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PubMed2002

The conjunction of feature and depth information.

By inducing feature-contingent depth aftereffects, we show that the human visual system combines feature information with depth information. These contingent aftereffects were revealed through the use of a novel selective adaptation paradigm whose stimuli required the combination of feature and depth information in order to segment two interleaved, transparent surfaces. We argue that this combined processing exemplifies the remarkable resourcefulness of a visual system that has adapted to exploit conjunctions of cues that can aid in the segmentation of visual surfaces.

Adaptation, Biological↗

PubMed2006

Contingent aftereffects distinguish conscious and preconscious color processing.

The brain can process input without perception, but what distinguishes conscious from preconscious processing? Using aftereffects induced by quickly alternating images, we show that cortical mechanisms track color much faster than perception, responding well to color alternations that are too rapid to be perceptible. The more restricted frequency response of the conscious perception of color suggests that extra integrative steps give conscious color perception a time course substantially slower than that of early cortical mechanisms.

Color↗

PubMed2002

Context and the motion aftereffect: occlusion cues in the test pattern alter perceived direction.

A horizontally moving vertical grating viewed through a diamond-shaped aperture can be made to appear to move either upwards or downwards by introduction of appropriate depth-ordering cues at the boundaries of the aperture (Duncan et al. 2000 Journal of Neuroscience 20 5885-5897). The grating is perceived to move towards (and sliding under) occluding 'near' surfaces, and parallel to 'far' surfaces. Here we show that these depth-ordering cues affect the perceptual interpretation of the motion aftereffect (MAE) as well. After adaptation to unambiguous horizontal motion, the MAE direction deviates from horizontal towards near surfaces. However, the influence of depth-ordering cues on the illusory motion of the MAE is generally less than that seen for 'real' motion. Implications for theories of depth-motion and depth-MAE interactions are discussed.

Adaptation, Psychological↗

PubMed1993

Dichoptic activation of the early motion system.

The short range or early motion system has long been considered incapable of binocular integration. We have developed dichoptic motion stimuli which are based upon the decomposition of traveling sinewave gratings into the sum of two standing waves in spatial and temporal quadrature. The monocular views of such displays appear as counterphase flicker but when presented dichoptically the perception is of movement in a unique direction. Two lines of evidence are presented for the binocularity of early motion mechanisms in human vision. First, adaptation to dichoptic motion sinewave gratings is found to result in a motion aftereffect. Second, random texture motion displays based on the quadrature decomposition are found to support dichoptic perception of motion direction, but not figure/ground. Unlike random dot kinematograms, these displays do not necessitate alternating the direction of motion during dichoptic presentation. This encumbrance, and the reliance on figure/ground discrimination, may have been responsible for prior failure to achieve dichoptic motion perception with short range stimuli.

Adaptation, Ocular↗

PubMed2000

Global motion adaptation.

Image motion is initially detected locally. Local motion signals are then integrated across space in order to specify the global motion of objects or surfaces. It is well known that prolonged exposure to motion causes adaptation at the local motion level. We have investigated whether adaptation also occurs at the global motion level. We have devised a global motion stimulus (a random dot kinematogram) which has equal motion energy in opposite directions but nonetheless gives rise to global motion perception. At the local motion level, adaptation to this stimulus should cause equal adaptation in both directions and should not give rise to an aftereffect. Any aftereffect seen must therefore be attributable to adaptation at the global motion level. We find that following adaptation to this stimulus, judgements of the perceived direction of a test pattern are systematically biased towards the direction opposite to the adapting direction, suggesting that adaptation does occur at a level of visual processing at which global motion is represented.

Adaptation, Physiological↗

PubMed1999

Visual adaptation as optimal information transmission.

We propose that visual adaptation in orientation, spatial frequency, and motion can be understood from the perspective of optimal information transmission. The essence of the proposal is that neural response properties at the system level should be adjusted to the changing statistics of the input so as to maximize information transmission. We show that this principle accounts for several well-documented psychophysical phenomena, including the tilt aftereffect, change in contrast sensitivity and post-adaptation changes in orientation discrimination. Adaptation can also be considered on a longer time scale, in the context of tailoring response properties to natural scene statistics. From the anisotropic distribution of power in natural scenes, the proposal also predicts differences in the contrast sensitivity function across spatial frequency and orientation, including the oblique effect.

Adaptation, Ocular↗

PubMed1984

A three-dimensional motion aftereffect produced by prolonged adaptation to a rotation simulation.

After adaptation to a perspective simulation of a square plane rotating in depth, an ambiguous rotation simulation (ie one containing no perspective information) appears to rotate in the direction opposite that of adaptation. The strength of this three-dimensional motion aftereffect (MAE) is proportional to the amount of perspective available in the adaptation display and, in the dark, decays to about 75% of its initial strength within about 546 s. The nature of the testing situation and a control experiment suggest that the three-dimensional MAE is not caused by retinal adaptation of two-dimensional directionally selective mechanisms.

Adaptation, Physiological↗

PubMedDate not supplied

Prism adaptation and aftereffect: specifying the properties of a procedural memory system.

Prism adaptation, a form of procedural learning, is a phenomenon in which the motor system adapts to new visuospatial coordinates imposed by prisms that displace the visual field. Once the prisms are withdrawn, the degree and strength of the adaptation can be measured by the spatial deviation of the motor actions in the direction opposite to the visual displacement imposed by the prisms, a phenomenon known as aftereffect. This study was designed to define the variables that affect the acquisition and retention of the aftereffect. Subjects were required to throw balls to a target in front of them before, during, and after lateral displacement of the visual field with prismatic spectacles. The diopters of the prisms and the number of throws were varied among different groups of subjects. The results show that the adaptation process is dependent on the number of interactions between the visual and motor system, and not on the time spent wearing the prisms. The results also show that the magnitude of the aftereffect is highly correlated with the magnitude of the adaptation, regardless of the diopters of the prisms or the number of throws. Finally, the results suggest that persistence of the aftereffect depends on the number of throws after the adaptation is complete. On the basis of these results, we propose that the system underlying this kind of learning stores at least two different parameters, the contents (measured as the magnitude of displacement) and the persistence (measured as the number of throws to return to the baseline) of the learned information.

Adaptation, Physiological↗

PubMed1979

The site of binocular rivalry suppression.

Two experiments were performed to localize the site of binocular rivalry suppression in relation to the locus of grating adaptation. In one experiment it was found that phenomenal suppression of a high-contrast adaptation grating presented to one eye had no influence on the strength of the threshold-elevation aftereffect measured interocularly. Evidently information about the adaptation grating arrives at the site of the aftereffect (presumably binocular neurons) even during suppression. In a second experiment 60 s of grating adaptation was found to produce a short-term reduction in the predominance of the adapted eye during binocular rivalry. These findings provide converging lines of evidence that suppression occurs at a site in the human visual system after the locus of grating adaptation and, hence, after the striate cortex.

Adaptation, Ocular↗

PubMedDate not supplied

Early visual processing over the menstrual cycle: the tilt aftereffect.

We have previously shown that the tilt aftereffect (TAE) appears to respond to changes in central dopaminergic function. In this study, the TAE was investigated during the preovulatory and the premenstrual phases of the menstrual cycle. Results in the preovulatory phase mimicked those previously found associated with increased dopaminergic function, compared to data produced in the premenstrual phase, suggesting changes in dopamine function over the cycle.

Adult↗

PubMed1976

Effects of prolonged practice on duration of spiral aftereffect: an ideographic study.

The effects of prolonged practice on the duration of the spiral aftereffect were investigated; 3,000 trials over 30 days with 5 levels of ambient illumination were randomly presented to a single subject. Scores gradually decreased until a plateau was reached during the last 13 days. A large decrement during the last 5 days was attributed to a decision process component. An early difference in performance at different illumination levels was largely eliminated by the last 5 days.

Decision Making↗

PubMed2007

The role of familiarity in three-dimensional view-transferability of face identity adaptation.

Recent studies show that face adaptation effects partially transfer across three-dimensional viewpoint change. Here we investigated whether the degree of adaptation transfer is mediated by experience with a face. We manipulated face familiarity and measured identity aftereffects both within- and across-viewpoint. Familiarity enhanced the overall strength of identity adaptation as well as the degree to which adaptation transferred across-viewpoint change. These findings support the idea that transfer effects in adaptation vary as a function of experience with particular faces, and suggest the use of adaptation as a tool for tracking face representations as they develop.

Adaptation, Physiological↗

PubMed1985

Velocity coding: evidence from perceived velocity shifts.

Measurements of the perceived velocities of moving patterns were made under a variety of conditions in an attempt to gain information concerning the way in which velocity is encoded in the visual system. Adaptation to a pattern moving in the same or opposite direction reduces the perceived velocity of a moving test pattern, but only if the adaptation pattern moves as fast as or faster than the test pattern. The aftereffect peaks at an adaptation velocity slightly higher than the test velocity and then remains constant at higher velocities. Similar results were obtained for several types of pattern. Perceived velocity reduction also follows adaptation to a flickering homogeneous field. The results can be explained in terms of a theory of velocity coding in which two channels are considered in terms of variations in the velocity sensitivities of the neurones they comprise.

Adaptation, Ocular↗

PubMed1990

Measurement of visual aftereffects and inferences about binocular mechanisms in human vision.

There is conflicting evidence concerning the characteristics of binocular channels in the human visual system with respect to the existence of a 'pure' binocular channel that responds only to simultaneous stimulation of both eyes. Four experiments were conducted to resolve these discrepancies and to evaluate the evidence for the existence of such an exclusive binocular channel. In the first three studies, tilt aftereffects were measured after monocular adaptation. The relative sizes of the direct, interocularly transferred, and binocular aftereffects were not influenced by the configuration of the adapting pattern (experiment 1), or by the eye used for adaptation (experiment 2). There were also consistent interobserver differences in the relative sizes of the aftereffect seen after monocular adaptation (experiment 3). Taken together, these data raise questions about the appropriateness of a monocular adaptation paradigm for evaluating the presence of a pure binocular channel in observers with normal binocular vision. In experiment 4, in which the paradigm of alternating monocular adaptation was used, data were obtained that are consistent with the presence of a pure binocular channel.

Adolescent↗

PubMed1999

Aftereffects and the representation of stereoscopic surfaces.

The structure of human disparity representation is examined through (i) adaptation experiments and (ii) model simulations of the data. Section 3 presents results of adaptation experiments designed to illuminate the structure of human disparity representation. Section 4 presents model simulations of three different disparity representation schemes. In the experiments, participants adapted to a 0.133 cycle deg-1 sinusoidally corrugated surface with 10 min of arc peak-to-trough disparity. A flat test surface was briefly presented, in which the aftereffect surface was perceived. Adapt and test surfaces were placed on disparity pedestals and thus presented in front of or behind the plane of fixation. The adapt surface could be offset from the fixation plane by +/- 8 to 24 min of arc. The test surface could be offset from the fixation plane by +/- 8 to 48 min of arc. The depth aftereffect was measured in different disparity planes by a nulling method and 'topping-up' procedure. Aftereffect tuning functions were obtained whose bandwidths, magnitudes, and tuning depended on the disparity planes of both the adapt and test surfaces. These parameters were used to constrain the models tested in section 4. On the basis of the two studies, it is argued that the human stereoscopic system encodes spatial changes of disparity using channels localised within disparity planes. A localised disparity-gradient model of the human representation of disparity is proposed.

Adaptation, Psychological↗

PubMed1983

Interocular transfer of a chromatic frequency shift.

Interocular transfer of a spatial frequency shift was obtained with equiluminous color gratings. Gratings which combined both color and luminance contrast yielded small aftereffects and no interocular transfer. Recent electrophysiological work has uncovered color-sensitive binocularly driven cells in visual cortex. These cells are transient and often respond to color contrast in the absence of luminance contrast. The stimulus parameters associated with successful interocular transfer, equiluminous colors and brief test, matched the properties of these cells. Previous failure to induce interocular transfer of color effects may be explained by inappropriate stimulus parameters.

Adaptation, Ocular↗

PubMed2006

In honour of Lothar Spillmann - filling-in, wiggly lines, adaptation, and aftereffects.

I have studied a number of visual phenomena that Lothar Spillmann has already elucidated. These include: Neon spreading: when a small red cross is superimposed on intersecting black lines, the red cross seems to spread out into an illusory disk. Unlike the Hermann grid, neon spreading is relatively unaffected when the black lines are curved or wiggly. This suggests that the Hermann grid, but not neon spreading, involves long-range interactions. Neon spreading can be shown in random-dot patterns, even without intersections. It is strongest when the red crosses are equiluminous with the gray background. Adaptation, aftereffects, and filling-in: direct and induced aftereffects of color, motion, and dimming. Artificial scotomata and filling-in: the "dam" theory is false. Staring at wiggly lines or irregularly scattered dots makes them gradually appear straighter, or more regularly spaced. I present evidence that irregularity is actually a visual dimension to which the visual system can adapt. Conjectures on the nature of peripheral fading and of motion-induced blindness. Some failed experiments on correlated visual inputs and cortical plasticity.

Adaptation, Physiological↗

PubMed2002

Compelling classroom demonstrations that link visual system anatomy, physiology, and behaviour.

One of our approaches to teaching a course in anatomy and physiology is to stress the fundamental, systems-level concepts. One successful strategy we use is to continually highlight the relationships among anatomy, physiology, and behavior. In this article, we describe a set of classroom demonstrations that stress these links while fostering critical thinking. These demonstrations, on the topic of sensory system structure and function, rely on two perceptual consequences of neural adaptation in the visual system: afterimages and aftereffects. Viewing specific visual stimuli under binocular or monocular conditions with interocular transfer permits several concepts to be observed and discussed, including neural adaptation, anatomical and functional segregation of visual system pathways, and the relationship among visual system structure, function, and perception. This article discusses how to produce and present the required visual stimuli, suggests a set of questions to stimulate critical thinking, and presents student evaluation of this activity.

Afterimage↗