A great deal of evidence suggests that early in processing, retinal images are filtered by parallel, spatial frequency selective channels. We attempt to incorporate this view of early vision with the principle of global precedence, which holds that Gestalt-like processes sensitive to global image configurations tend to dominate local feature processing in human pattern perception. Global precedence is inferred from the pattern of reaction times observed when visual patterns contain multiple cues at different levels of spatial scale. Specifically, it is frequently observed that global processing times are largely unaffected by conflicting local cues, but local processing times are substantially lengthened by conflicting global cues. The asymmetry of these effects suggests the dominant role of global configurations. Since global spatial information is effectively represented by low spatial frequencies, global precedence potentially implies a low frequency dominance. The thesis is that low spatial frequencies tend to be available before information carried by higher frequency bands, producing a coarse-to-fine temporal order in visual spatial perception. It is suggested that a variety of factors contribute to the "prior entry" of low frequency information, including the high contrast gain of the magnocellular pathway, the amplitude spectra typical of natural images, and inhibitory interactions between the parallel frequency-tuned channels. Evidence suggesting a close relationship between global precedence and spatial frequency channels is provided by observations that the essential features of the global precedence effect are obtained using patterns consisting of low and high frequency sinusoids. The hypothesis that these asymmetric interference effects are due to interactions between parallel spatial channels is supported by an analysis of reaction times (RTs), which shows that RTs to redundant low and high frequency cues produce less facilitation than predictions that assume the channels are independent. In view of previous work showing that global precedence depends upon the low frequency content of the stimuli, we suggest that low spatial frequencies represent the sine qua non for the dominance of configurational cues in human pattern perception, and that this configurational dominance reflects the microgenesis of visual pattern perception. This general view of the temporal dynamics of visual pattern recognition is discussed, is considered from an evolutionary perspective, and is related to certain statistical regularities in natural scenes. Potential adaptive advantages of an interactive parallel architecture that confers an initial processing advantage to low resolution information are explored.

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The processing of sine-wave gratings presented to the left and right visual fields was examined in four experiments. Subjects were required either to detect the presence of a grating (Experiments 1 and 2) or to identify the spatial frequency of a grating (Experiments 3 and 4). Orthogonally to this, the stimuli were presented either at threshold levels of contrast (Experiments 1 and 3) or at suprathreshold levels (Experiments 2 and 4). Visual field and spatial frequency interacted when the task required identification of spatial frequency, but not when it required only stimulus detection. Regardless of contrast level (threshold, suprathreshold), high-frequency gratings were identified more readily in the right visual field (left hemisphere), whereas low-frequency gratings showed no visual field difference (Experiment 3) or were identified more readily in the left visual field (right hemisphere) (Experiment 4). Thus, hemispheric asymmetries in the processing of spatial frequencies depend on the task. These results support Sergent's (1982) spatial frequency hypothesis, but only when the computational demands of the task exceed those required for the simple detection of the stimuli.Perceptual characteristics of input, as well as cognitive characteristics of task, have been shown (by, e.g., Sergent & Hellige, 1986) to influence obtained patterns of cerebral asymmetry. Sergent (1982Sergent ( , 1983 proposed that the right visual field/left hemisphere (RVF/LH) is specialized for the perceptual processing of higher spatial frequencies, and that the left visual field/right hemisphere (LVF /RH) is specialized for the processing of lower spatial frequencies. Two general strategies, one involving complex stimuli and the other, simple stimuli, have been employed in testing this hypothesis, and each strategy will be discussed below in turn. Strategy 1: Complex StimuliFirst, some researchers have used complex stimuli (e.g., alphanumeric characters, faces) and have varied input characteristics (e.g., size, eccentricity, luminance, exposure duration) in order to vary the proportion of high and low frequencies in the input. When Christman (1989) reviewed such studies, he found moderate support for the spatial frequency hypothesis. However, the manipulations used in these studies have only crude and/or indirect effects on the spatial frequency content of the input, and thus they cannot be considered simple or straightforward manipulations of spatial frequency as opposed to other input variables (e.g., stimulus perceptibility; see Michimata & Hellige, 1987).In only four studies have quantitative forms of spatial filtering been employed to directly test the spatial frequency hypothesis. Sergent (1985) presented clear versus low-pass blurred faces and found, as predicted by the hypothesis, that low-pass blurring produced greater relative LH impairment. In a similar experiment, however, Sergent (1987) obtained an LH advantage with broad-pass faces and no hemispheric differences with low-pass faces. Christman (1990) used dioptric blur...

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