Multiplicative neural responses — how attention and context reshape tuning curves
Gain modulation is a canonical computation in cortex: a contextual signal (attention, eye position, task context) multiplies the response of a sensory neuron without shifting its preferred stimulus (Salinas & Thier, 2000; McAdams & Maunsell, 1999). In V4, attention multiplies the tuning curve of orientation-selective neurons by a scalar gain factor — the preferred orientation doesn't change but the peak response scales up. This multiplicative operation is powerful: it enables coordinate transformations (e.g., retino- to body-centered coordinates in parietal cortex), efficient population coding, and allows downstream areas to distinguish "more signal" from "more noise." The gain is implemented neurally via divisive normalization and neuromodulators (ACh, NE).