Psychophysics of perceiving eye and head direction with peripheral vision : Implications for the dynamics of eye gaze behavior

Two psychophysical experiments are reported, one dealing with the visual perception of the head orientation of another person (the “looker”) and the other dealing with the perception of the looker’s direction of eye gaze. The participant viewed the looker with different retinal eccentricities ranging from foveal to far peripheral viewing. On average, judgments of head orientation were reliable even out to the extremes of peripheral vision (90o eccentricity), with better performance at the extremes when the participant was able to view the looker changing head orientation from one trial to the next. In sharp contrast, judgments of eye gaze direction were reliable only out to 4o eccentricity, signifying that the eye gaze social signal is available to people only when they fixate near the looker’s eyes. While not unexpected, this vast difference in availability of information about head direction and eye direction, both of which can serve as indicators of the looker’s focus of attention, is important for understanding the dynamics of eye gaze behavior. Like so many facets of non-verbal communication, signaling by eye gaze is phenomenologically transparent, allowing the perceiver to effortlessly know much about the other’s attentional focus, intentions, and desires (Baron-Cohen 1995; Tooby and Cosmides 1995). Contrasting with the phenomenological transparency of eye gaze signaling is its computational complexity. Just being able to perceive the other person’s attentional focus (“joint attention”) is a computational feat. It requires perceiving the distance and direction to the other’s head, perceiving the orientation of the other’s head, perceiving the orientation of the eyes within the other’s head, and then, on the basis of these, constructing the line in space representing the other’s gaze direction. Any object perceived to be on this line, which also requires distance perception, is then a candidate for the other’s attentional focus. Because of the intimate connection between visual perception and eye gaze processing, the dynamics of eye gaze behavior reflect the social signals that are and are not perceptible to the interactants. Thus, a full understanding of social interaction mediated by eye gaze requires psychophysical research to elucidate which signals can be sensed by the interactants. So far, there has been a modicum of research, mostly by vision scientists, devoted to the psychophysics of gaze direction, whether the eyes are directly observed or just the head (Anstis et al 1996; Cline 1967; Ehrlich and Field 1993; Gale and Monk 2000; Gibson and Pick 1963; Imai et al 2006; Langton et al 2004; Langton et al 2000; Popper et al 2007; Ricciardelli et al 2000; Sinha 2000; Symons et al 2004; Teske 1988; Watt et al 2007). Ultimately, the perceived social signals are used to attempt to gauge the mental states of the other, thus constituting the “psychophysics of the social world” (Tooby and Cosmides 1997). The dynamics of this social interaction go deeper than simple registration of social signals and linking them to first-order mental states, for each interactant is aware of being represented recursively within the experience of the other (“the spiral of reciprocal perspectives”; Laing et al 1966). The role of eye gaze in non-verbal communication has long been of interest to researchers in communication, social psychology, and developmental psychology (e.g. Adams and Kleck 2005; Argyle and Cook 1976; Baron-Cohen 1995; Kendon 1967; Kleinke 1986; Moore and Dunham 1995; Rutter 1984) and is now the focus of considerable research by scientists interested in communication through electronic media, such as video conferencing and virtual reality (e.g., Bailenson et al 2002; Bailenson et al 2005; Garau et al 2003; Grayson and Monk 2003; Monk and Gale 2002; Popper et al 2007; Vertegaal et al 2001). The prior psychophysical research on eye gaze, cited above, has been largely concerned with how well the perceiver is able to sense the direction of the looker’s eye gaze when the perceiver is fixating the eyes of the looker (i.e., not using peripheral vision). That research has shown that perceivers are exquisitely sensitive to the eye gaze of the looker both when it is directed toward the perceiver (“mutual eye gaze”) and when it is directed at other objects (“joint attention”). However, eye gaze sensing is imperfect, for besides some degree of imprecision (variability), there are constant errors in judgment as well, especially when the looker’s head is not viewed straight on by the perceiver (Anstis et al 1969; Gibson and Pick 1963; Todorović 2006). The research has also attempted to determine what visual information about the eyes relative to the head (e.g., visibility of the sclera on either side of the pupil) signifies looking direction. The visual stimuli signifying the looker’s eye gaze direction are of small angular extent, even when the looker is within a meter or two of the perceiver. Stimuli of small angular extent are best sensed when fixated by the perceiver, for fixation causes their retinal images to fall on the perceiver’s foveal regions, where visual acuity is greatest. Thus, perceivers seeking the social signals associated with eye gaze will often fixate the looker’s eyes. However, there are plenty of situations where fixating the looker’s eyes is impossible or infeasible. For example, it is not possible to see the eyes of a looker who is wearing dark sunglasses or is facing away nor is it feasible to track the eye gaze of all interactants in a small group. However, if one wishes to know the attentional focus of another person, monitoring that person’s head orientation is often a good substitute for monitoring the person’s eye gaze, because people typically align their heads with objects of interest shortly after directing their gaze toward them (directing the eyes way off to one side quickly results in physical discomfort). Because the head is a much larger visual stimulus than the eyes, the social signals associated with the facing direction of the head are still quite accessible in peripheral vision despite the lower visual acuity. This means that when we wish to