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Kane David, Guan Phillip, Hoffman David, Martin Banks; The Spatiotemporal Limits of Stereovision. Journal of Vision 2011;11(11):294. doi: 10.1167/11.11.294.
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© ARVO (1962-2015); The Authors (2016-present)
Sensitivity to luminance contrast varies with spatial and temporal frequency. Likewise, sensitivity to variations in binocular disparity also depends on spatiotemporal frequency. Disparity corrugations are visible only when their amplitude is between a lower and an upper limit. The lower limit reflects sensitivity to the smallest variation in disparity. The upper limit reflects the greatest change in disparity over space that can be perceived; this is the spatial disparity-gradient limit. We measured the spatiotemporal limits of stereopsis. In a 2-AFC task, observers discriminated between a sawtooth corrugation and a noise stimulus; the latter had the same distribution of disparities, but no spatial structure. We estimated the upper and lower amplitudes at which the sawtooth could be discriminated over a broad range of spatial (0.125–1.5 cpd) and temporal frequencies (0–16 Hz). We found that the lower limit is bandpass as a function of spatial frequency and lowpass as a function of temporal frequency. The lower limit is separable, which means that it can be described by the product of spatial- and temporal-frequency functions. For static gratings, we found that the upper limit is consistent with the spatial disparity-gradient limit. For moving corrugations of low spatial frequency, the upper limit is approximated by a temporal disparity-gradient limit. For other spatiotemporal frequencies, the upper limit is not described by a spatial or temporal gradient limit. Surprisingly, the upper limit is consistent with a spatiotemporal disparity-gradient limit (i.e., not exceeding a critical value in space-time). Unlike the lower limit, the upper limit is non-separable in spatial and temporal frequency. We show that non-separability is a consequence of a spatiotemporal gradient limit. The volume of spatial frequencies, temporal frequencies, and disparity amplitudes that are visible is quite constrained. Appreciating these constraints is important to the construction of effective stereoscopic imagery.
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