7) to process stimuli with a 1/ f amplitude spectrum. It is generally held that, for natural scenes, amplitude reduces with spatial and temporal frequency, such that A( f) ∝ 1/ f α, where A is amplitude, f is frequency, and α typically takes on values close to unity ( 6, 11 – 13), at least when averaging over an ensemble of images ( 14).Īs evidenced earlier, the statistical utility of a variety of perceptual cues has been established for natural images, and it follows that human vision is also optimized (see ref. The amplitude spectrum describes the distribution of energy across different spatiotemporal scales in an image. Here, we consider aspects of the spatiotemporal structure of natural images (and image sequences) to which the visual system is known to be sensitive, the amplitude and phase spectra, and their influence on binocular rivalry competition. Because most basic research into rivalry has used simple line or grating stimuli (the properties of which can be easily manipulated), relatively little is known about how the properties of broadband stimuli, such as natural images, affect predominance during rivalry. It is well established that some stimuli are preferred to others, for example, high-contrast stimuli will dominate over low-contrast stimuli, and thus will be perceived for a greater proportion of the presentation time ( 9, 10). Here, we directly address this hypothesis by asking if, when the visual system must choose between two competing inputs, it prefers the one most representative of the natural environment.ĭuring binocular rivalry, conscious perception alternates between different images presented to the two eyes. As a whole, these studies support the hypothesis that human visual processing has evolved to efficiently encode images from our natural environment (see ref. From simple image attributes such as luminance and contrast information ( 2) to Gestalt rules of perceptual organization such as proximity and good continuation ( 3, 4), known properties of perceptual systems appear tuned to the statistics of natural images ( 5 – 8). Recent investigations of the statistical properties of natural images indicate that the tuning characteristics of early visual mechanisms reflect measurable properties of the world ( 1).
The human visual system is tasked with processing and organizing perceptual information relevant to the tasks we routinely perform. Our findings demonstrate that human vision integrates information across space, time, and phase to select the input most likely to hold behavioral relevance. We propose that this phase specificity relates to contour information, and arises either from the activity of V1 complex cells, or from later visual areas, consistent with recent neuroimaging and single-cell work. We also compared rivalry between natural and phase-scrambled images and found a strong preference for natural phase spectra that could not be accounted for by observer biases in a control task.
Calculating the effective contrast following attenuation by a model contrast sensitivity function suggested that the strong contrast dependency of rivalry provides the mechanism by which binocular vision is optimized for viewing natural images. This could not be explained by perceived contrast measurements, and occurred even though all stimuli had equal energy. We found that noise stimuli with “natural” amplitude spectra (i.e., amplitude content proportional to 1/ f, where f is spatial or temporal frequency) dominate over those with any other systematic spectral slope, along both spatial and temporal dimensions. Using the binocular rivalry paradigm, we designed stimuli that varied in either their spatiotemporal amplitude spectra or their phase spectra. Here, we ask if this optimization biases perception of visual inputs that are perceptually bistable. Ecological approaches to perception have demonstrated that information encoding by the visual system is informed by the natural environment, both in terms of simple image attributes like luminance and contrast, and more complex relationships corresponding to Gestalt principles of perceptual organization.
0 kommentar(er)
