REPRESENTATION IS SPACE-VARIANT

Under shift, caused for example by eye movement, or by relative moveme nt of the subject or object of perception, the cortical representation undergoes very large changes in ''size'' and ''shape.'' Space-varianc e of cortical representation rules out models that fundamentally requi re linear interpolation between shifted patterns (e.g., Edelman's mode l) or rigid shift of an invariant retinal stimulus corresponding to sh ift at the cortex (e.g., the shifter theory of van Essen). Recently, a computational solution of ''quasi-shift'' invariance for space-varian t mappings has been constructed (Bonmassar & Schwartz 1997a; 1997b).