The Effect of Spatial Frequency and Orientation on Configural Face Discriminations in Adults with Synaesthesia

Abstract

The structural and functional differences observed in the brains of adults with synaesthesia is thought to arise, at least in part, from less-than-normal neural pruning of the exuberant connections present within and among sensory cortical areas in infancy (reviewed in Maurer, Gibson, & Spector, 2013). This hypothesis is supported by previous work that has demonstrated that synaesthetes are superior at processing foreign speech sounds and inverted faces (Maurer et al., in prep). The present study investigated a link between spatial frequency and face processing in adults with synaesthesia by testing synaesthetes and non-synaesthetes on their ability to discriminate upright and inverted faces filtered at high and low spatial frequencies. As predicted, synaesthetes (n=20) were significantly more accurate than non-synaesthetes (n=20) at discriminating among inverted full spectrum faces (p=0.0235), with no differences in upright faces, replicating previous findings that support the hypothesis that synaesthetes undergo less perceptual attunement (Ghloum et al., 2013). Unexpectedly, synaesthetes were faster at responding across all face conditions. Faster reaction times with no sacrifice to accuracy suggest that synaesthetes may be processing faces more efficiently. In addition, no significant differences in accuracy were observed for high and low filtered faces at any orientation between synaesthetes and non-synaesthetes. Future studies could further explore the basis of synaesthete’s face processing advantages by using eye movements and a narrow-band noise-masking paradigm.