Saturday, February 16, 2013
Mele was right, presaged Schurger et al's confirmation
In looking over Mele's response to Libet's work in Conscious Will and Responsibility (23-33), he wonders what happens in that 300 ms during the onset of the readiness potential (RP I) before the activation of the motor response to move (RP II). Is RP I a reliable predictor of the movement? As of his writing it was not known (27) but he guessed not. And guess what? That is exactly what Schurger et al. explored. Recall from their paper they differentiated the onset of the RP (RP I) with the neural decision to move (RP II). This gap is the very basis for the whole specious argument against conscious intent to move. But not only does RP II coincide with the awareness of intention to move, RP I's causal role is incidental to the movement. How can this not be any clearer unless you have serious confirmation bias? Unless of course Schurger et al are the ones with confirmation bias and designed their experiment to prove it? Uh huh... They said:
“It is widely assumed that the neural decision to move coincides with the onset of the RP (which, given its slow nonlinear character, is difficult to pinpoint) (11). Our model challenges that assumption by suggesting that the 'neural decision to move now' might come very late in the time course of the RP.
“Thus, according to our model, uncued movements in a task like Libet’s tend to be preceded by a gradual increase in neural activity [measured at the scalp (8, 9) or the single-neuron level (16)] whose causal role is incidental—not directed (consciously orotherwise) at producing a movement.
“Given that such spontaneous fluctuations are always present (55), even when we are not even thinking about moving, is it reasonable to conclude that the brain “decided” to move 2 s before the threshold crossing? We suggest reserving the term “decision” to the commitment to move achieved once neural activity (spontaneous or goal directed) crosses a specific threshold. Libet et al.’s (9) findings were surprising because they suggested that the neural decision to move happens well before we are aware of the urge to move, by 1/2 s or more. According to our model, this conclusion is unfounded. The reason we do not experience the urge to move as having happened earlier than about 200 ms before movement onset is simply because, at that time, the neural decision to move (crossing the decision threshold) has not yet been made. A very similar fluctuation in neuronal firing could equally well, at some other time, have not preceded a movement.
“Finally, although our model is silent with respect to the urge to move and its temporal relation to motor decisions, it helps dissolve another puzzling question that seemed to arise from Libet’s paradigm. Libet himself found that subjects were able to estimate the time of a tactile sensory decision in relation to a quickly rotating clock dial with only about 50 ms of error on average (9). Why then should there be such a long and variable gap between the time of a motor decision and the subjective estimate of the time of the motor decision, whereas no such gap exists for sensory decisions? In fact, this question arises only when we assume that the motor decision coincides in time with the onset of the RP. We have argued that this need not be the case and that the neural decision to move may come much closer in time to the movement itself (e.g., −150 ms). We propose that the neural decision to move coincides in time with average subjective estimates of the time of awareness of intention to move (9, 11) and that the brain produces a reasonably accurate estimate of the time of its movement-causing decision events.”