Poster C102, Sunday, March 25, 1:00-3:00 pm, Exhibit Hall C
A Number Signal in Early Visual Cortex
Nicholas DeWind1, Joonkoo Park2, Marty Woldorff3, Elizabeth Brannon1; 1University of Pennsylvania, 2University of Massachusetts Amherst, 3Duke University
The ability to estimate the number of items in a visual array arose early in evolution, develops early in human development, and is correlated with mathematical ability later in life. For these reasons approximate number processing has been hypothesized to be a core cognitive domain and to provide a cognitive scaffold upon which symbolic representations of number develop. Previous functional imaging work with visually presented arrays indicates that the intraparietal sulcus (IPS) represents number. However, it is not clear if the number signal originates in IPS or is propagated from earlier visual areas. Previous work from our group has demonstrated a rapidly instantiated representation of number in low-level regions of visual cortex using the high temporal resolution of event-related electro-encephalography (EEG). Here, we use a rapid event-related functional magnetic resonance imaging (fMRI) paradigm and found convergent evidence for a number signal in low-level visual cortex (areas V1, V2, and V3). Employing a stringent set of stimulus controls, we demonstrate that this signal cannot be explained by the total visual area of the array, the density of the items in the array, the combined visual area of the items, the total luminance of the display, the size of individual items, the proportion of the array covered by items, nor the overall scale of the array and items. Our findings thus provide further support for the hypothesis that number is rapidly and directly encoded at the earliest stages of cortical processing.
Topic Area: PERCEPTION & ACTION: Vision