Published online by Cambridge University Press: 21 September 2009
Voltage fluctuations above the intact human scalp are called chemosensory event-related potentials (CSERPs) (Evans et al., 1993) when these variations are caused by experimental manipulations of odor presentations. CSERPs function as indicators of the speed, strength, and local distribution of neuronal brain activity related to odor perception. CSERPs are very time-sensitive, which allows odor perception to be separated into different processing stages within the first second after odor presentation (Pause and Krauel, 2000). The aim of this chapter is to describe the biological and psychological meanings of the different processing stages. Between 300 and 500 msec after odor presentation, the specific features of the olfactory environment are encoded. This process is accompanied by a first distinct wave that appears within the CSERP; it is negatively charged and therefore is called the N1 component. The N1 component seems to reflect a pre-attentive level of stimulus encoding, but also depends on the level of the subject's alertness. The next prominent wave within the CSERP is the positively charged P3 component, appearing between 700 and 1,200 msec after odor presentation. Like the N1 component, the P3 is sensitive to the attentional investment of the subject, but in addition it is sensitive to the probability of the odor occurrence and to the subjective significance of the odor. The extraction of the significance of the olfactory event is an evaluative process that depends on cognitive and emotional resources.
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