The biology of attention.

The possibility of a biological understanding of the processes we call "attention" seemed so remote a few years ago that, were this article to have been attempted, it would, like the Cheshire cat, have faded away, leaving only its title. While there are not yet volumes to f i l l , there are some observations about the biology of attention which are definitely worth reporting. One of the most impressive advances is the discovery by Mountcastle (1975 and 1976), while studying the firing rates of single neurons in the awake, behaving monkey, of units in the parietal cortex which "increase their discharge rates abruptly when the animal fixates with his eyes objects of interest in his immediate surround" (Mountcastle 1975, p. 128). The firing rate changes only if the object of fixation has motivational significance; the mere process of gazing at a visual stimulus is not sufficient. For example, fixation of a food object leads to an increase in firing rate only when the animal is hungry. These cells are by no means rare; in the inferior parietal lobule, as many as half the neurons observed are of this type. Other neurons in this area fire just before visual saccades, evoked by interesting objects, but not before spontaneous eye movements. An interpretation in terms of selective attention seems very plausible. Ingle (1975) has made similar observations in the tectum of the frog.