Kanizsa's shrinkage illusion produced by a misapplied 3-D corrective mechanism

In order to include the monocular areas from the left and the right eye in the cyclopean view, the visual system displaces the occluded elements which would result in a horizontal elongation of the shape but does not occur thanks to a correction mechanism which preserves the shape. We hypothesised that this mechanism causes Kanizsa's amodal shrinkage illusion (the apparent elongation of a partially occluded square) when it is incorrectly applied by the visual system to a two-dimensional stimulus. Four experiments tested this hypothesis: (i) one-eyed observers were less susceptible to the illusion than people with normal binocular vision because, for them, the correction for shape is unnecessary; (ii) the illusion was stronger with binocular than with monocular vision since binocularity induces the visual system to correct for the shape distortion; (iii) the illusion diminished when the stimulus was rotated 90 degrees given that displacement and compression are not required for vertical occlusion; (iv) the magnitude of the illusion was a function of the width of the occluder because, as previous research has shown, the edges of a partially occluded square are less displaced the farther they are from the edges of the occluder. The data from the four experiments support our hypothesis even though no condition was able to eliminate the illusion; other possible causes are discussed.     

Adaptation to displaced vision: Amount of optical displacement and practice

The influence of two variables, length of exposure and amount of optical distortion, on adaptation to displaced vision was examined. The extent of adaptation was positively related to number of trials in a task involving spatial localization of a target displaced by a wedge prism. A substantial adaptation (38%) was produced after only two trials. The adaptation was also positively related to degree of optical displacement, except at the highest level used. The findings are discussed in terms of availability of information about the discrepancy between vision and task.     

A color-contingent prism displacement aftereffect

Observers were trained to point with feedback to red and blue dots whose images had been laterally displaced in opposite directions by a reversible prism. On pretraining and posttraining trials the red and blue dots were aligned vertically in the absence of visual orientation cues. The alignment was modified by the pointing training on the posttraining trials. The colors were aligned in the direction of their prior prismatic displacement. One control experiment showed that the alignment aftereffect requires feedback during the pointing task. Another experiment in which observers pointed to the red and blue dots with opposite arms showed that pointing to both dots with the same arm was necessary to produce the alignment aftereffect. Changes in the perceived position of objects in the visual field occur when changes in perceived limb position cannot compensate for a sensorimotor conflict. Eye torsion or fixation displacements are proposed as alternative mechanisms mediating the aftereffect.     

Conditioned adaptation to prismatic displacement with a tone as the conditional stimulus

Adaptation to prismatic displacement was conditioned to a tone in 72 min of training by employing Taylor’s alternation training technique. The alternation consisted of two training conditions. In one, S was exposed to the prism and tone; in the other, S was exposed to neither. After training, the pointing to a visual target test measured more aftereffects of adaptation when the tone was present than when it was absent. Conditioning was obtained in two testing situations: (1) with the training goggles still worn by S, and (2) with the goggles removed.     

Conditioned adaptation to prismatic displacement

Adaptation to prismatic displacement was conditioned to the wearing of a pair of goggles in 240 min of training by employing Taylor’s alternation training technique. The alternation was between training exposures with both the prism and the goggles presented to S and with both absent. After the training, both the pointing to a visual target test and the pointing straight ahead test measured more adaptation and more aftereffects of adaptation when the goggles were     

Binocular depth perception in the pigeon.

By means of a discrete-trial simultaneous discrimination procedure, pigeons were trained to respond differentially to visual arrays that were identical except that one of them contained a circle displaced in depth when viewed stereoscopically. Performance was severely disrupted when one eye was occluded. The monocular deficit was peculiar to the depth task, inasmuch as no such decrement was seen on a pattern discrimination. The results imply that presence of the displaced circle was discriminated on the basis of a binocular cue. It was also found that pigeons could discriminate the direction of the displacement. Discrimination of depth was independent of the global form and still occurred when elements of the array were randomly displaced in depth. Performance was not disrupted when the absolute convergence angle of the depth stimulus was changed. The cue that consistently accounted for the behavior seen was the detection of the relative angles of convergence--that is, the retinal disparity of the two planes in depth. Thus, despite the lateral position of the eyes of the pigeon, a small binocular field mediates the binocular discrimination of near objects in depth.     

Online control of discrete action following visual perturbation

We examined the spatial and temporal limitations of the visual corrective process in goal-directed aiming, as well as gender differences in online control. An initial experiment was conducted to test the utility of a monocular switch procedure as a method of rapidly introducing a visual perturbation. The results revealed minimal effect of the monocular switch on movement time and the endpoint error. Following this control experiment, prismatic displacement was introduced at the initiation of and during the movement. In the third experiment, the prism was presented prior to movement initiation, and then removed at the beginning of or during the movement. Movement trajectories were most influenced by the early presentation and removal of the prism, and female performance was significantly more affected by both perturbations than male performance.     

Lateral feature displacement and perceived facial attractiveness

Pairs of vertically adjacent facial features were laterally displaced in the same or opposite direction. Undergraduates rated the resulting images on attractiveness. Displacements were first made on normal faces. Symmetric faces were not rated more attractive than normal controls. Faces with two alternating adjacent pairs were rated lower than faces with one or no alternating pairs. In Exp. 2, the same displacements were made from symmetrical faces to control for distance. Symmetric faces again were not rated higher than normal ones, and both conditions were considered more attractive than faces with any type of displacement. This latter result suggests a greater sensitivity to feature displacement when performed from symmetry.     

An examination of stimulus technology level and preference displacement during multiple stimulus without replacement preference assessments

Researchers have observed that preference for edible items may displace preference for leisure items when items from the stimulus classes are assessed together within multiple stimulus without replacement (MSWO) preference assessments. The current study extends previous research by examining patterns of preference and displacement when assessing preference for high-tech and low-tech leisure items. We conducted three separate MSWO preference assessments; one assessing low-tech items, another assessing high-tech items, and a combined assessment (using the top four high- and low-tech items from the previous assessments) to test for displacement. Preference for high-tech items fully or partially displaced preference for low-tech items in five of eight participants. We then conducted concurrent and single operant reinforcer assessments using the highly preferred high-tech and low-tech items. Reinforcer assessment results demonstrated similar levels of responding for the highest preferred high-tech and low-tech items, indicating that combining high- and low-tech items within preference assessments may influence the validity of results.     

Target and arm observation effects on adaptation to prism displacement

Adaptation to displacement of objects in the visual field was studied as a function of preexposure test targets being absent or present in that field and lateral arm movement requiring no pointing at targets being observed or unobservable during prism exposure. Significantly greater adaptation was found when targets present during prism exposure were the same as those present during pre and postexposure test conditions. In addition, greater adaptation was found when S was permitted observation of lateral arm movement during prism exposure. Greatest adaptation was produced when both targets were present and arm movement was observable during prism exposure. In addition, when three targets were present during prism exposure, the greatest amount of adaptation was found for targets on S’s prismatically shifted visual field periphery.     

Factors affecting proprioceptive adaptation to prismatic displacement

Two prism displacement experiments were conducted to determine the effects of reducing proprioceptive feedback on resultant adaptation magnitude. In Experiment 1, proprioceptive reduction was produced by requesting subjects to employ passive Ivs. active) and/or fast- Ivs. slow-) paced arm movement during prism exposure. When both of these conditions were present, a significant reduction in the magnitude of proprioceptive adaptation and a significant increase in the magnitude of visual adaptation were produced. In Experiment 2, hypnotic anesthesia was employed to reduce felt sensation in an adapting limb during a prism displacement situation. This manipulation reduced proprioceptive adaptation to a nonsignificant level. The combined results of the two experiments reveal several conditions that can serve to reduce proprioceptive adaptation during prism displacement.     

Saccadic suppression of displacement is strongest in central vision

Perception of target displacement is severely degraded if the displacement occurs during a saccadic eye movement, but the variation of this effect across the visual field is unknown. A small target was displaced from a starting point at the midline, or 10 deg to the right or left, while the eye made a saccade from the 10 deg right position to the 10 deg left position. Saccades were detected and the target displaced on line. Assessed with a signal detection measure, suppression was stronger in central vision than in more peripheral locations for all three subjects. Leftward and rightward displacements yielded equal thresholds. The results complement the findings of others to reveal a picture of perceptual events during saccades, with both deeper saccadic suppression and faster correction of spatial values (the correspondences between retinal position and perceived egocentric direction), favouring more accurate spatial processing in central vision than in the periphery.     

Visuomotor coordination and intermanual transfer for a proprioceptive reaching task

Two experiments were conducted to determine the role of head constraint, whether present or absent and arm exposure type (terminal or continuous) on the production of intermanual transfer to two types of visual distortion. Experiment 1 investigated intermanual transfer to binocular, lateral prism displacement where the prism base orientation for both eyes was in the same direction. Experiment 2 determined whether intermanual transfer could be produced to squint prism viewing where the prism base orientation for each eye was in an opposite direction (base-out prisms). In both experiments transfer was produced when either head movement during prism exposure was unconstrained or when a terminal arm exposure was employed. Maximal transfer was produced when both of these conditions were employed.     

The effects of binocular and motion-generated information on the perception of depth and height

The perception of distance and size in the presence of optical gradient information was investigated under four viewing conditions—binocular view with and without head motion, and monocular view with and without head motion. Subjects (60 adults) matched distance intervals (from 15 to 127 cm) and heights of a target triangle (from 5 to 15 cm) by adjusting the length of a metal tape. Both linear and power functions were fitted to each individual’s distance judgments, and the competing perceptual models were compared. For both models, it was found that binocular information was sufficient to specify relative, but not absolute, distance, that monocular information was sufficient to specify an orderly relation between target distance and judgment but not absolute distance, that average error was less in the binocular conditions, and that perceived distance was not affected in either condition by the addition of head motion. The analysis of size judgments revealed that monocular and binocular judgments did not differ, that matches made with and without head motion did not differ, and that, in all conditions, matches exceeded target heights by an average 30% to 40%. Judged size was also analyzed as a function of target distance. In all conditions but monocular view with head motion, the effect of distance was to increase size judgments. The distance judgments support the hypothesis (Purdy, 1958) that the binocular stimulus carries information that the monocular stimulus does not; they fail to support the hypothesis (Gibson, 1966) that observer motion adds information to the static stimulus. The size judgments support neither hypothesis but suggest an independence of perceived size from perceived distance.     

The effect of feature displacement on the perception of well-known faces

The effect of feature displacement within two well-known faces (Terry Wogan and Cyril Smith) was examined. Image processing equipment was used to produce stimuli in which the features of an original facial image were displaced to form a number of modified images. This technique was first reported by Haig, in a recognition study in which the effect of feature displacement within unfamiliar faces was investigated. In the present experiment a perceptual judgement task was carried out in which subjects were presented with a number of modified faces and asked to judge how dissimilar these were with respect to an original image. A multi-dimensional scaling analysis of the comparative judgements of the subjects revealed a two-dimensional solution involving displacement of the eyes and mouth. A clear division between up/down and inward/outward displacement within these features (particularly the eyes) was observed. A similar pattern of results was found for both well-known faces. This result indicates that subjects were responding to changes in the facial configuration produced by the different types of feature displacement (horizontal or vertical), as opposed to movement of the features per se. Finally, the results also indicate that the displacement of inner features (mouth, eyes, nose) was more noticeable than displacement of the outer facial features (eg hairline).     

Binocular unmasking with vertical disparity

We recently found (Schneider, Moraglia, & Jepson, 1989) that the contrast threshold for the detection of a visual signal in a noisy background can be considerably lower when binocular cues are available then when monocular cues only are present. Here, we investigated the occurrence of binocular unmasking with vertical interocular disparities. Subjects reported about the presence of Gabor signals in fields of two-dimensional broadband Gaussian noise surrounded by a frame of uniform noise. They saw these stimuli through a stereoscope; in all cases, the right-eye noise field was vertically displaced relative to the left one in either an upward or a downward direction, by up to 67.6'. In one condition, the right-eye signal was displaced by an amount equal to that of the noise, so that no opportunities for binocular unmasking existed; in the other, it appeared in exactly corresponding locations in the two fields--here, binocular disparities could be used to unmask the signal. Enhanced signal detectability, by up to 12.7 dB, was observed in the latter case for both directions of displacement, but only for displacements of 13.52' and only when the signal's orientation was horizontal. We argue that these effects result from the summation of monocular inputs carried out by linear binocular mechanisms.     

Misconvergence to the stimulus plane causes apparent displacement of the stimulus elements seen monocularly1

Abstract: When one binocularly views a group of vertical lines through a ring, the outermost line segments (one on each side) seen within the ring are seen monocularly while the segments of the same lines outside the ring are seen binocularly. The monocular segments appear to be displaced outward with respect to the center of the ring and with respect to the corresponding binocular segments outside the ring. Three experiments examined the extent and direction of this illusory displacement as a function of viewing distance, fixation disparity created by varying the angles of the two arms of a haploscope, and fixation disparity created by a stereoscope and different Nonius stimuli. The results of the experiments confirmed the hypothesis that the apparent displacement is due to misconvergence in accordance with Wells‐Hering's laws of visual direction.     

Journal of experimental psychology: human perception and performance

We examined the nonveridicality of visual direction produced by monocular viewing. In Experiment 1, 19 subjects pointed to a small light and moved a small light to their subjective median plane. The extent of constant error under monocular and binocular viewing conditions differed in both tasks (p less than .001). The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm (p less than .01). Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of Hering's .001). The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm (p less than .01). Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of Hering's .001). The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm (p less than .01). Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of Hering's principle of visual direction can account for these results. In Experiment 2, the same subjects adapted to phoria-induced error by placing a finger over a monocularly viewed target. The difference in their pointing responses before and after the task were reliable (p less than .005), and the correlations between phoria and the pre- to posttest differences were .45 and .77, depending on the number of adaptation trials. We argue that all monocular experiments dealing with visual direction should control for these effects.     

Restricted adaptation to prism rearrangement

Changes in eye-foot and eye-hand coordination were measured following 20 min of squint prism viewing (alternate monocular viewing of the movements of each leg with the contralateral eye at 1-min intervals: prism base right for right eye and left for left eye). In different sessions, response changes were measured following the viewing of the left leg with the right eye (prism base right) for periods of i min interspersed with 1-min blank periods (periodic viewing). Sensorimotor changes following the alternate exposure condition were smaller and restricted to eye-foot responses.     

A structural dynamic of form: Displacements in memory for the size of an angle

Memory for the angular size of a chevron (V) shaped target was examined in four experiments. When the target was stationary, memory was displaced inwards (i.e., towards a smaller angle), and the magnitude of displacement increased with increases in absolute angle size. When the target moved vertically or horizontally, memory was displaced inwards, but the effect of absolute angle size was weakened, and displacement was not influenced by whether the direction of motion and the direction in which the angle pointed were the same or different. When the target expanded or contracted (i.e., increased or decreased in angular size), memory for expanding targets was displaced inwards more than was memory for contracting targets, and displacement was not influenced by whether motion was coherent or incoherent. Implications of the data for the possibility of dynamic aspects of mental representation based on the shape of a stimulus are discussed.