Foraging in the Global Workspace: The Central Executive Reconsidered

David L Barack, Postdoctoral Research Fellow, Salzman Lab, Columbia University

What is the central executive? In cognitive psychology, executive functioning concerns the computational processes that control cognition, including the direction of attention, action selection, decision making, task switching, and other such functions. In cognitive science, the central processor is sometimes modeled after the CPU of a von Neumann architecture, the module of a computational system that makes calls to memory, executes transformations in line with algorithms over the retrieved data, and then writes back to memory the results of these transformations. On my account of the mind, the central processor possesses the psychological functions that are part of executive functioning. I will refer to this combined construct of a central processor that performs executive functions as the central executive.

The central executive has a range of properties, but for this post, I will focus on domain generality, informational accessibility, and inferential richness. By domain general, I mean that the central executive contains information from different modalities (such as vision, audition, etc.). By informationally accessible, I mean both that the central executive’s algorithms have access to information outside of the central executive and that information contained in these algorithms is accessible by other processes, whether also part of the central executive or part of input or output specific systems. By inferentially rich, I mean that the information in the central executive is potentially combined with any other piece of information to result in new beliefs. The functions of the central executive may or may not be conscious.

Three concepts at the heart of my model of the central executive will provide the resources to begin to explain these three properties: internal search, a global workspace, and foraging.

The first concept is internal search. Newell famously said that search is at the heart of cognition (Newell 1994), a position with which much modern cognitive neuroscience agrees (Behrens, Muller et al. 2018; Bellmund, Gärdenfors et al. 2018). Search is the process of traveling through some space (physical or abstract, such as concept space or the internet) in order to locate a goal, and internal search refers to a search that occurs within the organism. Executive functions, I contend, are types of search.

The second concept in my analysis is the global workspace. Search requires some space through which to occur. In the case of cognition, search occurs in the global workspace: a computational space in which different data structures are located and compete for computational resources and operations. The global workspace is a notion that originated in cognitive theories of consciousness (Baars 1993) but has recently been applied to cognition (Schneider 2011). The global workspace can be conceptualized in different ways. The global workspace could be something like a hard drive that stores data but to which many different other parts of the system (such as the brain) simultaneously have access. Or, it could be something like an arena where different data structures literally roam around and interact with computational operations (like a literal implementation of a production architecture; see Newell 1994; Simon 1999). The central executive is partly constituted by internal search through a global workspace.

The third and final concept in my analysis is foraging. Foraging is a special type of directed search for resources under ignorance. Specifically, foraging is the goal-directed search for resources in non-exclusive, iterated, accept-or-reject decision contexts (Barack and Platt 2017;Barack ms). I contend that central executive processes involve foraging (and hence this third concept is a special case of the first concept, internal search). While central executive processes may not literally make decisions, the analogy is apt. The internal search through the global workspace is directed: a particular goal is sought, which in the case of the central executive is going to be defined by some sort of loss function that the system is attempting to minimize. This search is non-exclusive, as operations on data that are foregone can be executed at a later time. The search is iterated, as the same operation can be performed repeatedly. Finally, the operations of the central executive are accept-or-reject in the sense that computational operations performed on data structures either occur or they do not in a one-at-a-time, serial fashion.

The analysis of the central executive as foraging-type searches through an internal, global workspace may shed light on the three key properties mentioned earlier: domain generality, informational accessibility, and inferential richness.

First, domain generality is provided for by the global workspace and unrestricted search. This workspace is neutral with regard to the subject matter of the data structures it contains, and so is domain general. The search processes that operate in that workspace are also unrestricted in their subject matter—those processes can operate over any data that matches the input constraints for the production system. (While they may be unrestricted in their subject matter, they are restricted by the constraints on the data imposed by the production system’s triggering conditions.) The unrestricted subject matter of the global workspace and the unrestricted nature of the production processes both contribute to the domain general nature of the central executive. This analysis of domain generality suggests two types of such generality should be distinguished. There are constraints on what type of content (perceptual, motoric, general, etc.) can be contained in stored data structures, and there are constraints on the type of content that can trigger a transformation. A domain general workspace can contain domain specific productions, for example.

Second, informational accessibility reflects the global workspace’s structure. In order to be a global workspace, different modality- or domain-specific modules must have access to the workspace. But this access means that there must be connections to the workspace. Other aspects of informational access remain to be explained. In particular, while the global workspace may be widely interconnected, that does not entail that modules have access to information in specific algorithms in the workspace. The presence of a workspace merely insures some of the needed architectural features for such access are present.

Third, inferential richness results from this internal foraging through the workspace. Foraging computations are optimal in that they minimize or maximize some function under uncertainty. Such optimality implies that the executed computation reflects the best data at hand, regardless of its content. Any such data can be utilized to determine the operation that is actually executed at a given time. This explanation of inferential richness is not quite the sort described by Quine (Quine 1960)or Fodor (Fodor 1983), who envision inferential richness as the potential for any piece of information to influence any other. But with enough simple foraging-like computations and enough time, this potential widespread influence can be approximated.

These comments have been speculative, but I hope I have provided an outline of a sketch for a new model of the central executive. Obviously much more conceptual and theoretical work needs to be done, and many objections—perhaps most famously those of Fodor, who despaired of a scientific account of such central processes—remain to be addressed. I intend on fleshing out these ideas in a series of essays. Regardless, I think that there is much more promise in a scientific explanation of these crucial, central psychological processes than has been previously appreciated.

 

References:

Baars, B. J. (1993). A cognitive theory of consciousness, Cambridge University Press.

Barack, D. L. and M. L. Platt (2017). Engaging and Exploring: Cortical Circuits for Adaptive Foraging Decisions. Impulsivity, Springer: 163-199.

Barack, D. L. (ms). “Information Harvesting: Reasoning as Foraging in the Space of Propositions.”

Behrens, T. E., T. H. Muller, J. C. Whittington, S. Mark, A. B. Baram, K. L. Stachenfeld and Z. Kurth-Nelson (2018). “What is a cognitive map? Organizing knowledge for flexible behavior.” Neuron100(2): 490-509.

Bellmund, J. L., P. Gärdenfors, E. I. Moser and C. F. J. S. Doeller (2018). “Navigating cognition: Spatial codes for human thinking.”  362(6415): eaat6766.

Fodor, J. A. (1983). The modularity of mind: An essay on faculty psychology, MIT press.

Newell, A. (1994). Unified Theories of Cognition, Harvard University Press.

Quine, W. V. O. (1960). Word and object, MIT press.

Schneider, S. (2011). The language of thought, The MIT Press.

Simon, H. (1999). Production systems. The MIT Encyclopedia of the Cognitive Sciences: 676-677.