Since some readers may be dismayed by the stress I have put on so animistic a concept as ‘attention’ it may be well to review its basis once more. If we allow several figures to appear at once, the number of possible input configurations is so very large that a wholly parallel mechanism, giving a different output for each of them, is inconceivable. To cope with this difficulty, even a mechanical recognition system must have some way to select portions of the incoming information for detailed analysis. This immediately implies the existence of two levels of analysis: the preattentive mechanisms, which form segregated objects and help to direct further processing, and the act of focal attention, which makes more sophisticated analyses of the chosen object. The observation that even a competent automaton would require processes of figure-formation and attention lets us understand why they have appeared, explicitly or implicitly, in so many psychological theories… The notion that perception is basically a constructive act rather than a receptive or simply analytic one is quite old. It goes back at least to Brentano's ‘Act Psychology’ and Bergson's ‘Creative Synthesis’ and was eloquently advanced by William James (1890)… the mechanisms of visual imagination are continuous with those of visual perception – a fact which strongly implies that all perceiving is a constructive process.