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PubMed2000

Dynamic random noise shrinks the twinkling aftereffect induced by artificial scotomas.

Physiological alterations in cortical neurons are induced during adaptation to an artificial scotoma, a small homogeneous patch within a dynamic random noise or patterned background. When the dynamic noise is replaced by an equiluminant gray background, a twinkling aftereffect can be seen in the location of the artificial scotoma. Following binocular adaptation, we discovered that the perceived size of the twinkling aftereffect was dramatically smaller than the inducing artificial scotoma. Dichoptic adaptation induced shrinkage in the twinkling aftereffect that was similar to that found after binocular adaptation, suggesting that the twinkling aftereffect and its shrinkage both have cortical origins. We speculate that this perceptual shrinkage may reflect the interaction between two cortical mechanisms: a twinkling aftereffect mechanism that spreads throughout the artificial scotoma, and a filling-in mechanism that has a greater influence at the edges of the artificial scotoma and spreads inwards.

Adaptation, Ocular↗

PubMed1984

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.

Adaptation, Physiological↗

PubMed1996

The aftereffect to relative motion does not show interocular transfer.

The motion aftereffect is strongest after viewing a moving field embedded in a patterned stationary surround, which suggests that relative motion is an important signal for its generation. The contribution of relative motion to binocular aspects of the motion aftereffect was assessed. Subjects viewed uniformly moving random dots surrounded by a stationary random-dot annulus. These displays could be presented in a variety of combinations to each eye separately or to both eyes, during adaptation and test. It was found that, although the presence of relative motion during adaptation significantly extended the duration of the monocular motion aftereffect, it did not augment interocular transfer. The presence of stationary surround contours in the nonadapting eye did not influence the aftereffect in the adapting eye. The enhancement provided by stationary surround contours is largely dependent on their presence during adaptation. The presence or absence of surround contours during the test phase did not influence the duration of the aftereffect. These findings are consistent with previous suggestions that the motion aftereffect is, in part, the result of adaptation to relative motion that occurs relatively early in the visual pathway-before binocular integration.

Adaptation, Ocular↗

PubMed1971

Color- and edge-sensitive channels in the human visual system: tuning for orientation.

After subjects scanned red stripes tilted clockwise off vertical and green stripes tilted equally but counterclockwise, vertical test stripes appeared tilted counterclockwise when red but clockwise when green. As the angle between scanned and test stripes was increased from 0 degrees to 75 degrees , the magnitude of the tilt aftereffect rapidly increased to a peak between 10 degrees and 15 degrees and then dropped close to zero at about 40 degrees , a result consistent with narrowly tuned edge-sensitive channels.

Adaptation, Ocular↗

PubMed2005

Selective attention and cyclopean motion processing.

The effect of diverted selective attention on the induction of the cyclopean motion aftereffect (aftereffect induced from dynamic disparity information) was investigated. The luminance motion aftereffect was examined for comparison. During diverted-attention trials, observers ignored background adapting motion and performed a low-load or high-load rapid serial visual presentation (RSVP) task presented in the center of the motion display. Baseline motion aftereffects were obtained with no diverted attention. The results showed that the cyclopean motion aftereffect, similar to the luminance motion aftereffect, declined only modestly under diverted-attention conditions. Selective attention appears to play a modest role in the visual processing of cyclopean motion.

Adaptation, Ocular↗

PubMed1988

Adaptation to movement in right and left visual fields.

102 subjects reported on movement aftereffects (MAEs) produced by stimuli presented in the left or right visual field. MAEs were both faster and longer when the stimuli were presented in the right visual field. Possible reasons for the asymmetry are discussed.

Adaptation, Physiological↗

PubMed1981

Orientation selectivity of the human visual system as a function of retinal eccentricity and visual hemifield.

An adaptation method was used to determine the specificity of orientation-selective channels in the human visual system at different retinal eccentricities (up to 16 deg) in both hemifields of each eye. For a vertical test grating, the elevation in contrast threshold produced by adapting to a high-contrast grating of the same spatial frequency but variable orientation was equated with the contrast levels of a vertical adapting grating that produced equivalent effects (equivalent-contrast transformation). This enabled comparisons to be made between the orientation tuning of the aftereffect at different retinal loci. For the spatial frequency employed (3 cycles deg-1), no systematic change in orientation selectivity was found as a function of either retinal eccentricity or the hemifield (and hence the cerebral hemisphere) stimulated.

Adaptation, Ocular↗

PubMed2001

Calibration and alignment are separable: evidence from prism adaptation.

In 2 prism adaptation experiments, the authors investigated the effects of limb starting position visibility (visible or not visible) and visual feedback availability (early or late in target pointing movements). Thirty-two students participated in Experiment 1 and 24 students participated in Experiment 2. Independent of visual feedback availability, constant error was larger and variable error was smaller for target pointing when limb starting position was visible during prism exposure. Independent of limb starting position visibility, aftereffects of prism exposure were determined by visual feedback availability. Those results support the hypothesis that calibration is determined by limb starting position visibility, whereas alignment is determined separately by visual feedback availability.

Adult↗

PubMed1992

A square root law for adaptation to contrast?

Several characteristic of aftereffects (especially the motion aftereffect) depend upon the square root of the time spent adapting. The same parameters are here examined for the contrast threshold elevation aftereffect. The time taken to recover is shown to be well predicted by root adaptation time (beyond a minimum duration), but the amount of threshold elevation, the rate of recovery and the integrated recovery phase cannot be so predicted.

Adaptation, Ocular↗

PubMed2003

First-trial adaptation to prism exposure.

Terminal target-pointing error on the 1st trial of exposure to optical displacement is usually less than that expected from the optical displacement magnitude. Such 1st trial adaptation was confirmed in 2 experiments (N = 48 students in each) comparing pointing toward optically displaced targets and toward equivalent physically displaced targets (no optical displacement), with visual feedback delayed until movement completion. First-trial performance could not be explained by ordinary target undershoot, online correction, or reverse optic flow information about true target position and was unrelated to realignment aftereffects. Such adaptation might be an artifact of the asymmetry of the structured visual field produced by optical displacement, which induces a felt head rotation opposite to the direction of the displacement, thereby reducing the effective optical displacement.

Adaptation, Psychological↗

PubMed1994

An examination of colour-contingent pattern aftereffects.

The McCollough effect (ME) is an example of a pattern-contingent colour aftereffect. This study describes some characteristics of another visual aftereffect linking pattern and colour here called a colour-contingent pattern aftereffect (CCPA). After inducing with, for example, a magenta and black radial pattern and a green and black pattern of concentric circles, presentation of a green homogeneous field evoked a faint image of a radial pattern superimposed on the field, whereas presentation of a magenta homogeneous field produced a faint image of concentric circles. The pattern was blurred and fleeting, occurring with the onset of the homogeneous field, but nevertheless was evoked reliably. Various properties of these colour-contingent pattern aftereffects are reported. Although the aftereffects have some of the characteristics of the ME, the CCPA is not as long lasting as the ME, and, unlike the usual ME, it is abolished if eye-movements are made during induction.

Color Perception↗

PubMed2005

Two waves of a long-lasting aftereffect of prism adaptation measured over 7 days.

Prism adaptation is a useful paradigm to study the integration and reorganization of various sensory modalities involved in sensory-motor tasks. By prolonging the prismatic aftereffect and well-timed observation, we aimed to dissociate the components and mechanisms involved in human prism adaptation by their differential decay and development time courses. Here, we show that a single session of prism adaptation training, combining small increments of prism strength below the subjects' awareness threshold, during a pointing task with a free walk session with total prism exposure duration of 75 min, generated a surprisingly long-lasting aftereffect. The aftereffect was measured by the magnitude of the proprioceptive shift (assessed by straight-ahead pointing in the dark) for 7 days. An aftereffect was observed, which lasted for more than 6 days, by a single prism adaptation session. The aftereffect did not decay gradually. Unlike previous descriptions, the aftereffect showed two separate time-courses of decay and increase. After a significant initial decay within 6 h, the aftereffect increased again from 1 day up to 3 days. The novel decay and delayed development profile of this adaptation aftereffect suggests two separate underlying neural mechanisms with different time scales. Our experimental paradigms promise to reveal directly the temporal characteristics of early versus late long-term neural plasticity in complex human adaptive behavior.

Adaptation, Physiological↗

PubMed1984

Negative aftereffect arising from prolonged viewing of induced movement-in-depth.

Prolonged induced movement-in-depth in a static circle was elicited by a spiral stimulus. Afterwards an aftereffect was observed in the circle. The aftereffect was towards the subject after induced movement away from the subject, and away from the subject after induced movement towards the subject. Longer aftereffect was observed with a circle central to the inducing stimulus than with a circle peripheral to the inducing stimulus. In contrast to some other psychophysical effects, no clear-cut directional asymmetry was observed.

Adaptation, Ocular↗

PubMed1979

A test for contrast-polarity selectivity in the tilt aftereffect.

The tilt aftereffect (TAE) was studied with adapting and test stimuli consisting of black or white bars (experiment 1), and of luminance edges (experiment 2). Both experiments failed to demonstrate selectivity of the TAE to the polarity of luminance contrast.

Adaptation, Ocular↗

PubMed1979

Stimulus persistence and age.

Stimulus persistence theory states that the effects of stimulation are longer lasting in the nervous system of the old person than the younger one. This concept and its relation to perceptual functioning and age was examined via two perceptual aftereffect tasks, the Spiral and the Waterfall. Twenty-four elderly adults (mean age = 65.5) and twenty-four young adults (mean age = 24.8) were each exposed to both stimulus displays, at four exposure durations: 45, 60, 90, and 120 seconds. Following the offset of each display, the duration of any apparent motion aftereffect was recorded. Although on the basis of stimulus persistence theory it was expected that the elderly would exhibit longer mean aftereffects than the young, no support for this hypothesis was noted. Possible explanations of these results and their relation to previous findings, in terms of fatigue effects and sample characteristics, are discussed.

Adult↗

PubMed2003

The origin of the oblique effect examined with pattern adaptation and masking.

The decreased visibility of obliquely oriented patterns as compared to horizontal or vertical ones is termed the oblique effect. The origin of the oblique effect in the chain of visual processing was examined by comparing the potency of oblique adapting gratings to the potency of horizontal ones. Oblique gratings (which were less visible but of equal physical contrast) were as powerful or more powerful than horizontal gratings as adapting stimuli. Obliquely oriented stimuli also produced a slightly stronger tilt aftereffect than stimuli near the cardinal axes. These results suggest that the diminished neural representation of oblique stimuli arises in the human cortex, rather than from impairments of sensitivity or resolution in the initial geniculo-cortical projection.

Adaptation, Ocular↗

PubMed1996

Enduring stereoscopic motion aftereffects induced by prolonged adaptation.

This study investigated the effects of prolonged adaptation on the recovery of the stereoscopic motion aftereffect (adaptation induced by moving binocular disparity information). The adapting and test stimuli were stereoscopic grating patterns created from disparity, embedded in dynamic random-dot stereograms. Motion aftereffects induced by luminance stimuli were included in the study for comparison. Adaptation duration was either 1, 2, 4, 8, 16, 32 or 64 min and the duration of the ensuing aftereffect was the variable of interest. The results showed that aftereffect duration was proportional to the square root of adaptation duration for both stereoscopic and luminance stimuli; on log-log axes, the relation between aftereffect duration and adaptation duration was a power law with the slope near 0.5 in both cases. For both kinds of stimuli, there was no sign of adaptation saturation even at the longest adaptation duration.

Adaptation, Ocular↗

PubMed1997

Adaptation to motion of a second-order pattern: the motion aftereffect is not a general result.

It has become apparent from recent work that the spatial frequency and orientation content of the first-order (luminance) carrier is very important in determining the properties of a second-order (contrast) modulation of that carrier. In light of this we examined whether there was any evidence for a motion aftereffect in one-dimensional second-order patterns containing only two sinusoidal luminance components: a spatial beat. The stimuli were either 1 cpd luminance sinusoids or 1 cpd luminance beats modulating a carrier sinusoid of 5 cpd. The magnitude of any motion aftereffect, or any directionally specific effect of adaptation, was measured for all combinations of first and second-order test and adapting patterns. Both flickering and non-flickering stimuli were used. The results indicate that a motion aftereffect is only induced by first-order adapting stimuli, and likewise, is only measurable in first-order test stimuli. We find no evidence for any directionally specific effect of adaptation in second-order stimuli, whether the test is counterphased or otherwise. These results apparently conflict with recent reports of a second-order induced motion aftereffect, but are consistent with many other findings which show differences between the detection of motion for first and second-order stimuli. We conclude that the induction of a motion aftereffect for second-order stimuli is not a general result and is critically dependent upon (amongst other things) the local properties of the stimulus, including the spatial frequency and orientation content of the first-order carrier.

Adaptation, Ocular↗