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Robert F. Hess, Yi-Zhong Wang, Chang H. Liu; Accessibility of spatial channels. Journal of Vision 2005;5(8):179. doi: 10.1167/5.8.179.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. It is now well accepted that the early stages of visual processing comprise mechanisms that are relatively narrowband for spatial frequency (1 octave) and orientation (30°). It is less clear whether the outputs of these narrowband mechanisms can be individually accessed by later stages of perception. We address this question using elementary, local motion and stereo tasks. Methods Our stimulus comprised a disc containing fractal noise embedded in a field of fractal noise. The fractal noise in the disc was spatially displaced between eyes/frames resulting in either a near/far disparity task or a left/right motion task. The noise was stochastically filtered (amplitudes unaltered, just phases scrambled outside passband) using idealized filters of variable bandwidth and peak spatial frequency. In this way a band of correlated information was preserved with uncorrelated information at higher and lower spatial frequencies (a notched filter of signal correlation). Phase scrambling involved either spatial frequencies or orientations of noise components. We used a simple Gaussian signal/noise model to derive the minimum spectral region that subserved our tasks. Results Similar results were found for the stereo and motion tasks. In either case the minimum bandwidth necessary to accomplish these tasks was many times previous estimates of the bandwidth of early visual mechanisms. In fact it closely corresponded to the spatial frequency and orientation spectrum of the stimulus, suggesting that all stimulus information was necessary. Conclusion For both local motion and stereo, there is no individual access to information from narrowband channels tuned to either spatial frequency or orientation.
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