A. Ezra Sutter¹, Gerick M. Lee², Timothy D. Oleskiw^2,3, Najib J. Majaj², Lynne Kiorpes², J. Anthony Movshon²; ¹Drew University, ²Center for Neural Science, New York University, ³Center for Computational Neuroscience, Flatiron Institute

Neurons of cortical area V4 are selective for shape – the conformation of contrast boundaries that outline objects in a visual scene. However, it is unknown how this selectivity arises in the ventral visual pathway, and whether shape tuning depends on visual experience in early life. To answer these questions, our lab implanted 96-channel “Utah” electrode arrays in areas V2 and V4 of two fixation-trained juvenile Macaca nemestrina. We recorded neural responses to shape stimuli with a single parametrically-varied curvature component (El-Shamayleh & Pasupathy, 2016), at both 7 and 12 months of age. To assess curvature selectivity we fit neural responses with the Angular Position and Curvature (APC) model (Pasupathy & Connor, 2001). We found that it explained the response variance (r2 > 0.1) of many sites in both V2 (74% of n=64) and V4 (75% of n=95). Interestingly, we found that a simple image-computable model based on reverse correlation of local stimulus luminance could explain most sites in V2 (97%) and V4 (93%). 1% and 5% of sites (V2 and V4, respectively) were unexplainable by either model. To account for experimental differences between our work and prior studies, we performed control analyses using a previously-published dataset of well-isolated shape-selective V4 neurons (Pasupathy & Connor, 2001). We quantified our ability to characterize the selectivity of simulated multi-unit responses with an expanded shape set, and of single-unit responses with a range of shape stimuli chosen to match our experimental conditions. Collectively, these results support our observation of shape selectivity in ventral visual areas of the juvenile macaque. A comparison of model fits across developmental age points suggest that V2 and V4 sites are well-tuned for shape features from the earliest ages tested.