CONTRAST TRANSFER CHARACTERISTICS OF VISUAL SHORT-TERM-MEMORY

A two interval forced choice constant stimuli method was used to deter mine: (i) the point of subjective equality (PSE); and (ii) the just-no ticeable-difference (JND) in contrast for two luminance gratings, one held in short-term visual memory. Psychometric functions for delayed c ontrast discrimination were determined as a function of spatial freque ncy from 1 to 8 c/deg, reference contrast from 5 to 60% and inter-stim ulus interval from 1 to 10 sec The PSE for remembered contrast was inv ariant with spatial frequency and inter-stimulus interval for the thre e reference contrast levels tested. The JND contrast plotted against s patial frequency followed a U-shaped function with lowest thresholds a t around 4 c/deg. The threshold function translates parallel to the se nsitivity axis with an increase in either the reference contrast or th e inter-stimulus interval. However, the bandpass shape of the threshol d function is invariant with both reference contrast and inter-stimulu s interval. At 1, 3 and 10 sec inter-stimulus intervals, contrast JNDs increase with reference contrast according to a power law with an ave rage exponent of 0.70. Contrast JNDs also increase as a power function of the inter-stimulus interval with an average exponent of 0.38 for t he three reference contrasts tested. Copyright (C) 1996. Published by Elsevier Science Ltd.