WHERE AND WHEN TO PAY ATTENTION - THE NEURAL SYSTEMS FOR DIRECTING ATTENTION TO SPATIAL LOCATIONS AND TO TIME INTERVALS AS REVEALED BY BOTHPET AND FMRI

Although attention is distributed across time as well as space, the te mporal allocation of attention has been less well researched than its spatial counterpart. A temporal analog of the covert spatial orientati on task [Posner MI, Snyder CRR, Davidson BJ (1980) Attention and the d etection of signals. J Exp Psychol Gen 109:160-174] was developed to c ompare the neural systems involved in directing attention to spatial l ocations versus time intervals. We asked whether there exists a genera l system for allocating attentional resources, independent of stimulus dimension, or whether functionally specialized brain regions are recr uited for directing attention toward spatial versus temporal aspects o f the environment. We measured brain activity in seven healthy volunte ers by using positron emission tomography (PET) and in eight healthy v olunteers by using functional magnetic resonance imaging (fMRI). The t ask manipulated cued attention to spatial locations (S) and temporal i ntervals (T) in a factorial design. Symbolic central cues oriented sub jects toward S only (left or right), toward T only (300 msec or 1500 m sec), toward both S and T simultaneously, or provided no information r egarding S or T Subjects also were scanned during a resting baseline c ondition. Behavioral data showed benefits and costs for performance du ring temporal attention similar to those established for spatial atten tion. Brain-imaging data revealed a partial overlap between neural sys tems involved in the performance of spatial versus temporal orientatio n of attention tasks. Additionally, hemispheric asymmetries revealed p referential right and left parietal activation for spatial and tempora l attention, respectively. Parietal cortex was activated bilaterally b y attending to both dimensions simultaneously. This is the first direc t comparison of the neural correlates of attending to spatial versus t emporal cues.