The target article discusses a number of proposals concerning the reuse of neural mechanisms, and these fall broadly into two categories: those which are motivated primarily by representational considerations, and those which are motivated by purely neurophysiological considerations (e.g., cortical areas determined to be active during a variety of tasks). We won't discuss the latter sort of proposals, but will focus on the former. These all involve the reuse of something like a model of some domain. They differ on how the model is reused. In one sort of case, a model of some domain D1 is used to represent, or model, some distinct domain D2. An example would be using models of space, or movement through space, to represent time. Call this domain reuse. The other sort of case is where a model of D1 is still representing the same domain D1, but serves a different function. For example, a model used for perceptual processing of environmental scenes is used to generate imagery of those same scenes. In this case, the domain represented is the same, but the function (perception, imagery, memory, planning, language comprehension) may be different. Call this functional reuse. It isn't obvious what other sort of reuse there could be.
We want to point out that, remarkably, both these sorts of reuse are not limited to neural models. Domain reuse is evident in using physical lines (or circles on clocks) to represent time, or using parts of one's body, such as fingers, to represent numbers. Functional reuse occurs, for instance, when one uses a chess-board to not only play a game, but to plan moves by physically implementing mock sequences of moves on the board. Another example would be cultural rituals where important prior events are remembered, as opposed to performed, through re-enactment (re-enactments of Civil War battles are not battles, any more than a memory of a birthday party is itself a birthday party).
This suggests that what is most interesting about the human brain is not neural reuse per se, but the fact that the brain is able to use things as models, and then submit those models to both domain and functional reuse. The deep interesting principle here is model reuse. That some of these models are implemented neurally is obviously interesting, but it may not be the crucial organizational principle.
Domain reuse includes, among other things, the examples falling under the heading of conceptual metaphor theory. Most generally, a representation of the source domain is used to model the target domain. Familiar examples are space being used to represent time (or money, or state transitions). But the entity reused need not be neural: Fingers can be used to model numbers; drawn circles on the ground to represent logical inclusion relations, or possible state transitions. Interestingly, the latter is a strategy widely used in cognitive-behavioral therapy where drawn diagrams can represent emotional state transitions to help patients understand their situation and possible remedies.
Functional reuse includes the examples of so-called concept empiricism, among others. In concept empiricism, the idea is that some model or scheme that is used in perception, say, perceiving a spatial relationship such as spatial inclusion, is reused for a different function, such as imagery, information retrieval, or language comprehension (e.g., the word “in”). A related view is Grush's emulation theory of representation (Grush Reference Grush2004), which describes in detail how models used for perceptual functions can be reused for visual imagery, motor planning, and many others. Other examples include making a sensibility judgment (whether the sentences such as “kick a ball” or “kick a cloud” convey a feasible body movement), which, as the target article discusses, requires the activation of the motor circuits usually involved with modeling the body for planning and guidance of real actions. Here, a model of the body does not serve one of its primary functions, like motor planning, but is reused for a totally different purpose: language comprehension.
This ability, however, seems to transcend neural models. We can take a chess-board, from its primary use of an arena in which to make moves and play a game, and reuse it to plan moves, or even to help understand why someone might have made a certain move. Of course, we could also use a neural model for the purpose.
In some cases, it is not obvious whether functional or domain reuse is the best analysis. Mirror neurons, for example, could be analyzed either way. If one takes it that their proper domain is the agent's own behavior, then using mirror neurons to model or understand another agent's behavior would be domain reuse. On the other hand, if one takes their proper domain to be motor behavior generally, then using mirror neurons to execute behavior versus to understand another agent's motor behavior would be functional reuse. And sometimes there are combinations of both kinds. We can use an external spatial arrangement, like a calendar, to represent time, but we can also use it for different functions: to keep a record of what actually happened at various times, to plan what we might do at different times, to communicate to someone what we want them to do at some time, and so forth.
We can imagine that some might quibble with our use of the expression “model,” but in the relevant sense, what others call schemas or simulators are models, or degenerate cases of models. It also might be maintained that other kinds of reuse do not involve anything like a model – for example, some have claimed that merely reusing non-model-involving motor areas is sufficient for generating imagery. We have explained elsewhere (Foglia & Grush, in preparation) that such “simulation” or “enactive” accounts require a model in order to do their job, and we won't rehash those points here.
Our present points are that while we agree that neural reuse is interesting, it seems to us that (1) they are all examples of the reuse of one or another kind of a model, and (2) the human brain is not limited to neural models. Accordingly, we suggest that investigations into the architectural requirements for constructing, using, and reusing models, whether in neural or non-neural media, will teach us much about the brain.
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The target article discusses a number of proposals concerning the reuse of neural mechanisms, and these fall broadly into two categories: those which are motivated primarily by representational considerations, and those which are motivated by purely neurophysiological considerations (e.g., cortical areas determined to be active during a variety of tasks). We won't discuss the latter sort of proposals, but will focus on the former. These all involve the reuse of something like a model of some domain. They differ on how the model is reused. In one sort of case, a model of some domain D1 is used to represent, or model, some distinct domain D2. An example would be using models of space, or movement through space, to represent time. Call this domain reuse. The other sort of case is where a model of D1 is still representing the same domain D1, but serves a different function. For example, a model used for perceptual processing of environmental scenes is used to generate imagery of those same scenes. In this case, the domain represented is the same, but the function (perception, imagery, memory, planning, language comprehension) may be different. Call this functional reuse. It isn't obvious what other sort of reuse there could be.
We want to point out that, remarkably, both these sorts of reuse are not limited to neural models. Domain reuse is evident in using physical lines (or circles on clocks) to represent time, or using parts of one's body, such as fingers, to represent numbers. Functional reuse occurs, for instance, when one uses a chess-board to not only play a game, but to plan moves by physically implementing mock sequences of moves on the board. Another example would be cultural rituals where important prior events are remembered, as opposed to performed, through re-enactment (re-enactments of Civil War battles are not battles, any more than a memory of a birthday party is itself a birthday party).
This suggests that what is most interesting about the human brain is not neural reuse per se, but the fact that the brain is able to use things as models, and then submit those models to both domain and functional reuse. The deep interesting principle here is model reuse. That some of these models are implemented neurally is obviously interesting, but it may not be the crucial organizational principle.
Domain reuse includes, among other things, the examples falling under the heading of conceptual metaphor theory. Most generally, a representation of the source domain is used to model the target domain. Familiar examples are space being used to represent time (or money, or state transitions). But the entity reused need not be neural: Fingers can be used to model numbers; drawn circles on the ground to represent logical inclusion relations, or possible state transitions. Interestingly, the latter is a strategy widely used in cognitive-behavioral therapy where drawn diagrams can represent emotional state transitions to help patients understand their situation and possible remedies.
Functional reuse includes the examples of so-called concept empiricism, among others. In concept empiricism, the idea is that some model or scheme that is used in perception, say, perceiving a spatial relationship such as spatial inclusion, is reused for a different function, such as imagery, information retrieval, or language comprehension (e.g., the word “in”). A related view is Grush's emulation theory of representation (Grush Reference Grush2004), which describes in detail how models used for perceptual functions can be reused for visual imagery, motor planning, and many others. Other examples include making a sensibility judgment (whether the sentences such as “kick a ball” or “kick a cloud” convey a feasible body movement), which, as the target article discusses, requires the activation of the motor circuits usually involved with modeling the body for planning and guidance of real actions. Here, a model of the body does not serve one of its primary functions, like motor planning, but is reused for a totally different purpose: language comprehension.
This ability, however, seems to transcend neural models. We can take a chess-board, from its primary use of an arena in which to make moves and play a game, and reuse it to plan moves, or even to help understand why someone might have made a certain move. Of course, we could also use a neural model for the purpose.
In some cases, it is not obvious whether functional or domain reuse is the best analysis. Mirror neurons, for example, could be analyzed either way. If one takes it that their proper domain is the agent's own behavior, then using mirror neurons to model or understand another agent's behavior would be domain reuse. On the other hand, if one takes their proper domain to be motor behavior generally, then using mirror neurons to execute behavior versus to understand another agent's motor behavior would be functional reuse. And sometimes there are combinations of both kinds. We can use an external spatial arrangement, like a calendar, to represent time, but we can also use it for different functions: to keep a record of what actually happened at various times, to plan what we might do at different times, to communicate to someone what we want them to do at some time, and so forth.
We can imagine that some might quibble with our use of the expression “model,” but in the relevant sense, what others call schemas or simulators are models, or degenerate cases of models. It also might be maintained that other kinds of reuse do not involve anything like a model – for example, some have claimed that merely reusing non-model-involving motor areas is sufficient for generating imagery. We have explained elsewhere (Foglia & Grush, in preparation) that such “simulation” or “enactive” accounts require a model in order to do their job, and we won't rehash those points here.
Our present points are that while we agree that neural reuse is interesting, it seems to us that (1) they are all examples of the reuse of one or another kind of a model, and (2) the human brain is not limited to neural models. Accordingly, we suggest that investigations into the architectural requirements for constructing, using, and reusing models, whether in neural or non-neural media, will teach us much about the brain.