The view presented here does not amount to a distinction between stages of attention (cf. Neisser, 1967). It is, rather, a claim about per璫eptual analysis of whatever is attended to. Note that perceptual pro璫essing is viewed as a unified process, in that both the "where" and the "what" questions are answered while the scene is structured. Spatial organization is treated as a sort of crude figural analysis which some-limes may even be sufficient for recognition.
Functional Importance of Global-to-Local Processing
In most real situations the task of the human perceptual processor is not just to account for given input but also to select which part of the surrounding stimulation is worth receiving, attending to, and pro璫essing, The constraints imposed by the optical limits of our eyes and by the nature of the surroundings have a twofold implication for the pro璫essing structure in the visual domain. One, the resolution of most of the Stimuli in the picture plane (or the largest part of their visible surface) is low by default. The crude information extracted from the low-resolution parts of the visual field should be used for determining the course of further processing. Two, in an ecology where uncertainty is the rule, there is little to be gained from being set for a particular type of input. The system should be flexible enough to allow for gross initial cues to suggest the special way for processing a given set of incoming data. These two observations suggest that a multipass system, in which fine-grained processing is guided by prior cursory processing, may be superior to a system that tries to find a coherent structure for all pieces of data simultaneously.
One important function of the first pass is that of locating the stimuli, an obvious prerequisite for any figural analysis. Note, however, that