Re: Donders' Subtractive Method

From: HARNAD Stevan (
Date: Thu Jun 06 1996 - 22:27:49 BST

> From: "Champion, Jim" <>
> Date: Sun, 26 May 1996 17:23:25 +0100 (BST)
> Cognition is a complex activity, and the best way to try and understand
> it is to try and break it down into its constituent parts. Donders
> subtractive method makes use of the fact that all mental operations
> take time. Although the individual stages in cognition may not be
> directly observable, they may be uncovered by the effects they have on
> the brain (time of activity, and the location). This tool for finding
> out more about cognition is best described using an example.
> When considering how we mentally process visible English words, the
> task can be divided up into four steps:
> 1) Reacting to the visual stimulus (registering the sticks and curves
> that are the shapes of the letters).
> 2) Recognising the letters of the English alphabet.
> 3) Recognising that the letters are arranged in a way that can be
> pronounced according to the rules of English.
> 4) Recalling a meaning for the word.
> If subjects are presented with visual stimuli of four varieties (each
> variety containing the features required for the four different stages)
> then the brain activity can be measured using electrodes on the scalp.
> Assuming the process to be a serial one (the stages are carried out one
> after the other) then the time for the whole operation is the sum of
> the times taken to perform each step. The time taken, for example, to
> recognise the meaning of the word can be found by subtracting the time
> to do task 3 from the time of task 4 (as shown in the diagram below)
> 1. F * q |------->| | | |
> 2. q g m |--------|------------->| | |
> 3. g a n |--------|--------------|--------------->| |
> 4. g u n |--------|--------------|----------------|------------->|
> | | | | |
> t=0 Recognition Pronounceable Meaning
> of letters word
> This is the essence of Donders subtractive method. It is not restricted
> to the timing of cognition (finding out the "when?") - it can be used
> in finding out more about "where" cognition takes place. The parts of
> the brain involved in assigning meaning to a word (to use the above
> example) can be seen by subtracting a brain acivity image of someone
> performing task 3 from a task 4 scan. You can infer from this that what
> remained after subtraction was the part of the brain involved in
> assigning meaning to a word.

Ladies and Gentlemen, the above reply was an a (a 70).

To pump it a bit more safely into the A-zone, describe Sternberg's
more recent kid of work and relate it to the WHEN/WHERE:HOW question.

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