Prism adaptation with simultaneous receipt of normal input

A 20-diopter vertically-displacing prism was worn on one eye in conjunction with plane glass on the other. Five groups ofSs differed in the density of a neutral filter worn over one eye. No aftereffect could be measured in either eye in any condition where the luminance of the “normal” field was equal to or greater than that of the prism field. As the luminance of the “normal” field is decreased below that of the prism field, the magnitude of aftereffect increases and is measurable in each eye.     

Adaptation to displaced vision—the influence of distribution of practice on retention

Subjects pointed to a target viewed through a laterally displacing wedge prism that gradually varied in strength from 0 to 20 diopters over a series of 42 trials. Trials were administered under conditions of massed or distributed practice. The aftereffect that resulted was measured immediately after exposure to the prism and at intervals of 2, 4, 6, 8, 10, and 15 min. Distributed practice led to a gradual decrease in the aftereffect following prism exposure, whereas the massed practice condition produced a rapid decrease followed by a slight increase in the aftereffect.     

Eye direction aftereffect

Three experiments using computer-generated human figures showed that after a prolonged observation of eyes looking to the left (or right), eyes looking directly toward the viewer appeared directed to the right (or left). Observation of an arrow pointing left or right did not induce this aftereffect on the perceived eye direction. Happy faces produced the aftereffect more effectively than surprised faces, even though the image features of the eyes were identical for both the happy and the surprised faces. These results suggest that the eye direction aftereffect may reflect the adaptation of relatively higher-level mechanisms analyzing the others eye direction.     

Duration of the motion aftereffect as a function of retinal locus and visual field.

The duration of the aftereffect induced by viewing a rotating disc was recorded separately for the four hemiretinae of the left and right eyes using a new method of measurement. The results showed duration of aftereffect to differ between nasal and temporal hemiretinae of the right eye and between left and right cerebral hemispheres.     

Loss of wavelength selectivity in contour masking and aftereffect following dichoptic adaptation

Two experiments measured the apparent orientation (aftereffect) and the threshold for detection (masking) of a colored grating viewed by one eye after exposure to a colored grating to the same or the opposite eye (monoptic inspection) or after stimulation of one eye by color and the other eye by contours (dichoptic inspection). Under the monoptic condition, the color relationship between the inspection and test stimuli exerted control over the extent of aftereffect and masking when the two stimuli were viewed with the same eye, but not when they were seen with different eyes. Aftereffect and masking were nonselective to wavelength following dichoptic inspection, irrespective of whether the test stimulus was presented to the color-adapted or to the contour-adapted eye. The results support other claims that visual detectors with chromatic and spatial tuning have monocular specificity.     

Monocular-contingent and binocular-contingent aftereffects

Alternate monocular and binocular exposure to complementary stimulation can yield opposite but coexisting aftereffects that are contingent on whether the test display is viewed with one eye or two eyes. The motion aftereffect was studied by adapting each eye separately to a contracting spiral and both eyes together to an expanding spiral. The stationary test spiral subsequently appeared to be expanding when viewed monocularly, but to be contracting when it was seen with both eyes open. With respect to the McCollough effect, after monocular exposure to red-vertical and green-horizontal gratings and binocular exposure to red-horizontal and green-vertical gratings, the appearance of the color of the test gratings when viewed with one eye was different from that when viewed with both eyes. Opposite, coexisting aftereffects induced by complementary stimulation can be interpreted as evidence that there are unique binocular aspects to visual function.     

Selective adaptation of monocular and binocular neurons in human vision

Psychophysical techniques were used to examine how subpopulations of visual neurons varying in their ocular dominance interacted in determining performance on a visual task. Using an asymmetric alternating adaptation of the left and right eyes, we manipulated the sensitivity of monocularly driven neurons while keeping the sensitivity of binocularly driven neurons constant. Relative threshold elevations were measured in the left eye, right eye, and both eyes of five observers following different ratios of alternating adaptation. It was found that whereas monocularly measured aftereffects varied monotonically as a function of the adaptation duration of the measured eye, the magnitude of the binocularly measured aftereffect remained constant regardless of how the adaptation was divided between the two eyes. This suggests that neurons differing in their ocular dominance pool their activity in determining sensitivity to a test target.     

Slant perception and binocular brightness differences: Some aftereffects of viewing apparent and objective surface slants

Placing a neutral-density filter in front of one eye produces two kinds of distortion in the perceived slant of a binocularly viewed rotating disk: (1) the top or the bottom of a disk rotating in a frontoparallel plane appears displaced toward or away from the observer, depending on the direction of rotation and whether the left or right eye is filtered; and (2) the left or right side of such disk—rotating or stationary—appears closer, depending on whether the left or right eye is filtered. The Pulfrich phenomenon accounts for the first variety of apparent slant, and the Venetian blind effect accounts for the second. Viewing the apparent slant of the rotating disk produces an aftereffect of slant in the third dimension which is greater than the aftereffect of viewing an objective slant of the same direction and magnitude.     

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 eye position and expectation on sound localization

Ss who are exposed to a sound coming from straight ahead, but who turn their eyes 20 deg to the side toward a visible speaker during the exposure period and expect to hear the sound coming from the visible source, show a shift in localization of the sound up to a maximum of about 9 deg. Ss who only turn their eyes 20 deg to the side during the exposure period show a smaller but significant shift in sound localization, while Ss who do not turn their eyes, but are led to expect that the sound will appear to come from a visible loudspeaker 20 deg to the side, show no significant shift. Comparison of test results before and after the exposure period, with eyes directed straight ahead and no visible speaker present, shows the presence of a localization aftereffect for those experimental groups that showed a significant localization shift during the exposure period. Sounds are localized a few degrees to the side of their physical location in the same direction as the shift in localization during the exposure period. Further experiments show that part, but not all, of the shift in localization during the exposure period can be understood in terms of a shift in perceived head direction. The localization aftereffects are shown not to be due to change in physical or perceived eye or head position.     

Long-lasting aftereffect of brief prism exposure

The aftereffect of 15 min of active adaptation to wedge prism displacement was shown to persist for as long as 2 weeks.     

Discriminative conditioning of prism adaptation

Two experiments were used to demonstrate that adaptation to ll-deg prism displacement can be conditioned to the stimuli associated with the goggles in which the prisms are housed. In Experiment 1 it was found that repeated alternation between a series of target-pointing responses while wearing prism goggles and a series of responses without prism goggles led to larger adaptive shift when S was tested with nondisplacing goggles than when tested without goggles. The results of Experiment 2 indicated that the adaptation revealed in the first experiment was primarily proprioceptive, rather than visual. Surprisingly, most Ss reported greater difficulty during the exposure period in overcoming the negative aftereffect than they did the prism-induced error.     

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 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.     

Aftereffects in binocular rivalry

Five experiments are reported in which the aftereffect paradigm was applied to binocular rivalry. In the first three experiments rivalry was between a vertical grating presented to the left eye and a horizontal grating presented to the right eye. In the fourth experiment the rivalry stimuli consisted of a rotating sectored disc presented to the left eye and a static concentric circular pattern presented to the right. In experiment 5 rivalry was between static radiating and circular patterns. The predominance durations were systematically influenced by direct (same eye) and indirect (interocular) adaptation in a manner similar to that seen for spatial aftereffects. Binocular adaptation produced an aftereffect that was significantly smaller than the direct aftereffect, but not significantly different from the indirect one. A model is developed to account for the results; it involves two levels of binocular interaction in addition to monocular channels. It is suggested that the site of spatial aftereffects is the same as that for binocular rivalry, rather than sequentially prior.     

Adaptation to prism-displaced vision: The importance of target-pointing

Two experiments investigated the hypothesis that the experience of manually pointing at visual targets enhances motoric adaptation to prism-displaced vision. Experiment 1 indicated that when adaptation was measured by means of redirected pointing behavior (negative aftereffect) it varied directly with the specificity of the target, the least adaptation occurring when no target was available. This relationship was not observed when adaptation was measured in terms of a shift in the felt position of the prism-exposed hand (proprioceptive shift). Experiment 2 demonstrated that after double the prism-exposure trials used in Experiment 1, target-pointing experience continued to enhance adaptation (as indexed by both types of adaptation measure). In both experiments negative aftereffect was significantly larger than proprioceptive shift for all experimental conditions and the two measures were not correlated. These latter two findings cast doubt on Harris’s notion that negative aftereffect is entirely the result of altered position sense.     

Instrumentation designed to simulate the effects of prisms used in studies of visual rearrangement

A system is described which simulates some of the visual rearrangements and changes in sensorimotor relations that occur when experimental subjects move their eyes while looking through a contact lens with a prism attached. The simulated system is more convenient than a system based on the use of a contact lens, and it is based on measures of eye movement that are important in research on the perceptual effects of visual rearrangement. The effects that occur are reviewed in this paper. We also show in detail how the artificial system, which has an eye movement monitor interfaced with a computer and display, simulates the former effects. The data show that experimental subjects who experience visual rearrangement by simulated means manifest the same kind of perceptual adaptation produced in studies in which visual rearrangement is generated by means of a prism mounted on a contact lens.     

Prism adaptation: The “target-pointing effect” as a function of exposure trials

The amount by which target pointing enhances prism adaptation (the “target-pointing effect”) was examined as a function of exposure trials. Each S served in three conditions—target-pointing, no-target, and control—wearing 20-diopter prism goggles in the first two. The S was measured prior to the exposure period on target-pointing accuracy with normal vision but with no visual feedback regarding his performance. Similar measures were taken after the 5th, 10th, 15th, 25th, 35th, 55th, and 95th exposure trials and after each of two consecutive 5-min postexposure periods in the dark. The two experimental conditions led to sharply rising and negatively accelerated adaptation (“negative aftereffect”) curves, the asymptotes of which differed markedly, in favor of the target-pointing condition. This difference in asymptotes indicates that the target-pointing effect is not limited to the early portion of the exposure period but, instead, is a relatively permanent phenomenon. There was no decline in adaptation during the postexposure period.     

Perceptual aftereffects of sustained fixation and oculomotor changes

Several conditions induce correlated perceptual and oculomotor changes. Often the perceptual aftereffects are treated as a result of the oculomotor ones. Some results are reported that cast doubt on this interpretation of the aftereffects of sustained convergence. First, the inspection distance that induces no aftereffect is nearer than the vergence resting position. Second, there are at least two situations in which the expected correlation between perceptual and oculomotor changes breaks down: (1) inspection of a near stimulus below eye level tends to induce a subsequent overestimation of the distance of a test stimulus that is accompanied by an exophoric shift instead of the expected exophoric one, and (2) closing one's eyes for some minutes induces an exophoric shift without a perceptual aftereffect. These results suggest that at least in some situations perceptual and oculomotor changes may be functionally independent.     

Apparent head position as a basis for a visual aftereffect of prolonged head tilt

A possible explanation of the visual spatial aftereffect following head tilt with eyes closed is that it is an outcome of a proprioceptive aftereffect of head position. If the upright head is apparently tilted then it might be expected that a vertical line in a dark room would also be apparently tilted. This explanation predicts that the direction and magnitude of the visual and proprioceptive aftereffects would correspond. The second of two experiments showed that the trends of the two aftereffects as a function of head tilt angle were different. It was concluded that the visual aftereffect cannot be explained in terms of a proprioceptive aftereffect.