Effects of TMS to occipital face area on the perception of face viewpoint cued only by shape changes in the external contour of the face

Abstract

Changes in the outer contour of a face act as a cue to face viewpoint, and these changes can be captured using radial frequency (RF) pattern stimuli (Wilson et al., 2000). The face viewpoint aftereffect (FVA) is a visual illusion where adaptation to a left-facing face causes a front-facing face to appear as right-facing and vice versa (Fang and He, 2005). The occipital face area (OFA) has been implicated in both the FVA (Fang et al., 2007) and early face processing (Haxby et al., 2000; Pitcher et al., 2007). We replicated the FVA using synthetic head outline RF pattern stimuli. We then applied transcranial magnetic stimulation (TMS) to OFA and a nearby shape processing area, LO2 (Silson et al., 2013), during viewpoint discriminations of the same stimuli following adaptation to a forward- or lateral-facing stimulus. TMS to OFA resulted in significantly worse viewpoint discrimination than TMS to LO2, however neither condition was significantly different from control conditions. It was therefore impossible to determine whether our effect of TMS on discrimination was attributable to a facilitation of performance from TMS to LO2, or an inhibition of performance from TMS to OFA. In addition we found no effect of TMS to any brain regions on the magnitude of the FVA. We conclude that our differential effect of TMS to LO2 and OFA on viewpoint discrimination likely indicates a causal role for OFA in the processing of shape cues to viewpoint, however more data will be acquired to further clarify our results. This would be consistent with Silson et al.’s (2013) suggestion of parallel mechanisms for orientation and shape processing in LO1 and LO2, respectively. We add a potential third parallel mechanism for shape information that is relevant to face processing in OFA.

Meeting abstract presented at VSS 2015