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At least 397 records · Page 22Linked to original sources

PubMed1994

Multiple concurrent visual-motor mappings: implications for models of adaptation.

Previous research on adaptation to visual-motor rearrangement suggests that the central nervous system represents accurately only 1 visual-motor mapping at a time. This idea was examined in 3 experiments where subjects tracked a moving target under repeated alternations between 2 initially interfering mappings (the "normal" mapping characteristic of computer input devices and a 108 degree rotation of the normal mapping). Alternation between the 2 mappings led to significant reduction in error under the rotated mapping and significant reduction in the adaptation aftereffect ordinarily caused by switching between mappings. Color as a discriminative cue, interference versus decay in adaptation aftereffect, and intermanual transfer were also examined. The results reveal a capacity for multiple concurrent visual-motor mappings, possibly controlled by a parametric process near the motor output stage of processing.

Adult↗

PubMed2003

Attention affects the stereoscopic depth aftereffect.

'Preattentive' vision is typically considered to include several low-level processes, including the perception of depth from binocular disparity and motion parallax. However, doubt was cast on this model when it was shown that a secondary attentional task can modulate the motion aftereffect (Chaudhuri, 1990 Nature 344 60-62). Here we investigate whether attention can also affect the depth aftereffect (Blakemore and Julesz, 1971 Science 171 286-288). Subjects adapted to stationary or moving random-dot patterns segmented into depth planes while attention was manipulated with a secondary task (character processing at parametrically varied rates). We found that the duration of the depth aftereffect can be affected by attentional manipulations, and both its duration and that of the motion aftereffect varied with the difficulty of the secondary task. The results are discussed in the context of dynamic feedback models of vision, and support the penetrability of low-level sensory processes by attentional mechanisms.

Adaptation, Ocular↗

PubMed1982

Direction-specific tilt illusion: with and without gaze fixation.

The perceived orientation of a test grating is rotated from its veridical orientation if an annulus grating with a similar orientation is present. The magnitude of this misperception was measured and found to be greater when the two gratings moved in the same direction than when they moved in opposite directions. This demonstration of a direction-specific tilt illusion is similar to the previously demonstrated direction-specific tilt aftereffect--which is to be expected if similar mechanisms are responsible for both phenomena. If the tilt illusion is caused by lateral inhibition between orientation-selective units, then these findings indicate that such inhibition is principally between units with similar orientation and direction of motion selectivities.

Figural Aftereffect↗

PubMed1980

Adapting to two orientations: disinhibition in a visual aftereffect.

The tilt aftereffect of adapating to two different orientations simultaneously is weaker than the aftereffect of adapting to the more effective of the two orientations alone. This finding is consistent with explanations of orientational after-effects in terms of lateral inhibition between cortical orientation detectors, but not with explanations in terms of neural "fatigue" from excitation.

Adaptation, Physiological↗

PubMed1994

Conflict between aftereffects of retinal sweep and looming motion.

Observers looked monocularly into a tunnel, with gratings on the left and right sides drifting toward the head. An exposure period was followed by a test with fixed gratings. With fixation points, left and right retinal fields could be stimulated selectively. When exposure and test were on the same retinal fields, but fixation was on opposite sides of the tunnel during exposure and test periods, aftereffects of retinal sweep and of perceived looming were in opposite directions. The two effects tended to cancel, yielding no perceived aftereffect. When they did occur, aftereffects in the retinal and the looming directions were equally likely. Cancellation was significantly more likely in the experimental conditions than in the control, when fixation always remained on the same side. When areas of retinal stimulation in the exposure and test periods did not overlap, cancellation was less frequent and aftereffects of looming were more frequent. Results were not significantly different for left and right visual fields, indicating that cortical vs. subcortical OKN pathways do not influence the illusion. Vection resulted for 16 of 20 observers under one or another of our conditions.

Adult↗

PubMed2002

Color-selective analysis of luminance-varying stimuli.

Alternating adaptation to red and green luminance-varying gratings of different spatial frequencies simultaneously induces opposing color-selective size aftereffects (Blakemore & Sutton, 1969) in the same retinal locus. With single-color adaptation, the aftereffect is larger and affects test patterns of both colors, though not equally. The color-insensitive portion of the effect shows very substantial interocular and cross-orientation transfer. The color-selective aftereffect, which accounts for about 1/3 of the total effect, is highly selective for both orientation and eye of origin. Thus, both color-selective and color-insensitive mechanisms participate in determining the perceptual characteristics of luminance-varying patterns.

Adaptation, Ocular↗

PubMed1993

Effect of spatial configuration on motion aftereffects.

Sensitivity to motion was measured by the percentage of trials on which an observer reported seeing motion of briefly presented high-contrast sinusoidal gratings moving over a range of velocities. The psychometric curve was remeasured following adaptation to a grating moving in one direction for an extended period of time. Adaptation shifted the minimum of the psychometric curve toward the direction of the direction of the adapting stimulus. The shift was smaller when the adapting field was larger than the test. In a second set of experiments we measured the effect of motion adaptation on contrast thresholds for moving gratings of different sizes. Threshold elevation was maximal when adapting and test sizes matched. We present a mechanistic model of the motion aftereffect that consists of independent multiplicative gain controls in motion-sensing mechanisms tuned to different rates of motion. In addition, we discuss a model of size effects in motion adaptation that invokes diffuse inhibitory connections among motion-sensing mechanisms.

Adaptation, Ocular↗

PubMed1980

Size-analysis of retinal images by orientation detectors.

A model for the determination of retinal-image size is presented. The size-analysis is based upon the range of orientation detectors activated by a stimulus. The model is applied to size aftereffects and is also used to predict changes in perceived size in configurations which may be expected to affect the range of orientation detectors activated. The relevance of the model to illusions of direction and the perceived length of lines forming angles is also discussed.

Adaptation, Ocular↗

PubMed1981

Adaptation to the reversal of binocular depth cues: effects of wearing left-right reversing spectacles on stereoscopic depth perception.

The principle of stereopsis, that crossed disparity causes a convex perception and uncrossed disparity a concave one, has for a long time been considered to depend on a very rigid neural mechanism not affected by experience. Experiments are reported here which show that this relationship between disparity and perceived depth can be reversed by experience. An observer wore a pair of left-right reversing spectacles continuously for nine days. The spectacles also reversed the relation between the direction of perceived depth and the direction of binocular depth cues, ie disparity and vergence. For a period starting two days before wearing the spectacles and continuing until seventy-nine days after their removal the observer was examined with a haploscope and an electrooculograph. All the stereoscopic experiments were carried out without spectacles in order to examine some aftereffects of wearing spectacles. For the stereograms with linear contours not only the adaptive reversal of the relation between disparity and perceived depth, but also some abnormal depth perceptions and long-lasting aftereffects were found. For Julesz's random-dot stereograms, however, in which contours can be seen only after binocular combination, no adaptive change or reversal occurred. These results suggest that the process of stereopsis consists of two concurrent subprocesses.

Adaptation, Ocular↗

PubMed1989

Cyclopean tilt aftereffects can be induced monocularly: is there a purely binocular process?

A series of experiments have been reported by Wolfe and Held which they have taken as evidence for the existence of more than one binocular process in human vision, specifically a simple binocular process (OR-gate) and a purely binocular process (AND-gate). In one of their studies, it was shown that tilt aftereffects induced with cyclopean stimuli produced measurable effects only when testing was binocular, which suggested that cyclopean adaptation affects only the AND-gate mechanism. If the two alleged mechanisms (AND or OR) are independent, monocular adaptation with luminance contrast stimuli should produce aftereffects which can only be measured with luminance contrast test stimuli. Cyclopean test displays would probe only the unadapted AND-mechanism. Results to the contrary are reported, casting doubt upon the functional independence, perhaps even the existence, of the so-called purely binocular process.

Adaptation, Ocular↗

PubMed1978

The angular function of orientation illusions induced by projected images of tilted real object scenes.

Tilt aftereffects induced by line gratings are maximal when the test and inducing stimuli have an angular separation of 10 degrees-15 degrees. Similar effects induced by prismatically tilted real-object scenes have been found to increase monotonically with scene tilt. The difference between these two angular functions of aftereffect (that induced by gratings and that induced by real objects) has been attributed to the 'meaning' inherent in the real-object scenes. The preliminary experiments described here suggest that tilt aftereffects and illusions induced by projected slides of tilted real-object scenes have angular functions similar to that induced by a line grating. Hence, the monotonically increasing angular function obtained in the prism studies is not necessarily determined by the use of real-object scenes.

Female↗

PubMed1981

An attempt at correlating visuomotor-induced tilt aftereffect and ocular cyclotorsion.

Subjects were exposed to an optical rotation of visual reafferences from hand movements. This is known to produce visuomotor adaptation. An experiment is reported where it also induced a perceptual aftereffect measured as a displacement of the apparent vertical and as an ocular cyclotorsion, both in the direction of the optical rotation. No correlation could be found between the two phenomena which can be considered as independent adaptive responses to the visuomotor conflict.

Adaptation, Ocular↗

PubMed1991

Contingent aftereffects: lateral interactions between color and motion.

A randomly dotted yellow disk was rotated at a speed of 5 rpm, alternating in direction every 10 sec. Its change in direction of rotation was paired with a change in surround color, which was either red or green. After 15 min of exposure, observers reported vivid motion aftereffects contingent on the color of both the stationary disk and the surround, even though during adaptation only motion or color was associated with either alone. In further experiments, it was established that a change in color (or direction of motion) of the disk could be associated with a change in direction of motion (or color) of the surround. Such lateral effects were found even when a wide (5 degree) annulus was introduced between the disk and the surround during adaptation and testing. Furthermore, the aftereffects generalized to the annulus, which was not associated with either color or motion during adaptation. However, when the disk alone was adapted to color and motion, no generalization to the surround was found (and vice versa), suggesting that the effects are not produced by adaptation of large receptive fields or by scatter of light within the eye. The results appear to conflict with the ideas that contingent aftereffects are confined to the adapted area of the retina and that they are built up by links between single-duty neurones, and with an extreme view of the segregation of color and motion early in human vision.

Adult↗

PubMed1982

A depth aftereffect caused by viewing a rotating Ames window.

After a rotating Ames window has been viewed, a normal test window held diagonal to the subject's line of sight appears to be distorted, having a larger back than front. The effect does not occur if a normal window is rotated or if the test window is held perpendicular to the subject's line of sight.

Adolescent↗

PubMed2006

Adaptive norm-based coding of facial identity.

Identification of a face is facilitated by adapting to its computationally opposite identity, suggesting that the average face functions as a norm for coding identity [Leopold, D. A., O'Toole, A. J., Vetter, T., & Blanz, V. (2001). Prototype-referenced shape encoding revealed by high-level aftereffects. Nature Neuroscience, 4, 89-94; Leopold, D. A., Rhodes, G., Müller, K. -M., & Jeffery, L. (2005). The dynamics of visual adaptation to faces. Proceedings of the Royal Society of London, Series B, 272, 897-904]. Crucially, this interpretation requires that the aftereffect is selective for the opposite identity, but this has not been convincingly demonstrated. We demonstrate such selectivity, observing a larger aftereffect for opposite than non-opposite adapt-test pairs that are matched on perceptual contrast (dissimilarity). Component identities were also harder to detect in morphs of opposite than non-opposite face pairs. We propose an adaptive norm-based coding model of face identity.

Adaptation, Physiological↗

PubMed1988

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.

Figural Aftereffect↗

PubMed1994

Aftereffects of apparent motion: the existence of an AND-type binocular system in human vision.

There has been evidence for the existence of a purely binocular system in human vision that acts as an AND gate on information from the two eyes. There also has been evidence for the nonexistence of such a purely binocular system, indicating only the existence of an OR-type binocular system that responds to input from one or both eyes. As a result there are a number of possible explanations for the differing experimental results: the binocular system is an OR-type system only, it is a facilitating OR system that has AND-type characteristics, or it consists of independent OR and AND subsystems. Monocular adaptation, alternating monocular adaptation, or binocular adaptation were used to demonstrate the existence of the different systems, but in none of the previous experiments was the AND-type binocular system activated directly, and the existence of this AND system was deduced mostly because of differences in aftereffect strengths between monocular and binocular test conditions. Experiments are reported in which stimuli that activate the AND-type binocular system explicitly have been used, and the results show that we need the existence of such an AND-type binocular system to account for the results.

Adaptation, Ocular↗

PubMed1973

Curvature as a feature of pattern vision.

Prolonged inspection of convex lines of one color and concave lines of another color can cause the appearance of oppositely colored aftereffects in curved, achromatic test lines. These effects, strongly dependent on radius of curvature, cannot be attributed to tilt or orientation. It is concluded that these results are not encompassed by models of the visual system that are based on rectilinear arrays and that curvature is a specific feature of human visual perception.

Color Perception↗