GLOBAL-MOTION PERCEPTION - INTERACTION OF CHROMATIC AND LUMINANCE SIGNALS

A global dot-motion stimulus was employed in order to investigate the interaction between luminance and chromatic signals in motion processi ng. Thresholds are determined by measuring the minimum number of dots which need to move in a coherent fashion in a field of randomly moving dots in order for the observers to be able to determine the direction of coherent motion. We found that: (1) observers could not track an a chromatic signal-dot which changes its luminance polarity between fram e transitions. The addition of a consistent chromatic signal allowed o bservers to track such a dot when the dot contained low- (8%) luminanc e contrast but this ability was impaired as the luminance contrast was increased; (2) the addition of chromatic contrast to a dot which cont ained consistent low-luminance contrast could result in threshold elev ation. For fixed contrast chromatic and luminance signals, the presenc e and degree of threshold elevation depended upon the spatiotemporal p roperties of the dot motion; (3) the ability of observers to extract a global-motion signal carried by a group of dots of one colour was imp aired by the addition of a number of additional-noise dots of a differ ent colour. These results are interpreted as indicating that: (1) the motion-selective cells that are sensitive to chromatic signals are als o sensitive to luminance signals; (2) the combined chromatic and lumin ance and purely luminance motion cells are pooled to form a single pat hway prior to global-motion extraction; and (3) the negative interacti on observed between the chromatic and luminance signals is likely to b e due to the differences in the processing speeds of the combined lumi nance and chromatic and the purely luminance sensitive motion cells. C opyright (C) 1996 Elsevier Science Ltd.