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John Cass, Sjoerd Stuit, Peter Bex, David Alais; Orientation bandwidths are invariant across spatiotemporal frequency after isotropic components are removed. Journal of Vision 2009;9(12):17. doi: 10.1167/9.12.17.
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© ARVO (1962-2015); The Authors (2016-present)
It is well established that mammalian visual cortex possesses a large proportion of orientation-selective neurons. Attempts to measure the bandwidth of these mechanisms psychophysically have yielded highly variable results (∼6°–180°). Two stimulus factors have been proposed to account for this variability: spatial and temporal frequency; with several studies indicating broader bandwidths at low spatial and high temporal frequencies. We estimated orientation bandwidths using a classic overlay masking paradigm across a range of spatiotemporal frequencies (0.5, 2, and 8 c.p.d.; 1.6 and 12.5 Hz) with target and mask presented either monoptically or dichoptically. A standard three-parameter Gaussian model (amplitude and width, mean fixed at 0°) confirms that bandwidths generally increase at low spatial and high temporal frequencies. When incorporating an additional orientation-untuned (isotropic) amplitude component, however, we find that not only are the amplitudes of isotropic and orientation-tuned components highly dependent upon stimulus spatiotemporal frequency, but orientation bandwidths are highly invariant (∼30° half width half amplitude). These results suggest that previously reported spatiotemporally contingent bandwidth effects may have confounded bandwidth with isotropic (so-called cross-orientation) masking. Interestingly, the magnitudes of all monoptically derived parameter estimates were found to transfer dichoptically suggesting a cortical locus for both isotropic and orientation-tuned masking.
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