Expectation induced curvature perception in V2
33.328, Sunday, May 12, 8:30 am - 12:30 pm, Royal Ballroom 6-8
Carmel Mevo1, Zoe Kourtzi1, Yehoshua Tsal2; 1School of Psychology, University of Birmingham, UK, 2Psychology department, Tel Aviv University, Israel
According to hierarchical models that advocate cognitive impenetrability, early visual processing feeds into conceptual systems, but the latter do not influence visual processes (e.g., Pylyshyn,1999; Riesenhuber & Poggio, 2000). In contrast, according to interactive views low-level visual representations are constantly influenced by higher-level representations, leading to activity that is context dependent (e.g., Di Lollo, Enns & Rensink, (2000); Lamme &Roelfsema, (2000); Tsal & Avital, 2012). Here we explore early brain structures potentially subject to top down context effects by examining neuronal responses to curvature for non-curved angular stimuli, the perceptual representation of which is induced with curvature by top down processes of context and expectation. Using fMRI we have recorded early visual cortex (V1, V2, V3 , V4) responses under three conditions; (a) The Curved Condition presented with random repetitions of: 0, 2, 3, 6, 8 and 9, including primarily curved features. The Angular Condition presented the same digits in a digital format including only non-curved angular features. The Shape Condition presented repetitions of 6 nonsense figures, each obtained by shifting or relocating one feature in each of the angular digits. Contrasting activity for the Shape and Curved conditions revealed extensive activation in V1 reflecting the physical difference between the two categories. Most importantly, contrasting activation for the Digital and Shape conditions revealed unique activation within V2. As the low-level bottom-up features of the two display categories were identical we conclude that this V2 activation can only reflect top-down processes that effect perceptual processes in early visual cortex. As V2 in particular has been associated with curvature processing (e.g., Hedge & Van Essen, 2000) we suggest that its activation here reflects context induced curvature perception. These results provide support of cognitive penetration and to the notion that categorical perception results from the modulation of very early visual representations by higher-level conceptual representations.