The brain should integrate related but not unrelated information from different senses. Temporal patterning of inputs to different modalities may provide critical information about whether those inputs are related or not. We studied effects of temporal correspondence between auditory and visual streams on human brain activity with functional magnetic resonance imaging (fMRI). Streams of visual flashes with irregularly jittered, arrhythmic timing could appear on right or left, with or without a stream of auditory tones that coincided perfectly when present (highly unlikely by chance), were noncoincident with vision (different erratic, arrhythmic pattern with same temporal statistics), or an auditory stream appeared alone. fMRI revealed blood oxygenation level-dependent (BOLD) increases in multisensory superior temporal sulcus (mSTS), contralateral to a visual stream when coincident with an auditory stream, and BOLD decreases for noncoincidence relative to unisensory baselines. Contralateral primary visual cortex and auditory cortex were also affected by audiovisual temporal correspondence or noncorrespondence, as confirmed in individuals. Connectivity analyses indicated enhanced influence from mSTS on primary sensory areas, rather than vice versa, during audiovisual correspondence. Temporal correspondence between auditory and visual streams affects a network of both multisensory (mSTS) and sensory-specific areas in humans, including even primary visual and auditory cortex, with stronger responses for corresponding and thus related audiovisual inputs.

Recordings of event-related potentials (ERPs) and event-related magnetic fields (ERMFs) were combined with functional magnetic resonance imaging (fMRI) to study visual cortical activity in humans during spatial attention. While subjects attended selectively to stimulus arrays in one visual field, fMRI revealed stimulus-related activations in the contralateral primary visual cortex and in multiple extrastriate areas. ERP and ERMF recordings showed that attention did not affect the initial evoked response at 60-90 ms poststimulus that was localized to primary cortex, but a similarly localized late response at 140-250 ms was enhanced to attended stimuli. These findings provide evidence that the primary visual cortex participates in the selective processing of attended stimuli by means of delayed feedback from higher visual-cortical areas.

The spatial focus of attention has traditionally been envisioned as a simple spatial gradient of enhanced activity that falls off monotonically with increasing distance. Here, we show with highdensity magnetoencephalographic recordings in human observers that the focus of attention is not a simple monotonic gradient but instead contains an excitatory peak surrounded by a narrow inhibitory region. To demonstrate this center-surround profile, we asked subjects to focus attention onto a color pop-out target and then presented probe stimuli at various distances from the target. We observed that the electromagnetic response to the probe was enhanced when the probe was presented at the location of the target, but the probe response was suppressed in a narrow zone surrounding the target and then recovered at more distant locations. Withdrawing attention from the pop-out target by engaging observers in a demanding foveal task eliminated this pattern, confirming a truly attention-driven effect. These results indicate that neural enhancement and suppression coexist in a spatially structured manner that is optimal to attenuate the most deleterious noise during visual object identification.attention ͉ magnetoencephalography ͉ visual I t is a common experience that one is able to focus on relevant parts of a visual scene even when irrelevant parts of the scene are more salient. It has been suggested that this voluntary focusing is mediated by a biasing of competitive stimulus interactions in the visual cortex, which promotes preferential processing of relevant over irrelevant input (1-3). This competitive advantage can be achieved by enhancing the processing of relevant inputs or by attenuating the processing of irrelevant inputs. Evidence has accumulated that attention operates by means of both neural enhancement (4-7) and neural suppression (8-13). More recent data from functional MRI in humans indicate that enhancement and suppression may cooperate across the visual scene (14, 15), leading to an increase in selectivity in a push-pull-like manner (15). That is, a spatially organized combination of enhancement and suppression may effectively sharpen the demarcation of relevant from irrelevant inputs, particularly in cluttered visual scenes in which neural representations of relevant and irrelevant information may become mixed together (16, 17) .Many behavioral and electrophysiological studies of attention have indicated that attending to a location produces a monotonic gradient of processing efficiency around the attended location (18)(19)(20)(21)(22). In contrast, computational models motivated by the known anatomy and physiology of the primate visual system have predicted that the spatial distribution of cortical activity around the focus of attention may be more complex than a simple gradient. In particular, the selective tuning model (ST) of Tsotsos et al. (23,24) proposes an architecture of attentional selection that explicitly predicts a suppressive zone surrounding the focus of attention. In short, ST provides an acc...