Natural scene statistics at the centre of gaze

Abstract

Early stages of visual processing may exploit the characteristic structure of natural visual stimuli. This structure may differ from the intrinsic structure of natural scenes, because sampling of the environment is an active process. For example, humans move their eyes several times a second when looking at a scene. The portions of a scene that fall on the fovea are sampled at high spatial resolution, and receive a disproportionate fraction of cortical processing. We recorded the eye positions of human subjects while they viewed images of natural scenes. We report that active selection affected the statistics of the stimuli encountered by the fovea, and also by the parafovea up to eccentricities of 4 degrees. We found two related effects. First, subjects looked at image regions that had high spatial contrast. Second, in these regions, the intensities of nearby image points (pixels) were less correlated with each other than in images selected at random. These effects could serve to increase the information available to the visual system for further processing. We show that both of these effects can be simply obtained by constructing an artificial ensemble comprised of the highest-contrast regions of images.

The world from a cat?s perspective ? statistics of natural videos

“…Previous studies on human eye movement (Reinagel and Zador 1999) demonstrated a higher contrast at the fixation points compared with randomly chosen parts of static pictures. Therefore, one might expect a higher contrast at the positions that the cats are looking at.…”

“…A recent study reports a 20% higher contrast at fixation points selected by humans scanning still images (Reinagel and Zador 1999). Hence we compare the contrast at the center of the image, which is the direction the cat preferentially looks at (Guitton et al 1984), with the contrast at higher eccentricities (Fig.…”

Conditional control in visual selection

“…Even though the observed correlation between salience and overt visual selection behavior has been confirmed in multiple studies (e.g., Baddeley & Tatler, 2006;Foulsham & Underwood, 2008;Masciocchi et al, 2009;Parkhurst & Niebur, 2003, 2004Peters et al, 2005;Reinagel & Zador, 1999;Tatler, Baddeley, & Gilchrist, 2005), the answer to the question as to what causes fixations to be predominantly directed toward salient locations still remains unsettled. Showing a correlation between salience and visual selection behavior does not necessarily imply that salience determines visual selection behavior.…”

On the discriminability of hROIs, human visually selected regions-of-interest

“…The work by Reinagel and Zador (1999), for example, shows how subjects look at loci that have high spatial contrast and poor pair-wise pixel correlation, a definition of internal intensity non-uniformity. Edge-density conspicuity is significantly correlated to eye movements loci by Mannan et al (1996).…”