By 1950, the results of attempts to relate brain processes to mental experience appeared rather discouraging. Such variations in size, shape, chemistry, conduction speed, excitation threshold, and the like -- as had been demonstrated in nerve cells -- remained negligible in significance for any possible correlation with the manifold dimensions of mental experience.
Near the turn of the century, it had been suggested by Hering that different modes of sensation, such as pain, taste, and sight, might be correlated with the discharge of specific kinds of nervous energy. However, subsequently developed methods of recording and analyzing nerve potentials failed to reveal any such qualitative diversity. It was possible to demonstrate by other methods the presence of refined structural differences among neuron types; however, proof was lacking that the quality of the impulse or its conduction was influenced by these differences, which seemed instead to influence the developmental patterning of the neural circuits. Although qualitative variance among nerve energies was never rigidly disproved, the doctrine was generally abandoned in favor of the opposing view, namely, that nerve impulses are essentially homogeneous in quality and are transmitted as "common currency" throughout the nervous system. According to this theory, it is not the quality of the sensory nerve impulses that determines the diverse conscious sensations they produce, but, rather, the different areas of the brain into which they discharge. And there is some evidence for this view. In one experiment, when an electric stimulus was applied to a given sensory field of the cerebral cortex of a conscious human subject, it produced a sensation of the appropriate modality for that particular locus, that is, a visual sensation from the visual cortex, an auditory sensation from the auditory cortex, and so on. Other experiments revealed slight variations in the size, number, arrangement, and interconnection of the nerve cells, but as far as psychoneural correlations were concerned, the obvious similarities of these sensory fields to each other seemed much more remarkable than any of the minute differences.
However, cortical locus, in itself, turned out to have little explanatory value. Studies showed that sensations as diverse as those of red, black, green, and white, or touch, cold, warmth, movement, pain, posture, and pressure apparently may arise through activation of the same cortical areas. What seemed to remain was that some kind of differential patterning effects in the central distribution of impulses counts. In short, brain theory suggested a correlation between mental experience and the activity of relatively homogeneous nerve-cell units conducting essentially homogeneous impulses through homogeneous cerebral tissue. To match the multiple dimensions of mental experience psychologists could only point to a limitless variation in the spatiotemporal patterning of nerve impulses.
It can be inferred from passage that the author's assessment of the theory that various parts of the brain regulate the perceptions yielded by sensory nerve impulses is that
A.its rationale is believable but has yet to be fully substantiated
B.it is the most accurate explanation of nerve stimulus known
C.it has been refuted by recent developments in neurology
D.there is some evidence to corroborate it but it can not completely account for the full range of mental experience
E.there exists some empirical data to prove its validity
According to the author, up until 1950, efforts to establish that brain processes and mental experience are related would most likely have been met with