Objects play an important role in guiding spatial attention through a cluttered visual environment. We used event-related functional magnetic resonance imaging (ER-fMRI) to measure brain activity during cued discrimination tasks requiring subjects to orient attention either to a region bounded by an object (object-based spatial attention) or to an unbounded region of space (location-based spatial attention) in anticipation of an upcoming target. Comparison between the two tasks revealed greater activation when attention selected a region bounded by an object. This activation was strongly lateralized to the left hemisphere and formed a widely distributed network including (a) attentional structures in parietal and temporal cortex and thalamus, (b) ventral-stream object processing structures in occipital, inferior-temporal, and parahippocampal cortex, and (c) control structures in medial-and dorsolateral-prefrontal cortex. These results suggest that object-based spatial selection is achieved by imposing additional constraints over and above those processes already operating to achieve selection of an unbounded region. In addition, ER-fMRI methodology allowed a comparison of validly versus invalidly cued trials, thereby delineating brain structures involved in the reorientation of attention after its initial deployment proved incorrect. All areas of activation that differentiated between these two trial types resulted from greater activity during the invalid trials. This outcome suggests that all brain areas involved in attentional orienting and task performance in response to valid cues are also involved on invalid trials. During invalid trials, additional brain regions are recruited when a perceiver recovers from invalid cueing and reorients attention to a target appearing at an uncued location. Activated brain areas specific to attentional reorientation were strongly right-lateralized and included posterior temporal and inferior parietal regions previously implicated in visual attention processes, as well as prefrontal regions that likely subserve control processes, particularly related to inhibition of inappropriate responding.

Event-related brain potentials (ERPs) to words, pseudowords, and nonwords were recorded in three different tasks. A letter search task was used in Experiment 1. Performance was affected by whether the target letter occurred in a word, a pseudoword, or a random nonword. ERP results corroborated the behavioral results, showing small but reliable ERP differences between the three stimulus types. Words and pseudowords differed from nonwords at posterior sites, whereas words differed from pseudowords and nonwords at anterior sites. Since deciding whether the target letter was present or absent co-occurred with stimulus processing in Experiment 1, a delayed letter search task was used in Experiment 2. ERPs to words and pseudowords were similar and differed from ERPs to nonwords, suggesting a primary role of orthographic and phonological processing in the delayed letter search task. To increase semantic processing, a categorization task was used in Experiment 3. Early differences between ERPs to words and pseudowords at left posterior and anterior locations suggested a rapid activation of lexico-semantic information. These findings suggest that the use of ERPs in a multiple task design makes it possible to track the time course and the activation of multiple sources of linguistic information when processing words, pseudowords, and nonwords. The task-dependent nature of the effects suggests that the language system can use multiple sources of linguistic information in flexible and adaptive ways.