Abstract
Previous work (Kersten, 1987; Taylor et al., 2003) has shown that the summation of spatial frequency information in one-dimensional noise patterns is well described by an ideal observer, indicating that human observers summate spatial frequency information optimally over a six-octave wide band. Given that many models of vision contain independent channels that only sum probabilistically across “far-apart” values of orientation as well as spatial frequency (Graham, 1989), here we investigated whether optimal summation could be extended from the dimension of spatial frequency to summation across orientation bandwidth. Observers detected Gaussian white noise with a center-frequency of 5 cycles/degree and a fixed spatial frequency bandwidth of one octave. The orientation bandwidth of the stimulus ranged from 4 degrees to 128 degrees. Six bandwidths were used and a detection threshold measured in a two-interval forced choice task for each bandwidth in both the presence and absence of a Gaussian white noise mask. Stimuli were presented for 200ms. As was found for spatial frequency, noise detection r.m.s. contrast thresholds increased with the quarter-root of the number of orientation components, consistent with the pattern of performance demonstrated by the ideal observer. Efficiency was found to be constant for bandwidths greater than 16 degrees. Currently we are investigating whether optimal summation of orientation information can be disrupted with discontinuous spectra, using the response classification technique to reveal the perceptual template for orientation summation and whether summation remains optimal as both orientation and spatial frequency bandwidth of the stimulus are increased.
Supported by the Canada Research Chair program and NSERC grants OGP0042133 & OGP0105494