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PubMed1989

Pattern-contingent color aftereffects on noninduced patterns.

In a series of experiments, we found that in addition to expected reports of color aftereffects on patterns viewed during induction, reliable and predictable reports of color were given by subjects to patterns they did not view during induction. These reports to noninduced patterns were generally to patterns that were orthogonal to the patterns seen during induction. Induction with, for example, a red vertical grating led to appropriate aftereffects (i.e., green) on that vertical pattern and to the complementary aftereffect (i.e., pink) on a horizontal grating. We suggest that such color aftereffects on noninduced patterns are based on a shift in the activity of orientation coding mechanisms as a result of viewing the inducing patterns. We further propose that the results are consistent with the Lie transformation group theory of neuropsychology and that they add to a growing body of research demonstrating the applicability of this theory to the understanding of pattern-contingent color aftereffects.

Attention↗
PubMed1981

Inhibitory circuits accounting for development of visual cortical mappings, stimulus preferences, and psychophysical performance.

A developmental rationale is proposed for the circuitry underlying the generation of fine retinotopic mappings, the quantitative range of simple-cell stimulus preferences, and the psychophysical performance of the visual system. It is assumed that the retina consists of a mosaic of partially overlapping elements, or hyperfields, which are laid down in a sunflower-seed pattern. These hyperfields project to a corresponding rectilinear mosaic of hypercolumns in the cortex, according to a pattern of chemoaffinities. Each hyperfield, in turn, consists of a sunflower-seed mosaic of nonoverlapping ganglion-cell receptive-field centres, which project to a matching rectilinear mosaic of minicolumns in the corresponding hypercolumn. Retinotopic order is produced in the hyperfield-hypercolumn mapping by radially symmetric inhibitory links, between cortical cells more than two minicolumns apart, which operate on Hebb-modifiable retinocortical excitatory afferent fibres. Under this mapping, hyperfield radii map onto parallel rows of minicolumns (orientation columns), and concentric semicircles of ganglion-cell receptive fields map onto spatial-frequency columns, crossing orientation columns at right angles. The 'scatter' in this mapping is equivalent to one local average receptive-field diameter. Orientation-related stimulus preferences ar produced by asymmetrical inhibitory links between cells more than two minicolumns apart, in the same spatial-frequency columns. A third network of inhibitory circuits, with Hebb-modifiable synapses, is assumed to operate between cells in the same or immediately adjacent minicolumns. This network enhances stimulus selectivity and sensitivity in simple and hypercomplex cells, and is responsible for adaptation aftereffects and sensory information storage.

Adaptation, Ocular↗
PubMed1986

Apparent velocity of motion aftereffects in central and peripheral vision.

Adapting to a drifting grating (temporal frequency 4 Hz, contrast 0.4) in the periphery gave rise to a motion aftereffect (MAE) when the grating was stopped. A standard unadapted foveal grating was matched to the apparent velocity of the MAE, and the matching velocity was approximately constant regardless of the visual field position and spatial frequency of the adapting grating. On the other hand, when the MAE was measured by nulling with real motion of the test grating, nulling velocity was found to increase with eccentricity. The nulling velocity was constant when scaled to compensate for changes in the spatial 'grain' of the visual field. Thus apparent velocity of MAE is constant across the visual field, but requires a greater velocity of real motion to cancel it in the periphery. This confirms that the mechanism underlying MAE is spatially-scaled with eccentricity, but temporally homogeneous. A further indication of temporal homogeneity is that when MAE is tracked, by matching or by nulling, the time course of temporal decay of the aftereffect is similar for central and for peripheral stimuli.

Adaptation, Ocular↗
PubMed1973

Prism adaptation: control of intermanual transfer by distribution of practice.

Correction of errors in localizing movements produced by laterally displacing vision by means of wedge prisms has been termed "prism adaptation." Intermanual transfer of prism adaptation from an exposed to an unexposed hand, with subject's head immobilized, has been reported not to occur. However, it was found that a standard learning variable, distribution of practice, controls the occurrence or nonoccurrence of transfer. When practice is massed, there is no transfer of adaptation; when it is spaced, the transfer is extensive. Spacing of practice also influences the amount of aftereffect displayed by the exposed hand.

Adaptation, Ocular↗
PubMed1978

Storage of spatially specific threshold elevation.

The decay of several visual aftereffects may be prolonged by interposing a period of light-free or pattern-free viewing between adaptation and testing. We demonstrate that this storage phenomenon can be observed using the threshold elevation aftereffect that follows inspection of a high-contrast grating pattern. Control experiments comparing thresholds for vertical and horizontal gratings after adaptation to a vertical grating reveal that the stored aftereffect, like its unstored counterpart, is pattern-selective. Storage is equally pronounced with stimuli that are detected by pattern-analyzing or movement-analyzing visual channels. Unlike other aftereffects, the threshold-elevation aftereffect requires that the storage period be light-free; no storage is seen if a blank field is inspected between adaptation and testing. The results are discussed with respect to the nature of visual aftereffects, and possible cognitive or physiological models of storage.

Figural Aftereffect↗
PubMed1978

Form-colour aftereffects: selectivity to local luminance contrast.

For long periods observers fixated low spatial frequency coloured gratings. Black and white test gratings of the same spatial frequency and orientation as the adapting gratings appeared coloured with the hue complementary to the adapting patterns when the dark test stripes fell on retinal areas previously occupied by the dark adapting stripes; no colour or very weak colour was seen when the test gratings were reversed in phase (contrast reversed). No colour aftereffects were produced with coloured gratings that lacked luminance contrast. The selectivity to the polarity of local luminance contrast can be explained by mechanisms that respond conjointly to colour and luminance contrast. The aftereffects are selective to spatial phase.

Afterimage↗
PubMed1985

Perception of movement and correlation in stroboscopically presented noise patterns.

The detection of spatiotemporal correlation in visual displays has been studied with stroboscopically presented random-noise patterns and with a signal-to-noise ratio paradigm in which the moving pattern was masked with spatiotemporal white noise. These methods reveal the ability of the visual system to detect correlation of spatiotemporal structures, rather than luminance contrast. The effects of stroboscopic rate, exposure duration, target size, and the extent of discrete spatial shifts were studied in both the central and the peripheral visual field. Evidence for orientation-selective and speed-selective mechanisms was found, as well as for extensive spatiotemporal integration. Bounds on parameters of spatial and temporal correlation and integration were obtained. The results are similar to those reported earlier, and also extend them. Their relation to results obtained through other paradigms (eg the motion aftereffect) is explored.

Figural Aftereffect↗
PubMed1985

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.

Adaptation, Physiological↗
PubMed1993

The time course of direction-selective adaptation in simple and complex cells in cat striate cortex.

1. Responses of single cortical neurons in area 17 of anesthetized cats were recorded in response to prolonged stimulation with a patch of drifting square-wave grating. 2. During adaptation in the preferred direction, all neurons showed some reduction in response to motion in the stimulated direction and most showed some reduction in the opposite, nonstimulated direction. 3. For complex cells, the time course of response decrement in both the stimulated and nonstimulated directions was exponential, with an average time constant of 5 s. Response recovery was also exponential but significantly slower, with time constants of 8 and 13 s in the stimulated and nonstimulated directions, respectively. 4. For simple cells the dynamics of the adaptation effect depended on the direction of testing. In the nonstimulated direction the time course of the change in sensitivity was similar to that of complex cells. In the stimulated direction during both the adaptation and recovery periods, simple cells showed an initial rapid exponential change on the order of a few seconds that was followed by a more gradual exponential change. 5. During prolonged stimulation in the nonpreferred direction, there was less overall change in sensitivity. For some neurons the change in sensitivity during adaptation and recovery was exponential, with a short time constant for both simple and complex cells and for stimulated and nonstimulated directions. Other neurons showed no change in sensitivity in either direction and a few neurons showed facilitation during the adaptation period. 6. There appears to be a rapid general or nonspecific process, which may be related to contrast gain control, underlying motion adaptation in striate cortical neurons. An additional slow, direction-selective process is revealed when simple but not complex cells are stimulated in the preferred direction. We suggest that this latter type of adaptation is a key feature underlying the perceptual motion aftereffect.

Animals↗
PubMed2003

The extra-retinal motion aftereffect.

Repetitive eye movements are known to produce motion aftereffect (MAE) when made to track a moving stimulus. Explanations typically centre on the retinal motion created in the peripheral visual field by the eye movement. This retinal motion is thought to induce perceived motion in the central test, either through the interaction between peripheral MAE and central target or by adaptation of mechanisms sensitive to the relative motion created between centre and surround. Less attention has been paid to possible extra-retinal contributions to MAE following eye movement. Prolonged eye movement leads to afternystagmus which must be suppressed in order to fixate the stationary test. Chaudhuri (1991, Vision Research, 131, 1639-1645) proposed that nystagmus-suppression gives rise to an extra-retinal motion signal that is incorrectly interpreted as movement of the target. Chaudhuri's demonstration of extra-retinal MAE depended on repeated pursuit to induce the aftereffect. Here we describe conditions for an extra-retinal MAE that follows more reflexive, nystagmus-like eye movement. The MAE is extra-retinal in origin because it occurs in part of the visual field that received no retinal motion stimulation during adaptation. In an explicit test of the nystagmus-suppression hypothesis, we find extra-retinal MAE fails to store over a 30s delay between adaptation and test. Implications for our understanding of motion aftereffects are discussed.

Eye Movements↗
PubMed1984

Prism Adaptation in hypnotically limb-anesthetized subjects: more disconfirming data.

Two experiments assessed the effect of hypnotically suggested arm anesthesia on adaptation to displacing prisms. In Study 1, 30 highly susceptible subjects adapted to prisms by pointing at a visual target for 2 min. with their hypnotically anesthetized dominant arm. Suggestion and hypnosis were then "lifted," and subjects were randomly assigned to three groups: subjects in one group were asked to move the hand slowly during the posttest (slow motion); those in a second group were told that hypnotic anesthesia would enable them to overcome displacement aftereffects (hypothesis informed); the remaining subjects (controls) were given no special instructions. During posttesting, all groups showed a significant displacement aftereffect, with no differences occurring between groups. Study 2 followed the same procedure except that during adaptation the usual target was removed and subjects pointed towards a homogeneous backboard. 20 highly susceptible subjects were assigned to an hypothesis-informed or control group immediately before posttesting. All subjects showed a significant displacement aftereffect. Both studies provide further evidence that hypnotic suggestions do not influence automatic perceptual processes. The results of Exp. 2 contradict the suggestion that hypnotic limb anesthesia eliminates the displacement aftereffect when the target is removed during adaptation trials.

Figural Aftereffect↗