Can neural realizations be neither holistic nor localized? Commentary on Anderson’s redeployment hypothesis Pete Mandik Chairman, Department of Philosophy Coordinator, Cognitive Science Laboratory William Paterson University, New Jersey USA

2 My aim… To raise two questions concerning the viability of Anderson’s Massive Redeployment Hypothesis (hereafter “redeploymentism”) as an alternative to holism and localism. My first question concerns the relative merits of redeploymentism and holism. My second, redeploymentism and localism.

3 Two questions If redeploymentism is to be distinct from holism, then what further refinements are there to the problematic idea of brain units “doing the same thing” during different redeployments? If redeploymentism is to be distinct from localism, then what reasons are there for not revising cognitive function attributions to conform to localism?

4 To flesh out these questions I will provide … 1. A review of the relevant “ism”’s (that is importantly oversimplified)… 2...and an illustration of the relevant “ism”’s (that is importantly underdetermined)

5 The three isms: A review Localism Different cognitive functions realized by different brain units C1C2 B1 B2B1B2 t2t2 t1t1 C1C2 B1 B2B1B2 t2t2 t1t1 C1C2 B1 B2B1B2 t2t2 t1t1 Holism Different cognitive functions realized by the same brain units doing different things Redeploymentism Different cognitive functions realized by the same brain units doing the same things

6 A crucial oversimplification on my part Anderson does not describe his hypothesis simply as I have: “Different cognitive functions realized by the same brain units doing the same things” But instead: “parts of the brain are specialized, in that they do the same thing each time they are activated. However, the thing that they do—the function they compute or transformation they effect— does not line up with any specific cognitive function.”

7 I interpret Anderson’s un- simplification as follows Brain units may be viewed as state machines that always obey the same state transition rules but contribute to the realization of different cognitive functions by being in different states

8 The simplified version is incoherent… On pain of contradicting physicalism, different cognitive functions cannot be implemented by the same brain units unless the brain units are doing different things Consider, by analogy, the incoherence of the suggestion that a chemical sample undergoes a phase change without its molecules doing anything different. C1C2 B1 B2B1B2 t2t2 t1t1

9 A rock and a hard place… Oversimplified redeploymentism entails dualism Un-simplified redeploymentism is respectably physicalist, but in order to constitute an option distinct from holism, un-simplified redeploymentism needs a way of distinguishing (in biological, not abstract, cases) when a brain unit has changed its state and when a brain unit has changed the state- transition rule it is following.

10 Illustrating the “ism”’s: Localist implementation of chemotaxis: An artificial creature with distinct networks for orientation and propulsion In the orientation network (top), degree of neural activation determines degree of turning. In the propulsion network (bottom), frequency and amplitude of neural oscillation determines speed of propulsion.

11 Illustrating the “ism”’s: Non-localist implementation of chemotaxis: An artificial creature with a single network for orientation and propulsion Average degree of neural activation determines degree of turning and frequency and amplitude of neural oscillation determine speed of propulsion.

12 Is the non-localist creature holist or redeploymentist? Because all the neurons in the model compute the same function (a sigmoidal function of the weighted sum of the inputs) all of the time, it seems to be redeploymentist. However, this is a much easier determination to make in a computer model than in biological reality. When is a real brain unit doing something different but computing the same function and when is it computing a different function? Insofar as this is underdetermined, so is the choice between redeploymentism and holism.

13 Regarding the choice between localism and non-localism… …what reasons are there for not revising cognitive function attributions to conform to localism? Prior to knowing any neurophysiology or neuroanatomy we might have evidence to attribute two distinct cognitive functions to a creature. But if subsequent investigations unearthed a neural unity, why not revise the cognitive attribution to be similarly unified?

14 In terms of the above illustration the point becomes… …instead of considering these two networks as two different implementations—localist and non- localist—of the same function, it is open to us to regard them as both localist implementations of different functions.

15 I end with questions: If redeploymentism is to be distinct from holism, then what further refinements are there to the problematic idea of brain units “doing the same thing” during different redeployments? If redeploymentism is to be distinct from localism, then what reasons are there for not revising cognitive function attributions to conform to localism?

16 THE END