It has been shown that that there is strong inhibition between opposite motion directions at the global motion stage, while at the local motion stage opposite directions are processed independently. We predict that adaptation to opposite motion vectors - even in the case of locally-paired opposite motion which is perceived as motionless flicker - will lead to a local, direction-specific motion adaptation. Procedure: Observers viewed two fields of superimposed, limited-lifetime (6 frames) drifting dots. One field (of black dots) drifted rightward, the other (white dots) leftward. In one condition, black and white dots were strewn independently, so transparent motion was seen; in another condition, each black dot was locally paired with a white dot, so the display appeared as directionless flicker. These stimuli were used as adaptors in a motion aftereffect (MAE) paradigm, using a top-up procedure. Test stimuli consisted of one field of static, infinite-lifetime dots (either black or white) and another field of dots (of opposite polarity to static field) drifting upward. Any polarity-contingent MAE (PCMAE) would introduce a tilt in the motion vector of the upward drifting field; this tilt was taken as a measure of the direction and magnitude of the PCMAE. (At last year's VSS we reported that the addition of a relative motion cue to the presence of two surfaces is necessary for expression of the PCMAE when both polarities are in the test.) Results: In both non-paired and locally-paired conditions, both naïve and expert observers showed significant PCMAE's of comparable magnitude. Conclusion: Adaptation to opposite motion leads to polarity-contingent motion aftereffects at the local motion processing stage even in those cases when, due to the short range integration of locally paired motion vectors, global motion is cancelled and only local signals remain. Such local PCMA's can be a useful new tool for the study of the mechanisms of local motion processing.
ASJC Scopus subject areas
- Sensory Systems