Sunday, September 23, 2007

Meta-ling tasks - Lt. Columbo Finale II ("Just one more thing ...")

As Greg showed very clearly in the last few posts -- and as we have argued in our papers, as well -- one has to be very *very* careful to interpret the task-related cognitive neuroscience data, because the execution of the speech tasks can mask, disguise, or distort the findings vis-a-vis speech processing in its ecologically natural form.

[Greg: nice job with the historical argumentation :-) I like how you nail Lichtheim and show how his approach led to a modification of the Wernicke model for all the wrong reasons.]

I wanted to add one more small point, as we leave this issue (just like Peter Falk as Columbo). Even 'early' cortical responses are changed dramatically during the execution of experimental task demands, a phenomenon exploited extensively in the attention literature. One example comes from work we did 10+ years ago at UCSF, using MEG to characterize the neuromagnetic responses evoked by CV syllables. In a within-subjects design, we recorded neuronal activity while participants listened to CV syllables passively (no explicit task required) and when they listened to the very same material when making a phonological judgment. When we examined the N100m (M100) response, the pattern of data showed that executing the task differentially modulated the N100m amplitude and lateralization. The critical finding in the context of speech perception research was that -- compared to the baseline (same stimuli but no meta-linguistic task -- lateralization was induced by the task when in the passive case there was none! ** This illustrates that even temporally early cortical responses are affected by tasks in a way that complicate the interpretation of how speech perception is implemented in the brain.

**Poeppel, D., Yellin, E., Phillips, C., Roberts, T.P.L., Rowley, H., Wexler, K., Marantz, A. (1996). Task-induced asymmetry of the auditory evoked M100 neuromagnetic field elicited by speech sounds. Cognitive Brain Research 4: 231-242.

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