Visual Evoked Potential Change during Information Processing: Correlates of Cognition or Reactive Change.
NAVAL HEALTH RESEARCH CENTER SAN DIEGO CALIF
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Two experiments investigated a change in the late positive activity 200 to 550 msec of the visual evoked potential VEP. This P2-effect, maximal at the occiput, appeared related to cognitive aspects of information processing. Results did not support an interpretation of the P2-effect in cognitive terms Experiment 1 but rather in terms of shifts in cortical arousal and in expectancy Experiment 2. In both studies, subjects viewed letter-pair stimuli, e.g., HH or bD, responding when they saw a stimulus SIGHT task, or when they determined whether the two letters were the same or different in either size or name SIZE and NAME tasks. Reaction times increased from the SIGHT to the SIZE to the NAME task, objectifying the increase in task complexity. The P2-effect occurred with the increase in task complexity from the SIGHT to the SIZE task, but did not increase further in the NAME task or show asymmetry in relation to lateralized processing. In Experiment 2, slow wave shifts were observed. These slow waves revealed subject-specific ranges of cortical arousal. The P2-effect appeared to result primarily from continued or noncontinued expectancy following stimulus reception. This work demonstrates the difficulty involved in controlling for and evaluating the effects of shifts in cortical arousal and in expectancy during cognitive information processing. The results are relevant to the question of CNV-P300 dissociability.
- Anatomy and Physiology