Parietal control of attentional guidance: The significance of sensory, motivational and motor factors

Abstract

The lateral intraparietal area (LIP), a portion of monkey posterior parietal cortex, has been implicated in spatial attention. We review recent evidence showing that LIP encodes a priority map of the external environment that specifies the momentary locus of attention and is activated in a variety of behavioral tasks. The priority map in LIP is shaped by task-specific motor, cognitive and motivational variables, the functional significance of which is not entirely understood. We suggest that these modulations represent teaching signals by which the brain learns to identify attentional priority of various stimuli based on the task-specific associations between these stimuli, the required action and expected outcome.

Introduction

Judicious selection is at the heart of goal directed behavior. To select appropriately in a complex environment an intelligent agent (be it a person, a rat or a monkey), must solve two problems. First, the agent must identify the most relevant source of information from among many potential alternatives. Second, it must be able to focus on the relevant source and block out irrelevant distractions. In both intuitive and scientific terms, we think of the cognitive operations that allow such adaptive selection as falling into the broad realm of “attention”.

It is often claimed that attention is necessary for overcoming capacity limitations inherent in neural processing. Because the brain is “bombarded” with more sensory information than it can process in depth, the argument goes, attention is needed to prioritize and limit the amount of information that reaches higher processing stages at any one time. However, the need for selection remains even in simple environments that do not seriously tax capacity limitations. Even in such environments, we must decide which objects are helpful to us and which are not. The essence of attention is therefore the act of assigning credit, or identifying the sources of information that are most relevant in a given context. Generally this decision requires learning about the statistical contingencies between various objects, actions and outcomes. It follows that attention must be a dynamic selection mechanism that is exquisitely sensitive to immediate task demands.

Neurophysiological investigations in non-human primates have focused on three areas as being important for the control of attention: the frontal eye field in the frontal lobe, the superior colliculus in the midbrain, and the lateral intraparietal area (LIP) in the parietal cortex. In this review we describe the state of our knowledge about one node of this network, area LIP, which has been especially well investigated and provides an excellent model system for further inquiry into the mechanisms of attention. Investigations into LIP began with the somewhat naïve view that an area controlling attention must simply represent objects or locations that are attended at a given moment and respond relatively weakly to distractors. To a first approximation, this is indeed what is found in LIP. However, recent evidence shows that this “priority map” is more complex and in particular that it takes on a wide range of task-specific properties – i.e., it appears to be plastic and adaptable to task demands. The specific significance of these modulations is not fully understood. However, we suggest that these modulations represent teaching signals through which the brain learns to assign attentional priority to various stimuli based on their significance for a specific action or a specific outcome. We end by describing a computational model (Roelfsema & van Ooyen, 2005) that may be a good starting point for formalizing inquiry into the links between learning and attention.