Journal

A common feature of our nervous system is that the prop-erty of intensity—for example, the loudness of a tone, the luminance contrast of a light (its brightness relative to the background), or the strength of a muscular contraction—is encoded by the discharge frequency of neurons. Attention to a stimulus increases that stimulus’s evoked firing rate, and, in the early visual system, attention ostensibly func-tions to increase the effective contrast of a stimulus, operat-ing through what has become known as the contrast gain model of attention. For example, in neurons in areas V4 and MT of the macaque visual cortex, attention directed to a stimulus increases firing rates similar to an increase in the stimulus contrast (Martínez-Trujillo & Treue, 2002; Reyn-olds, Pasternak, & Desimone, 2000). In macaque V4, atten-tion has an effect on orientation tuning curves of single neu-rons similar to that of contrast increments in the cat visual cortex, multiplicatively increasing the amplitude without changing the tuning width (McAdams & Maunsell, 1999