Premium
Weber's law for position is incidental rather than fundamental
Author(s) -
Latham Keziah,
Whitaker David
Publication year - 1996
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1046/j.1475-1313.1996.96833473.x
Subject(s) - eccentricity (behavior) , contrast (vision) , position (finance) , scale (ratio) , separation (statistics) , geometry , mathematics , physics , law , optics , mathematical analysis , statistics , quantum mechanics , finance , political science , economics
Purpose: Weber's law for position states that the minimum discriminable change in separation between two objects is proportional to the separation itself. This study aimed to disentangle the individual effects of separation, eccentricity and spatial scale in determining Weber's law for position. Methods: Spatial interval discrimination thresholds were measured for two Gabor patches at twice contrast detection threshold. The patches varied in spatial scale (blur parameter of the patch), eccentricity (using isoeccentric arcs of different radii), and separation (varied by moving the patches around the isoeccentric arc). The effect of contrast on thresholds was also examined. Results: Weber's law holds for geometrically similar stimuli, i.e. stimuli with a constant separation/eccentricity ratio, over a range of spatial scales and eccentricities. Thresholds are contrast dependent at small geometric ratios, and contrast‐independent at large ratios. The Weber fraction is optimum (4%) for fovea‐centred stimuli, and is contrast dependent at smaller geometric ratios, becoming smaller at higher contrasts. Conclusions: Weber's law is observed at large geometric ratios because thresholds are proportional to eccentricity. At small geometric ratios, thresholds show a greater dependence on separation which increases with increasing contrast. Weber's law arises not from a single fundamental process, but from both increasing separation and increasing eccentricity, regardless of spatial scale.