Responses of neurons in macaque area V4 during memory-guided visual search.
Motivation: Visual attention is a crucial mechanism for the brain to filter out unwanted information from typically very cluttered real-world scenes and to focus on what is important in a given situation. A large body of experimental literature in neurophysiology and psychophysics has dealt with attention and its effects on both neuronal activity and performance of subjects in behavioral tasks. Single-neuron studies have established that attention can alter firing rates of neurons in visual cortex such that neurons selective for an attended stimulus fire more strongly while neurons coding for irrelevant stimuli are attenuated [4, 3]. Psychophysical research has shown that subjects display higher performance in detecting objects in rapidly presented streams of images when they are given more specific cues about what to search for . Thus, attention seems to increase the perceptual salience of objects. Attentional influences on stimulus processing are generally thought to be mediated by top-down connections from higher areas in the brain to the visual processing areas in striate and extrastriate cortex. However, the question of the relation between changes in neuronal firing rates and subjects’ performance due to attention has not yet been addressed systematically.