MOTION COHERENCE ACROSS DIFFERENT CHROMATIC AXES

It has been reported that equiluminant plaid patterns constructed from component gratings modulated along different axes of a cardinal colou r space fail to create a coherent impression of two-dimensional motion [Krauskopf and Farell (1990), Nature, 348, 328-331], In this paper we assess whether this lack of interaction between cardinal axes is a ge neral finding or is instead dependent upon specific stimulus parameter s, Type I and Type II plaids were made from sinusoidal components (1 c pd) each modulated along axes in a cardinal colour space and presented at equivalent perceived contrasts, The spatial angular difference bet ween the two components was varied from 5 to 90 deg whilst keeping the Intersection of Constraints (I.O.C.) solution of the pattern constant , Observers were required to indicate the perceived direction of motio n of the pattern in a single interval direction-identification task. W e find that: (i) When plaids were made from components modulated along the same cardinal axis, coherent ''pattern'' motion was perceived at all angular differences, As the angular difference between the compone nts decreased in a Type II plaid, the perceived direction of motion mo ved closer to the I.O.C. solution and away from that predicted by the vector sum, (ii) A plaid made from components modulated along red-gree n and blue-yellow cardinal axes (cross-cardinal axis) did not cohere a t high angular differences (>30 deg) but had a perceived direction of the fastest moving component, At lower angular differences, however, p attern motion was detected and approached the I.O.C. solution in much the same way as a same-cardinal axis Type II plaid, (iii) A plaid made from a luminance grating and a cardinal chromatic grating (red-green or blue-yellow) failed to cohere under all conditions, demonstrating t hat there is no interaction between luminance and chromatic cardinal a xes, These results indicate that there are conditions under which red- green and blue-yellow cardinal components interact for the purposes of motion detection. Copyright (C) 1996 Elsevier Science Ltd.