Object recognition by a donut

Olzak and Thomas posited "cigar" channels, which integrate across a wide range of frequency and a narrow range of orientation, and "donut" channels, which integrate across all orientations and a narrow range of frequency. Majaj et al. (Vision Research, in press) used critical band masking to measure the radial frequency tuning of the channel that observers use to identify letters, and always found the same one-or-so-octave bandwidth: no cigar. We did similar critical band masking experiments, but restricting orientation instead of radial frequency of the noise spectrum. With a grating signal, we reveal a channel tuned to the grating orientation, as expected. Witha letter signal, we reveal a channel that is equally sensitive to all orientations: a donut. It is a first-, not second-, order channel, as shown by the fact that the threshold energy elevation sums linearly across orientations. Thus, the letter identification channel is a donut.