It may be debated whether individual neurons are "tuned" to react to only asingle tastant such as salt or sugar--and therefore signal only one tastequality--or whether the activity in a given neuron contributes to the neuralLine representation of more than one taste. Studies show that both peripheral and(5) central gustatory neurons typically respond to more than one kind of stimulus,and although each neuron is attuned most acutely to one tastant, it usually alsogenerates a reaction to others with dissimilar taste qualities. How then can thebrain represent various taste qualities if each neuron is receptive to manydifferent-tasting stimuli(10) Electrophysiological studies of gustatory sensory neurons, first performedby Pfaffmann, demonstrated that peripheral neurons are not specificallyresponsive to stimuli representing a single taste quality (which might besymbolized by the pattern of activity across gustatory neurons because theactivity of any one cell was ambiguous) but instead record a spectrum of tastes.(15) But in the 1970s and 1980s several scientists began to accumulate data indicatingthat individual neurons are tuned maximally for one taste, and they interpretedthis as evidence that activity in a particular type of cell represented a given tastequality--an idea they called the labeled-line hypothesis. According to this idea,activity in neurons that experience the strongest reaction to sugar would signal(20) "sweetness," activity in those that are most sensitive to acids would signal"sourness", and so forth.Smith later proved that the same cells that previous researchers hadinterpreted as labeled lines actually defined the similarities and differences inthe patterns of activity across taste neurons, suggesting that the same neurons(25) were responsible for taste-quality representation, whether they were viewed aslabeled lines or as critical parts of an across-neuron pattern. These investigatorsfurther established that the neural distinction among stimuli of differentqualities depended on the simultaneous activation of different cell types, muchas with the function of color vision, but unlike auditory perception. These and(30) other considerations have led us to favor the idea that the patterns of activityare key to coding taste information.Scientists now know that things that taste similarly evoke similar patternsof activity across groups of taste neurons. Furthermore, we can compare thesepatterns and use multivariate statistical analysis to plot the similarities in the(35) patterns elicited by various tastants. Taste researchers have generated suchcomparisons for gustatory stimuli from the neural responses of hamsters andrats and these correspond very closely to similar plots generated in behavioralexperiments, from which we may infer which stimuli taste alike and which tastedifferent to animals. Such data show that the across-neuron patterns contain(40) sufficient information for taste discrimination and this may be a reasonableexplanation for neural coding in taste, though researchers continue to debatewhether individual neuron types play a more significant role in taste coding thanthey do in color vision. Scientists question whether taste is an analytic sense, inwhich each quality is separate, or a synthetic sense like color vision, where(45) combinations of colors produce a unique quality. According to the passage, Pfaffman's theory differs from that which has been most recently considered by scientists in that it（）

A. postulates that peripheral neurons do not respond to a greater extent to stimuli representing a single taste quality
B. ignores the crucial difference between central and peripheral gustatory neurons in their role as mechanisms of taste
C. implies that the activity of any individual taste cell, taken by itself, is ambiguous
D. fails to acknowledge that specific gustatory neurons are associated with particular tastes
E. relies primarily upon research data that has come from human, rather than animal, subjects