Beyond the retina: Evidence for a face inversion effect in the environmental frame of reference

Beyond the retina: Evidence for a face inversion effect in the environmental frame of reference Nicolas Davidenko (ndaviden@stanford.edu) Stephen J. Flusberg (sflus@stanford.edu) Stanford University, Department of Psychology Jordan Hall, 450 Serra Mall, Building 420, Stanford, CA 94305 USA Abstract frames). In a typical laboratory study, therefore, several reference frames are conflated. This begs the question: in relation to which reference frame(s) does the face inversion effect occur? There is reason to believe that both retinal and environmental reference frames matter in visual information processing. Irvin Rock (1973) conducted a series of pioneering experiments on object form perception, demonstrating that both retinal and environmental reference frames impact participants’ memory for and interpretation of novel objects under certain circumstances. More recently, researchers have shown that our ability to perceive the stability of human body postures as well as the direction of bodily motion depends on both retinal and environmental cues (Chang, Harris & Troje, 2010; Lopez et al., 2009). Finally, research on spatial cognition has found that people are sensitive to a variety of spatial reference frames and flexibly adopt multiple different frames for representing the environment as they perform different tasks and communicate with others (Tversky, Lee, & Mainwaring, However, to date there is no evidence that multiple frames of reference play a role in face processing. In fact, Rock (1973) himself suggested that because faces are familiar objects that have an intrinsic spatial structure (i.e. a top and bottom), their environmental orientation should not affect how we perceive them. Recent research seems to support this view that face orientation effects are restricted to the retinal frame of reference (Troje, 2003; Chang et al., 2010). In one experiment (Troje, 2003), participants had to indicate whether or not a face image displayed on a computer screen was the same face they had seen moments before. The images could be oriented upright on the screen or rotated by 90o. The participant’s head was orientated upright in the room for half of the trials and rotated by 90o in the other half of the trials. The results indicated that performance was fastest and most accurate when the orientation of the face image matched the orientation of the participant’s retinal frame, regardless of the environmental orientation of the image and the participant. Troje’s (2003) experiment (and related work; see Rock, 1973) was designed to pit the retinal frame against the environmental frame to see which one mattered more for face processing. However, it is possible that both reference frames affect face processing, but by pitting the two against one another the relatively large retinal frame effect masked Across a wide range of face perception tasks, observers show drastically worse performance when faces are oriented upside-down versus upright. However, the meaning of orientation must be established in relation to a particular frame of reference. In relation to which reference frame(s) does the face inversion effect occur? Here we describe a simple, novel method for investigating potentially independent effects of retinal and environmental reference frames on face processing. Participants performed one of two face-processing tasks (emotional expression classification and recognition memory) as they lay horizontally, which served to disassociate the retinal and environmental reference frames. In both experiments we found a large effect of retinal orientation on performance and a small but reliable effect of environmental orientation. In a follow-up control study, we consider an alternative explanation based on our experimental setup. We argue that environmental orientation influences face processing, which is revealed when retinal orientation is kept constant. Keywords: face perception, reference frames, face inversion effect, embodiment Background Over 50 years of research has demonstrated that orientation dramatically affects the visual processing of faces; across a wide range of perception and memory tasks, observers show markedly worse performance when faces are presented upside-down compared to upright (Yin, 1969). This face inversion effect is perhaps most famously illustrated by the classic Thatcher Illusion (Thompson, 1980); a picture of the former prime minister that appears normal when presented upside-down is revealed to be a disturbing grotesque of inverted features when rotated upright. The dramatic effect of inversion on face perception sets faces apart from other objects and has led many researchers to consider faces a special visual category (Rhodes et al., 1993; Farah et al., 1998). Notice, though, that the meaning of orientation (i.e. what counts as upright or upside-down) must be established in relation to a particular frame of reference. The vast majority of experiments examining orientation effects in visual perception have participants seated in front of a computer screen. A face image displayed on the monitor might be upright with respect to the participant’s retina (retinal frame), but it would also be upright with respect to the computer screen itself, the room the computer is situated in, and even the directional pull of gravity (environmental