DETECTION AND DISCRIMINATION OF OPTICAL-FLOW COMPONENTS

Observers viewed animation sequences consisting of random dots, some o f which moved coherently in a given direction (signal dots) and the re st of which moved randomly (noise dots). Using forced-choice procedure s, detectability of weak signals within noise was measured for transla tion, rotation, and expansion/contraction. Sensitivity to all motion t ypes was approximately equal, with practiced observers reliably detect ing coherent motion at signal levels as low as 4%. Observers were able to identify the motion structure presented on a given trial at signal levels corresponding to the detection threshold, implying that the ne ural signals supporting detection are labeled for motion type. Results are discussed in the context of hierarchical analysis of optic flow i n which all motion types are registered as patterns of activity among neurons comprising a single mechanism.