Top-down control of visual attention

Top-down visual attention improves perception of selected stimuli and that improvement is reflected in the neural activity at many stages throughout the visual system. Recent studies of top-down attention have elaborated on the signatures of its effects within visual cortex and have begun identifying its causal basis. Evidence from these studies suggests that the correlates of spatial attention exhibited by neurons within the visual system originate from a distributed network of structures involved in the programming of saccadic eye movements. We summarize this evidence and discuss its relationship to the neural mechanisms of spatial working memory.

Introduction

Selective attention is the basic cognitive faculty that allows us to filter out irrelevant sensory information in favor of the relevant. Disorders of attention are frequently occurring among the symptoms of many neuropsychiatric disorders [33], most notably attention-deficit hyperactivity disorder (ADHD), which afflicts more than 4% of the population [34]. To date, the neural circuits and neural computations underlying normal and abnormal attention are only poorly understood. However, recent experimental work suggests that an understanding of how networks of neurons control the selection of relevant sensory input might be at hand. Much of what is known so far about the neural basis of attention comes from studies of the primate visual system, particularly that of the macaque monkey, which has proven to be a highly valuable model system. In recent years, neurophysiological studies have not only provided a more rigorous description of the correlates and signatures of attention in neural activity, but they have begun identifying the sources of attentional influences on neural activity and perception.The deployment of attention to a particular location in space (spatial attention) or to a particular feature or object (feature-based or object-based attention) can occur either by virtue of a stimulus’ physical salience (exogenous, involuntary or bottom-up attention) or according to internal, behavioral goals (endogenous, voluntary or top-down attention). Most of the studies over the past few years that we discuss, particularly those aimed at identifying neural circuits controlling attention, have focused primarily on top-down, spatial attention. Although it is clear that feature-based attention (e.g. [23, 35]) and bottom-up attention (e.g. [12•, 36]) both modulate neuronal activity within the visual system, the neurophysiological effects of these forms of attention are less well understood.