Thursday, April 9, 2009

Free Will and Free Won't


American Scientist July-August 2004, p. 358-365, or on the internet at http://www.americanscientist.org/template/AssetDetail/assetid/34008/page/5
Motor activity in the brain precedes our awareness of the intention to move, so how is it that we perceive control?
Sukhvinder S. Obhi, Patrick Haggard

Experiments on the relationship between "thoughts" and motor activity. Very insightful.--jk
It's a Saturday afternoon in midwinter, and, having just finished all of his weekend chores, a man sits down by the fireplace to read his favorite novel over a hot cup of coffee. As the daylight in his apartment fades, he reaches out to flick on a lamp switch. With more light, he makes himself comfortable and begins to read. We all recognize this scenario, or one like it. Every day, we perform actions that create some state of affairs in our external environment, such as increasing the level of light in a room. Although we pay little attention to such actions, we believe that we—through intentions and decisions—control the movements of our arms and hands. That sounds plausible enough, but it can be quite difficult to prove.

Any action—even one as simple as turning on a light—consists of many parts. In this lamp-switch example, the man realizes that the room is too dark to read and forms the goal of making the room brighter. To achieve this goal, the reader decides to turn on a light. More specifically, this reader forms an intention to reach for a switch and then executes the movement to achieve that goal. So the overall action encompasses a number of events: formulating a goal, formulating an intention, initiating the movement and actually turning on the lamp switch. Could the order in which we experience such events create our subjective experience of control? We seem aware of a certain temporal order of events that contributes to our perception of the direction of causation that flows from within our minds (such as formulating an intention) to external space (such as turning on a light switch to light up a room). Nonetheless, our feeling of control could come from more than the order of events. To understand the neural basis of the human perception of control, scientists must study the sequence of subjective experiences and see if they follow a pattern of neural events with the same characteristic order.


More than a matter of simply turning on a switch, this feeling of control over actions might even contribute to a conscious sense of self. In other words, I am because I control my actions. The question is: How do we go from mundane, everyday actions—like turning on a light—to developing a sense of self as a causal agent? One can try tries to answer that question by examining the subjective sensations that humans experience during actions, the corresponding activities in the nervous system and the subjective experiences of individuals who do not have an ordinary sense of control. As we shall show, recent evidence from the field of cognitive neuroscience sheds light on the brain processes that underlie our sense of conscious will. Moreover, this evidence also indicates that we may not control our actions with entirely free will.

Free Will and Free Won't
Who's in Control?
In 1983, Benjamin Libet and his colleagues at the University of California, San Francisco published a profoundly influential paper on the source of control. In this study, participants watched a small clock hand that completed one full revolution in 2.56 seconds. While fixated on the clock, a participant voluntarily flexed his wrist at a time of his choosing. After the movement, the clock hand continued to rotate for a random time and then stopped. Then, a participant reported the position of the clock hand at the time when she first became aware of the will to move. Libet and his colleagues called this subjective judgment W, for "will." In other parts of the experiment, participants judged when they actually moved, and Libet called this judgment M, for "movement." The timing of the W and the M told Libet and his collaborators when—subjectively speaking—a participant formulated a will to move and actually moved.
In addition, Libet's team measured two objective parameters: the electrical activity over the motor areas of the brain, and the electrical activity of the muscles involved in the wrist movement. Over the motor areas, Libet recorded a well-known psychophysiological correlate of movement preparation called the readiness potential (RP), which Hans H. Kornhuber and L├╝der Deecke first described in 1965. The RP is measured using electroencephalographic recording electrodes placed on the scalp overlying the motor areas of the frontal lobe, and appears as a ramplike buildup of electrical activity that precedes voluntary action by about 1 second. By also recording the electrical activity of the muscles involved in the wrist movement, Libet precisely determined the onset of muscle activity related to the RP.
Libet and his colleagues examined the temporal order of conscious experience and neural activity by comparing the subjective W and M judgments with the objective RP and muscular activity. First, the investigators found that, as expected, W came before M. In other words, the subjects consciously perceived the intention to move as occurring before a conscious experience of actually moving. This suggests an appropriate correspondence between the sequence of subjective experiences and the sequence of the underlying events in the brain. But Libet also found a surprising temporal relation between subjective experience and individual neural events. The actual neural preparation to move (RP) preceded conscious awareness of the intention to move (W) by 300 to 500 milliseconds. Put simply, the brain prepared a movement before a subject consciously decided to move! This result suggests that a person's feeling of intention may be an effect of motor preparatory activity in the brain rather than a cause. As Libet himself indicated, this finding ran directly contrary to the classical conception of free will.
Fig 2.
Subjects watch a virtual clock on a computer monitor that completes a revolution in 2.56 seconds and voluntarily moves his wrist. In some experiments (left), he notes the position of the hand on the clock when he decides to move his wrist. After the action is made, he reports this tie, which is called the W judgment for the will to move. In other experiments (right), a subject notes when he thinks that he actually starts moving, which is called the M judgment for movement. In both cases, the investigators measure the so-called readiness potential from the motor cortex and the muscles that make his wrist move.


New evidence suggests that awareness of intention relates more closely to the onset of a later component of the RP that is known as the lateralized readiness potential (LRP). Although the RP develops on both sides of the brain for any motor activity, the LRP develops in just one hemisphere—the one opposite of the side where the action will be made. That is, because the left side of the brain controls motor activity on the right side of the body, and vice versa. The one-sided nature of the LRP makes it a more specific correlate of movement preparation than the RP. Also, the LRP develops about 500 milliseconds before movement, which is after the general RP. In 1999, one of us (Haggard) and Martin Eimer measured RPs and LRPs in a Libet-type experiment at the Max Planck Institute for Psychological Research in Munich. The results showed that a subjects' conscious experience of the intention to move covaried with the LRP rather than the RP. This suggests that awareness of intention correlates with the choice of which movement will be made, rather than simply that a movement of some kind will be made. This suggests that the conscious experience of control may be linked to the brain process that selects how we will use a particular movement to achieve a general goal. For example, the experience that precedes turning on the light in our example might be linked to the decision about which hand to use to reach for the switch.
However a scientist looks at all of these data, the brain is going full speed ahead well before a person experiences the conscious intention of moving. Consequently, no role appears for conscious processes in the control of action—or so it might seem. Although the results of Libet and one of us (Haggard) cast doubt on whether conscious processes cause actions, these data remain consistent with the idea that conscious processes could still exert some effect over actions by modifying the brain processes already under way. The fact that conscious awareness of intention precedes movement by a couple of hundred milliseconds means that a person could still inhibit certain actions from being made. Libet apparently replaced free will with free won't.
In some ways, Libet's findings suggest that a person's brain jumps the gun, or gets a head start, since movement-related neural activity comes before a person experiences the intention of making the movement. In addition, Libet found another seeming false start: A person's subjective judgment of when movement started came an average of 86 milliseconds before the onset of electrical activity in the muscles specific to the movement. That means that our subjective experience of the beginning of the movement must also come from some premotor process—something that takes place before the muscles themselves contract. Although some investigators questioned the validity of the timing as judged by subjects in Libet's experiment, his results have had considerable impact and have been interpreted as casting serious doubt on the existence of a mind-body chain of causation. Moreover, numerous other studies now confirm the phenomenon of anticipatory awareness of action.
These experiments reveal that the chain of causation going from our intentions to our actions is not in the intuitive direction. If we are not aware of our actions when we believe we are, then what are we perceiving? This question leads us directly into a minefield that surrounds the free-will debate. Instead of risking a philosophical firestorm, we might sidestep free will and pursue more scientifically accessible questions, such as: How does our conscious sense of free will arise from the neural activity of the brain?see link to website above for more

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