Localization and identification tasks rely on different temporal frequencies

The temporal frequencies underlying character localization and identification tasks are measured, as suggested by a model that assumes that the two tasks are processed in different cortical pathways and receive contributions from different populations of visual cortical neurons. Data from two-pulse and temporal contrast sensitivity experiments demonstrate that character localization depends upon much higher temporal frequencies than character identification when both are tested in the periphery. Foveal presentations demonstrate that detection and identification tasks rely on the same temporal frequencies. In a control experiment, the letters were blurred to restrict the range of spatial frequencies. However, these stimuli replicated earlier results and demonstrates that the use of higher temporal frequencies by the localization tasks cannot be attributed to the use of different spatial frequencies for different tasks. In addition, near-foveal presentations of the localization task replicate findings from the far periphery, suggesting that the localization task may be processed differently from the detection task regardless of location on the retina. Finally, the temporal frequency differences persist when a single sine-wave grating is used in localization and identification tasks. The results are consistent with any anatomical model that assumes that the neural substrates underlying localization receive or maintain a higher range of temporal frequencies than areas responsible for identification. The findings demonstrate how the time-course of different stimulus attributes can be quantified, and have implications for theories of information processing in which different stimulus attributes are combined.