Adding a veiling luminance is not sufficient to explain the effects of glare on simple reaction times

AGUIRRE R.C.; BARRAZA J.F.; COLOMBO E.M.

Sarasota, Florida, USA

Congreso; 6th Annual Meeting of the Vision Sciences Society; 2006

Vision Sciences Society

Purpose. The reduction of visual performance due to glare was traditionally modeled by adding to the stimulus a uniform veiling luminance (Lv), which reduces the effective contrast of the image. We investigate whether this model can account for the increase of simple reaction times obtained when a steady glare source is presented in the periphery of the visual field. Methods. We measured Simple Reaction Times (RT) of mesopic achromatic sinusoidal gratings as a function of contrast, for three levels of glare (0, 15, and 60lx) and four spatial frequencies (1, 2, 4, and 8c/deg). Results. When we plot RT as a function of the inverse of contrast, RT increases linearly for all levels of glare and spatial frequencies. The higher is the glare the steeper are these lines. This effect is stronger for low than for high spatial frequencies. We used the formula proposed by Plainis and Murray (Neuropsychologia, 2000), which relates RT with contrast, luminance, and spatial frequency and estimated the Lv that produces the best fit of the model to the experimental data. We now re-plotted the data as a function of the inverse of the effective contrast and found that, for low spatial frequencies, the reduction of effective contrast can explain the increase of slopes. However, this explanation does not hold for high spatial frequencies. Conclusion. The veiling luminance model, which is independent from spatial frequency, cannot account for the effect of glare on the Simple Reaction Times.