nature neurOSCIenCe VOLUME 13 | NUMBER 4 | APRIL 2010 5 0 7 a r t I C l e S Reading this manuscript requires attention to be voluntarily deployed, in a 'top-down' fashion, to this task. As a consequence of selectively attending to the page, one might become oblivious to surrounding sounds and sights. However, if a fire alarm suddenly blares, this salient stimulus will probably capture attention in a 'bottom-up' manner and interrupt the ongoing task so that an appropriate course of action can be initiated. This simple example illustrates a fundamental aspect of attention: what ultimately reaches our awareness and guides our behavior depends on the interaction between goal-directed and stimulusdriven attention 1,2 . Although much is known about the neural mechanisms that support goal-directed 1,3-7 and stimulus-driven attention 1, 5, [8] [9] [10] [11] [12] , how these two forms of attention are ultimately coordinated is not yet understood. The finding that these attentional forms are supported by largely distinct neural networks, with a dorsal network that includes the frontal eye field (FEF) and superior parietal cortex 1,4-7,13 supporting goaldirected attention and a ventral one that consists of the lateral and inferior frontal/prefrontal cortex and the temporo-parietal junction (TPJ) underlying stimulus-driven attention 1, 3, 8, 9, 12, 13 , has further complicated the issue. As a result, several hypotheses have been proposed to explain how these two forms of attention might be coordinated: through an interaction between the ventral and dorsal networks 1 , across the dorsal 14,15 or ventral 5 attention network, or in the anterior component of the ventral network 16 . However, many of these proposals are based on studies that used tasks that conflate stimulus-driven and goal-directed attention, thereby making it difficult to determine the relative contributions of bottom-up and top-down neural processes to task performance. For example, the brain mechanisms of stimulusdriven attention cannot easily be dissociated from those of goal-directed behavior if the stimulus-driven attention task involves spatial shifts of attention, goal-oriented processes, or motor responses, as none of these cognitive processes is necessary to capture attention exogenously but all are known to engage the dorsal attentional network 1,3-6 . The same concern also applies to our current understanding of how attention controls awareness. Both the ventral and dorsal attentional networks have been associated with conscious perception 5,17-23 , lending support to theories of awareness in which widespread changes in brain activity accompany conscious perception 17,24 . However, there has been no specific attempt to assess the relative contributions of the dorsal and ventral networks to the neural basis of attentional limits to conscious perception by using tasks that dissociate between stimulusdriven and goal-directed attentional processes. Hence, the extent to which each of these attention networks is necessary for awareness is currently unclear 22, 23, 25 . We have recently developed an experimental procedure that reveals a profound but fleeting deficit in visual awareness resulting from the foveal presentation of an unexpected, task-irrelevant stimulus that involves neither an overt response nor a shift in spatial attention. The deficit, termed surprise-induced blindness (SiB), is triggered by an event that is absent from the observer's goal-directed attentional set and is not under the observer's initial control 26 . As such, the procedure represents a powerful way to assess whether stimulusdriven attentional limits to conscious perception can arise within the ventral attention network in the absence of dorsal network involvement. Moreover, because the unexpected event ultimately affects the goal-directed task of detecting a target, SiB experiments are also well suited to reveal the neural mechanisms by which stimulus-driven attention affects goal-directed behavior. We scanned 30 participants while they were searching for a target in a rapid serial visual presentation (RSVP) stream of distractor Attention is the process that selects which sensory information is preferentially processed and ultimately reaches our awareness. Attention, however, is not a unitary process; it can be captured by unexpected or salient events (stimulus driven) or it can be deployed under voluntary control (goal directed), and these two forms of attention are implemented by largely distinct ventral and dorsal parieto-frontal networks. For coherent behavior and awareness to emerge, stimulus-driven and goal-directed behavior must ultimately interact. We found that the ventral, but not dorsal, network can account for stimulus-driven attentional limits to conscious perception, and that stimulus-driven and goal-directed attention converge in the lateral prefrontal component of that network. Although these results do not rule out dorsal network involvement in awareness when goal-directed task demands are present, they suggest to a general role for the lateral prefrontal cortex in the control of attention and awareness.
Their conclusion was also supported by Asplund and his colleagues, who found that the ventral network can account for stimulus-driven attention REF .
A central role for the lateral prefrontal cortex in goal-directed and stimulus-driven attention
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