Response properties of a typical oriented, linear unit. A , Spike rasters in response to drifting bars in 16 directions. B , Orientation tuning curve from rasters in A demonstrates sharp tuning. Dashed curve is fit to a sum of Gaussians. C , Spike rasters in response to drifting gratings of 12 directions and six spatial frequencies. Periodic response is indicative of a linear response type. D , Orientation tuning curve from rasters in C . E , Spatial frequency tuning curve shows bandpass selectivity. Dashed curve is fit to difference of Gaussians.