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PubMed2004

Components of motion perception revealed: two different after-effects from a single moving object.

If motion that one has been looking at for some time suddenly stops, or if one shifts one's gaze to a static object, one will see motion in the opposite direction: the motion after-effect. If two transparent surfaces move with different speeds in different directions, then the direction of the motion after-effect will depend on the test pattern. For such transparent surfaces both the local motion and the global percept have two components. When looking at a normal moving object, there is only one perceived global motion. However, we know that locally there can be considerable ambiguity (the aperture problem). Does one adapt to all the local components, including those that one does not perceive, or only to the perceived global motion? We designed a stimulus that is perceived to be a fast rotating object, but also has a slow local radial component of motion. By selecting an appropriate test pattern we could either get a radial or a rotating motion after-effect. Thus we show that adaptation to motion must (also) occur at a stage at which local motions have not yet been integrated to give a unified percept.

Adaptation, Physiological↗
PubMed2004

Attention enhances adaptability: evidence from motion adaptation experiments.

Several previous psychophysical and neurophysiological studies have investigated the separate effects of attention and adaptation on visual processing. Here, we investigated the combined effects of attention and adaptation on motion processing by measuring the effects of spatial attention on the duration of the motion after-effect (MAE) over a wide range of stimulus contrasts. MAE duration was compared between two conditions: full-attention, subjects were required to pay attention to the adapting motion stimulus, and poor-attention, subjects performed a difficult vowel detection task at the center of gaze and ignored the adapting motion stimulus. Attention was found to increase the MAE duration by a factor of 1.4, which was approximately constant over a wide range of stimulus contrasts (3.22-80.6%). Notably, this included contrasts for which the MAE duration had reached its asymptotic value. We show that a quantitative model based on known properties of directionally selective MT neurons can explain these results by assuming that attention enhances the effects of adaptation, a phenomenon we refer to as "adaptation gain". Specifically, attending to an adapting motion stimulus shifts the semi-saturation point (C50) of the underlying contrast response function (CRF) of motion detectors roughly 1.4-fold more to the right than does ignoring that same stimulus. By enhancing the effects of adaptation in this fashion, attention is predicted to enhance the adaptability of the visual motion system.

Adaptation, Physiological↗
PubMed2005

Learning to suppress task-irrelevant visual stimuli with attention.

While the importance of attention in perceptual learning is widely recognized, the mechanisms through which it affects learning are poorly understood. Here we show that attentional mechanisms themselves are modified during learning. Attentional suppression of task-irrelevant stimuli becomes more efficient with practice. Attentional learning was found to be stimulus-specific and to persist for several weeks, suggesting that the plasticity of attentional mechanisms is an inherent component of visual perceptual learning.

Attention↗
PubMed2004

Attention-based motion perception and motion adaptation: what does attention contribute?

Attention-based motion perception refers to the phenomenon that a stimulus with ambiguous motion energy can be seen to move in a direction that is under attentive control of the observer. The role of attention is obvious when the stimulus is ambiguous: it makes the stimulus move in one direction. The goal of the current experiment is to investigate what the contribution of attention under attentive tracking conditions actually is, especially while viewing-time progresses. We had our observers look at a circular array of four evenly spaced discs whose motion direction was biased in the clockwise direction. Observers either viewed the stimulus moving around a circular path passively or actively. In the latter case they attentively tracked one of the discs. The observer's task was to indicate the perceived direction of motion. As time progresses, this kind of stimulus will undergo spontaneous motion direction reversals. We analyzed the time course of the reversals and show that actively attentive tracking the stimulus massively delays the reversal time. These results suggest that attention can temporarily overrule lower level adaptation.

Adaptation, Physiological↗
PubMed2005

Motion induced spatial conflict following binocular integration.

When a moving border defined by small changes in luminance (or by differences in colour) is placed in close proximity to moving borders defined by large changes in luminance, the low contrast border can appear to jitter. Previously, the existence and characteristics of this phenomenon were established using subjective reports. Here, we show that spatial judgments become more difficult in the presence of illusory jitter, presumably because of the positional uncertainty that is induced. We also explore the influence of the distance between the different types of moving border. We find that this manipulation influences the salience and amplitude, but not the perceived rate, of illusory jitter. Finally, we show that illusory jitter remains when the different types of moving border are presented to different eyes. These observations suggest that this phenomenon arises at the cortical level and are consistent with our earlier proposal--that illusory jitter can occur because the visual system periodically resolves a spatial conflict that arises when a rigid moving object contains different apparent speeds.

Color Perception↗
PubMed2005

Backscroll illusion: apparent motion in the background of locomotive objects.

Backscroll illusion is an apparent motion perceived in backgrounds of movie images that present locomotive objects such as people, animals, and vehicles. This illusion is from the visual system registering retinal motion signals in relation to high-level object motion signals. We confirmed this notion from psychophysical experiments that mainly presented a realistic human figure on a treadmill walking or running in front of a counterphase grating. The apparent grating motion was consistently induced in the direction opposite to the locomotion. The induction was tuned to a gait velocity. The time course showed that the illusion arose as if it was synchronized with gait recognition, and that it was sustained against several reversals of limb swings so that local motion accounts were denied. A weak but significant illusion was observed from a static figure that implied a gait. Thus, we concluded that the illusion was determined by the high-level recognition of biological motion. An additional experiment found a similar effect from a vehicle with rotating wheels but no induction from a rotating wheel per se. This result led us to hypothesize that the backscroll illusion is generalized to objects that have shapes implying their moving directions.

Adult↗
PubMed2006

Evaluating shape after-effects with radial frequency patterns.

Mechanisms selective for complex shape are vulnerable to adaptation techniques historically used to probe those underlying performance in lower-level visual tasks. We explored the nature of these shape after-effects using radial frequency patterns. Adapting to a radial frequency pattern resulted in a strong and systematic after-effect of a pattern that was 180 degrees out of phase with the adapting pattern. This after-effect was characterized as both a shift in the point of subjective equality and an increase in response uncertainty. The after-effect transferred across adapting pattern contrast and adaptor amplitude, suggesting an involvement from shape-specific mechanisms located at higher processing stages along the visual pathway. Moreover, our results suggested that the shift in the point of subjective equality was guided by global processing mechanisms, whereas the increase in uncertainty reflected activity from local processing mechanisms. Together, these results suggest that shape-specific after-effects reflect gain control processes at various stages of processing along the ventral pathway.

Adaptation, Physiological↗
PubMed2006

Reversal of apparent rotation in the Enigma-figure with and without motion adaptation and the effect of T-junctions.

We studied the time course of apparent rotation and directional reversal in Leviant's Enigma figure. On average, periods of clockwise rotation lasted 5.0 s as opposed to 4.4 for counter-clockwise rotation, resulting in an average reversal frequency of 6.4 within 30 s. At the beginning of a trial, clockwise rotation was perceived almost twice as often as counter-clockwise rotation. This bias could be shifted by previous adaptation to a black-and-white rotating sector disk, suggesting a neural interaction between real motion and illusory motion. We further studied Enigma-type motion on a chromatic bar superimposed onto a black-and-white linear grating. Illusory motion was strongest when the bar was oriented at 90 deg to the grating lines and became progressively weaker with a decrease in angle. This suggests that T-junctions formed by the radial rays impinging onto the colored rings of the Enigma figure are instrumental for eliciting the rotary motion and may rule out a low-level sensory origin of the illusion.

Adult↗
PubMed2006

Luminance-contrast properties of contour-shape processing revealed through the shape-frequency after-effect.

We investigated the first-order inputs to contour-shape mechanisms using the shape-frequency after-effect (SFAE), in which adaptation to a sinusoidally modulated contour causes a shift in the apparent shape-frequency of a test contour in a direction away from that of the adapting stimulus [Kingdom F. A. A., & Prins N. (2005a). Different mechanisms encode the shapes of contours and contour-textures. Journal of Vision 5(8), 463, (Abstract)]. We measured SFAEs for adapting and test contours (and edges) that differed in the contrast-polarity, scale (or blur) and magnitude of luminance contrast. The rationale was that if the SFAE was found to be reduced when adaptor and test differed along a particular dimension of luminance contrast, contour-shape mechanisms must be tuned to that dimension. Our results reveal that SFAEs manifest (i) a degree of selectivity to luminance contrast polarity for both even-symmetric (contours only) and odd-symmetric (both contours and edges) luminance profiles; (ii) a degree of selectivity to luminance scale (or blur); (iii) higher selectivity to fine compared to coarse scale for broadband edges (iv) a small preference for equal-in-contrast adaptors and tests. These results suggest that contour shapes are not encoded in the form of a sparse, cartoon-like sketch, as might be presumed by local energy (i.e. non-phase-selective) or form-cue invariant models, but instead in a form that is relatively 'feature-rich.'

Computer Graphics↗
PubMed2006

The continuous Wagon Wheel Illusion is object-based.

The occurrence of perceived reversed motion while observers view a periodic, continuously moving stimulus (the "continuous Wagon Wheel Illusion") has been taken as evidence that some aspects of motion perception rely on discrete sampling of visual information. The spatial extent of this sampling is currently under debate. When two separate motion stimuli are viewed simultaneously, the illusion of reversed motion rarely occurs for both objects together: this rules out global sampling of the visual field. The same result holds when the objects are superimposed by transparency: this argues against location-based sampling. Here we show that the sampling is in fact object-based: we use a rotating ring stimulus split in two halves. When the two halves move in opposite directions, appearing to belong to separate objects, perceptual reversals occur in either half at a time, but rarely in both. When the two halves physically move in compatible directions, they generally appear to reverse simultaneously: the illusion keeps the perceptual object united. Rather than the local low-level properties of the motion stimulus (which are comparable in both cases), it is thus the high-level organization of the scene that determines the extent of perceived motion reversals. These results imply that the continuous Wagon Wheel Illusion, and any discrete perceptual sampling that may cause it, is restricted to the object of our attention.

Adaptation, Physiological↗
PubMed2006

Reduction in the motion coherence threshold for the same direction as that perceived during adaptation.

When a stimulus of equally spaced parallel lines is displaced slightly in a direction perpendicular to the lines, low-speed motion toward the displacement direction can be perceived. Such a stimulus embodies both a low-speed and a high-speed component in opposite directions. The dominance of the former would result in the perception of low-speed motion. To see how the unperceived high-speed component is processed by the visual system, I measured coherence thresholds for random-dot test-motion with and without prior adaptation to the low-speed motion of the equally spaced parallel lines. The results depended on the test speeds. At low speeds, the coherence thresholds for the same direction as that perceived during the adaptation phase increased and the coherence thresholds for the opposite direction decreased. At high speeds, the same adaptation resulted in an opposite effect. The threshold reduction for high-speed motion in the same direction as that perceived during the adaptation phase and the threshold elevation in the opposite direction might be due to adaptation of a high-speed processing channel to the high-speed component that was not perceived but was nevertheless detected.

Adaptation, Ocular↗
PubMed1978

Processing of visual contour orientation information in normal and disabled reading children.

Four experiments comparing the processing of contour orientation information in normal and specific reading disabled children were conducted. The first two experiments demonstrated that the reading disabled subjects had significantly longer visual information store durations than did the control subjects. In addition differences in visual information store durations for different orientations were found between the two groups. The final two experiments investigated processing of contour orientation information in the visual cortex. Results of Experiment IV suggested that the two groups differ in their processing of information in the visual cortex as well as in VIS. Because of the importance of feature detection in letter recognition, it is suggested that the present results may be important in understanding letter recognition is disabled readers.

Child↗
PubMed1984

Visible persistence as a function of viewing condition and eye-handedness relationship.

Duration of visible persistence was investigated as a function of spatial frequency, orientation and viewing condition (binocular, dominant eye and non-dominant eye). Persistence increased with increasing spatial frequency and was longer for oblique than vertical gratings. Viewing condition also influenced visible persistence such that binocular persistence was significantly shorter than for either monocular condition. A post-hoc analysis indicated that this was only true with subjects who were right-handed and right-eyed. Subjects mixed on this relationship showed no differences in persistence across viewing conditions. A second experiment which selected subjects on the basis of this relationship confirmed the results of Experiment 1. The results for the right-right group broaden the generality of the rule showing an inverse relationship between response strength and persistence duration. The results for the Mixed group indicate a lack of binocular summation.

Dominance, Cerebral↗
PubMed2001

Visual jitter: evidence for visual-motion-based compensation of retinal slip due to small eye movements.

When dynamic random noise is replaced by static noise after a period of adaptation, adjacent unadapted regions filled with static noise appear to 'jitter' coherently in random directions for several seconds, actually mirroring the observer's own eye movements of fixation [Murakami, I. & Cavanagh, P. (1998). Nature, 395, 798-801]. The present study aims at psychophysically locating two distinct stages underlying this visual jitter phenomenon: a monocular, adaptable stage that measures local retinal motion and a compensation stage that estimates a baseline motion minimum and subtracts it from motion vectors nearby. The first three experiments revealed that visual jitter has storage, directional selectivity, and spatial frequency selectivity, like the motion after-effect does. These results suggest some overlap in the adaptation mechanisms for the two effects, possibly at or below the level of primary visual cortex. The next two experiments revealed the transfer of the effect across the vertical meridian as well as the existence of a preferred stimulus size that is a linear increasing function of eccentricity, mimicking the RF size of the monkey MT neurons. These results suggest that some extrastriate motion area along the parietal pathway including MT mediates motion-based compensation of retinal slip.

Adaptation, Physiological↗
PubMed2001

Perceived motion in orientational afterimages: direction and speed.

Two sets of experiments demonstrate new properties of motion in orientational after-effects. In a previous report, we showed that when observers adapted to a static bar grating whose elements varied in size or intensity from one side to the other, offset of the grating resulted in a motion after-effect, with the perceived motion in the direction of the largest or most intense bar. In the first new experiment, we show that similar results can be produced by varying the duration of the bar elements, with the direction of the motion after-effect toward the bar with the longest duration. In the second new experiment we demonstrate that the perceived speed of the motion after-effect is influenced by the spatial extent of the after-effect, with larger extents corresponding to faster speeds. The experimental findings are discussed in the context of a neural network theory of visual perception. In this theory, a moving oriented contour leaves a trail of activity among cortical cells tuned to orthogonal orientations. We hypothesize that the grating stimuli produce after-effects that mimic the pattern of oriented responses produced by a true moving contour, and the visual system interprets this pattern as a cue for motion. We also show how the model connects the properties of these motion after-effects to properties of visual persistence.

Figural Aftereffect↗
PubMed2001

Orthogonal adaptation improves orientation discrimination.

We investigated the effect of adaptation on orientation discrimination using two experienced observers, then replicated the main effects using a total of 50 naïve subjects. Orientation discrimination around vertical improved after adaptation to either horizontal or vertical gratings, but was impaired by adaptation at 7.5 or 15 degrees from vertical. Improvement was greatest when adapter and test were orthogonal. We show that the results can be understood in terms of a functional model of adaptation in cortical vision.

Adaptation, Physiological↗
PubMed2001

Increased sensitivity to speed changes during adaptation to first-order, but not to second-order motion.

Observers adapted to drifting patterns varying either in luminance (first-order pattern), or in contrast (second-order pattern). Sensitivity to increases or decreases in the speed of the first-order pattern increased sharply as adaptation time increased, but sensitivity to speed changes of the second-order pattern remained unchanged throughout the adaptation time. Adaptation of first-order motion mechanisms seems thus to mediate increased sensitivity to variations in speed around the adapting speed. No evidence was found for such effects of adaptation to second-order motion. The observed differences in the effects of adaptation accord well with reports of fundamental differences between after-effects to drifting first- and second-order patterns and are in harmony with models of motion perception emphasizing different mechanisms for the detection of first- and second-order motion.

Adaptation, Physiological↗