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IN THE EARLIER CHAPTERS, WE HAVE SEEN how sensory input is transformed into neural activity that is then processed by the brain to give rise to immediate percepts and how those percepts can be stored as short- and long-term memories (Chapters 52, 53, 54). We have also examined in detail how movement is controlled by the spinal cord and brain. Here, we begin to consider one of the most challenging aspects of neuroscience: the transformation of sensory input to motor output through the higher-order cognitive process of decision-making. In doing so, we are afforded a glimpse of the building blocks of higher thought and consciousness.

Outside neuroscience, the term cognitive typically connotes some distinction from reflexes and dedicated routines, and yet as we shall see, neuroscience recognizes the rudiments of cognition in simple behaviors that display two types of flexibility—contingency and freedom from immediacy. Contingency means that a stimulus does not command or initiate an action in the way it does for a reflex. A stimulus might motivate a particular behavior, but the action may be delayed, pending additional information, or it may never occur. This freedom from immediacy of action means there are operations that transpire over time scales that are not immediately beholden to changes in the environment or the real-time demands of control of the body.

Both types of flexibility—contingency and time—are on display when we make decisions. Of course, not all decisions invoke cognition. Many behavioral routines—swimming, walking, feeding, and grooming—have branch points that may be called decisions, but they proceed in an orderly manner without much flexibility or control of tempo. They are governed mainly by the time steps of nervous transmission and are dedicated for the most part to particular input–output relationships. The point of drawing these distinctions is not to establish sharp boundaries around decision-making, but to help us focus on aspects of decisions that make them a model for cognition.

For present purposes, we will use the following definition: A decision is a commitment to a proposition, action, or plan based on evidence (sensory input), prior knowledge (memory), and expected outcomes. The commitment is provisional. It does not necessitate behavior, and it can be modified. We can change our mind. The critical component is that some consideration of evidence leads to a change in the state of the organism that we liken to a provisional implementation of an action, strategy, or new mental process.

Such propositions can be represented as a plan of action: I decide to turn to the right, to leave safe shelter, to look for water, to choose a path least likely to encounter a predator, to approach a stranger, or to seek information in a book. The concept of a plan emphasizes freedom from immediacy. Moreover, not all plans come to fruition. Not all thought leads to action, but it is useful ...

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