridically matched perception, was observed only at small disparity values and with the larger square-formed stimulus; under these conditions, perceived depth corresponded well with real depth intervals for close viewing distances. Additionally, a model for perceptual processing of both variables, disparity and viewing distance, was applied to the data.     

Relationship of induced motion and apparent straight-ahead shifts to optokinetic stimulus velocity

Induced motion (IM) of a fixated spot stimulus and shifts of the apparent straight-ahead (ASA) from the objective median plane were studied as a function of the velocity of a full-field optokinetic background stimulus. Both IM and ASA were influenced similarly by changes in stimulus velocity. The magnitude of both responses, averaged across subjects, increased to a peak level with background velocities of 40-80 deg/sec and decreased at higher velocities. Individual subjects differed with respect to the precise functions by which IM and ASA shifts were related to stimulus velocity. However, for individual subjects, the effects of velocity on IM and ASA shifts were typically highly correlated. Although IM is correlated with shifts of ASA in the opposite direction, the magnitude of the ASA shift is insufficient to account for the observed IM.     

Stereoscopic matching and the aperture problem

In order to perceive stereoscopic depth, the visual system must define binocular disparities. Consider an oblique line seen through an aperture formed by flanking occluders. Because the line is perceived behind the aperture, the line must have disparity relative to the aperture. What is the assigned disparity of the line in this aperture problem? To answer this question five observers adjusted the horizontal disparity of a probe until it was perceived at the same depth as the disparate line behind the aperture. The results show that, when both the horizontal and the vertical disparities of the occluders are well-defined, the probe must have the same horizontal disparity as the horizontal separation between the line half-images. However, when the horizontal and vertical disparities of the occluders are ill-defined, the intersections of the line and the occluder borders can determine the matching direction. In the latter case, the matching direction varies with the aperture orientation and there is considerable variability across observers.     

错误再认:意识、注意和刺激特性

该研究基于错误再认现象,确立了意识知觉和无意识知觉在行为结果上的质的差异。在决定一个刺激是被有意识知觉还是无意识知觉时,刺激特性和注意之间存在着相互补偿的作用。实验一表明,当一个刺激短暂呈现而被无意识知觉的时候,增强刺激特性或提高注意水平都能使它的知觉变为有意识的;相对应地,实验二表明,一个处于分散注意条件下被无意识知觉的刺激,也可以通过使注意集中或增强刺激特性而使它的知觉变为有意识的。该研究对意识、注意和刺激特性三者间的关系进行了讨论。