Aftereffects support opponent coding of face gender

Abstract

Many aspects of faces derived from structural information appear to be neurally represented using norm-based opponent coding. Recently, however, Zhao, Seriès, Hancock, and Bednar (2011) have argued that another aspect with a strong structural component, namely face gender, is instead multichannel coded. Their conclusion was based on finding that face gender aftereffects initially increased but then decreased for adaptors with increasing levels of gender caricaturing. Critically, this interpretation rests on the untested assumption that caricaturing the differences between male and female composite faces increases perceived sexual dimorphism (masculinity/femininity) of faces. We tested this assumption in Study 1 and found that it held for male, but not female faces. A multichannel account cannot, therefore, be ruled out, although a decrease in realism of adaptors was observed that could have contributed to the decrease in aftereffects. However, their aftereffects likely reflect low-level retinotopic adaptation, which was not minimized for most of their participants. In Study 2 we minimized low-level adaptation and found that face gender aftereffects were strongly positively related to the perceived sexual dimorphism of adaptors. We found no decrease for extreme adaptors, despite testing adaptors with higher perceived sexual dimorphism levels than those used by Zhao et al. These results are consistent with opponent coding of higher-level dimensions related to the perception of face gender.

Norms are Not the Norm: Testing Theories of Sensory Encoding Using Visual Aftereffects

“…The tuning of the facial gender aftereffect therefore appeared similar to the tuning of the tilt aftereffect, if a sufficiently broad range of adaptors is considered. Several subsequent studies have also found that facial expression (Skinner & Benton, 2010), gender (Pond et al, 2013), and identity (McKone et al, 2014) aftereffects increase over a broad range of adapting values. These results are inconclusive, since they are consistent with either opponent-channel encoding, or with a scheme involving multiple broadly tuned channels.…”

“…It has been suggested that shifts in neutral category boundaries can differentiate locally repulsive from renormalising aftereffects if one compares the magnitudes of shifts induced by different 'strengths' of adaptor (Burton, Jeffery, Skinner, Benton, & Rhodes, 2013;Jeffery et al, 2010Jeffery et al, , 2011McKone et al, 2014;Pond et al, 2013;Skinner & Benton, 2010, 2012Zhao et al, 2011). A continuum of facial images morphing between different genders (for example) can be thought of as a one-dimensional slice through an artificial face space.…”

“…Regan and Hamstra (1992) proposed that aspect ratio is encoded relative to a 'neutral' normative aspect ratio (perceptually neither tall nor squashed). They proposed a model involving two opposing channels, which was later to become influential in models of face representation (Burton, Jeffery, Calder, & Rhodes, 2015;McKone, Jeffery, Boeing, & Clifford, 2014;Pond et al, 2013;Rhodes et al, 2005;Robbins, McKone, & Edwards, 2007;Susilo, McKone, & Edwards, 2010). In the model, one channel is activated by vertically elongated shapes, the other by horizontally elongated shapes (see Figure 3a).…”

“…Norm-based opponent-channel coding proposals have been particularly prevalent in the face perception literature (Giese & Leopold, 2005;Leopold et al, 2001;McKone et al, 2014;O'Neil et al, 2014;Pond et al, 2013;Rhodes et al, 2005;Susilo et al, 2010;Webster & MacLeod, 2011;Webster & Maclin, 1999). There is, however, mounting evidence questioning accounts of facial aftereffects that rely on norm-based encoding.…”

“…Face aftereffects have repeatedly been attributed to a form of perceptual re-normalisation (Burton et al, 2015;Jeffery et al, 2010Jeffery et al, , 2011Leopold et al, 2001;McKone et al, 2014;Pond et al, 2013;Rhodes & Jeffery, 2006;Rhodes et al, 2005;Robbins et al, 2007;Susilo et al, 2010;Webster & Maclin, 1999). According to this account, faces are represented in terms of how they differ from a perceptual norm.…”