Displacement effects caused by converging lines and dots

Changes induced in orientation were examined under conditions of a dot or full-line version of a stimulus consisting of a test and inducing line. 44 subjects visually extended the test line to the surrounding circle on 11 trials and indicated their response by a mark on the circle. Magnitude of illusion was reduced by 54% for the dot version compared with the full-line form, but both produced an illusion significantly greater than zero. A significant practice effect was obtained with full lines but not with the dot form. Results are discussed in terms of lateral inhibition theory and related research.     

New motion illusion caused by pictorial motion lines

Motion lines (MLs) are a pictorial technique used to represent object movement in a still picture. This study explored how MLs contribute to motion perception. In Experiment 1, we reported the creation of a motion illusion caused by MLs: random displacements of objects with MLs on each frame were perceived as unidirectional global motion along the pictorial motion direction implied by MLs. In Experiment 2, we showed that the illusory global motion in the peripheral visual field captured the perceived motion direction of random displacement of objects without MLs in the central visual field, and confirmed that the results in Experiment 1 did not stem simply from response bias, but resulted from perceptual processing. In Experiment 3, we showed that the spatial arrangement of orientation information rather than ML length is important for the illusory global motion. Our results indicate that the ML effect is based on perceptual processing rather than response bias, and that comparison of neighboring orientation components may underlie the determination of pictorial motion direction with MLs.     

Motion capture of stationary lines by apparently moving terminators

Several studies and observations of a new form of motion capture are reported: frames containing identical rows of evenly spaced vertical lines are alternated in a standard apparent-motion paradigm. However, one vertical line in the first frame has short horizontal 'terminators' attached; the terminators are shifted to a different line in the second frame. Alternation that includes an unpatterned, nonzero interstimulus interval results in perceived motion of a vertical line along with the terminators. This motion can 'cross over' other stationary vertical lines and persists when light-filled interstimulus intervals and gaps between lines and terminators are introduced. It can also be obtained with different line sizes and spacings. The present motion capture does not appear to rely on a global-frame effect. Alternative explanations are considered.     

Motion induction from biological motion

A new type of motion illusion is described in which ambiguous motion becomes unidirectional on superimposition of a human figure walking on a treadmill. A point-light walker in profile was superimposed on a vertical counterphase grating backdrop. Eleven na?ve observers judged the apparent direction of motion against the grating as left or right in a two-alternative forced-choice task and found that the grating appeared to drift in a direction opposite to the walking. The illusion disappeared when the point lights moved in scrambled configurations. This indicates that the illusion is caused by biological motion that provides recognition of gaits. A human figure walking backwards produced no illusion because of the difficulty in identifying the gait. This indicates that the illusion is determined by translational motion rather than form represented from biological motion.     

Motion aftereffects and retinal motion

Two experiments are described in which it was investigated whether the adaptation on which motion aftereffects (MAEs) are based is a response to retinal image motion alone or to the motion signal derived from the process which combines the image motion signal with information about eye movement (corollary discharge). In both experiments observers either fixated a stationary point or tracked a vertically moving point while a pattern (in experiment 1, a grating; in experiment 2, a random-dot pattern) drifted horizontally across the field. In the tracking condition the adapting retinal motion was oblique. In the fixation condition it was horizontal. In every case in both conditions the MAE was horizontal, in the direction opposite to that of pattern motion. These results are consistent with the hypothesis that the adaptation is a response to the motion signal derived from the comparison of eye and image motion rather than to retinal motion per se. An alternative explanation is discussed.     

Motion integration during motion aftereffects

The perceived global motion of a stimulus depends on how its different local motion-direction vectors are distributed in space and time. When they are explicitly co-localized, as in the case of locally paired motion, competitive motion integration mechanisms produce a unitary global motion direction determined by their vector average. During motion aftereffects induced by simultaneous adaptation to multiple motion directions, just as in the case of locally paired motion, different directional signals originate simultaneously from exactly the same position in space. Therefore, the perceived global motion direction during motion aftereffects results from local vector averaging of the co-localized motion-direction signals induced by adaptation.     

The role of converging lines on the perception of vertical lines: A Ponzo illusion variant

An experiment was performed to examine the effect of the angle of converging contours on the subjective midpoints of vertical lines. According to the inappropriate size-constancy scaling theory of Gregory (1963) increasing the angle of converging contours should increase the apparent depth of the figure and therefore exert a measureable influence on the subjective midpoints of vertical lines enclosed by the contours. However, this manipulation was not found to affect the subjective midpoints of test lines indicating that an explanation of the Ponzo illusion based on the operation of inappropriate size-constancy scaling must be restricted to certain test configurations.     

Visual impressions of penetration in the perception of objects in motion

Observers viewed visual stimuli in which one object moved to a position of partial occlusion by another. The objects were presented as two-dimensional profiles moving in an undefined space, so the partial occlusion supports several different physical interpretations. In fact some stimuli reliably gave rise to a perceptual impression that the moving object penetrated or pierced the stationary one. This kind of interaction impression has not previously been reported. The impression was maximized by rapid deceleration to a halt with minimal occlusion. If the object decelerated more slowly, so that it was completely occluded or projected from the far side of the stationary object, it was perceived as moving behind the stationary object. The shape of the moving object and its speed prior to occlusion had significant but small effects.     

Reduction of the Poggendorff effect by the motion of oblique lines

The magnitude of the Poggendorff illusion was measured when the test lines were moved up or down and tracked by subjects. The difference between test lines and inducing lines caused by motion of the test lines significantly reduced the magnitude of illusion (60%). Supplementary experiments seemed to indicate that location of test lines, perceptual shrinkage of space in the vertical dimension, and effective display time were not the main factors contributing to the reduction in illusion magnitude. Instead, it seems that some reduction in interaction between test and inducing lines was the main cause of the reduction. The rising curve of the reduction was very steep with velocity, and the reduction magnitude was almost constant over most of the range of velocities studied. The current evidence seems to suggest that moving and stationary figures are processed by separate channels and that, therefore, the interaction between them is reduced.     

Motion direction discrimination training reduces perceived motion repulsion

Participants often exaggerate the perceived angular separation between two simultaneously presented motion stimuli, which is referred to as motion repulsion. The overestimation helps participants differentiate between the two superimposed motion directions, yet it causes the impairment of direction perception. Since direction perception can be refined through perceptual training, we here attempted to investigate whether the training of a direction discrimination task changes the amount of motion repulsion. Our results showed a direction-specific learning effect, which was accompanied by a reduced amount of motion repulsion both for the trained and the untrained directions. The reduction of the motion repulsion disappeared when the participants were trained on a luminance discrimination task (control experiment 1) or a speed discrimination task (control experiment 2), ruling out any possible interpretation in terms of adaptation or training-induced attentional bias. Furthermore, training with a direction discrimination task along a direction 150° away from both directions in the transparent stimulus (control experiment 3) also had little effect on the amount of motion repulsion, ruling out the contribution of task learning. The changed motion repulsion observed in the main experiment was consistent with the prediction of the recurrent model of perceptual learning. Therefore, our findings demonstrate that training in direction discrimination can benefit the precise direction perception of the transparent stimulus and provide new evidence for the recurrent model of perceptual learning.     

Motion aftereffect of combined first-order and second-order motion

When, after prolonged viewing of a moving stimulus, a stationary (test) pattern is presented to an observer, this results in an illusory movement in the direction opposite to the adapting motion. Typically, this motion aftereffect (MAE) does not occur after adaptation to a second-order motion stimulus (i.e. an equiluminous stimulus where the movement is defined by a contrast or texture border, not by a luminance border). However, a MAE of second-order motion is perceived when, instead of a static test pattern, a dynamic test pattern is used. Here, we investigate whether a second-order motion stimulus does affect the MAE on a static test pattern (sMAE), when second-order motion is presented in combination with first-order motion during adaptation. The results show that this is indeed the case. Although the second-order motion stimulus is too weak to produce a convincing sMAE on its own, its influence on the sMAE is of equal strength to that of the first-order motion component, when they are adapted to simultaneously. The results suggest that the perceptual appearance of the sMAE originates from the site where first-order and second-order motion are integrated.     

Motion over the retina and the motion aftereffect.

The motion aftereffect (MAE) was measured with retinally moving vertical gratings positioned above and below (flanking) a retinally stationary central grating (experiments 1 and 2). Motion over the retina was produced by leftward motion of the flanking gratings relative to the stationary eyes, and by rightward eye or head movements tracking the moving (but retinally stationary) central grating relative to the stationary (but retinally moving) surround gratings. In experiment 1 the motion occurred within a fixed boundary on the screen, and oppositely directed MAEs were produced in the central and flanking gratings with static fixation; but with eye or head tracking MAEs were reported only in the central grating. In experiment 2 motion over the retina was equated for the static and tracking conditions by moving blocks of grating without any dynamic occlusion and disclosure at the boundaries. Both conditions yielded equivalent leftward MAEs of the central grating in the same direction as the prior flanking motion, ie an MAE was consistently produced in the region that had remained retinally stationary. No MAE was recorded in the flanking gratings, even though they moved over the retina during adaptation. When just two gratings were presented, MAEs were produced in both, but in opposite directions (experiments 3 and 4). It is concluded that the MAE is a consequence of adapting signals for the relative motion between elements of a display.     

Motion cues that make an impression: Predicting perceived personality by minimal motion information

The current study presents a methodology to analyze first impressions on the basis of minimal motion information. In order to test the applicability of the approach brief silent video clips of 40 speakers were presented to independent observers (i.e., did not know speakers) who rated them on measures of the Big Five personality traits. The body movements of the speakers were then captured by placing landmarks on the speakers' forehead, one shoulder and the hands. Analysis revealed that observers ascribe extraversion to variations in the speakers' overall activity, emotional stability to the movements' relative velocity, and variation in motion direction to openness. Although ratings of openness and conscientiousness were related to biographical data of the speakers (i.e., measures of career progress), measures of body motion failed to provide similar results. In conclusion, analysis of motion behavior might be done on the basis of a small set of landmarks that seem to capture important parts of relevant nonverbal information.     

Motion transparency: making models of motion perception transparent

In daily life our visual system is bombarded with motion information. We see cars driving by, flocks of birds flying in the sky, clouds passing behind trees that are dancing in the wind. Vision science has a good understanding of the first stage of visual motion processing, that is, the mechanism underlying the detection of local motions. Currently, research is focused on the processes that occur beyond the first stage. At this level, local motions have to be integrated to form objects, define the boundaries between them, construct surfaces and so on. An interesting, if complicated case is known as motion transparency: the situation in which two overlapping surfaces move transparently over each other. In that case two motions have to be assigned to the same retinal location. Several researchers have tried to solve this problem from a computational point of view, using physiological and psychophysical results as a guideline. We will discuss two models: one uses the traditional idea known as ‘filter selection’ and the other a relatively new approach based on Bayesian inference. Predictions from these models are compared with our own visual behaviour and that of the neural substrates that are presumed to underlie these perceptions.     

Motion adaptation shifts apparent position without the motion aftereffect

Adaptation to motion can produce effects on both the perceived motion (the motion aftereffect) and the position (McGraw, Whitaker, Skillen, & Chung, 2002; Nishida & Johnston, 1999; Snowden, 1998; Whitaker, McGraw, & Pearson, 1999) of a subsequently viewed test stimulus. The position shift can be interpreted as a consequence of the motion aftereffect. For example, as the motion within a stationary aperture creates the impression that the aperture is shifted in position (De Valois & De Valois, 1991; Hayes, 2000; Ramachandran & Anstis, 1990), the motion aftereffect may generate a shift in perceived position of the test pattern simply because of the illusory motion it generates on the pattern. However, here we show a different aftereffect of motion adaptation that causes a shift in the apparent position of an object even when the object appears stationary and is located several degrees from the adapted region. This position aftereffect of motion reveals a new form of motion adaptation--one that does not result in a motion aftereffect--and suggests that motion and position signals are processed independently but then interact at a higher stage of processing.     

A computational and perceptual account of motion lines

To indicate motion in a static drawing, artists often include lines trailing a moving object. The use of these motion lines is notable because they do not seem to be related to anything in the optic array. The dynamic behavior of a neural-network model for contour detection is analyzed and it is shown that it generates trails of oriented responses behind moving stimuli. The properties of the oriented response trails are shown to correspond to motion lines. The model generates trails of different orientations depending on the speed and length of the movement, and thereby predicts different uses of two types of motion lines. The model further predicts that motion lines should bias real motion in some situations. An experiment relating motion lines to ambiguous motion percepts demonstrates that motion lines contribute to motion percepts.     

Memory displacement of an object with motion lines

This study explored how motion lines (ML) can contribute to the memory displacement of an object. Three experiments were conducted to examine the memorized position of a target with ML using manual localization tasks, revealing that the reproduced position was biased in the direction implied by the ML. Two further experiments successfully ruled out the possibility that the memory displacement stemmed from a repulsive manual localization tendency, an attention repulsion-like effect, or perceptual illusory displacement of the object. These results indicated that ML trigger anticipation of the future position of the object, resulting in memory displacement.     

Motion parallel to line orientation: disambiguation of motion percepts

Four experiments demonstrate that lines indicating path of movement can generate rotational percepts in a multistable motion display that usually produces only horizontal or vertical motion percepts. The properties of the path-of-movement lines are predicted by a neural-network theory of visual perception. Experimental results validate the theory's predictions by demonstrating that movement of the display elements seems to follow an increasing luminance gradient in lines but not bars, and that illusory contours have similar effects. Experimental results also demonstrate that, in a choice between movement along lines drawn parallel or orthogonal to possible motion paths, observers more often see movement along the lines parallel to the motion path. These results suggest modifications to current computational and neurophysiological theories of motion perception.     

Motion detection and motion verbs: language affects low-level visual perception

Recent theories propose that semantic representation and sensorimotor processing have a common substrate via simulation. We tested the prediction that comprehension interacts with perception, using a standard psychophysics methodology. While passively listening to verbs that referred to upward or downward motion, and to control verbs that did not refer to motion, 20 subjects performed a motion-detection task, indicating whether or not they saw motion in visual stimuli containing threshold levels of coherent vertical motion. A signal detection analysis revealed that when verbs were directionally incongruent with the motion signal, perceptual sensitivity was impaired. Word comprehension also affected decision criteria and reaction times, but in different ways. The results are discussed with reference to existing explanations of embodied processing and the potential of psychophysical methods for assessing interactions between language and perception.     

Motion perception in the ageing visual system: minimum motion, motion coherence, and speed discrimination thresholds

We aimed to address two issues: first, to describe how the perception of motion differs in elderly observers as compared to younger ones; and, second, to see if these changes in motion perception could be accounted for by the known changes in the ability of elderly observers to detect patterns (as indexed via contrast sensitivity). The lower threshold of motion, motion coherence, and speed discrimination were measured, alongside contrast sensitivity, in a group of thirty-two older (mean age 61.5 years) and thirty-two younger (mean age 23.2 years) subjects. The older observers showed losses in their ability to detect slow motions as indexed via the lower threshold of motion for random-dot patterns and for gratings of a range of spatial frequencies. They also were impaired on a test of motion coherence, but only for stimuli of a slow to medium speed, whereas faster speeds showed no decline with age. Finally, at all speeds tested the older observers required greater differences in speed in order to discriminate between patterns moving at different speeds. The pattern of losses on motion perception tasks was not predicted by the deficits of the older groups, such as loss of detection thresholds for high spatial and/or temporal frequencies. It is concluded that these hypotheses do not provide an adequate account of the data, and therefore that the losses occurring with age are complex and probably are a result of the loss of several types of cell.