TOKYO —

What we experience when making a decision may be fundamentally different from the intricate, dynamic processes unfolding within the brain, according to groundbreaking research by Indiana University Professor Tom James. For decades, a prevailing paradigm, both within scientific circles and in our intuitive understanding of ourselves, has depicted decision-making as a neat, sequential operation. This established "sandwich model" posits a linear progression: first, sensory input is received, then it is cognitively processed to form a decision, culminating in a motor action. However, Professor James, in his recent publication in the Journal of Cognitive Neuroscience, challenges this long-held view, proposing that behavior emerges not from a distinct decision-making module, but from the continuous, integrated interplay of sensory, sensorimotor, and motor systems.

The Linear Paradigm Under Scrutiny

The traditional framework for understanding decision-making is deeply ingrained in scientific theory and everyday language. It suggests a clear division of labor within the brain, where distinct neural processes are responsible for perception, cognition, and action. This linear sequence aligns with our subjective experience; actions feel like direct consequences of our desires, beliefs, and intentions. As Professor James himself observes, "Our actions feel like they are caused by decisions based on desires, beliefs, and intentions." This intuition has shaped numerous scientific approaches, particularly in model-based cognitive neuroscience, which often constructs its models around this sequential flow.

However, Professor James argues that this familiar explanation, often termed the "sandwich model," fails to adequately account for the complexities revealed by modern neuroscience. While specific neural mechanisms for sensation and action are well-established, the proposed intermediate cognitive stage—the presumed locus of decision-making—lacks a corresponding, distinct neural process that functions as an independent "decision maker."

A New Framework: Action Selection Through Integrated Processes

Instead of positing a dedicated decision-making system that dictates behavior, Professor James offers a compelling alternative: ‘action selection.’ In this revised view, behavior is understood as an emergent property arising from the continuous, dynamic interactions among the brain, the body, and the surrounding environment. These processes, he contends, do not unfold in a rigid, step-by-step sequence but can occur simultaneously, influencing and feeding back into one another in real-time.

This does not imply that decisions are illusory. Professor James clarifies, "Of course they do. We use this language all the time and it’s very helpful in terms of describing behavior. The leap, I think, is to say that the brain works by having decision-making or control processes. It produces behavior that is well described in that way. But it doesn’t need a process that does that to make it look that way." The distinction lies in understanding how behavior that we describe as decision-making is physically realized in the brain, rather than assuming a separate, abstract entity orchestrates it.

Professor James, a distinguished figure in the Department of Psychological and Brain Sciences at Indiana University, articulates this argument in his paper, "Sensorimotor Mechanisms of Decisions and Actions."

Philosophical Underpinnings: A Physicalist Perspective

Professor James grounds his argument in a "physicalist" framework, a philosophical stance often associated with thinkers like Daniel Dennett. This approach emphasizes that physical phenomena are the fundamental drivers of reality. A core tenet of physicalism is that while physical events can cause both physical and nonphysical phenomena, nonphysical phenomena cannot independently initiate physical events.

Applying this to decision-making, Professor James notes that sensory and motor processes are undeniably physical. Decisions, in this context, are conceptualized as nonphysical phenomena. Therefore, according to this physicalist perspective, a nonphysical decision cannot directly cause a physical action. This philosophical underpinning necessitates a re-examination of how we conceptualize the brain’s role in guiding behavior.

Decisions as Abstract Descriptions: The Center of Mass Analogy

To elucidate this complex idea, Professor James employs several insightful analogies. One particularly striking comparison draws from Daniel Dennett’s work, likening decisions to a "center of mass" (CoM) or "center of gravity." A center of mass is a powerful and useful mathematical concept for describing the distribution of mass in an object, but it is not a physical entity that can independently exert force. One cannot move an object’s center of mass without moving the object itself.

Similarly, Professor James proposes that a decision might function as an abstract description of a complex set of physical processes, rather than a distinct physical entity that directly initiates an action. It is a convenient label we use to summarize a confluence of neural activity that results in behavior.

The "University" Analogy: Bridging High-Level Concepts and Detailed Mechanisms

Another analogy highlights how high-level conceptual descriptions, while useful for everyday communication, can become less informative when seeking a detailed scientific understanding. Consider the term "the university." This single phrase efficiently represents a vast collection of people, buildings, departments, and intricate processes. When we say, "the university took certain actions during a campus protest," it serves as a general statement. However, a truly detailed explanation would require delving into the specific actions of administrators, the communications between different departments, the calls made to law enforcement, and the individual contributions of countless people.

Professor James argues that "decisions" present a similar challenge for neuroscience. They offer a valuable, high-level description of behavior, enabling us to understand and communicate about actions in a general sense. However, this descriptive utility can obscure the underlying physical mechanisms that actually generate the behavior. As Professor James states, "As mental phenomena, they are defined on too abstract a level for the goals of cognitive neuroscience." In essence, simply stating that someone "made a decision" does not explain the intricate neural and bodily processes that made the action possible.

The Robot’s Dilemma: Purposeful Behavior Without a Decision-Maker

Pushing his argument further, Professor James introduces a third illustrative example: a simple robot designed with a limited set of sensory, motor, and sensorimotor modules. This robot exhibits "wall-following" behavior, a seemingly purposeful and strategic action. From an external perspective, it might appear to possess goals, strategies, and even rudimentary intentions.

However, this robot is explicitly designed without any system dedicated to making decisions. "The robot does not have decisions built into it," Professor James explains. "It just senses its environment and moves around accordingly. And based on the environment, wall-following turns out to be a good thing. It looks intentional. It looks strategic. It looks like the robot is making decisions. And yet, it is not. The reason we know it is not is that there are no systems built into it to do that."

This robotic demonstration raises a profound question: if a relatively uncomplicated machine can generate behavior that appears intentional without an internal decision-making system, could human behavior similarly appear to result from centralized decisions even if no such central process exists in the brain?

Professor James posits that this explanation is more parsimonious—that is, it requires fewer assumptions—than positing the existence of a "higher-level, central controller that monitors and regulates sensory and motor processes" within the human brain.

The Cartesian Theater Problem: An Infinite Regress

The concept of a central controller faces not only empirical challenges but also a significant philosophical hurdle, one that has been debated since the time of René Descartes. If a higher-level entity within the brain is responsible for observing information and issuing commands, then the question inevitably arises: how does that controller itself function?

Professor James eloquently describes this dilemma: "Explaining that the brain works by way of a central controller suggests that you haven’t figured out how the brain works, because you’ve just put a person inside your brain." This notion, famously termed the "Cartesian Theater" by Dennett, implies an infinite regress. If a controller needs a controller, and that controller needs another, the problem of explaining decision-making is never truly solved; it is merely deferred indefinitely.

Instead of invoking such an elusive internal decision maker, Professor James advocates for a direct investigation of the interacting sensory and motor systems that collectively generate behavior.

An Experimental Path Forward: Embracing Complexity

If decision-making is indeed an emergent property of continuous interactions among the brain, body, and environment, then studying it demands experimental methodologies capable of capturing this inherent complexity. This presents both exciting opportunities and considerable methodological challenges for cognitive neuroscience. Researchers will need to move beyond strictly linear models and develop approaches that can examine processes occurring simultaneously, their mutual influences, and their dynamic changes as an individual engages with their surroundings.

Professor James’s own laboratory is actively pursuing this new direction, drawing inspiration from fields such as embodied cognition and ecological psychology. These approaches emphasize the integrated nature of perception, action, and cognition, and how they are shaped by the organism’s interaction with its environment.

This shift in perspective, Professor James believes, holds the potential to unlock a deeper understanding of the neural mechanisms that give rise to what we commonly label as decision-making. Furthermore, it may offer novel avenues for investigating a wide array of other cognitive and mental phenomena that have traditionally been compartmentalized as discrete internal processes. By focusing on the dynamic interplay of physical systems, neuroscience can move closer to unraveling the true nature of our actions and the complex processes that underlie them.