Spatial selectivity in adaptation to gaze direction

Abstract

A person's focus of attention is conveyed by the direction of their eyes and face, providing a simple visual cue fundamental to social interaction. A growing body of research examines the visual mechanisms that encode the direction of another person's gaze as we observe them. Here we investigate the spatial receptive field properties of these mechanisms, by testing the spatial selectivity of sensory adaptation to gaze direction. Human observers were adapted to faces with averted gaze presented in one visual hemifield, then tested in their perception of gaze direction for faces presented in the same or opposite hemifield. Adaptation caused strong, repulsive perceptual aftereffects, but only for faces presented in the same hemifield as the adapter. This occurred even though adapting and test stimuli were in the same external location across saccades. Hence, there was clear evidence for retinotopic adaptation and a relative lack of either spatiotopic or spatially invariant adaptation. These results indicate that adaptable representations of gaze direction in the human visual system have retinotopic spatial receptive fields. This strategy of coding others' direction of gaze with positional specificity relative to one's own eye position may facilitate key functions of gaze perception, such as socially cued shifts in visual attention.

Keywords: adaptation; face perception; gaze perception; retinotopy; spatial receptive field; spatiotopy.

Figure 1.

Dissociating retinotopic from spatiotopic representations of gaze direction. (a) The test and adapting stimuli were always presented in approximately the same spatiotopic location—the centre of the screen. Participants fixated on a cross that varied in location between the left and right side of the screen, determining the retinotopic location of the stimuli. To test retinotopic selectivity of adaptation, participants were adapted to faces presented in one side of their visual field, and tested on faces presented in either the same or opposite side of their visual field. For a full illustration of the trial cycle, see electronic supplementary material, figure S1. (b) The gaze direction of the test faces varied along the horizontal dimension. A subset of horizontal gaze angles is shown here for a single identity. A stimulus gaze direction of 0° indicates that the face was looking straight-ahead. Positive angles indicate rightwards gaze direction, and negative angles indicate leftwards gaze direction. (c) Participants judged whether the test faces were looking direct, left or right, while the gaze direction of the faces varied across trials. A psychophysical model of gaze perception was fit to the data that quantifies the position and width of category boundaries (blue and red dashed lines) and the midpoint of perceived direct gaze (black dashed line). The effect of adaptation on perceived gaze direction was quantified in terms of the change in the midpoint of perceived direct gaze following adaptation compared to baseline. This figure shows the model fit to baseline response data from a single subject and condition. (Online version in colour.)

Figure 2.

Perceptual aftereffects averaged across the sample. The data are plotted as a function of the visual field location of the adapting and test stimuli. Aftereffects are shown here as the difference in the perceived gaze direction of test stimuli before and after adaptation. Positive aftereffects indicate a shift in the perceived angle of gaze toward the right following adaptation, and negative aftereffects indicate a shift in the perceived angle of gaze toward the left. Markers show the mean ± 1 s.e., and colour indicates whether the adapting stimulus had leftwards or rightwards gaze direction. The results show that perceived gaze direction was biased away from the gaze direction of the adapting stimulus, but only when the adapting and test stimuli were presented in the same side of the visual field. (Online version in colour.)

Figure 3.

Perceptual aftereffects for individual subjects. Aftereffects are shown here as a shift in the perceived gaze direction of test stimuli away from the gaze direction of the adapting stimulus (i.e. a repulsive perceptual aftereffect). Aftereffects are averaged across conditions in which the adapting and test stimuli were each presented in the same visual hemifield versus the opposite visual hemifield. Markers show the mean ± 1 s.e. There was a consistent pattern across subjects of stronger repulsive aftereffects for test stimuli presented in the same visual hemifield as the adapting stimulus compared to test stimuli presented in the opposite visual hemifield. Across this comparison, the adapting and test stimuli were matched in their spatiotopic position (but not their retinotopic position).