Inan effort to explain the role ofspatial frequency chan­nels in vision, there have been many suggestions, nota­bly by Julesz (1975, 1980; Julesz & Schumer, 1981),Levinson and Frome (Frome, Levinson, Danielson, C Levinson & Frome, 1979), andBraddickand Atkinson (1982), linking them to attention.This idea seems very reasonable in view ofthe fact thatthe visual system can selectively attend to stimuliofdiffer­ent spatial frequency spectra that are simultaneouslypresent in a visual scene provided their spectra are morethan about 1.5 octaves distant from each other. Consider,for instance, Figure I, in which the letter T can be easilyrecognized and, without change ofregard, the tine textconsisting ofthe characters E, F, Q, and 0 can also be"read" ifthis is what the observerdesires to do. Extend­ing from this, one can imagine a text oftine letters whosedensity variations formed not just a single letter T, butan entire text made up of characters the size of T ofFigure 1 (for practical reasons, we chose to illustrate thepoint with a single letter).