Strength Of Motion Aftereffect Research Articles

Inattentional aftereffects: The role of attention on the strength of the motion aftereffect.

The way that attention affects the processing of visual information is one of the most intriguing fields in the study of visual perception. One way to examine this interaction is by studying the way perceptual aftereffects are modulated by attention. In the present study, we have manipulated attention during adaptation to translational motion generated by coherently moving random dots, in order to investigate the effect of the distraction of attention on the strength of the peripheral dynamic motion aftereffect (MAE). A foveal rapid serial visual presentation task (RSVP) of varying difficulty was introduced during the adaptation period while the adaptation and test stimuli were presented peripherally. Furthermore, to examine the interaction between the physical characteristics of the stimulus and attention, we have manipulated the motion coherence level of the adaptation stimuli. Our results suggested that the removal of attention through an irrelevant task modulated the MAE's magnitude moderately and that such an effect depends on the stimulus strength. We also showed that the MAE still persists with subthreshold and unattended stimuli, suggesting that perhaps attention is not required for the complete development of the MAE.

Invisible Adaptation: The Effect of Awareness on the Strength of the Motion Aftereffect.

The ability to process information despite the lack of perceptual awareness is one of the most fascinating aspects of the visual system. Such unconscious processing is often investigated using adaptation, where any presence of the former can be traced by its footprint on aftereffects following the latter. We have investigated the mechanisms of the motion aftereffect (MAE) using random dot displays of varying motion coherence as well as crowding to modulate both the physical as well as the perceptual strength of the adaptation stimulus. Perceptual strength was quantitatively measured as the performance in a forced-choice direction-discrimination task. A motion-nulling technique was used to quantitatively measure the strength of the MAE. We show that the strength of the dynamic MAE is independently influenced by both the physical stimulus strength as well as the subjective perceptual strength, with the effect of the former being more prominent than that of the latter. We further show that the MAE still persists under conditions of subthreshold perception. Our results suggest that perceptual awareness can influence the strength of visual processing, but the latter is not fully dependent on the former and can still take place at its partial or even total absence.

A model of encoding and decoding in V1 and MT accounts for motion perception anisotropies in the human visual system

We used the motion aftereffect (MAE) to psychophysically characterize tuning of motion perception in the human visual system. The function relating MAE strength and the range of directions present in the adapter stimulus provides information regarding the width of direction tuning of motion adaptation. We compared the directional anisotropy in MAE tuning width to the well-known oblique effect in motion direction discrimination. In agreement with previous research, we found that subjects had lower motion direction discrimination thresholds for cardinal compared to oblique directions. For each subject, we also estimated MAE tuning width for a cardinal and an oblique direction by measuring the strength of the MAE for adapter stimuli containing different directional variances. The MAE tuning width was smaller for the cardinal direction, suggesting a fundamental similarity between motion direction discrimination and tuning of the MAE. We constructed a model of encoding of motion stimuli by V1 and MT and decoding of stimulus information from the cells in area MT. The model includes an anisotropy in the representation of different directions of motion in area V1. As a consequence of the connections implemented in the model, this anisotropy propagates to cells in MT. Model simulations predicted an oblique effect for both direction discrimination thresholds and MAE tuning width, consistent with our experimental results. The model also concurs with a recent report that the magnitude of the oblique effect for direction discrimination is inversely proportional to the directional variance of the stimulus. The agreement between model predictions and empirical data was obtained only when the model employed a maximum likelihood decoding algorithm. Alternative decoding mechanisms such as vector averaging and winner-take-all failed to account for the psychophysical results.

Topography of the motion aftereffect with and without eye movements

Although a lot is known about various properties of the motion aftereffect (MAE), there is no systematic study of the topographic organization of MAE. In the current study, first we provided a topographic map of the MAE to investigate its spatial properties in detail. To provide a fine topographic map, we measured MAE with small test stimuli presented at different loci after adaptation to motion in a large region within the visual field. We found that strength of MAE is highest on the internal edge of the adapted area. Our results show a sharper aftereffect boundary for the shearing motion compared to compression and expansion boundaries. In the second experiment, using a similar paradigm, we investigated topographic deformation of the MAE area after a single saccadic eye movement. Surprisingly, we found that topographic map of MAE splits into two separate regions after the saccade: one corresponds to the retinal location of the adapted stimulus and the other matches the spatial location of the adapted region on the display screen. The effect was stronger at the retinotopic location. The third experiment is basically replication of the second experiment in a smaller zone that confirms the results of previous experiments in individual subjects. The eccentricity of spatiotopic area is different from retinotopic area in the second experiment; Experiment 3 controls the effect of eccentricity and confirms the major results of the second experiment.

Spatial Offset of Test Field Elements from Surround Elements Affects the Strength of Motion Aftereffects

Static movement aftereffects (MAEs) were measured after adaptation to vertical square-wave luminance gratings drifting horizontally within a central window in a surrounding stationary vertical grating. The relationship between the stationary test grating and the surround was manipulated by varying the alignment of the stationary stripes in the window and those in the surround, and the type of outline separating the window and the surround [no outline, black outline (invisible on black stripes), and red outline (visible throughout its length)]. Offsetting the stripes in the window significantly increased both the duration and ratings of the strength of MAEs. Manipulating the outline had no significant effect on either measure of MAE strength. In a second experiment, in which the stationary test fields alone were presented, participants judged how segregated the test field appeared from its surround. In contrast to the MAE measures, outline as well as offset contributed to judged segregation. In a third experiment, in which test-stripe offset was systematically manipulated, segregation ratings rose with offset. However, MAE strength was greater at medium than at either small or large (180 degrees phase shift) offsets. The effects of these manipulations on the MAE are interpreted in terms of a spatial mechanism which integrates motion signals along collinear contours of the test field and surround, and so causes a reduction of motion contrast at the edges of the test field.

Adaptation to spiral motion: global but not local motion detectors are modulated by attention

In this study, we investigated the effect of attention on local motion detectors. For this purpose we used logarithmic spirals previously used by Cavanagh and Favreau [ Perception, 1980, 9(2), 175–182]. While the adapting stimulus was a rotating logarithmic spiral, the test stimulus was either the same spiral or its mirror image. When superimposed, all contours of the spiral stimulus and its mirror image are 90° apart. Presenting the same spiral during the test period shows adaptation of both local motion detectors and global rotation detectors, whereas showing the mirror-spiral stimulates another set of local motion detectors, and therefore illustrates adaptation at only the global motion level. To manipulate the attentional state of observers, a secondary task was presented during the adaptation phase and observers either performed the task or ignored it. Motion aftereffect (MAE) duration was measured afterwards. While the effects of attention and test stimulus type on MAE duration were both significant, the difference in the MAE strength between the attention-distracted and attention-not-distracted conditions was equal when the test stimulus was the same-spiral or the mirror-spiral, suggesting that attention to spiral motion modulates only global rotation units and does not affect local motion detectors located at V1. Our results are in accord with those reported by Watanabe et al. [ Proceedings of the National Academy of Sciences of the USA, 1998, 95(19), 11489–11492] which showed differential modulation of motion processing areas depending on the type of motion being attended. Therefore our data are supportive of the notion that attentional modulation of V1 is highly task-dependent.

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.

Strength of Motion Aftereffect Varies with Segregation of Test Field and Surround

It is widely accepted that the motion aftereffect (MAE) results from the adaptation of visual motion detectors. However, recent work suggests that how the effects of that adaptation are expressed (the nature of the perceived MAE) depends on the nature of the inducing and test fields. We investigated how the strength of the MAE varied with the nature of the boundary between the test field and the surround. The surround (18.5 deg wide × 13.5 deg high) to the adapting and test fields was an area of vertical square-wave grating of 0.7 cycle deg−1. During adaptation, vertical stripes of the same spatial frequency as the background moved horizontally at a speed of 2 deg s−1 for 14 s within a central rectangular window of 9.7 deg wide × 7.6 deg high. At the end of adaptation, one of six different test fields was presented in the central window. In three of these, the stationary test stripes were exactly aligned with the surrounding stripes, and in the other three they were offset by half a stripe width. For two of these conditions (one aligned, one offset), a black outline was drawn around the edge of the adapting window (and so was visible only where it crossed white areas), and for two others (one aligned, one offset) the outline was red, and so visible in its entirety. The strength of MAEs in twelve subjects was assessed both by ratings at an auditory signal which occurred 0.5 s after the end of adaptation and also by measurement of their durations. There was good agreement between these two measures. MAEs were significantly stronger on the offset than on the aligned test fields. The presence of an outline increased MAE strength compared with no outline, but these outline effects were much weaker than those of offsetting the test stripes from the surround. We suggest that the MAE depends in part on the presence of a visually separable test pattern to which motion may be allocated.

Motion aftereffect with flickering test stimuli depends on adapting velocity

Temporal tuning property of motion aftereffect (MAE) with flickering test stimuli (flicker MAE) was examined. Using sinusoidal gratings of several spatial frequencies (SF), MAE strength was measured for various adapting temporal frequencies (TF). Unlike the traditional MAE with static test field, the results indicated that flicker MAE did not depend on TF. Rather, when plotted as a function of velocity, the peaks had approximately the same adapting velocity of 5–8 deg/sec for all SF conditions tested, suggesting velocity dependence. This is further support of the idea that the two kinds of MAE are of different origin and suggests a higher origin of flicker MAE, perhaps in the area MT or MST.

Difference of spatial frequency selectivity between static and flicker motion aftereffects.

The strength of motion aftereffect (MAE) was measured with the use of sinusoidal gratings of several spatial frequencies, to examine the spatial frequency selectivity of two types of MAE. With ordinary static grating as a test stimulus, to measure 'static MAE', the maximum aftereffect for each adapting spatial frequency was obtained at the testing stimuli of the same spatial frequency, showing spatial frequency selectivity. However, in the case when the sinusoidally flickering grating was used as a test stimulus, to measure 'flicker MAE', no spatial frequency selectivity was observed. The two types of MAE were considered to be based on different mechanisms. Static MAE is thought to depend on the spatiotemporal channel mechanism in the early processing stages, whereas flicker MAE might reflect higher-level processes which might occur at the extrastriate regions.