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At least 757 records · Page 42Linked to original sources
PubMed2002

Increased visual after-effects in migraine following pattern adaptation extend to simultaneous tilt illusion.

Much previous research into visual processing in migraine supports a model of abnormal cortical processing, in between the headache attacks, that is characterised by hyperexcitability, heightened responsiveness, a lack of habituation and/or a lack of intra-cortical inhibition. Shepherd (2001) reported two adaptation studies that challenged this view, one using the tilt after-effect, the second using the motion after-effect. Models of cortical function in migraine based on hyperexcitability and a lack of inhibition lead to specific predictions in an adaptation study: there should have been smaller after-effects in people with migraine than in people without. Both experiments, however, revealed larger after-effects in the migraine group than in the control group. Here, these results are extended to the simultaneous tilt illusion and an identical pattern of results was obtained: there were consistently larger effects in the migraine group than in the control group. The results from the three experiments are not consistent with a lack of inhibition in migraine. The results are discussed in terms of alternative models of cortical function, including a lack of excitation and reduced central energy reserves.

Adaptation, Ocular↗
PubMed2005

Interactions between pattern and color in the visual system: temporal aspects of the McCollough effect.

The perception of the color of a surface can be influenced by many factors including its material properties and the composition of the illuminant. McCollough demonstrated that sensory conditioning could also influence the perception of surface color by inducing a long-lasting pattern specific color aftereffect. This effect has been extensively studied since its original report and a number of increasingly complex explanations have been proposed. In this article I examine the temporal properties of a simple learning model of the McCollough effect (ME). This model has previously been used to account for quantitative data sets obtained from a series of monocular and binocular variants of the ME. The model replicates the acquisition and decay of the ME, pre- and post-induction interference effects, and can also simulate the effects of various cholinergic and anticholinergic drugs that have been shown to influence ME induction and decay.

Afterimage↗
PubMed2006

Fechner-Benham subjective colors do not induce McCollough after-effects.

Fechner-Benham subjective color is widely believed to be governed by local interactions in early (probably retinal) mechanisms. Here we report three lines of phenomenological evidence that suggest otherwise: subjective colors seen in spatially extended stimuli (a) are dependent on global aspects of the stimuli; (b) can become multistable in position; and (c) even after being stabilized do not support the creation of McCollough's colored after-effects--a cortically based phenomenon generally thought to be more central than Fechner-Benham color. These phenomena suggest a central locus that controls perception of subjective color, characterized by pattern dependent interactions among cortical mechanisms that draw their inputs from peripheral units.

Adaptation, Ocular↗
PubMed1985

The tilt after-effect: changes with stimulus size and eccentricity.

Previous evidence that the tilt after-effect (TAE) is larger when the stimuli are viewed peripherally rather than centrally was confirmed. An increase in viewing distance also increased TAE size. However, the increase in the TAE in peripheral vision was abolished if stimuli were increased in size to compensate for the change in the cortical magnification factor. Both the decrease in field diameter and increase in spatial frequency with viewing distance were found to influence the size of the TAE. When the data were expressed in cortical terms, the TAE was found to increase with spatial frequency, and decrease with field diameter, regardless of retinal position. The functional significance of these effects is discussed.

Adaptation, Ocular↗
PubMed1988

A model of visible persistence and temporal integration.

A quantitative model of temporal integration and visible persistence is described and tested. The model treats visible persistence as resulting from processing activity within sustained visual channels whose temporal response is modelled using a second-order control system. Temporal integration of two successive stimuli is assumed to be enabled by the overlap between the two periods of activity and to be impaired by the non-overlapping activity. The model successfully predicts the effects of inter-stimulus interval and of stimulus duration on goodness of temporal integration.

Afterimage↗
PubMed1992

Comparing local and remote motion aftereffects.

A new method, using phase-reversing sinusoidal gratings to cancel perceived motion, was developed to measure the motion aftereffect (MAE). This technique was used to show the existence of a remote MAE, i.e. an MAE in areas that were not directly stimulated during adaptation. In several experiments, this remote MAE was compared to the local MAE. The remote effect was generally weaker and of shorter duration. It showed no directional tuning within the investigated range, as compared to a tuning of +/- 60 deg of the local MAE. There was no adaptation effect to the component gratings of a plaid, indicating that the plaid was treated as a coherent pattern. The local MAE showed clear spatial frequency tuning, whereas the remote MAE varied little with spatial frequency difference, although there was a tendency towards frequencies lower than the adaptation frequency. The possibility is considered that both local and remote MAEs are generated in extrastriate areas.

Adaptation, Ocular↗
PubMed2002

Nulling the motion aftereffect with dynamic random-dot stimuli: limitations and implications.

We used biased random-dot dynamic test stimuli to measure the strength of the motion aftereffect (MAE) to evaluate the usefulness of this technique as a measure of motion adaptation strength. The stimuli consisted of noise dots whose individual directions were random and of signal dots moving in a unique direction. All dots moved at the same speed. For each condition, the nulling percentage (percentage of signal dots needed to perceptually null the MAE) was scaled with respect to the coherence threshold (percentage needed to perceive the coherent motion of signal dots without prior adaptation). The increase of these scaled values with the density of dots in the test stimulus suggests that MAE strength is underestimated when measured with low densities. We show that previous reports of high nulling percentages at slow speeds do not reflect strong MAEs, but are actually due to spatio-temporal aliasing, which dramatically increases coherence thresholds. We further show that MAE strength at slow speed increases with eccentricity. These findings are consistent with the idea that using this dynamic test stimulus preferentially reveals the adaptation of a population of high-speed motion units whose activity is independent of adapted low-speed motion units.

Adaptation, Ocular↗
PubMed2004

Strong influence of test patterns on the perception of motion aftereffect and position.

In a completely linear system, the behavior of a square wave pattern can be predicted by its sinusoidal components. However, we observed a complete breakdown of the linear system prediction in the perception of the motion aftereffect (MAE). The duration of the MAE was measured following a one-minute adaptation to a rotating radial grating. Three different luminance patterns were used for both the adaptation and test stimulus: (1) sine wave, (2) square wave, and (3) complex grating with the same Fourier amplitude spectrum as the square wave, but with randomized phases. The sine wave stimulus generated the highest magnitude MAE, followed by the random-phase complex grating, and lastly the square wave grating. To test whether the square wave grating is a weak adaptor or a weak test for the MAE, we performed a cross adaptation experiment in which the sine wave, square wave, and complex gratings were paired in seven ways. Results show that the strength of the MAE critically depended on the test pattern. Regardless of the adaptor, MAE strength is in a decreasing order with the test pattern as sine wave grating, complex grating, and square wave grating. Further experiments ruled out the possibility that differential MAEs between these conditions are due to different peak contrasts in these patterns. Additionally, the MAE from a square wave grating as the test pattern is not accompanied by a significant concurrent shift in the apparent position. Linear system theory cannot predict the magnitude of the MAE using complex gratings. The spatial features of a test stimulus, such as position reliability or luminance uniformity, strongly influence the magnitude of MAE. Sharp edges and local luminance uniformity can greatly reduce MAE.

Adaptation, Ocular↗
PubMed2005

Adaptation to the induced effect stimulus normalizes surface slant perception and recalibrates eye position signals for azimuth.

A frontoparallel plane viewed with unequal vertical magnification of the two ocular images appears rotated about a vertical axis (i.e., induced effect; Ogle, 1938). Several experiments were conducted to investigate changes in the visual system that occurred after adapting to the induced effect. Adaptation at 57 cm was tested using tall stimuli at various viewing distances to test for the adaptation of vertical size ratio (VSR) information and normalization of the slant percept. When aftereffects were expressed in units of slant, they were larger at 57 cm than other test distances and were not significantly different from each other at other distances. Short stimuli were used to test adaptation of eye position signals for azimuth. The aftereffects were in the opposite direction to those measured with tall stimuli. The combined results suggest that the visual system normalizes slant percepts based on the surface slant of the adaptation stimulus and when there is a conflict between VSR signals and eye position cues for azimuth that the primary eye position signal for azimuth is recalibrated toward the direction indicated by the binocular differential vertical magnification in the adaptation stimulus.

Adaptation, Ocular↗
PubMed2006

Tilt aftereffect for texture edges is larger than in matched subjective edges, but both are strong adaptors of luminance edges.

The tilt aftereffect (TAE) has been used previously to probe whether contours defined by different attributes are subserved by the same or by different underlying mechanisms. Here, we compare two types of contours between texture surfaces, one with texture orientation contrast across the edge (orientation contrast contour; OC) and one without, commonly referred to as a subjective contour (SC). Both contour types produced curves of TAE versus adapting angle displaying typical positive and negative peaks at approximately 15 and 70 deg, respectively. The curves are well fit by difference of Gaussian (DoG) functions, with one Gaussian accounting for the contour adaptation effect and the other accounting for the texture orientation adaptation effect. Adaptation to OC elicited larger TAEs than did adaptation to SC, suggesting that they more effectively activate orientation-selective neurons in V1/V2 during prolonged viewing. Surprisingly, both contour types adapted a luminance contour (LC) as strongly as did an LC itself, suggesting that the second-order orientation cue contained in the texture edge activates the same set of orientation-selective neurons as does an LC. These findings have implications for the mechanisms by which the orientations of texture edges and SCs are encoded.

Adaptation, Physiological↗
PubMed2006

Motion aftereffect elicits smooth pursuit eye movements.

A moving stimulus is normally required to elicit smooth pursuit eye movements that serve to keep the retinal image of moving objects on the fovea. Recent experiments have shown that in cases where motion cues are ambiguous, pursuit eye movements tend to agree in direction and speed with the percept of motion. Here, we exploit the motion aftereffect (MAE) to show for the first time that smooth pursuit eye movements can also be elicited by the illusory motion of a stationary stimulus. After prolonged exposure to a moving stimulus, subjects show reliable pursuit of a physically stationary stimulus that is perceived to be moving. Conversely, the eyes remain stationary when viewing a physically moving stimulus that is perceived to be stationary. The MAE biases smooth eye movements in a way that agrees with the constant offset that is required to null the MAE perceptually. The agreement between perception and pursuit holds over a variety of stimulus conditions that modulate the magnitude of the MAE.

Adult↗
PubMed2006

Adaptation aftereffects in the perception of gender from biological motion.

Human visual perception is highly adaptive. While this has been known and studied for a long time in domains such as color vision, motion perception, or the processing of spatial frequency, a number of more recent studies have shown that adaptation and adaptation aftereffects also occur in high-level visual domains like shape perception and face recognition. Here, we present data that demonstrate a pronounced aftereffect in response to adaptation to the perceived gender of biological motion point-light walkers. A walker that is perceived to be ambiguous in gender under neutral adaptation appears to be male after adaptation with an exaggerated female walker and female after adaptation with an exaggerated male walker. We discuss this adaptation aftereffect as a tool to characterize and probe the mechanisms underlying biological motion perception.

Adaptation, Physiological↗