The role of adaptation mechanisms at the mesopic range to achieve lightness constancy under glare conditions

BARRIONUEVO, PABLO A.; COLOMBO, ELISA M.; ISSOLIO, LUIS A.

Naples

Congreso; VSS 2010; 2010

The Vision Sciences Society

Purpose: Previous results have shown the influence of glare on the brightness evaluation of a foveal test in the mesopic range depends on the test luminance as well as the surround luminance. In this work we perform new experiments in order to find which variable determines lightness constancy. Methods: Patches subtending 1.2 degrees placed on the center of a display of 7 × 9,5 degrees were shown binocularly to 3 subjects (25.7±2.9 years old) in a sequential way. In each trial, a comparison patch (Pc) before a standard patch (Pstd) were presented. Simultaneously to Pstd a transient peripheral glare source (10° temporal) was turned on. The task was to choice the brighter patch. The matching luminance (Lm) was obtained when both patches were equal in brightness. In a first experiment, the luminance values were: 4 cd/m2 for Pstd and 0.75, 1, 1.5, 2 and 3 cd/m2 for the surround. In a second experiment, the surround luminance was 0.001 cd/m2 and the values of Pstd were 0.3, 0.35, 0.4 and 0.45 cd/m2. The glare source illuminances were 60 and 30 lx measured between the two eyes. Results: We found lightness constancy in the first experiment but that was not the case in the second one, in which Lm was reduced. When the test and surround luminances have enough level to excite cones, a mechanism of adaptation maintains lightness constancy. But when the surround is in the scotopic range, the luminance veil over the scene saturates the rods and the cones adaptation takes a time in which produces a transient loss of lightness constancy.