Early Visual Cortex Reflects Object-Based Perceptual Warping

Perceptual organization of incoming visual information gives rise to distinct objects. It has previously been demonstrated that the presence of an object can warp the spatial region within object boundaries. This effect, known as Object-Based Warping (OBW), occurs when two items placed within the contours of an object are perceived to be further apart relative to two equidistant items not enclosed within an object (Vickery & Chun, 2010). Here, we used fMRI to investigate the neural representation of object-based warping. To measure the strength of the behavioral effect, participants adjusted the perceived distance between two letters so as to match two reference letters (either enclosed within an object or not). A subset of participants (n=7) who exhibited a behavioral effect of substantial magnitude also completed an fMRI experiment consisting of a letter discrimination task. The task included 3 conditions: (1) two letters enclosed within an object, (2) two letters without an object at the same spatial distances as in condition 1, and (3) two letters without an object at the “warped” distances (calculated from behavioral data). We separately localized retinotopic regions corresponding to the real and warped positions at which the letters were presented. Using BOLD activation extracted from these regions, an MVPA classifier was trained on the two no-object conditions (conditions 2 & 3) and tested on the object-present condition (condition 1). Activation corresponding to letters presented within an object (condition 1) were classified significantly above chance as matching the warped locations (condition 3) in both V1 & V2d; constituting evidence of OBW only in these regions. This warping effect in early visual cortex is likely driven by feedback from higher-level regions and suggests a fundamental change to visual perception caused by the presence of a simple object.