Contrast adaptation and the spatial structure of natural images

Abstract

Natural images have a characteristic spatial structure, with amplitude spectra that decrease with frequency roughly as 1/f. We have examined how contrast (pattern-selective) adaptation to this structure influences the spatial sensitivity of the visual system. Contrast thresholds and suprathreshold contrast and frequency matches were measured after adaptation to random samples from an ensemble of images of outdoor scenes or of synthetic images formed by filtering the amplitude spectra of noise over a range of spectral slopes. Adaptation selectively reduced sensitivity at low-to-medium frequencies, biasing contrast sensitivity toward higher frequencies. The pattern of aftereffects was similar for different natural image ensembles but varied with large changes in the slope of the noise spectra. Our results suggest that adaptation to the spatial structure in natural scenes may exert strong and selective influences on perception that are important in characterizing the normal operating states of the visual system.

Sustained effects of adaptation on the perception of familiar faces.

“…However, as Leopold and Bondar (2005) pointed out, adaptation to any visual stimulus is likely to affect neurons in not only the early stages but also the intermediate and late stages of the visual pathway, all of which may contribute to the aftereffect in one way or another. Such higher level contributions are also suggested by more recent findings in adaptation research based on the use of more complex stimuli, for example, natural images (Webster & Miyahara, 1997), artworks (Carbon, Ditye, & Leder, 2007;Carbon & Leder, 2006), body parts (Kovacs et al, 2006), and not least, faces (e.g., Carbon, Strobach, et al, 2007;Leopold, O'Toole, Vetter, & Blanz, 2001;Webster & MacLin, 1999). Faces are objects of tremendous social importance whose stimulus dimensions are subject to higher cognitive processing and usually cannot be found (or tested) in simpler visual materials (e.g., identity, emotional expression, attractiveness).…”

Figural aftereffects in the perception of faces

“…Yet the patterns of adaptation that might routinely arise in natural viewing, and how these adaptational adjustments might influence normal visual perception, have received little attention. Webster and Mollon (1997) and Webster and Miyahara (1997) found large changes in color and spatial sensitivity that result from adaptation to the color and spatial statistics of natural images, and suggested that these adjustments are an intrinsic part of the visual response to any image. Here we examine the implications of these natural sensitivity adjustments for suprathreshold form perception.…”

Different spatial frequency bands selectively signal for natural image statistics in the early visual system

“…The resulting averaged ratio therefore serves as an index of local filter activity (which is dependent on the number of edges/lines at different scales and orientations) and therefore corresponds to the relative density of edges and lines making up the structure of a given image. Such physical characteristics of scenes are important because both the slope of the amplitude spectra and structural complexity of natural scene stimuli have been shown to modulate behavioral performance on a number of different tasks involving the detection, discrimination, or identification of different visual stimuli (Bex et al 2009;Hansen and Essock 2005;Hansen and Hess 2007;Párraga et al 2000;Tadmor and Tolhurst 1994;Thomson and Foster 1997;Webster and Miyahara 1997). Correspondingly, Hansen et al (2011) found an interaction between early VEP component magnitude that was dependent on both the structural complexity and amplitude spectrum slope.…”