Orientation anisotropies in visual search revealed by noise.pdf

Journal of Vision (2007) / 1 DOI Received; update ISSN ? ARVO Orientation anisotropies in visual search revealed by noise Abtine Tavassoli Department of Electrical and Computer Engineering, and Center for Perceptual Systems, The University of Texas at Austin, Austin, TX, USA Ian van der Linde Center for Perceptual Systems, The University of Texas at Austin, and Department of Computing, Anglia Ruskin University, Chelmsford CM1 1SQ, England Alan C. Bovik Department of Electrical and Computer Engineering, and Center for Perceptual Systems, The University of Texas at Austin, Austin, TX, USA Lawrence K. Cormack Department of Psychology, and Center for Perceptual Systems, The University of Texas at Austin, Austin, TX, USA The human visual system is remarkably adept at finding objects of interest in cluttered visual environments, a task termed visual search. Because the human eye is highly foveated, it accomplishes this by making many discrete fixations linked by rapid eye movements called saccades. In such naturalistic tasks, we know very little about how the brain selects saccadic targets (the fixation loci). In this paper, we use a novel technique akin to psychophysical reverse correlation and stimuli that emulate the natural visual environment to measure observers’ ability to locate a low-contrast target of unknown orientation. We present three main discoveries. First, we provide strong evidence for saccadic selectivity for spatial frequencies close to the target’s central frequency. Second, we demonstrate that observers have distinct, idiosyncratic biases to certain orientations in saccadic programming, although there were no priors imposed on the targets orientation. These orientation biases cover a subset of the near-cardinal (horizontal/vertical) and near-oblique orientations, with orientations near vertical being the most common across observers. Further, these idiosyncratic biases were stable across time. Third, withi