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N2pc
N2pc refers to an ERP component linked to selective attention.〔Luck, S. J. (2005). “The operation of attention—millisecond by millisecond—over the first half second.” In H. Ogmen & B. G. Breitmeyer (Eds.), ''The first half second: The microgenesis and temporal dynamics of unconscious and conscious visual processes.'' Cambridge, MA: MIT Press〕 The N2pc appears over visual cortex contralateral to the location in space to which subjects are attending; if subjects pay attention to the left side of the visual field, the N2pc appears in the right hemisphere of the brain, and vice versa. This characteristic makes it a useful tool for directly measuring the general direction of a person's attention (either left or right) with fine-grained temporal resolution.
==History==
Researchers first observed the N2pc while seeking to document electrophysiological correlates of focused attention using ERPs. Subjects viewed pairs of letters on either side of a computer screen. They were instructed to pay attention to either the left or right side of the screen and report (using a button-press) whether or not the two letters on that side were the same. Compared to the waveform over cortex ipsilateral to the direction of subjects' attention, experimenters observed a consistently greater negative deflection of the ERP waveform at approximately 200 ms after the stimulus at posterior sites (i.e., over visual cortex) contralateral to the side of the screen subjects attended.
The N2pc first received its name from Luck and Hillyard (1994),〔Luck, S. J., & Hillyard, S. A. (1994). Electrophysiological correlates of feature analysis during visual search. ''Psychophysiology 31,'' 291-308.〕 who named the component after its characteristic features. The “N” denotes a negative polarity; “2” describes its latency in the waveform (i.e., the second negative deflection, typically around 200 ms); and “pc” stands for “posterior-contralateral,” as the component appears over posterior electrode sites contralateral to the direction of attention. The experimenters explored what factors would modulate the N2pc using a visual search paradigm in which subjects had to report the presence of a target object in a display (e.g., a green box or a horizontal bar). They confirmed that the N2pc appeared contralateral to attended stimuli, and furthermore found that it did not appear when subjects saw only one object at a time or had to spread their attention over all the items in the display. These data led the experimenters to believe the N2pc corresponds to a filtering process that occurs whenever people focus attention on one object while ignoring others.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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