Control of goal-directed and stimulus-driven attention in the brain

This review proposes that two networks of brain areas are involved in controlling attention. One network is primarily responsible for applying cognitive, top-down selection for stimuli and responses, whereas the other detects behaviourally relevant stimuli and might act as a 'circuit breaker' for the first system. Humans use cognitive information to direct attention to relevant objects (targets) in a visual scene. Information such as the target's colour or location is represented as a 'perceptual set'. Similarly, advance information about the required response to a target is represented as a 'motor set'. These can be considered together as an 'attentional set', which aids the detection of and response to targets. Such top-down control of attentional processes activates dorsal posterior parietal and frontal regions of the brain bilaterally in both monkeys and humans. This dorsal frontoparietal system is responsible for the generation of attentional sets. Attention can also be driven by stimulus properties rather than cognitive processes. This 'bottom-up' control of attention explains why we find ourselves drawn to 'oddball' stimuli that are very different from the background, or to salient stimuli that share some sensory features, such as colour, with the target for which we are searching. The dorsal frontoparietal system seems to maintain a 'salience map' that combines bottom-up with top-down information during visual search. Potentially important sensory stimuli, such as loud alarms or sudden movement, can attract our attention regardless of the ongoing task. This sensory orienting process seems to be mediated by the second attentional network, which is mainly lateralized to the right side of the brain and includes the temporoparietal junction and the ventral frontal cortex. This network seems to interrupt ongoing cognitive activity when a stimulus that might be behaviourally important is detected. These two networks could interact in humans to control attention. It is possible that damage to these networks is responsible for the syndrome of neglect, in which patients that have suffered damage to the right side of the brain tend to ignore stimuli on the left side of space. The authors suggest that neglect results from damage to the ventral network that also 'functionally inactivates' the dorsal network.