DISENTANGLING THE ROLE OF SPATIAL SCALE, SEPARATION AND ECCENTRICITY IN WEBERS LAW FOR POSITION

Factors underlying Weber's law for position were investigated by measu ring spatial interval discrimination accuracy for spectrally narrow-ba nd stimuli. These stimuli were positioned around an iso-eccentric are in order to allow separation and eccentricity to be varied independent ly. We find that Weber's law occurs at individual spatial scales, and holds true not just for stimuli positioned either side of fixation, bu t for any series of stimuli which possess the same ratio of separation to eccentricity. When the separation/eccentricity ratio is large, thr esholds are proportional to eccentricity and demonstrate contrast inde pendence. At smaller separation/eccentricity ratios, thresholds are de termined by a contrast-dependent combination of separation and eccentr icity. (C) 1997 Elsevier Science Ltd.