How does covert attention modulate visual perception? Psychophysics, neurostimulation and neuroimaging

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Project Summary Covert spatial attention is a selective process that filters incoming information. Given the high cost of cortical computation, such a mechanism is needed for optimal management of resources. Studies focused on the cortical implementation of exogenous (involuntary; bottom-up) and endogenous (voluntary; top-down) attention often implicate frontal and parietal areas in attentional modulation and assume similar effects in occipital areas. Though a handful of fMRI studies suggest a link between early visual areas and covert attention, fMRI records but does not manipulate brain function, leaving questions regarding causality unanswered. Additionally, research implicating exogenous, bottom-up, modulations to frontal areas is lacking. Behaviorally, differences between both covert attention systems have also been reported. In tasks for which increasing spatial resolution is detrimental to performance, exogenous attention impairs performance, but endogenous attention always improves performance. Using selective adaptation, studies have revealed that unlike endogenous attention which flexibly increases or decreases spatial resolution, exogenous attention always increases resolution. These results suggest that both covert attention systems may alter visual representations to basic visual dimensions (e.g. spatial frequency and contrast) in a differential way. More empirical work is needed to delineate the cortical computations and regions responsible for attentional modulations in performance. Addressing these questions requires an innovative research program that integrates model-based psychophysical approaches, non-invasive brain stimulation (TMS) and human electrophysiology. My dissertation work so far has employed model-based psychophysics and TMS to test the hypotheses that: (1) exogenous attention alters sensory tuning by boosting the gain of the target orientation along with spatial frequencies greater than the target; (2) a brief disruption (via TMS) of early visual areas would diminish benefits and costs on performance brought about by exogenous attention. This work has produced several significant results and generated follow-up questions that I will address in the proposed research plan. To do so, I will use computational modeling and reverse correlation to test differences at the level of representation between both covert attention systems. Additionally, with the help of fMRI guided TMS I will test the functional role of occipital and frontal areas in endogenous and exogenous attention’s effect on performance. This experience will provide training in model-based psychophysics, neuroanatomy, and fMRI guided TMS. In the proposed postdoctoral training phase, I will gain theoretical and methodological training in human electrophysiology which will introduce temporal dynamics into my research. Such a combination of experiments and methods has the potential to generate highly impactful findings and novel lines of research as well as inform studies involved in the rehabilitation of attention related disorders.