The influence of natural contour and face size on the spatial frequency tuning for identifying upright and inverted faces

It has previously been proposed that holistic face processing is based on low spatial frequencies (SFs) whereas featural processing relies on higher SFs, a hypothesis still widespread in the face processing literature today (e.g. Peters et al. in Eur J Neurosci 37(9):1448–1457, 2013). Since upright faces are supposedly recognized through holistic processing and inverted faces, using features, it is easy to take the leap to suggest a qualitatively different SF tuning for the identification of upright and vs. inverted faces. However, two independent studies (e.g. Gaspar et al. in Vision Res 48(28):2817–2826, 2008; Willenbockel et al. in J Exp Psychol Human 36(1):122–135, 2010a) found the same SF tuning for both stimulus presentations. Since these authors used relatively small faces hiding the natural facial contour, it is possible that differences in the SF tuning for identifying upright and inverted faces were missed. The present study thus revisits the SF tuning for upright and inverted faces face identification using the SF Bubbles technique. Our results still indicate that the same SFs are involved in both upright and inverted face recognition regardless of these additional parameters (contour and size), thus contrasting with previous data obtained using different methods (e.g. Oruc and Barton in J Vis 10(12):20, 1–12, 2010). The possible reasons subtending this divergence are discussed.