Orientation bandwidths are invariant across spatiotemporal frequency after isotropic components are removed

Abstract

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.

Orientation tuning of contrast masking caused by motion streaks

“…Orientation-dependent elevations in detection threshold have been consistently reported in masking studies since the late 1960s (Blake & Holopigian, 1985;Bonds, 1989;Campbell & Kulikowski, 1966;Phillips & Wilson, 1984;Ross & Speed, 1991). Estimates of orientation tuning based on Gaussian bandwidths (half-widths at half-height) typically vary in the range of 7-40-, although depending on approach and methodology estimates of orientation bandwidth can vary far more widely (for a meta-analysis, see Cass, Stuit, Bex, & Alais, 2009). Recent evidence, however, indicates that orientation masking functions can be decomposed into orientation-tuned and -untuned components, and that by this analysis the bandwidths of the tuned components are approximately constant over a wide range of spatial and temporal frequencies at È30- (Cass, Stuit et al, 2009;Meese & Holmes, 2003).…”

“…Estimates of orientation tuning based on Gaussian bandwidths (half-widths at half-height) typically vary in the range of 7-40-, although depending on approach and methodology estimates of orientation bandwidth can vary far more widely (for a meta-analysis, see Cass, Stuit, Bex, & Alais, 2009). Recent evidence, however, indicates that orientation masking functions can be decomposed into orientation-tuned and -untuned components, and that by this analysis the bandwidths of the tuned components are approximately constant over a wide range of spatial and temporal frequencies at È30- (Cass, Stuit et al, 2009;Meese & Holmes, 2003). The orientationtuned components in our monoptic condition have a bandwidth of È33-and therefore fit well with these latter studies.…”

The nature of anisotropy in gain control pools.

“…Orientation tuning (half-width at half-height) is similarly narrow (15-30 deg, Campbell and Kulikowski, 1966;Phillips and Wilson, 1984;Blake and Holpigian, 1985;Anderson, Burr, & Morrone, 1991;Snowden, 1992;Snowden & Hammett, 1996;Cass, Stuit, Bex, & Alais, 2009), which also supports the idea that pattern masking taps mechanisms at the level of the cortex. Thus, masking studies have assumed that psychophysical masking functions directly reflect the responses of pattern-sensitive cortical mechanisms.…”

“…The functions subserved by these two mechanisms have been characterized in many ways: spatio-temporal tuning (Keesey, 1972;Kulikowski & Tolhurst, 1973;Kulikowski, 1971, Tolhurst, 1973a, 1973bKelly, 1979;Wilson, 1980;Gorgeson, 1987;Fredericksen & Hess, 1998), contrast gain control (Burbeck & Kelly, 1981;Wilson & Humanski, 1993;Wilson & Kim, 1998;Snowden, 2001;Hammett & Snowden, 1995;Boynton & Foley, 1999;Essock et aI., 2009;Kim et aI., 2010;, temporal properties (Breitmeyer & Julesz, 1975;Keesey, 1972;Tolhurst, 1973aTolhurst, , 1973bStromeyer et aI., 1982), reaction time (Breitmeyer, 1975;Breitmeyer & Julesz, 1975;Tolhurst, 1975a;Harwerth & Levi, 1978;Vassilev & Mitov, 1976;Totev & Mitov, 2000;Mitov & Totev, 2005), temporal integration (Nachmias, 1967;Spitzberg & Richards, 1975;Breitmeyer & Ganz, 1977;Legge, 1978;Hammett & Snowden, 1995 Phillips & Wilson, 1985;Anderson, Burr, & Morrone, 1991;Snowden, 1991;Snowden & Hammett, 1996;Cass, Stuit, Bex, & Alais...…”

“…C is vertical shift constant, which is also termed to an isotropic amplitude component (i.e., Cass, Stuit, & Bex, 2009).…”