The decrease in responsiveness that follows continuous stimulation (adaptation)  is common to all sensory systems, including olfaction. With continued exposure to chronically present ambient odors, individuals’ perception of odor intensity is greatly reduced. Moreover, these perceptual changes can be profound and durable. It is commonly reported that following extended absences from the odorous environment, reexposure may still fail to elicit perception at the original intensity. Most research on olfactory adaptation examines relatively transient changes in stimulus detection or perceived intensity—rarely exceeding several hours and often less—but because olfactory adaptation can be produced with relatively short exposures, these durations are sufficient for investigating many parameters of the phenomenon. However, exposures to odors in natural environments often occur over far longer periods, and the resulting adaptations may differ qualitatively from short-term olfactory adaptation. For example, studies show that even brief periods of odorant stimulation produce transient reductions in receptors in the olfactory epithelium, a process termed “receptor fatigue.” Prolonged odor stimulation, however, could produce more long-lasting reductions in response, possibly involving structures higher in the central nervous system pathway.

22. The author of the passage discusses “receptor fatigue”(line 24 ) primarily in order to 
A. explain the physiological process through which long-lasting reductions in response are thought to be produced 
B. provide an example of a process that subjects would probably not experience during a prolonged period of odorant stimulation 
C. help illustrate how the information gathered from most olfactory research may not be sufficient to describe the effects of extended exposures to odors 
D. show how studies of short-term olfactory adaptation have only accounted for the reductions in response that follow relatively brief absences from an odorous environment 
E. qualify a statement about the severity and duration of the perceptual changes caused by exposure to chronically present ambient odors 

答案是C。选C的原因是不是因为“receptor fatigue”所在的那句话就是起到C所说的那个作用。而不选B的原因是因为“receptor fatigue”并不是example?


提问者: lenilegno 2015-11-18 17:07


Stan95 2015-11-29 14:34

B错的原因不是它不是example 而是后面错了。B说在prolonged period of odorant stimulation中它不能经历receptor fatigue 与原文事实相反。
C正确,receptor fatigue之前一直在描述receptor的情况,这里就是help illustrate。

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