Electrophysiological Evidence Of Interaction Research Articles

Contextual task difficulty modulates stimulus discrimination: Electrophysiological evidence for interaction between sensory and executive processes

The occipital-temporal N1 component of the event-related potential (ERP) has previously been shown to index a stimulus discrimination process. However, the N1 has not consistently been shown to be sensitive to the difficulty of stimulus discrimination. Here, we manipulated the difficulty of stimulus discrimination by modulating the similarity between serially presented targets and nontargets. The same target stimulus was employed in both easy and difficult discrimination contexts, and these physically identical target stimuli elicited a larger N1 and smaller P3b in the difficult task context. Moreover, when targets were incorrectly categorized, N1 amplitude was diminished and a P3b was not elicited. These findings provide evidence that the N1 component reflects a sensory discrimination process that is modulated by executive control, and that this component can index discrimination errors when stimulus discrimination is difficult.

Electrophysiological evidence of interaction between contextual expectation and semantic integration during the processing of collocations

Despite the potentially infinite creativity of language, many words are patterned in ordered strings called collocations. Final words of these clusters are highly predictable; in addition, their overall meaning can vary on the literality dimension, ranging from (figurative) idiomatic strings to literal strings. These structures thus offer a natural linguistic scenario to contrast ERP correlates of contextual expectation and semantic integration processes during comprehension. In this study, expected endings elicited a positive peak around 300ms compared to less expected synonyms, suggesting that the earlier recognition of the string leads to the specific pre-activation of the lexical items that conclude the expression. On the other hand, meaning variations of these fixed strings (either a literal or a figurative whole meaning) affected ERPs only around 400ms, i.e. in the frontal portion of the N400. These findings are discussed within a more general cognitive framework as outlined in Kok's (2001) dual categorization model.

Electrophysiological evidence for interaction between retinula cells in the flesh-fly

In the electrical response of retinula cells to polarized light in the flesh-flyBoettcherisca peregrina, the polarization plane which showed the maximum sensitivity (Polmax phase) to illumination by a small spot of light just large enough to cover only one retinula cell was found to differ from that with illumination by a larger spot of light which included adjacent cells. There was a difference of about 30°.