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.     

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.     

Interaction between perceived and imagined rotation

In Experiment 1, subjects performed a mental-rotation task in which they were timed as they decided whether rotated letters were normal or backwards. Between presentations of the letters, they watched a rotating textured disk that induced an aftereffect of rotary movement on the letters. The function relating reaction times to orientation was influenced asymmetrically by the aftereffect, suggesting that perceived movement interacts with imagined movement. Experiment 2 showed that the aftereffect produced a negligible influence on perceived orientation, suggesting that the influence of the aftereffect on mental rotation was not caused by changes in the perceived orientations of the letters. Detailed analysis of the mental-rotation functions suggested that the aftereffect may sometimes have induced subjects to rotate letters through the larger rather than the smaller angle back to the upright where the aftereffect was in the appropriate direction.     

Color-selectivity in simultaneous motion contrast

Thirty-two Ss were required to estimate the apparent motion of stationary vertical lines viewed against a background of moving vertical lines when both patterns were seen by the same eye (monoptic conditions) or the center pattern was seen by one eye and the surrounds by the other eye (dichoptic conditions). The stationary lines appeared to be moving from right to left as the surrounds moved left to right. The simultaneous motion contrast found under monoptic conditions was maximal when the center pattern and the surrounds were the same color and was reduced when they differed in color. The surrounds had limited influence on the apparent motion of the center section under dichoptic condition, and the color relationship was no longer important. Related color selectivity has been reported for the motion aftereffect (successive motion contrast), and both sets of data can be attributed to inlaibitory interaction (simultaneous in one case and successive in the other) among neural detectors tuned to wavelength as well as the direction of image motion.     

Visual orientation during and after lateral head,body, and trunk tilt

Visual judgments of orientation were investigated during (effect) and after (aftereffect) different body postures. In Experiment 1 four trained Ss made apparent verticality (AV) judgments before and after 2 min in each of seven orientations: head tilt left and right, body tilt left and right, trunk tilt left and right and a control condition with head ’and body upright. The aftereffect was significant for all postures excepting trunk tilt left and the control. The aftereffect from head tilt was greater than that from the same degree of body tilt, and that in the trunk tilt condition was in the same direction as’ predicted from neck stimulation. In Experiment 2, 30 Ss made AV judgments during tilt in the same seven postures. The E-phenomenon resulted from both head and body tilts, and an effect was found for trunk tilt in the direction predicted from neck stimulation. The results are discussed in terms of the otolith, neck, and trunk receptor systems.     

Estimator reliability and distance scaling in stereoscopic slant perception

When a horizontal or vertical magnifier is placed before one eye, a frontoparallel surface appears slanted. It appears slanted away from the eye with horizontal magnification (geometric effect) and toward the eye with vertical magnification (induced effect). According to current theory, the apparent slant in the geometric and induced effects should increase with viewing distance. The geometric effect does scale with distance, but there are conflicting reports as to whether the induced effect does. Ogle (1938 Archives of Ophthalmology 20 604-623) reported that settings in slant-nulling tasks increase systematically with viewing distance, but Gillam et al (1988 Perception & Psychophysics 44 473-483) and Rogers et al (1995 Perception 24 Supplement, 33) reported that settings in slant-estimation tasks do not. We re-examined this apparent contradiction. First, we conducted two experiments whose results are consistent with the literature and thus replicate the apparent contradiction. Next, we analyzed the signals available for stereoscopic slant perception and developed a general model of perceived slant. The model is based on the assumption that the visual system knows the reliability of various slant-estimation methods for the viewing situation under consideration. The model's behavior explains the contradiction in the literature. The model also predicts that, by manipulating eye position, apparent slant can be made to increase with distance for vertical, but not for horizontal, magnification. This prediction was confirmed experimentally.     

The influence of perceived rotary motion on the recognition of rotated objects

Subjects either named rotated objects or decided whether the objects would face left or right if they were upright. Response time in the left-right task was influenced by a rotation aftereffect or by the physical rotation of the object, which is consistent with the view that the objects were mentally rotated to the upright and that, depending on its direction, the perceived rotary motion of the object either speeded or slowed mental rotation. Perceived rotary motion did not influence naming time, which suggests that the identification of rotated objects does not involve mental rotation.     

Visual texture as a factor in the apparent velocity of objective motion and motion aftereffects

The apparent velocity of an objectively rotating visually textured disk is an increasing monotonic function of the coarseness (size) of visual texture. The apparent velocity of a negative motion aftereffect increases with coarseness of moving induction texture but decreases with coarseness of stationary test texture, and there is an interaction between induction and test textures. An explanation of these effects is based principally on the assumption of greater lateral inhibition between neighboring elements in finer textures.     

Discontinuity of seen motion reduces the visual motion aftereffect

Would a motion-picture film of a rotating spiral induce a spiral aftereffect? This question was studied in two experiments in which Ss viewed an animated film of circles collapsing to a point. The rate of apparent motion of the collapsing circles and the discontinuity of motion—the length of jump between successively projected circles—were varied independently. A visual aftereffect like the spiral aftereffect was created. The aftereffect increased in strength and duration with the rate of motion, but at all rates of motion it declined as discontinuity of motion increased. The results are taken as evidence that motion aftereffects are caused by selective fatigue of small, directionally sensitive motion-receptive fields.     

Auditory motion aftereffects

Observers were adapted to simulated auditory movement produced by dynamically varying the interaural time and intensity differences of tones (500 or 2,000 Hz) presented through headphones. At lO-sec intervals during adaptation, various probe tones were presented for 1 sec (the frequency of the probe was always the same as that of the adaptation stimulus). Observers judged the direction of apparent movement (“left” or “right”) of each probe tone. At 500 Hz, with a 200-deg/sec adaptation velocity, “stationary” probe tones were consistently judged to move in the direction opposite to that of the adaptation stimulus. We call this result an auditory motion aftereffect. In slower velocity adaptation conditions, progressively less aftereffect was demonstrated. In the higher frequency condition (2,000 Hz, 200-deg/sec adaptation velocity), we found no evidence of motion aftereffect. The data are discussed in relation to the well-known visual analog-the “waterfall effect.” Although the auditory aftereffect is weaker than the visual analog, the data suggest that auditory motion perception might be mediated, as is generally believed for the visual system, by direction-specific movement analyzers.     

Mechanisms underlying the slant aftereffect

Transfer of the median plane slant aftereffect was assessed across changes in the type of depth information for the slant of the display. In addition, the effectiveness of monocularpictorial and binocular information in inducing the aftereffect was measured. Binocular information produced a larger aftereffect than did monocular-pictorial information, and adaptation created with one type of depth information induced an aftereffect assessed with presentation of the other type of depth information. The results suggest that the slant aftereffect is not entirely specific to type of depth information presented. The induction of the aftereffect involves a process more general than the sensory mechanisms responsible for adaptation to twodimensional tilt or adaptation to a texture gradient.     

Perceptual depth synthesis in the visual system as revealed by selective adaptation

Selective adaptations was used to determine the degree of interactions between channels processing relative depth from stereopsis, motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surfaces, viewed either stationary binocularly or monocularly with motion parallax, to appear to slant in the opposite direction compared with the slant initially adapted to. Monocular adaptations on frontoparallel surfaces covered with a pattern of texture gradients caused a subsequently viewed test surface, viewed either monocularly with motion parallax or stationary binocularly, to appear to slant in the opposite direction as the slant indicated by the texture in the adaptation condition. No aftereffect emerged in the monocular stationary test condition. A mechanism of independent channels for relative depth perception is dismissed in favor of a view of an asymmetrical interactive processing of different information sources. The results suggest asymmetrical inhibitory interactions among habituating slant detector units receiving inputs from static disparity, dynamic disparity, and texture gradients.     

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.     

Effect of image orientation on the eye direction aftereffect

After observing a face with the eyes looking to the left or right (adaptation stimulus), the perception of the eye direction of the subsequent face (test stimulus) is biased in the opposite direction of the adapted eye direction; this is called the eye direction aftereffect (EDAE). In the present study, the adaptation stimuli were rotated 90° (clockwise or counterclockwise) or 180° relative to the viewer. The EDAE was measured using upright test stimuli. For the 90° rotation, prior observation of the leftward and rightward eye directions biased the perceived eye directions of the upright test stimuli to the right and left, respectively. These results suggest that the adaptation was induced utilizing an object-based (or face-based) reference frame. For the 180° rotation, however, the results suggest that the adaptation was induced in a viewer-centered reference frame. The involvement of an object-based reference frame suggests that the EDAE reflected the adaptation of a relatively higher-level mechanism at least when the rotation angle from the upright position did not exceed 90°.     

Visual laterality in the domestic horse (Equus caballus) interacting with humans

Most horses have a side on which they are easier to handle and a direction they favour when working on a circle, and recent studies have suggested a correlation between emotion and visual laterality when horses observe inanimate objects. As such lateralisation could provide important clues regarding the horse’s cognitive processes, we investigated whether horses also show laterality in association with people. We gave horses the choice of entering a chute to left or right, with and without the passive, non-interactive presence of a person unknown to them. The left eye was preferred for scanning under both conditions, but significantly more so when a person was present. Traditionally, riders handle horses only from the left, so we repeated the experiment with horses specifically trained on both sides. Again, there was a consistent preference for left eye scanning in the presence of a person, whether known to the horses or not. We also examined horses interacting with a person, using both traditionally and bilaterally trained horses. Both groups showed left eye preference for viewing the person, regardless of training and test procedure. For those horses tested under both passive and interactive conditions, the left eye was preferred significantly more during interaction. We suggest that most horses prefer to use their left eye for assessment and evaluation, and that there is an emotional aspect to the choice which may be positive or negative, depending on the circumstances. We believe these results have important practical implications and that emotional laterality should be taken into account in training methods.     

Psychophysical evidence for an extrastriate contribution to a pattern-selective motion aftereffect

A stationary vertical test grating appears to drift to the left after adaptation to an inducing grating drifting to the right, this being known as the motion aftereffect (MAE). Pattern-specific motion aftereffects (PSMAEs) induced by superimposed pairs of gratings in which the component gratings drift up and down but the observer sees a single coherent plaid drifting to the right have been investigated. Two experiments are reported in which it is demonstrated that the PSMAE is tuned more to the motion of the pattern than to the orientation and direction of motion of the component gratings. However, when subjects adapt to the component gratings in alternation, aftereffect magnitude is dependent upon the individual grating orientations and motion directions. These results can be interpreted in terms of extrastriate contributions to the PSMAE, possibly arising from the middle temporal area, where some cells, unlike those in striate cortex (V1), are tuned to pattern motion rather than to component motion.     

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.     

A moving display which opposes short-range and long-range signals

A novel display is described which stimulates both the long-range and the short-range motion detecting processes simultaneously, but with opposing directions of movement. The direction in which the stimulus appears to move depends on retinal eccentricity and element size, but adaptation to the display always produces a motion aftereffect (MAE) direction opposite to the direction of the short-range component. The display may offer insights into the properties of the two-process motion detecting system.     

After effect of seen movement: Evidence for peripheral and central components

Three experiments showed that the movement after-effect (MAE) contains both peripheral and central components. In Experiment I, the left eye viewed a sectored disc rotating to the left, and the right eye viewed a disc rotating to the right, on corresponding retinal areas. Result: when each eye in turn then viewed a stationary disc, the left eye saw a MAE to the right, and the right eye a MAE to the left. These MAE_s must be peripheral.

In Experiment II, it was arranged that the movement information was shared out between the eyes, using a ring of lights which were switched on and off to give rotating phi movement. It was arranged that each eye on its own saw a random flashing oscillation but the two eyes together saw rotation anticlockwise. Result: a clockwise MAE was seen, which must be central.

In Experiment III, the switching programme was modified to arrange that now each eye on its own saw rotation clockwise, but the two eyes together saw rotation anticlockwise. Result: a clockwise MAE was seen, which must be central. (Peripheral MAE_s from each eye on its own would have been anticlockwise.)