Biomedical subjects

Christopher Westphal

Publications and source records attributed to Christopher Westphal.

3 recordsLinked to original sources

PubMed2003

Comparison of block and event-related fMRI designs in evaluating the word-frequency effect.

Printed word frequency can modulate retrieval effort in a task requiring associative semantic judgment. Event-related fMRI, while avoiding stimulus order predictability, is in theory statistically less powerful than block designs. We compared one event-related and two block designs that evaluated the same semantic judgment task and found that similar brain regions demonstrated the word frequency effect. Although the responses were lower in amplitude, event-related fMRI was able to detect the word frequency effect to a comparable degree compared to the block designs. The detection of a frequency effect with the event-related design also suggests that stimulus-order predictability may not be as serious a concern in block designs as might be supposed.

Adult↗

PubMed2003

Reproducibility of the word frequency effect: comparison of signal change and voxel counting.

We determined the reproducibility of both the direction and the effect size of the word frequency effect (WFE) as it relates to associative semantic judgments. Sixteen volunteers were scanned twice. At the group level of analysis, signal change and voxel counting could both reproducibly detect the existence of a WFE. However, signal change data showed less intersession variation, particularly in the left inferior frontal gyrus. The effect size of WFE was well reproduced only with signal change measurements. In consideration of the signal change data, statistical threshold did not have a major effect on the detection or determination of the effect size. In general, while the direction of the WFE was reasonably reproducible at the individual level, the effect size was far less well reproduced. These findings suggest that with existing techniques, fMRI may be used to track changes in brain activation stemming from improvement in language proficiency at the group level but not at the individual level.

Adult↗

PubMed2003

Word frequency and subsequent memory effects studied using event-related fMRI.

Event-related fMRI was used to evaluate the effect of printed word frequency on the subsequent recognition of words incidentally encoded while 16 healthy right-handed volunteers performed living/nonliving judgments. Semantic judgment took longer for low-frequency words. These words were more accurately recognized than high-frequency words at later testing. Low-frequency words were also associated with relatively greater left prefrontal, left fusiform gyrus, and anterior cingulate activation. Words that were subsequently recognized were associated with greater activation in the left prefrontal region compared to those that were forgotten. These findings suggest the specific brain regions where less commonly encountered words are processed in a manner that facilitates their subsequent recognition.

Adult↗