In their review of 'The Neuropsychological Theories of Lashley and Hebb,' Kaplan & Fu suggest that I did not accord Hebb the recognition he deserved. They try to explain the popularity of his 1949 monograph by citing Hebb's associative perspective, something that was anathema to Lashley. On the other hand, Lashley contributed the reverberatory circuit to neuropsychological theory. In addition, I cite Lashley's latter day conceptual legacies to neuro-psychological theory.
"Probably the most enduring idea embodied in the 1949 monograph, and for which the monograph is justly famous, is the empirically assembled nerve net that Hebb dubbed the 'cell assembly'...I would venture the opinion that the conception that functional neural nets can be assembled by experience is one of the more important ideas in neuropsychological theory of the twentieth century. Lashley never developed that idea, nor did he ever acknowledge it in print. We have to credit the 1949 monograph for its dissemination. Modern neuropsychologists have been so well inculcated in cell assembly theory that, today, it is almost a given rather than a theory" (Orbach, 1998, p. 71).
2. If I gave the impression that I favored Lashley's views over Hebb's, I did not mean to. It is true that I spent more time clarifying Lashley's views; that was because I believe that he has been egregiously misunderstood and misinterpreted. As I explained in my book, even Hebb was guilty of misrepresenting Lashley (1949). Here are two examples:
"In his argument in favor of a structural memory trace, Hebb presented Lashley's view in a confused way. On p. 12 of his 1949 monograph he wrote: 'Lashley has concluded that a learned discrimin-ation is not based on the excitation of any particular neural cells. It is supposed to be determined solely by the pattern or shape of the sensory excitation.' Furthermore, 'he explicitly denies that the same cells need to be excited to arouse the same perception.' This, it seems to me, is a caricature of Lashley's view. Lashley never argued that the memory trace is not structural. He did argue that the memory trace is diffuse or, more precisely, reduplicated in the cerebral cortex. One page later...Hebb wrote that, in 1929, Lashley offered the interpretation 'that the trace is structural but diffuse, involving...a large number of cells widely spaced in the cortex, physiologically but not anatomically unified.' This, it seems to me, is a more accurate representation of Lashley's conception. It is important to note that non-localized does not mean non-structural to Lashley. Unfortunately, later, in Chapter 3, Hebb forgot this distinction and incorrectly classified Lashley with Kohler as a non-structuralist." (ibid, 1998, p. 9).
"It is widely believed that Lashley abandoned the idea of a structural memory trace in the cerebral cortex in favor of a field theoretical view (as in Kohler...). Hebb must have been one of these believers since he fostered that idea, in his critique in Chapter 3 of his monograph, by treating equipotentiality and field theory together as if they were one and the same. But the evidence presented in this volume does not support this belief..." (ibid, 1998, p. 8).
3. Lashley's brilliant idea for neuropsychological theory was derived from Lorente de No's anatomically derived reverberatory circuit of 1934. I believe that Hebb got this idea from Lashley (at that time, Hebb was just completing his PhD disseration in which he adopted Lashley's nativistic position). Hebb himself claimed to have gotten the reverberatory circuit from Hilgard and Marquis in 1940. . 4. Another of Lashley's conceptual legacies is what I referred to in my book as "Lashley's lesson:"
"From 1924, when he published his critique of changes in resistance at the synapse underlying learning, Lashley repeated over and over again what I believe should be remembered as his enduring legacy to neuropsychology: that the effects of learning can be seen at synapses that were not excited during original learning. Behavioral examples include stimulus and response equivalence, stimulus generalization, transfer of training and recovery of function after brain injury. This lesson, of primary importance to the development of neuropsychological theory of the twentieth century, is not often referred to since Lashley's death. Hebb did not refer to it in 1949 or thereafter. (ibid, 1998, p. 108).
5. Kaplan & Fu suggest that I did not accord Hebb the recognition he deserves. They hold that Hebb's position is "stronger" (Kaplan & Fu's expression) than that of Lashley and, to support their position, they cite Hebb's views on stimulus generalization and association. I am beholden to them for expounding their views on Hebb's contributions and achievements. However, I remain a skeptic on Hebb's explanation of stimulus generalization:
"There is some doubt regarding the universality of stimulus generalization according to Hebb. His theory does not always predict stimulus generalization from the learning of a simple discrimination. Take, for example, the learning to discriminate a vertical from a horizontal line. In this case, the stimuli belong to the category of primitive unity for which, unlike a triangle, no learning is required to build a unified percept, according to Hebb. Nevertheless, our best guess is that, empirically, after the initial learning, the organism would show a stimulus generalization to vertical rectangle vs. horizontal rectangle and even to a vertical row of circles vs. a horizontal row of circles. Since there was no initial learning to build up a unified perception of the vertical and horizontal lines, it is hard to see how Hebb would derive the empirical data of stimulus generalization in this case." (ibid., 1998, pp. 103-104).
6. There is also no change in my conviction that Lashley (1942) won the debate he engaged in with Spence (1940) on the continuity-noncontinuity controversy. Kaplan & Fu argue that this is not an 'either-or' matter. Under the proper circumstances, both positions are correct. Perhaps. But Spence finally did concede to Lashley that attention plays a role in discriminative learning.
Hebb, D.O. (1949) The organization of behavior. NY: Wiley.
Hilgard, E. R. and Marquis, D. G. (1940) Conditioning and learning. NY: Appleton-Century.
Kaplan, S. and Fu, L.L. Making room for insight and incrementalism in the same brain: The contribution of D.O. Hebb. PSYCOLOQUY 10(76) ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/1999.volume.10/ psyc.99.10.076.lashley-hebb.8.kaplan http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy?10.076
Lashley, K. S. (1942) An examination of the "continuity theory" as applied to discriminative learning. J. gen Psychol., 26, 241-265.
Lorente de No, R. (1934) Studies on the structure of the cerebral cortex: continuation of the study of the ammonic system. . Psychol. Neurol. Lpz, 46, 113-177.
Orbach, Jack (1998) The neuropsychological theories of Lashley and Hebb. MD: University Press of America.
Orbach, J. (1999) Precis of: The Neuropsychological Theories of Lashley and Hebb. PSYCOLOQUY 10(23). ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/1999.volume.10/ psyc.99.10.029.lashley-hebb.1.orbach http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy?10.029
Spence, K. W. (1940) Continuous vs. non-continuous interpretations of discrimination learning, Psychol. Rev., 47, 271-288.