Overt verbal responding during fMRI scanning: Empirical investigations of problems and potential solutions

This paper presents a pair of studies designed to empirically explore the s everity of potential artifacts associated with overt verbal responding duri ng fMRI scanning and to examine several different solutions to these artifa cts. In Study One, we compared susceptibility artifacts, signal-to-noise ra tios, and activation patterns when overt versus covert verbal responses wer e elicited during fMRI scanning using both individual and group analyses. T he results indicated that different patterns of brain activation were elici ted during covert as compared to overt verbal responses. This suggests that covert responses cannot be used as a simple substitute for overt verbal re sponses. Further, the results suggested that the use of overt verbal respon ses during fMRI scanning can produce interpretable results if: (1) the prim ary comparison is between two conditions that both use overt verbal respons es, and (2) analyses are conducted on pooled group data rather than individ ual participant data. In Study Two, we evaluated the feasibility and validi ty of a method for acquiring participants' overt responses during fMRI scan ning. The results indicated that our method was very accurate in acquiring the content of participant's responses. Further, inspection of the response s demonstrated that participants do not always comply with task instruction s and highlighted the importance of obtaining behavioral performance measur es during fMRI scanning. (C) 1999 Academic Press.