Critical band masking in optic flow

Abstract

Visual processing has been widely investigated with narrow band stimuli at low contrasts. We used a masking paradigm to examine how visual sensitivity under these conditions compares with the perception of the direction of heading in real scenes (i.e., with dynamic natural images at high contrasts). We first confirmed and extended previous studies showing biases in the amplitude distribution for spatial frequency, temporal frequency, speed and direction in dynamic natural movies. We then measured contrast thresholds for identification of the direction of motion for an observer traveling at various speeds. In spite of differences in contrast sensitivity and large non-uniformities in the amplitude content of the stimuli, contrast thresholds were relatively invariant of spatial frequency and completely invariant of temporal frequency, speed and direction. Our results suggest that visual processing normalises responses to supra-threshold structure at different spatial and temporal frequencies within natural stimuli and so equates their effective visibility.

(In) Sensitivity to spatial distortion in natural scenes

“…van Hateren & van der Schaaf, 1998) because they contained a greater variation of image content, including more people, interior images and man-made objects and fewer close-up images of natural foliage which were considered a more representative sample of everyday natural scenes. Elsewhere, single frames from many different commercial movies (including cartoons) have been examined and it has been shown that with an assumed luminance gamma value of 2 for the camera, their amplitude spectra are comparable to those of images from calibrated databases (Bex, Dakin, & Mareschal, 2005). If there are residual concerns about the use of this class of image rather than those obtained in rural settings, US individuals 12 years and older spend an average of 4.7 hours per day watching television (not including time spent observing computer images and movies, U.S. Census Bureau 2008) and so this class of image represents a significant proportion of natural (or at least ‘everyday’) retinal input.…”

The perception of suprathreshold contrast and fast adaptive filtering

“…Its amplitude spectrum falls approximately as "1/5" for 5 d A, which is a characteristic of the temporal amplitude spectrum dynamic natural images (Atick, 1992;Bex, Dakin, & Mareschal, 2005;Billock, de Guzman, & Scott Kelso, 2001;Dong & Atick, 1995;van Hateren, 1997).…”

Adaptation to Skew Distortions of Natural Scenes and Retinal Specificity of Its Aftereffects

“…Natural images contain a great variety of visual features such as spatial frequency, luminance, contrast, orientation, texture, color, or optic flow signals (Dong and Atick, 1995; Billock et al, 2001; Bex and Makous, 2002; Betsch et al, 2004; Bex et al, 2005, 2007, 2009). Optically induced image modifications such as astigmatic blur and distortions of spectacles alter multiple features of the natural world; and the visual system adapts to them (Adams et al, 2001; Sawides et al, 2010; Yehezkel et al, 2010; Vinas et al, 2012, 2013).…”