Re: Libet: Mental Timing

From: Stevan Harnad (
Date: Mon Jan 22 1996 - 19:23:49 GMT

> Date: Mon, 22 Jan 1996 13:40:10 GMT
> From: nicholas bollons <>
> Subject: Libet: Mental Timing
> This is only a quick comment on the seminar on Friday when we discussed
> the relationship between the potential of firing neurons before the
> subject had consciouslly willed it.
> Unfortunately my Hypothesis was destroyed the reasoning that to create
> this potential, the subject has to predict that he/she is going to
> elicit a willing of a response in the first place ie the prediction of
> a prediction.
> Using the clock analogy there would have to be something starting at 12
> 0'Clock in order to create the potential at 2 leading to consciouslly
> aware of carrying out a task (3 O'Clock) to motor movement at 6
> O'Clock.
> (The fact that neurons fire even before the brain is consciously aware
> that it is to carry out a task)
> But if you see it from the context of the patient being tested in a
> controlled environment then they are aware that in a certain time frame
> (12 O'Clock AM to 12 O'Clock PM they are going to make somesort of
> pre-defined response/movement. A conscious prediction of a pre-defined
> outcome may cause the un-conscious prediction (potential of neurons to
> fire) before the next conscious process of willing the movement.
> The idea of knowing what to do in a certain situation will increase the
> speed (by potential neuron firing) to react in that situation.
> Not a particularly in-depth explanation to this strange phenomena but
> may be a possible one?
> What do you think? NIK

This basically interprets the motor readiness potential not as a
movement trigger, but as a generalised anticipation of triggering the
movement. It's possible, but unlikely, since the Readiness potential is
usually observed in tasks in which there is no anticipation time:

An event-related potential is time-locked to an event. Most of the ones
that have been studies have been time locked to an input, but the
readiness potential is time-locked to an output, and it always precedes

In a way, rescaling it all to speak in terms of hours rather than
milliseconds perhaps confuses more than it clarifies: It does let you
sort the compnents out conceptually, but it disguises the fact that
these things all happen very quickly indeed!

Have a look at the Foundations Skywriting, as well as last year's
Current Debates Skywriting, for more on Libet and Mental Timing.

Chrs, S

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