Identifying Facial Images in the Visual Periphery

Identification sensitivity for four different faces was measured at the fovea and in the periphery to find out whether foveal and peripheral visual performance in this complex spatial task can be made equivalent simply by changing image magnification. Identification sensitivity was measured as a function of image magnification. The lowest contrast for identification was determined by a 4AFC method. Observers indicated via the keyboard which of the four faces was presented on the CRT screen. The images were shown monocularly at the fovea and at 2.5, 5, and 10 deg eccentricities in the nasal visual field of the right eye (eccentricity measured from the right- hand edge of the image).

If scaling is successful, the foveal and peripheral sensitivity vs size functions collapse together when shifted along the size dimension only (Watson, 1987 Journal of the Optical Society of America A 4 1579). Although the foveal and peripheral sensitivity functions could be superimposed, they did not fully superimpose without also shifting them in vertical direction, as foveal sensitivity at largest sizes was slightly superior to that of any eccentric location. Thus, size scaling alone was not adequate for this task, in agreement with the contrast sensitivity results of Valeton and Watson (1990 Perception 19 Supplement, 393). In this identification task, performance deteriorated towards the periphery at approximately the same rate as visual acuity, when the size corresponding to half-maximal sensitivity at each eccentricity was used as a measure.