Re: Categorical Perception

From: HARNAD Stevan (
Date: Fri Jun 07 1996 - 21:58:54 BST

> Date: Mon, 27 May 1996 16:28:03 +0100 (BST)
> From: "Nethercott, C.T." <>
> In aquiring a category we learn to label or identify positive and
> negative instances from a sample of non-definable unknowns.

Nondefinable unknowns? Why? If I'm sorting mushrooms I'm sorting
mushrooms; the only thing that I might not know is the definition of the
right features.

> Two types of
> representation are built up in this learning by aquaintance;1) an
> iconic representation that subserves each category and 2) a feature
> filter which picks out invariant information allowing us to categorise
> the instances correctly.This categorical representation is associated
> with the category name which is held in the symbolic representational
> system.It has been suggested that connectionism is the mechanism that
> associates the invariants between categorisation and naming.

Unfortunately, this just echoes one model for categorical perception
(mine) but it still does not define what it is.

> In the case of colour categorical perception, where differences in
> wavelegnth within the range we know as yellow are percieved as being
> less than equal sized differences that cross the border between
> "yellow" and "green".

Lurking in there is the definition of categorical perception, which
occurs when equal-sized physical differences are not equal-sized
psychologically, depending on whether they are differences within or
between categories: Within-category differences are compressed and
between-category differences are expanded. The effect is usually
associated with a continuous dimension, such as the wave length of

> Our ability to interperate the physical world
> directly has been "warped",with some regions being compressed
> (yellow-yellow differences) and some being stretched
> out(yellow-green).The effect of the category boundry has therefore been
> shown to be not only Quantitative but also Qualitive.Most of the
> warping seems to be done by evolution,probably being an inborn property
> of our sensory processing systems.When a child is born into the
> "blooming buzzing confusion",it can distinguish a yellow from a
> green,but without knowing that this is being done, as the connection
> with the symbolic "niche" for the colour blue has not been
> strengthened.

You are merely repeating material you read in the chapter, but you are
not making sense of it, and not answering the question.

> Categorical perception is intrinsicaly involved in differentiation
> processes such as pattern recognition,the ability to do of which is the
> basis of the"larger scale" cognitive thought processes.

You have obviously taken the trouble to do some reading for this, but
you have to sort out more carefully the concepts you get from the
reading. Don't just repeat the words; and make sure you answer the
question that is being asked, so kid-sib comes out knowing the answer
too; here, he would have no idea what categorical perception was from
what you have written.

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