Representation of orientation and spatial frequency in perception and memory: a choice reaction-time analysis.

Discrimination and short-term memory for the orientation of sinusoidal gratings that differed in spatial frequency, and for the spatial frequency of gratings that differed in orientation, were measured in a same-different task with 0-10 s interstimulus intervals (ISI) between test and reference stimuli. Introducing a difference between test and reference stimuli on a second dimension, or increasing ISI, did not impair spatial discrimination in terms of accuracy, but choice reaction times for correct decisions were prolonged by both manipulations. Results suggest that perceptual discrimination is based on representations in which orientation and spatial frequency are conjointly coded and that decisions are reached by a serial process scanning multiple-tuned, labeled channels; short-term memory may involve reactivation of these channels.