Abstract
The main objective of this study is to examine the relationship between mechanisms for luminance- and motion-defined contours through VEP. Jeffreys et al.(1977) reported that the polarity of VEPs elicited by luminance pattern presented in upper visual field was reversed from that elicited by patterns in lower visual field. If similar mechanisms are involved in detection of motion-defined contours, similar polarity reversals should be observed.
We prepare two types of random dot kinematograms (RDK). The stimulus for experimental condition was a motion-defined 4 × 4 checkerboard pattern Each square subtended 1.5 × 1.5 deg visual angle, and contained either motion in upper-left or lower-right direction. It had clearly defined contours. The motion directions was alternated every 500 ms. The stimulus for control condition was a whole field homogeneous motion. It had no motion-contour. For this, the whole field was moved in one direction, in either upper-left or lower-right direction and the direction was alternated every 500 ms. In both conditions, each dot subtended 1.5 ×1.5 minute and dot velocity was 3 deg/sec. Transient VEPs were recorded from an electrode at Oz using left-earlobe as a reference.
For the checkerboard pattern, three components with latencies of 100, 200, and 250 ms were identified (C100, C200, and C250). The polarity for all three components was reversed by the changing stimulus position. For the homogenous motion, in contrast, the polarity for C100 and C250 were reversed, but that for C200 was not reversed. These results demonstrate similarities between processings of motion- and luminance-defined contours. They also support Jeffrey's conjecture that 2nd component is closely related to contour perception.