On timing relations between brain and world.

The questions dealt with in this special issue are fundamental to the neuroscience of consciousness. They relate, as well, to questions that date from the beginnings of philosophy. We hope this set of articles represents a significant empirical and theoretical advance on these issues, which seem to have been stuck at about the same point since the measurements by Benjamin Libet and colleagues raised the empirical and philosophical questions addressed here. These experiments have been taken to imply that perception lags about 500 ms behind events in the world and further that our sense of exactly when we make a decision to act seems to locate the intention about 500 ms after the act. If the intention follows the act, the commonsense idea that conscious intentions are responsible for our actions is wrong. The 500 ms by which our perceptions lag events in the world would put in doubt our impression that perceptual awareness corresponds to reality. For the conceptual difficulties this research creates, consider a homely example, the difficulties the timing relations make for our notions of conscious intention and action in something as simple as throwing and catching a ball. The delay between perception and reality would make it nearly impossible to use conscious monitoring of the location of the ball to catch it, since in 500 ms it would move several feet and not be where we thought we had to reach. Our idea of when to throw it will also be off and we could not consciously execute the intention to throw the ball at the right time. In this simple case the awareness of action and intention is something of a fiction, and a not very useful one. A generalization of this point challenges basic ideas about volition, responsibility, and the veridicality of our conscious representation of the world. The Sheverin, Ghannam, and Libet (2002) article also suggests that the delay of access to consciousness may involve not just neural delays but active unconscious processes. As the articles in this issue discuss, a number of solutions to these problems have been suggested. One is that consciousness really is restricted to observing alone, without any capacity for action. Another is to assume ''exotic physics'' in which backwards referral—a form of reverse time travel—takes place to correct the temporal anomalies. Another is to take a close look at the measurement of time relations themselves to see if …