The meaning of the term reductionism is discussed. It is argued that reductionism is one of the ways in which psychology makes progress, and philosophical arguments against reductionism seem to have little impact on research in, for example, biological psychology.
2. Rakover refers to a philosophical school called holism that provides a historical and theoretical analysis of the way in which science actually progresses. However, it occurs to me that the subject of reductionism should have been more thoroughly dealt with, first of all because the meaning of this central concept is not clear, and second because it is one of the ways in which science progresses.
3. The psychology of learning is one area where "reductionism" is practiced. An example of this is research on classical conditioning. Pavlov (1927) observed that dogs learned to salivate to a stimulus that preceded the presentation of food; he gave generality to this finding by terming the originally neutral stimulus preceding food a conditioned stimulus (CS), the food the unconditioned stimulus (US), and the response elicited by the CS a conditioned response (CR). This relationship between stimuli and responses is called classical conditioning, and has been observed in several response systems, both somatic and autonomic, and in several species, including humans. Thus, several stimuli may serve as CSs and USs, and several responses may serve as CRs. According to some philosophers, this should be a problem for a "reduction" of classical conditioning to neurophysiology, because classical conditioning is a general or abstract concept, and thus cannot be "reduced" to one single neurophysiological mechanism.
4. Several research programs have investigated the neurophysiology and anatomy of classical conditioning, and have used different response systems (e.g., the rabbit nictitating membrane response and the gill withdrawal reflex in Aplysia) for this purpose. The neural basis of classical conditioning of the two responses mentioned here is different from what we now know, and there is probably no common mechanism in the nervous system that is responsible for classical conditioning. Thus, classical conditioning is realized by different neurophysiological mechanisms for different species, and most likely for different responses within the same species. For example, simultaneous conditioning of two different responses (blink and heart rate) in the same individual has revealed that the development of the CR is different for these responses, and may not be accounted for by a common mechanism (e.g., Powell & Levine-Bryce, 1988).
5. Does this mean that classical conditioning cannot be reduced to a neurophysiological mechanism? Yes it does. There is no single neurophysiological mechanism that can account for all instances of classical conditioning. And what are the implications of this? I see at least two: (1) classical conditioning is not one process, but several processes that had best been called by different names, since what applies to one may not apply to the others; (2) if a psychological concept cannot be given one neurophysiological meaning then it is the psychological concept that needs to be changed; and this does not mean that reductionism as a research strategy has failed or is "wrong" in some other way. The finding that two processes once called by a common name are different, since their underlying processes are different, is one of the ways in which science makes progress.
6. There is one more comment I would like to make about reductionism: the term implies that a psychological process is "reduced", that is, made less, according to my dictionary. This is a connotation of the term reductionism that is not intended. My argument here is that the term is not a good description. Let me give an example from research on classical conditioning to illustrate this. For decades classical conditioning was a description of an observation of a precisely defined relationship between stimuli and responses. The neurophysiological mechanism was hidden from view, but the aim was to describe the mechanism(s) of classical conditioning. When a description of the mechanism(s) was not available, one had to construct theories, but these were only valid as long as the mechanism was not known. A revelation of the mechanism(s) would be a description of the pathways in the nervous system activated by the stimuli, their connection, and the motor pathway. I cannot see that this "reduces," that is, makes the concept of classical conditioning less. However, I can see that it reduces the number of theories about classical conditioning, and that may be for the good. From this viewpoint the term "mechanism" should replace "reductionism," for what one ultimately looks for in psychobiological research is a mechanism to explain one's observations.
7. There are numerous observations in psychology that cannot at present be explained by a neurophysiological mechanism, to my knowledge, and an example of this is Shepard and Metzler's (1971) well-known demonstration of "mental rotation" (p. 239 in Rakover's book). Rakover argues that this finding cannot be explained unless one assumes the existence of a mental image or operation executed by a subject who is aware of what he is doing. Then he goes on to specify what a neurophysiological theory would have to describe in order to explain Shepard and Metzler's results, and his conclusion is probably that a neurophysiological theory could not explain this finding in principle, since it is a goal-directed behaviour. Rakover is right that this finding poses problems for a neurophysiological account, but then many things do, and one does not refute the possibility of a neurophysiological account for that reason. One does not solve any problems by giving a cognitive explanation of this phenomenon, since any cognitive process or structure must have a physiological or anatomical basis. I want to draw attention to an experiment performed by Hollard and Delius (1982). They did a conceptual replication of the Shepard and Metzler experiment, but with pigeons as well as humans as subjects. The pigeons were trained in a matching-to-sample procedure where they matched a rotated comparison stimulus to a sample stimulus that was not rotated. The results showed that the pigeons had shorter overall reaction times than humans, and whereas humans showed longer reaction times as a function of the degrees of rotation of the comparison stimulus, pigeons did not. Thus, pigeons were faster than humans at deciding whether a shape was the same as the sample stimulus or not. According to a theory explaining these findings in terms of mental rotation, pigeons seem to rotate a mental image faster than humans. However, I am not sure if pigeons have mental images and I do not intend to discuss the issue, either, because it cannot be decided.
8. What needs to be underscored is the difference between observation and explanation. What is rotated in these experiments is the stimulus, not a mental image, and what is observed is reaction times. From this stimulus-response relationship Rakover deduces that a mental image is rotated, but there are, in principle, an infinite number of mechanisms that could explain these findings. The findings of Hollard and Delius underscore this. Rakover is not very happy with the distinction between observation and theory, since it may be difficult to differentiate between concepts referring to observations and theoretical processes. However, if this distinction is not made, there will be no difference between data and explanation, and there will not be any objectivity in science.
9. In sum, the fact that there is no one-to-one relationship between psychological concepts and physiological mechanisms is no unsurmountable obstacle to finding the neurophysiological mechanisms underlying psychological processes. The problem is that our psychological concepts have not differentiated between processes that are served by different mechanisms.
Hollard, V.D. & Delius, J.D. (1982). Rotational Invariance in Visual Pattern Recognition by Pigeons and Humans. Science, 218, 804-806.
Pavlov, I.P. (1927). Conditioned Reflexes (G.V. Anrep, transl.). Dover Publications: New York.
Powell, D.A. & Levine-Bryce, D. (1988). A Comparison of Two Model Systems of Associative Learning: Heart Rate and Eyeblink Conditioning in the Rabbit. Psychophysiology, 25, 672-682.
Rakover, S.S. (1990). Metapsychology: Missing Links in Behavior, Mind, and Science. New York: Paragon/Solomon.
Rakover, S.S. (1993). Precis of "Metapsychology: Missing Links in Behavior, Mind, and Science." PSYCOLOQUY 4(55) metapsychology.1.rakover.
Shepard, R. N. and Metzler, J. (1971) Mental rotation of three-dimensional objects. Science 171: 701-703.