Abstract
For many stimulus dimensions, the appearance of a central stimulus is strongly affected by the presence of contrasting stimuli in the surround. We examined spatial contrast interactions in face perception and found the opposite effects - a centrally fixated face can strongly bias the appearance of surrounding faces, while faces in the periphery conversely have little influence on the central face. The interactions were measured using morphs between a male and female face cropped to remove external features. Images were displayed for 1 sec intervals every 3 sec while the morph level was adjusted with a 2AFC staircase to determine the gender boundary. Judgments were made in the fovea and periphery, either for the test face alone or in the presence of a simultaneously presented male or female face from the extremes of the morph. Settings for most subjects exhibited an asymmetric contrast effect in which the central face biased the peripheral face toward the opposite gender, with similar shifts from 1.5 to 6 deg in eccentricity and for face widths ranging from 1 to 2 deg. However, evidence for assimilation effects - in which peripheral faces appeared more like the central face - was also observed, suggesting that the interactions are labile and at least in some cases in directions opposite to those predicted by adaptation. Similar biases were also observed along other facial dimensions including expressions. Our results are consistent with a foveal specialization in face perception, but could also reflect differences in attention. Faces even in the near periphery are difficult to resolve and perceptually unstable, and thus their perceived attributes may be more susceptible to the more robust representations formed for the centrally attended face.