Illusory position shift induced by motion within a moving envelope during smooth-pursuit eye movements

Distinct temporal developments of visual motion and position representations for multi-stream visuomotor coordination

A fundamental but controversial question in information coding of moving visual target is which of 'motion' or 'position' signal is employed in the brain for producing quick motor reactions. Prevailing theory assumed that visually guided reaching is driven always via target position representation influenced by various motion signals (e.g., target texture and surroundings). To rigorously examine this theory, we manipulated the nature of the influence of internal texture motion on the position representation of the target in reaching correction tasks. By focusing on the difference in illusory position shift of targets with the soft- and hard-edges, we succeeded in extracting the temporal development of an indirect effect only ascribed to changes in position representation. Our data revealed that the onset of indirect effect is significantly slower than the adjustment onset itself. This evidence indicates multi-stream processing in visuomotor control: fast and direct contribution of visual motion for quick action initiation, and relatively slow contribution of position representation updated by relevant motion signals for continuous action regulation. The distinctive visuomotor mechanism would be crucial in successfully interacting with time-varying environments in the real world.

Dynamic Dazzle Distorts Speed Perception

Static high contrast (‘dazzle’) patterns, such as zigzags, have been shown to reduce the perceived speed of an object. It has not escaped our notice that this effect has possible military applications and here we report a series of experiments on humans, designed to establish whether dynamic dazzle patterns can cause distortions of perceived speed sufficient to provide effective defence in the field, and the extent to which these effects are robust to a battery of manipulations. Dynamic stripe patterns moving in the same direction as the target are found to increase the perceived speed of that target, whilst dynamic stripes moving in the opposite direction to the target reduce the perceived speed. We establish the optimum position for such dazzle patches; confirm that reduced contrast and the addition of colour do not affect the performance of the dynamic dazzle, and finally, using the CO₂ challenge, show that the effect is robust to stressful conditions.

Field-like interactions between motion-based reference frames

A reference frame is required to specify how motion is perceived. For example, the motion of part of an object is usually perceived relative to the motion of the object itself. Johansson (Psychological Research, 38, 379-393, 1976) proposed that the perceptual system carries out a vector decomposition, which rewsults in common and relative motion percepts. Because vector decomposition is an ill-posed problem, several studies have introduced constraints by means of which the number of solutions can be substantially reduced. Here, we have adopted an alternative approach and studied how, rather than why, a subset of solutions is selected by the visual system. We propose that each retinotopic motion vector creates a reference-frame field in the retinotopic space, and that the fields created by different motion vectors interact in order to determine a motion vector that will serve as the reference frame at a given point and time in space. To test this theory, we performed a set of psychophysical experiments. The field-like influence of motion-based reference frames was manifested by increased nonspatiotopic percepts of the backward motion of a target square with decreasing distance from a drifting grating. We then sought to determine whether these field-like effects of motion-based reference frames can also be extended to stationary landmarks. The results suggest that reference-field interactions occur only between motion-generated fields. Finally, we investigated whether and how different reference fields interact with each other, and found that different reference-field interactions are nonlinear and depend on how the motion vectors are grouped. These findings are discussed from the perspective of the reference-frame metric field (RFMF) theory, according to which perceptual grouping operations play a central and essential role in determining the prevailing reference frames.