The visual filter mediating letter identification.

We hear periodic sounds, or tones, by means of parallel auditory filters, each tuned to a band of temporal frequency, and we see periodic patterns, or gratings, by means of parallel visual filters, each tuned to a band of spatial frequency. Beyond helping us to see gratings, do these visual filters participate in everyday tasks such as reading and object recognition? After all, grafting visibility only requires the distinguishing of pattern from blank, whereas object recognition, for example letter identification, requires classification by the observer into one of many learned categories. Here we make use of results from hearing research, applying to vision a noise-masking paradigm that reveals the filter(s) mediating any threshold task. We find that letter-identification and grating-detection filters are identical, showing that the recognition of these objects at one size is mediated and constrained by a single visual filter, or 'channel'.