Re: Donders' Subtractive Method

From: HARNAD Stevan (
Date: Tue Jun 04 1996 - 10:39:37 BST

> From: "Dale, Becky" <>
> Date: Fri, 24 May 1996 10:16:12 gmt
> Donder's work attempts to describe the processes going on in the
> mind, by analyzing cognitive activity into separate stages. Until
> Donder's work, many scientists had assumed that the mental operations
> involved in responding to a stimulus occurred instantaneously.
> Donder was particularly interested in "timing the mind" and used a
> subtraction technique to time the different mental processes that the
> brain goes through when faced with different tasks.
> Donders performed experiments using reaction time tasks in 1868. His
> was the first attempt to analyze and measure the component processes
> of a simple task. He used three tasks :
> 1. a simple reaction time task - e.g. you are seated in front of a
> panel that contains a light bulb and a response button. When
> the light comes on, you must press the button.
> 2. a discrimination reaction time task - e.g. you are seated in front
> of a panel with 5 light bulbs and one reponse button. When the
> target light goes on you must press the button - but not if the 4
> other lights come on.
> 3. a choice reaction time task - e.g. you are seated in front of 5
> light bulbs, each with their own button. You must press the
> button corresponding to the appropriate light.
> Donder's then predicted the kinds of processes that might be involved
> in each task :
> 1. A simple time task would require perception and motor stages -
> time to receive and then execute the stimulus.
> 2. A discrimination reaction time task requires the above plus a
> discrimination stage.
> 3. A choice reaction time task requires all of the above -
> time to receive and execute the stimulus, and discriminate plus
> a choice stage.
> As expected, simple tasks take the shortest amount of time, followed
> by discrimination tasks, with choice tasks taking the longest amount
> of time. Donders calculated the time required for each stage by
> using a subtraction technique :
> perception and motor time - time required for simple task
> discrimination time - time for discrimination task minus simple task
> choice time - time for choice task minus discrimination time.
> This demonstrated a simple conclusion - more stages should require
> more time.

For a higher B or an A, discuss also Sternberg's use of the method,
as described by Posner, and the modern uses of it in brain localisation.
Also, don't forget the question of whether one can learn HOW from

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