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PubMed2006

Generalization of prism adaptation.

Prism exposure produces 2 kinds of adaptive response. Recalibration is ordinary strategic remapping of spatially coded movement commands to rapidly reduce performance error. Realignment is the extraordinary process of transforming spatial maps to bring the origins of coordinate systems into correspondence. Realignment occurs when spatial discordance signals noncorrespondence between spatial maps. In Experiment 1, generalization of recalibration aftereffects from prism exposure to postexposure depended upon the similarity of target pointing limb postures. Realignment aftereffects generalized to the spatial maps involved in exposure. In Experiment 2, the 2 kinds of aftereffects were measured for 3 test positions, one of which was the exposure training position. Recalibration aftereffects generalized nonlinearly, while realignment aftereffects generalized linearly, replicating Bedford (1989, 1993a) using a more familiar prism adaptation paradigm. Recalibration and realignment require methods for distinguishing their relative contribution to prism adaptation.

Adaptation, Psychological↗

PubMed1981

A study of interocular transfer of spatial adaptation.

The threshold-elevation aftereffect was measured ipsiocularly and interocularly following grating adaptation of one eye. The functions relating aftereffect magnitude to adapting contrast and adaptation time were similar under the two testing conditions, with interocular transfer remaining fairly constant; decay times were similar for ipsiocular and interocular aftereffects of comparable magnitude, and their frequency selectivities were the same. It is concluded that the stimulus-response characteristics of monocular and binocular spatial channels are fundamentally similar.

Adaptation, Ocular↗

PubMed2005

Gaze direction modulates visual aftereffects in depth and color.

Prior physiological studies indicate that gaze direction modulates the gain of neural responses to visual stimuli. Here, we test gaze modulation in the perceptual domain using color and depth aftereffects. After confirming retinotopy of the effects, we employed a balanced alternating adaptation paradigm (adaptation alternates between opponent stimuli) to demonstrate that opposite color and depth aftereffects can co-develop at the same retinal location for different gaze directions. The results provide strong evidence for (a) gaze modulation of aftereffects, (b) generality of gaze modulation across two visual attributes, and (c) perceptual correlates of the modulation of neural activity by gaze direction.

Color Perception↗

PubMed1998

Long-range twinkle induction: an achromatic rebound effect in the magnocellular processing system?

After viewing a blank region surrounded by a dynamic noise stimulus, viewers report the perception of prolonged dynamic twinkle in the unstimulated blank region. This twinkle aftereffect may be induced over long ranges in the visual field, up to 10 degrees from the edge of the noise in central vision. Our previous studies of the properties of this aftereffect suggested mediation by the magnocellular processing system. We therefore evaluated the properties predicted by the magnocellular hypothesis by varying the coloring, the temporal and the spatial frequency of the stimulus. No aftereffect could be induced by an equiluminant color stimulus or by luminance noise below the temporal frequency of 5 Hz. The aftereffect obtained by luminance noise above 5 Hz was stronger for larger inducing elements. These results are consistent with known properties of the magnocellular processing system.

Color Perception↗

PubMed1991

Does intermittence in induced rotary movement have any explanatory significance?

Induced rotary movement has been reported to start and stop repeatedly during 1 min of observation. This has been taken as evidence for the involvement either of cyclorotational optokinetic nystagmus or of roll vection. Both assertions are dubious. Regarding cyclorotational optokinetic nystagmus, available evidence shows that it is too weak to be important in induced rotary movement. Also, induced rotary movement and cyclorotational optokinetic nystagmus are affected differently by the velocity of eliciting stimulation. Regarding roll vection, the conditions for its intermittence do not match those for induced rotary movement. Also, although aftereffects for induced rotary movement are negative, those for roll vection are positive and negative. Intermittence in induced rotary movement may be parsimoniously explained as characteristic of a weak effect.

Eye Movements↗

PubMed1997

Activation of human V5 complex and rolandic regions in association with moving visual stimuli.

We recorded magnetoencephalographic responses from seven healthy humans during the presentation of stationary and rotating radial gratings. Rotations lasting 1 s evoked movement-specific sustained activity in the parieto-occipitotemporal border area, in agreement with the activation of the V5 complex specialized for the analysis of movement. The source areas of the movement-specific sustained fields were transiently active 100-130 ms after the onsets of both rotating and stationary stimuli, suggesting that movement-related cortical areas respond to any transient changes in the visual environment. Transients were evoked also in other brain areas 60-200 ms after onsets of both stimuli. Four subjects displayed additional motion-related sustained activity in the rolandic region. Sustained activity continued after the stimulus movement in several subjects during perception of the movement aftereffect. The transient activity may evoke visual attention while sustained activity of the V5 complex may be related to the conscious perception of movement.

Adult↗

PubMed1996

Modification of the Filehne illusion by conditioning visual stimuli.

During smooth pursuit eye movements made across a stationary background an illusory motion of the background is perceived (Filehne illusion). The present study was undertaken in order to test if the Filehne illusion can be influenced by information unrelated to the retinal image slip prevailing and to the eye movement being executed. The Filehne illusion was measured in eight subjects by determining the amount of external background motion required to compensate for the illusory background motion induced by 12 deg/sec rightward smooth pursuit. Using a two-alternative forced-choice method, test trials, which yielded the estimate of the Filehne illusion, were randomly interleaved with conditioning trials, in which high retinal image slip was created by background stimuli moving at a constant horizontal velocity. There was a highly reproducible monotic relationship between the size and direction of the Filehne illusion and the velocity of the background stimulus in the conditioning trials with the following extremes: large Filehne illusions with illusory motion to the right occurred for conditioning stimuli moving to the left, i.e. opposite to the direction of eye movement in the test trials, while conversely, conditioning stimuli moving to the right yielded Filehne illusions close to zero. Additional controls suggest that passive motion aftereffects are unlikely to account for the modulation of the Filehne illusion by the conditioning stimulus. We hypothesize that this modification might reflect the dynamic character of the networks elaborating spatial constancy.

Adult↗

PubMed1985

A moving display which opposes short-range and long-range signals.

A novel display is described which stimulates both the long-range and the short-range motion detecting processes simultaneously, but with opposing directions of movement. The direction in which the stimulus appears to move depends on retinal eccentricity and element size, but adaptation to the display always produces a motion aftereffect (MAE) direction opposite to the direction of the short-range component. The display may offer insights into the properties of the two-process motion detecting system.

Adaptation, Physiological↗

PubMed1988

Adaptation to telestereoscopic viewing measured by one-handed ball-catching performance.

A one-handed ball-catching task was used to study the disturbance of depth judgement induced by telestereoscopic viewing (ie viewing with increased effective interocular separation), the recovery of performance with experience in the telestereoscope, and the errors that subsequently arose when the telestereoscope was removed. The ball's trajectory was variable so that subjects had to control both the position and the timing of the grasp in order to catch the ball. On first wearing the telestereoscope, subjects closed the hand when the ball was approximately twice as far away from the eyes as the hand was. After fewer than twenty trials in the telestereoscope subjects were closing the hand at approximately the correct time and place, although rather more trials were needed for ball-catching performance to recover to normal. When the telestereoscope was removed there was an aftereffect, with subjects making the opposite errors to when they began the task. The existence of an aftereffect shows that the process of adaptation involves reevaluation rather than neglect of the misleading binocular information. Helmholtz's theory that telestereoscopes cause the world to be perceived as a scale model is considered. Initial misreaching is roughly consistent with this theory, but there are insufficient data to test it rigorously. Data from the aftereffect phase are clearly inconsistent with the theory. The results confirm the importance of binocular information in dynamic motor tasks, such as ball catching.

Adaptation, Ocular↗

PubMed2004

Decay of prism aftereffects under passive and active conditions.

In prism adaptation, subjects adapt to new visuospatial coordinates imposed by wedge prisms that laterally displace the visual field. During this process, subjects develop and store new visuomotor coordinates in order to compensate for the displacement of visual stimuli. After the prisms are removed, subjects show an aftereffect in the opposite direction of the original perturbation. The aftereffect is a manifestation of the recently stored information. In the present article, we were interested in studying the properties of the aftereffect. Specifically, we investigated the fate of the aftereffect under active conditions with motor reafferences but without visual input, and during passive conditions without visual or motor reafferences. The results in the motor active condition show that motor reafference (proprioceptive or corollary discharge information) led to a faster, but incomplete, aftereffect decay. The results in the passive condition show a bimodal aftereffect behavior, with a fast decay within the initial minutes, followed by a sustained aftereffect up to 20 min later. These data suggests that two different memory processes may contribute to the aftereffect, one showing a fast decay mainly within 1 min, and another that shows a stable endurance for more than 20 min.

Adaptation, Physiological↗

PubMed1979

The relational determination of length illusions and length aftereffects.

When two lines were presented simultaneously, in an illusion paradigm, the judged length of one of the lines (the focal line) assimilated toward the length of the contextual line. When the lines were presented sequentially, in an aftereffect paradigm, the apparent length of the focal line was displaced away from the length of a previously presented contextual line (i.e. contrast). The largest effects obtained at inverse contextual-to-focal length ratios: 1.67:1 for contextual lines longer than the focal line and 0.60:1 for contextual lines shorter than the focal line. Overestimation of focal length was larger than underestimation for both illusions and aftereffects despite the fact that identical stimuli produced effects in opposite directions in the two paradigms. Results were discussed in terms of a neural length-coding model and were related to visual size constancy.

Figural Aftereffect↗

PubMed1989

Color aftereffect contingent on text.

During adaptation, two different letter strings (each five or six letters) were presented to subjects alternately, one in green and the other in magenta. The extent to which these letter strings subsequently elicited a color aftereffect was assessed. In different experiments, the chromatic letter strings consisted of words and nonwords. The results indicated that letter strings that form English words can contingently elicit a color aftereffect. This was the case even when the words were anagrams. There was no evidence that nonword letter strings could contingently elicit such an aftereffect, even when the nonwords conformed to English orthography. The results are relevant to understanding other contingent color aftereffects (McCollough effects), illusory color noted by computer operators who work at monochrome (green or amber) displays, and the processing of text.

Adult↗

PubMed1982

Directional specificity in tilt aftereffect induced with moving contours: a reexamination.

In the tilt aftereffect a grating or bar is perceived as being slightly rotated from its veridical orientation if it is preceded by a similar adaptation stimulus with a slightly different orientation. It has been reported that the tilt aftereffect is not direction specific. That is, the magnitude of the misperception was not affected by whether the adaptation and test stimuli were moving in the same or the opposite directions. However, when we required subjects to fixate on a stationary spot during adaptation to a moving grating, the tilt aftereffect was strongest when both stimuli moved in the same direction. Moreover, the tilt aftereffect was not direction specific without such fixation. These results are consistent with the distribution shift model in which the perceived orientation reflects the distribution of orientation selective units, some of which are also direction selective.

Adaptation, Ocular↗

PubMed1998

Shifts in perceived position following adaptation to visual motion.

Where do we perceive an object to be when it is moving? Nijhawan [1] has reported that if a stationary test pattern is briefly flashed in spatial alignment with a moving one, the moving element actually appears displaced in the direction in which it is moving. Nijhawan postulates that this may be the result of a mechanism that predicts the future position of the moving element so as to compensate for the fact that the element will have moved position from the time at which the light left it to the time at which the observer becomes aware of it (as a result of the finite time taken for neural transmission). There is an alternative explanation of this effect, however. Changes in the stimulus presentation could affect perceptual latency [2], and therefore the perceived position if in motion (as suggested for the Pulfrich pendulum effect [3] [4]). In other words, if the flashed probe of the Nijhawan demonstration takes longer to reach perceptual awareness than the moving stimulus, the latter will appear to be ahead of the probe. Here, I demonstrate an alternative way of testing this hypothesis. When an illusory movement is induced (via the motion aftereffect) within a stationary pattern, it can be shown that this also produces a change in its perceived spatial position. As the pattern is stationary, one cannot account for this result via the notion of perceptual lags.

Figural Aftereffect↗

PubMed2006

Representations of familiar and unfamiliar faces as revealed by viewpoint-aftereffects.

A viewpoint-dependent aftereffect occurs after prolonged viewing of a stimulus of a particular orientation, with the result that the test image is perceived to be facing away from the adapting orientation. Prior psychophysical work has led to the suggestion that the visual brain encodes a limited range of viewpoint information with regard to complex images. In this study, we investigated whether familiar faces were susceptible to a viewpoint aftereffect. Familiar faces are believed to be represented in a view-invariant manner, whereas unfamiliar faces are represented in a viewpoint-dependent manner. Adaptation to both familiar and unfamiliar faces influenced the perception of viewpoint of subsequent face images. However, category-specific transfer of a repulsive viewpoint-dependent aftereffect was observed with unfamiliar faces. Our results suggest that neural networks that mediate viewpoint information are also involved in view-invariant representation of familiar faces.

Adult↗

PubMed2003

The effect of trajectory on the auditory motion aftereffect.

The auditory motion aftereffect (aMAE) can be induced in listeners after repeated presentation of a horizontally moving sound source. Aftereffects have also been found for the individual acoustic consequences of source motion such as amplitude or frequency modulations (AM, FM). No study, however, has investigated whether combining these changes would enhance the magnitude of the aMAE, which has appeared otherwise weak relative to its visual counterpart. AM, FM and binaural changes can occur simultaneously when sources move along common translational trajectories rather than the restricted rotational paths used in previous adaptation studies. This raises the question whether the observed weakness of the aMAE is due to the improper stimulation of units responsive to the entire macrostructure induced by translational motion. The hypothesis is tested here that if integrated motion detectors exist, then including lawful amplitude and frequency changes in adapting stimuli may enhance aftereffects. Though results indicate that interaurally moving stimuli in general induce an aMAE, the acoustic macrostructure of translational motion does not appear to increase the aftereffect. A simple cross-correlation model is used to illustrate that such acoustic modulations may allow brainstem auditory centers time to recover from adaptation to translational motion.

Acoustic Stimulation↗

PubMed1990

An increase in strength of tilt aftereffect associated with tryptophan depletion.

The effects of a tryptophan-free amino acid mixture on tilt aftereffect, movement aftereffect, and the Mueller-Lyer illusion were studied. 12 male subjects ingested either a balanced amino acid mixture or a tryptophan-free mixture which causes a marked depletion of brain tryptophan and serotonin. The tryptophan-free mixture significantly increased the strength of tilt aftereffect but had no effect on movement aftereffect or the Mueller-Lyer illusion. These results were discussed with reference to the pharmacological activity of serotonin and its influence on the strength of lateral inhibition in mammalian brains.

Adult↗

PubMed1984

The influence of background motion on the motion aftereffect.

The motion aftereffect caused by adaptation to moving bars is visible in a stationary test pattern consisting of static visual noise (texture). The aftereffect resulting from adaptation to moving bars presented on a background of texture is highly dependent on the direction and velocity of motion of the background during adaptation, and less dependent on the nature of the test pattern. Background motion in the same direction as bar motion during adaptation enhances the aftereffect, whilst a stationary background or background motion in the opposite direction suppresses, and in some cases reverses the direction of, the aftereffect. The influence of background motion is greatest using a textured test pattern, a low adapting texture velocity, and a low grating spatial frequency. The physiological implications of these results are discussed.

Adaptation, Ocular↗