SPATIAL-FREQUENCY DISCRIMINATION - VISUAL LONG-TERM-MEMORY OR CRITERION SETTING

A long-term sensory memory is believed to account for spatial frequenc y discrimination when reference and test stimuli are separated by long intervals. We test an alternative proposal: that discrimination is de termined by the range of test stimuli, through their entrainment of cr iterion-setting processes. Experiments 1 and 2 show that the 50% point of the psychometric function is largely determined by the midpoint of the stimulus range, not by the reference stimulus. Experiment 3 shows that discrimination of spatial frequencies is similarly affected by o rthogonal contextual stimuli and parallel contextual stimuli and that these effects can be explained by criterion-setting processes. These f indings support the hypothesis that discrimination over long intervals is explained by the operation of criterion-setting processes rather t han by long-term sensory retention of a neural representation of the s timulus. (C) 1998 Elsevier Science Ltd. All rights reserved.