Modulatory Effects of Attention

One early fMRI-based study demonstrated that the use of voluntary attention (deciding whether to attend to a subset of moving dots or to a subset of stationary dots in a field of moving and stationary dots) caused detectable changes in MR signals associated with a visual motion processing area in cortex (Fig. 5). This study did not have an overt behavioral measure to provide external evidence that subjects were actually performing their assigned tasks. However, the data were sufficiently clean and unambiguous that this study was published and gained considerable attention.

During the ensuing years the study was replicated and extended in a number of ways by different laboratories throughout the world. The initial basic demonstration of attentional modulation became the starting point for much more subtle experiments— experiments that were more tightly tied to behavioral measures. Importantly, both the qualitative and the quantitative measures of attentional modulation were replicated. For instance, the motion processing area was active whenever there was visual movement present, but that activity increased by about 50% when the subject was attending to the movement compared to when the subject was not attending to the movement. The studies that used analogous tasks as part of their design found quantitatively similar changes.

The basic paradigm was adapted to more complex stimulus situations in which subjects could attend to various different aspects of a complex scene. This permitted the testing of specific hypotheses about the allocation and connection of visual attention to different aspects of a stimulus. For example, it was demonstrated that when an object was attended because of one attribute (e.g., motion), there was increased processing of other attributes of that object (e.g., whether it was a familiar face or represented a familiar location) even though the other attributes were irrelevant to the attentional task. Thus, fMRI-based experiments were being applied to theoretical questions of long-standing interest in cognitive psychology.

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