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PubMed2000

Prism adaptation in normal aging: slower adaptation rate and larger aftereffect.

The effect of aging on prism adaptation, a motor learning paradigm, was evaluated. Different measures were obtained from a task consisting of throwing clay balls to a target in front of the subjects before, during, and after wearing prisms that deviate the visual field by several degrees. When performing the task without wearing the prisms, the aged subjects showed a larger hit variance, whereas the young subjects hit closer to the target. When donning the prisms, the aged group adapted more slowly than the controls, although after throwing all the balls both groups showed the same adaptation levels. After removing the prisms, the aged group showed a larger aftereffect. These findings suggest that the aftereffect requires the involvement of non-cognitive and cognitive processes and indicate that both adaptation and aftereffect are influenced by aging.

Adaptation, Physiological↗
PubMed1979

Interactions between simultaneous contrast and adaptation to gradual change of luminance.

Following adaptation to a field of light which was modulated by a rising ramp so that it repetitively grows gradually brighter, a steady test field of light appears to be gradually growing dimmer. In this study, if a small grey spot of constant luminance was centered in the brightening field, it appeared to be growing gradually dimmer by simultaneous contrast. This apparent dimming led to a brightening aftereffect in the spot. It was shown that this spot aftereffect had two independent components: the apparent dimming of the adapting spot produced its own aftereffect (contrast produced an aftereffect) and also the dimming aftereffect in the surround field spatially induced an aftereffect into the spot during the test period (aftereffect produced simultaneous contrast). Thus simultaneous contrast can both precede and follow successive contrast in the visual system.

Adaptation, Ocular↗
PubMed1986

Aftereffects in binocular rivalry.

Five experiments are reported in which the aftereffect paradigm was applied to binocular rivalry. In the first three experiments rivalry was between a vertical grating presented to the left eye and a horizontal grating presented to the right eye. In the fourth experiment the rivalry stimuli consisted of a rotating sectored disc presented to the left eye and a static concentric circular pattern presented to the right. In experiment 5 rivalry was between static radiating and circular patterns. The predominance durations were systematically influenced by direct (same eye) and indirect (interocular) adaptation in a manner similar to that seen for spatial aftereffects. Binocular adaptation produced an aftereffect that was significantly smaller than the direct aftereffect, but not significantly different from the indirect one. A model is developed to account for the results; it involves two levels of binocular interaction in addition to monocular channels. It is suggested that the site of spatial aftereffects is the same as that for binocular rivalry, rather than sequentially prior.

Adaptation, Ocular↗
PubMed1992

Motion aftereffects with rotating ellipses.

The perceptual outcome and the motion-aftereffect duration generated by the rotation on the frontal plane of an ellipse with a bar depend on whether the bar is placed along the major or the minor axis. When the bar is placed along the minor axis, a stereokinetic transformation occurs, and the pattern looks like a tilting ring with a perpendicular bar moving rigidly with it. Placing the bar along the major axis prevents the stereokinetic transformation: subjects report deformations and relative motion of the bar with respect to the ellipse. We found that motion aftereffects last longer when the bar is placed along the minor rather than along the major axis. A series of experiments was carried out to investigate whether differences in aftereffect duration are related to the stereokinetic transformation. Results seem to suggest that they are not.

Adult↗
PubMed1999

The stereoscopic (cyclopean) motion aftereffect is selective for spatial frequency and orientation of disparity modulation.

Across two experiments, this study investigated the spatial frequency tuning and orientation tuning (both in the disparity domain) of the stereoscopic (cyclopean) motion aftereffect. In Experiment 1, observers adapted to a moving stereoscopic grating of a given cyclopean spatial frequency and tested for the motion aftereffect with a static grating of the same or different spatial frequency. Robust motion aftereffects were induced only when the spatial frequency of the adapt and test stimuli was the same. In Experiment 2, observers adapted to a moving stereoscopic grating of a given cyclopean orientation and tested for the motion aftereffect with a static grating of the same or different orientation. Robust motion aftereffects were induced only when the orientation of the adapt and test stimuli was the same. Together, these results suggest that the stereoscopic motion aftereffect is tuned for cyclopean spatial frequency and orientation which, in turn, suggest that the stereoscopic motion aftereffect is mediated by low-level oriented spatial-frequency mechanisms.

Adaptation, Physiological↗
PubMed1983

Psychophysical studies on the binocular processes of amblyopes.

It has frequently been assumed that humans with abnormal binocular vision resulting from amblyopia or strabismus lack binocular cortical neurons. From this assumption, it would be predicted that amblyopes would fail to show binocular interactions on any psychophysical tasks. This paper describes some recent psychophysical experiments investigating the binocular processes of amblyopes. The results of these experiments have shown that most humans with abnormal binocular vision fail to show binocular interactions for psychophysical tasks such as stereopsis or binocular summation, but show partially normal binocular interactions for interocular transfer of visual aftereffects and show normal interactions for dichoptic masking with grating stimuli.

Amblyopia↗
PubMed1991

Characteristics of the indirect McCollough effect.

Induction of contingent color aftereffects with a single chromatic grid sometimes results in an illusory color on a grid different from the one presented during induction. Such illusory color, contingently elicited by a noninduced grid, has been termed the indirect McCollough effect (indirect ME). We show that the indirect ME occurs only when the color complementary to the grid color is present during induction (either physically present or as a color afterimage), and that the indirect ME is seen only on gratings that are orthogonal to the induction orientation. These findings are in accord with the account of the indirect ME proposed by Humphrey, Dodwell, and Emerson (1989). We also show that characteristics of the indirect ME (seen following one-grid induction), both on induced and orthogonal orientations, are similar to those observed with the direct ME (seen following the usual two-grid induction procedure). Both procedures result in contingent aftereffects that display substantial retention and that do not display interocular transfer.

Adult↗
PubMed1993

Effect of depth information on a bistable spiral-motion aftereffect.

Two types of spiral-motion aftereffects were elicited by a single pattern: subjects reported seeing the pattern expand in the two-dimensional viewing plane or bulge toward them in three-dimensional space. Under binocular-viewing conditions reports of two-dimensional translations predominated. But when depth information was restricted under monocular-viewing conditions, reports of three-dimensional translations were more frequent. It appears that the bistability of these aftereffects can be influenced by the degree of depth information available about a stimulus pattern.

Attention↗
PubMed1979

Duration of the motion aftereffect as a function of retinal locus and visual field.

The duration of the aftereffect induced by viewing a rotating disc was recorded separately for the four hemiretinae of the left and right eyes using a new method of measurement. The results showed duration of aftereffect to differ between nasal and temporal hemiretinae of the right eye and between left and right cerebral hemispheres.

Dominance, Cerebral↗
PubMed1997

Contingent color aftereffects: reassessing old conclusions.

Although there is considerable evidence supporting an associative interpretation of contingent color aftereffects, there are data that appear inconsistent with this interpretation. New findings from seven experiments are presented indicating that, contrary to earlier claims, contingent color aftereffects are observed after induction with (1) single orthogonal black bars on colored backgrounds, (2) geometric forms, and (3) two orthogonal grids of the same color. The results of these experiments are relevant to an associative interpretation of contingent color aftereffects, as well as to assessing alternative interpretations of the phenomenon.

Adult↗
PubMed1979

A length aftereffect from grating adaptation: now you see it ... now you don't.

Adaptation to a grating of short bars has the effect of increasing the apparent length of a subsequently viewed test bar, and adaptation to a grating of long bars has the effect of decreasing the apparent length of a subsequently viewed test bar. However, decreasing the interspace between the long adaptation bars has the effect of (1) negating the length aftereffect and (2) reducing the apparent width of the test bar viewed by the retina previously adapted to the grating of long bars.

Figural Aftereffect↗
PubMed2000

Do McCollough effects provide evidence for global pattern processing?

Contingent color aftereffects (CAEs, or McCollough effects) were induced using two pairs of orthogonally related patterns (horizontal/vertical and concentric/radial) to determine whether the CAEs of the four patterns are independent. Tests using composite test patterns (like those employed by Emerson, Humphrey, & Dodwell, 1985) suggested independent aftereffects. However, tests using unitary patterns indicated additive or competing effects of the four patterns in regions where line orientations were similar, and tests isolating such regions showed clear interactions between the pattern aftereffects. The results fail to support the claim that global (rather than local) features of the patterns control these CAEs.

Adult↗
PubMed1996

Visual aftereffect of texture density contigent on color of frame.

An aftereffect of perceived texture density contingent on the color of a surrounding region is reported. In a series of experiments, participants were adapted, with fixation, to stimuli in which the relative density of two achromatic texture regions was perfectly correlated with the color presented in a surrounding region. Following adaptation, the perceived relative density of the two regions was contingent on the color of the surrounding region or of the texture elements themselves. For example, if high density on the left was correlated with a blue surround during adaptation (and high density on the right with a yellow surround), then in order for the left and right textures to appear equal in the assessment phase, denser texture was required on the left in the presence of a blue surround (and denser texture on the right in the context of a yellow surround). Contingent aftereffects were found (1) with black-and-white scatter-dot textures, (2) with luminance-balanced textures, and (3) when the texture elements, rather than the surrounds, were colored during assessment. Effect size was decreased when the elements themselves were colored, but also when spatial subportions of the surround were used for the presentation of color. The effect may be mediated by retinal color spreading (Pöppel, 1986) and appears consistent with a local associative account of contingent aftereffects, such as Barlow's (1990) model of modifiable inhibition.

Adult↗
PubMed2003

Gaze modulation of visual aftereffects.

Physiological studies of non-human primates have suggested that the direction of gaze can modulate the gain of neuronal responses to visual stimuli in many cortical areas including V1. The neural gaze modulation is suggested to subserve the conversion from gaze-independent (eye-centered) to dependent (e.g., head-centered) representations. However, it has not been established whether the gaze modulation has significant influences on human visual perception. Here we show that gaze direction modestly but significantly modulates the magnitudes of the motion aftereffect, the tilt aftereffect and the size aftereffect. These aftereffects were stronger when the adaptation and test patterns were presented in the same gaze direction, than when they were presented in different gaze directions, even though the patterns always stimulated the same retinal location. The gaze modulation effect was not statistically significant for the post-adaptation elevation of contrast detection thresholds. The gaze modulation of visual aftereffects provides a useful psychophysical tool to analyze human cortical processes for coordinate transformations of visual space.

Figural Aftereffect↗
PubMed1986

Fatigue and structural change: two consequences of visual pattern adaptation.

In a tilt aftereffect (TAE) paradigm, 2 min of adaptation produced an aftereffect that decayed almost completely within 4 min. Four minutes of adaptation produced a TAE that lasted more than 2 wk. Two modes of adaptation contribute to the TAE and account for other aftereffects: short-term fatigue, produced very quickly and long-term structural change, requiring more extended adaptation.

Adaptation, Ocular↗
PubMed2005

Lateral modulation of BOLD activation in unstimulated regions of the human visual cortex.

After staring at a blank region surrounded by a dynamic background for a few seconds, observers report a twinkle aftereffect in the unstimulated blank region. The significance of this twinkle aftereffect is that it occurs at a location that received no stimulation, and therefore reflects a rebound from lateral inhibition within the dynamic processing system. To study this inhibitory rebound effect, the blood oxygenation level dependent (BOLD) activation in the visual cortex was measured while the observers were viewing a flickering pin-wheel pattern alternating with a blank test. Retinotopic regions corresponding to the inter-wedge regions in the pin-wheel pattern showed activation negatively correlated with the test sequence. While the BOLD activation in the visual cortex is generally considered to be retinotopically driven by the visual stimuli, we were able to show a sustained negative activation in the unstimulated regions, with properties that correspond to those of the inhibitory rebound of the perceived aftereffect.

Adult↗