Interpreting response time effects in functional imaging studies.
Bottom Line: However, even for contrasts designed to tap neural effort, activity remained after factoring out the RT-BOLD response correlation.This may reveal unpredicted differences in neural engagement (e.g., learning phonological forms for pseudowords>words) that could further the development of cognitive models of reading aloud.Our framework provides a theoretically well-grounded and easily implemented method for analysing and interpreting RT effects in neuroimaging studies of cognitive processes.
Affiliation: Department of Psychology, Royal Holloway University of London, Egham Hill, Egham TW20 0EX, UK. Electronic address: firstname.lastname@example.org.Show MeSH
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Mentions: Our framework suggests that a stimulus type that is represented by a particular brain region should engage that region more than another non-represented stimulus type. Here and throughout, we use the term “represents” to mean “represents some property of the stimulus”, for example, for written words this could be letters, phonemes, more basic visual or acoustic properties, as well as higher level conceptual information. These representations may be permanently instantiated in a neural system (e.g. specialized neurons that code for specific letters or words in posterior regions), or transient reading-related representations in frontal regions that serve related functions in other tasks (e.g. phonological output representations also used during object naming and spontaneous speech). This seems appropriate given that we are not committed to any particular representational system (e.g., localist versus distributed). As contrasts between represented and non-represented stimuli tap differences in engagement, clusters of activity revealed by such contrasts should survive correction for RT. However, if a brain region represents both stimulus types, then differential activity will be driven by processing effort and hence should positively correlate with RT. In such cases, correcting for RT should account for differential activity. Given these proposals, we can distinguish four possible outcomes in functional neuroimaging studies, as illustrated in Fig. 2, panels A to D.(A)
Affiliation: Department of Psychology, Royal Holloway University of London, Egham Hill, Egham TW20 0EX, UK. Electronic address: email@example.com.