From Another Angle: Differences in Cortical Coding Between Fine and Coarse Discrimination of Orientation

Abstract

We measured the information available for orientation discrimination from metric distances for 24 cells in area 17 of cats that were paralyzed and anesthetized with Propofol and N2O. The metric distance information confirms fundamental coding differences for discrimination between fine (<10°) and coarse (>10°) orientation differences. The information for discriminating larger orientation differences is contained mainly in the firing rate, with minor enhancements from the coarse (30-70 ms) temporal structure in the firing rate. Both precise spike timing (9.2 ms) and intervals (6.8 ms) sustained over the stimulus presentation provide information for fine discrimination of orientation, where almost no reliable information is provided by the spike count. We compare and confirm the results (using the same data set) to vector distances based on classification theory. The results support a dynamic spiking mechanism where coordinated activity could provide fast and reliable information about detailed angle and/or direction information in the region of the preferred orientation.