Negative associations and book news

[Christian J Lebiere]

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Luis Botelho asked (in a message that was sent to the act-r-users mailing list but could not be distributed properly):


> Hi all,

> I would like to know if associations between nodes in ACT-R can take

> negative strengths. If so, how do they appear. I mean, what mechanism is

> responsible for associations with negative strength?

> 

> -- Luis

> -----------------------------

> Lums Miguel Botelho, PhD

> Departamento de Cijncias e Tecnologias da Informagco

> ISCTE: Instituto Superior de Cijncias do Trabalho e da Empresa

> Av. das Forgas Armadas, Edifmcio ISCTE, 2600, Lisboa, Portugal

> Tel: 351-1-7903099

> Fax: 351-1-7964710


Negative associations between chunks can of course be set, but they can also be learned.  The Posterior Strength Equation (p. 130 of The Atomic Components of Thought - ACT) specifies that associations are equal to the logarithm of a frequency ratio.  Since that ratio can be less than 1.0, its logarithm, and therefore the association, can be negative.  If the ratio becomes very small, due to the logarithm form the association will in fact become unboundedly negative, effectively acting as an inhibiting connection.  That point turns out to be crucial to the lifetime simulation of cognitive arithmetic presented in Chapter 9 of ACT.


As you may have gathered from the previous paragraph, the new book about the ACT-R theory, The Atomic Components of Thought, has just been published by Lawrence Erlbaum Associates.  It is in fact Erlbaum's special web offer of the month, so order your copy now to take advantage of the discount (except of course workshop attendees who will receive a complimentary copy).  For ordering information, you can find a pointer to Erlbaum's web page on the ACT-R home page (http://act.psy.cmu.edu) or you can go directly to http://www.erlbaum.com/spot.htm


Happy reading!


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