Re: Event Related Potentials

From: HARNAD Stevan (
Date: Sun Jun 02 1996 - 15:24:34 BST

> From: "Sharples Karen" <>
> Date: Wed, 22 May 1996 13:15:17 +0100 (BST)
> The principle use of Event Related Potentials (ERP) is to determine the
> time course of higher level processes in the human brain. ERP's occur
> as small fluctuations in Electroencephalogram (EEG) recordings in
> response to the presentation of a single stimulus, either sensory,
> motor or a mental event, eg the participant maybe asked to add two and
> two together.

How could you pick out the EEG time-locked to an event that was not
external and observable, in the way a stimulus or a response are
external? If the event was mentally adding, how would you know exactly
when it was happening? (Cf. Libet on mental timing.)

> On an EEG recording these event related fluctuations
> maybe difficult to detect as they are often masked by electrical
> signals generated by other unrelated brain activity. To 'unmask' the
> true ERP it is necessary to take recordings from repeated presentations
> of the stimulus in order for a computer to produce an averaged, much
> clearer ERP wave form. By measuring the time it takes for an ERP to
> occur after presentation of the stimulus, and by taking recordings from
> several areas of the brain, it is possible to determine the sequence
> and timing of the specific areas activated within the brain. These
> results are often analysised in accordance with visual images taken of
> the brain during presentation of the stimulus, eg through PET scans.
> The results of these studies, more often than not, are conclusive with
> those of the ERP recordings.

In agreement, not "conclusive."

> Areas of higher mental processing that
> have already been, (and still are being), investigated using this
> technique include perception and attention.

A bit narrow; this kind of reply, largely correct, will earn a 2(2),
but for a better mark, you need to put more into it, and connect it
-- kid-sib style, not just by lists or keywords -- to the themes of the

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