TIME-ORDER EFFECTS IN TIMED BRIGHTNESS AND SIZE DISCRIMINATION OF PAIRED VISUAL STIMULI

  • Geoffrey R. Patching
  • Mats P. Englund
  • Ã…ke Hellström

Abstract

An aim of the present paper is to examine changes in the magnitude and direction of timeordereffects with changes in the physical magnitude of the stimuli, overall levels ofperformance, and with changes in load processing capacity. Increments and decrements inperformance are gauged by means of the steepness of psychometric and chronometricfunctions. Load processing capacity is assessed by dividing integrated hazard functions forstimuli varying congruently along the dimensions of both size and brightness by the sum ofthose for stimuli varying along either dimension alone. Taken altogether the findings suggestthat time–order effects in timed brightness and size discrimination are perceptual, and therelative sensory weighting of stimulus magnitudes related to the alertness of participants andtheir capacity to process the stimuli. Implications of these findings for common random walkand diffusion models of sensory discrimination are discussed.
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