Local orientation and texture fixation statistics during free-viewing of natural scene images following brief adaptation

Abstract

While the global structure of natural scene images is known to exhibit relatively stable biases across a large number of images with respect to the 1/f^a amplitude relationship and horizontal-vertical amplitude biases, the local structure within given images varies considerably as a function of distance. It has recently been shown that when macaque (Dragoi, Sharma, Miller, & Sur, Nat. Neurosci., 2002) or rhesus (Dragoi & Sur, J. Cog. Neurosci., 2006) monkeys free-view natural scene images, a largely orthogonal difference between the orientation statistics of sequential fixations was observed for long saccades. Dragoi and colleagues proposed that orientation-selective neurons in V1 have evolved to take advantage of such eye movement statistics with respect to orientation discrimination, and that adaptation in V1 was unlikely to contribute to fixation region selections. Here, we sought to extend this paradigm to human observers by examining the local orientation statistics or local amplitude spectrum slope of fixated natural or synthetic image regions during free-viewing following brief adaptation to narrow or broadband orientation patterns or isotropic visual noise patterns possessing different amplitude spectrum slopes. The data showed that while human observers tended to fixate image regions containing orientation statistics approximately orthogonal to the adapting patterns, this effect was dependent on global structural sparseness of the free-viewed images, with the strongest effects occurring for scenes possessing sparse structure. A similar effect was observed when the adapting pattern possessed a steep or shallow amplitude spectrum slope, only this effect was less dependent on the global structural sparseness of the free-viewed images. Taken together, these findings argue that when specific processing units of V1 are briefly adapted, the selection of content at subsequent fixation regions in natural images possessing sparse structure is influenced by adaptation.

Footnotes

 Institutes of Health Research (CIHR) grant: MT 108-18 to RFH.