Blackwell Publishing Journal Backfiles 1879-2005
Single trial event-related potentials at Fz, CZ, P7, and OZ were measured concurrently with the skin conductance response (SCR) in a habituation paradigm. Half the subjects (26) were told that the same stimulus would be presented a number of times in the middle of a TV screen (“certain condition”), and the other half were not informed about the stimuli (“uncertain condition”). Within each of these groups, half of the subjects received 32 stimuli of 4 bits of information and the other half received 32 stimuli of 60 bits of information. No task-relevance was given to the stimuli. Larger vertex P300 waves were associated with more complex stimuli, but uncertainty had no effect on the P300. A significant complexity × uncertainty × trials interaction was found on a sustained late positive activity, called the Slow Wave (SW), which was maximal at Pz and habituated rapidly. As before, we found that both the SCR and the vertex P300 habituated. No effect of uncertainty or complexity was found on the SCR. The results suggest that the SW is a useful index of information processing, and that the SCR and P300 must be considered to index different aspects of information processing.
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