Anisotropic local contrast normalization: The role of stimulus orientation and spatial frequency bandwidths in the oblique and horizontal effect perceptual anisotropies

Visual ability for sine waves and other narrowband stimuli shows an oblique effect-worst performance at obliques, best at horizontal and vertical orientations. Recently, we have shown that with broadband stimuli (either 1/f(alpha) visual noise or natural scenes), performance for detecting oriented content is worst at horizontal, best at the obliques, and intermediate at vertical orientations (a horizontal effect). This horizontal effect has been explained by a cortical contrast normalization model that is both local (over orientation and spatial frequency) and anisotropic (due to a numerical bias of neurons with different preferred orientations). Here, the bandwidth of content at which an oblique effect or horizontal effect occurs was assessed in two suprathreshold matching experiments conducted with 1/f(alpha) noise stimuli filtered with a triangle increment function of varied bandwidth (16 levels of orientation and spatial frequency bandwidth). The results provided further support for the local anisotropic normalization model in that an oblique effect was observed when a fairly small range of orientations and high spatial frequencies were tested and the horizontal effect was observed for broadband increments >= 20 degrees orientation bandwidth and >= 1-octave in frequency. At intermediate spatial frequency and orientation increment bandwidths, a blend of the two anisotropies was observed. (c) 2006 Elsevier Ltd. All rights reserved.