One focus of my research has been the investigation of the neural consequences of reflexive, or automatic, shifts of visual attention (in other words, the type of attention that is at work when something suddenly captures your attention, despite your intentions). In this work, I have combined behavioral (e.g., reaction time) measures with recordings of event-related brain potentials (ERPs) in humans. A second line of research has been to gain a more temporally precise and anatomically specific understanding of human attention systems, through the development of a multi-methodological approach that combines event-related potentials with neuroimaging methods including positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). Finally, a third, more recent line of research has involved the investigation of mechanisms of top-down attentional control, and is aimed at understanding the cognitive neural architecture of executive attentional processes.

Reflexive Attention Mechanisms. A major focus of my research is determining the neural consequences of reflexive attention on visual processing. Through a series of studies, we have shows that reflexive shifts of attention produce an enhancement of visual processing at a relatively early stage of visual processing within the brain (please see Hopfinger & Mangun, 1998; Hopfinger & Mangun, 2001). These studies provided new evidence that reflexive and voluntary attention mechanisms are able to affect visual processing at a similar locus. [Link to animation of scalp recorded ERPs from these experiments, showing brain activity from 50-250 msec after a visual target was presented]. However, differences between the two types of attention were also found, as the enhancement following shifts of reflexive attention was only present at very short intervals after the attention-grabbing event. By contrast, voluntary attention effects are observed at longer intervals between cue and target, intervals at which the reflexive attention enhancements are no longer present. In addition, these studies revealed evidence suggesting that another effect of reflexive attention is that the brain briefly treats the cued location as if it were potentially more relevant than other locations in space.

Spatiotemporal Analyses of Voluntary Attention. A second line of research has involved integrating ERPs with neuroimaging techniques to elucidate the spatio-temporal properties of voluntary (based upon your intentions and current goals) selective attention. While ERPs provide excellent temporal resolution of mental processes (at the millisecond level), they are limited in the ability to localize the activity to specific brain structures. Neuroimaging methods (PET, fMRI), on the other hand, provide excellent spatial precision, but have a relatively poor temporal resolution (on the order of hundreds of milliseconds under the best of conditions). However, by combining these methodologies, we have been able to gain a better understanding of the brain regions and temporal dynamics underlying the effects of spatial attention on visual processing. For instance, we have been able to provide strong evidence that an effect of voluntary attention on early visual processing can be localized to activity in the fusiform gyrus of the occipital lobe, 100 msec following the presentation of the eliciting stimulus (e.g., Hopfinger et al., 2001).

Attentional Control Mechanisms. More recently, I have pursued a third line of research: investigation of the mechanisms of the top-down control of spatial attention. Previous neuroimaging studies had implicated a wide network of brain regions as being involved in visual attention processes, but lacked the temporal resolution to specify how they were involved. Through the use of a powerful new analytic approach known as event-related fMRI, we have been able to separate regions involved in attentional control from those regions involved only in subsequent target processing. In regards to attentional control, we have been able to identify a number of brain regions, including the intraparietal sulcus, the frontal eye fields, and the superior temporal sulcus, that are involved in orienting attention to visual locations before the target stimuli appear (Hopfinger, Buonocore, & Mangun, 2000). A largely distinct set of cortical regions was found to be involved in selection and response processes.

Studies of Memory Mechanisms. Another line of research has focused on the mechanisms of memory processes, specifically the neural systems underlying different forms of explicit memory (e.g., recollection versus familiarity for previously observed stimuli). Previous research has suggested that these different types of memory may be affected in distinct ways by attentional processes. I am also very interested in how these types of memory may affect the allocation of attention.

Future Directions. Future directions for my research include several key extensions of the research described above, as well as integration among the different topics. Specially, event-related fMRI techniques are now allowing a greater variety of cognitive experimental paradigms to be used in neuroimaging experiments. Combining ERPs with this method of fMRI will now allow reflexive attention mechanisms to be identified with the same degree of anatomical and temporal precision as that obtained previously in studies of voluntary attention. Having gained knowledge from previous experiments regarding the similarities and differences between voluntary and reflexive attention, I now plan to examine more directly the interaction of voluntary and reflexive attention mechanisms. The control of attention, in real life, is determined by a complex interaction of reflexive and voluntary attention mechanisms, as well as our memory of past events (i.e., what’s important, what’s novel, what can be ignored). A goal of my research in the future will be to investigate the mechanisms by which these two types of attention interact with memory systems to determine how attention is distributed during the performance of complex tasks, and thereupon, how short and long term representations of visual information are modulated by top-down and bottom-up influences.