The impact of simulated hemianopia on visual search for faces, words, and cars.

Tests of visual search can index the effects of perceptual load and compare the processing efficiency for different object types, particularly when one examines the set-size effect, the increase in search time for each additional stimulus in an array. Previous studies have shown that the set-size effect is increased by manoeuvres that impede object processing, and in patients with object processing impairments. In this study, we examine how the low-level visual impairment of hemianopia affects visual search for complex objects, using a virtual paradigm. Forty-two healthy subjects performed visual search for faces, words, or cars with full-viewing as well as gaze-contingent simulations of complete left or right hemianopia. Simulated hemianopia lowered accuracy and discriminative power and increased response times and set-size effects, similarly for faces, words and cars. A comparison of set-size effects between target absent and target present trials did not show a difference between full-view and simulated hemianopic conditions, and a model of decision-making suggested that simulated hemianopia reduced the rate of accumulation of perceptual data, but did not change decision thresholds. We conclude that simulated hemianopia reduces the efficiency of visual search for complex objects, and that such impairment should be considered when interpreting results from high-level object processing deficits.