contributed model

[Scott Peterson]

I would like to announce that a new model has been added to the ACT-R 
Contributed Models page (http://act.psy.cmu.edu/ACT/ftp/contributions).  
This is an ACT-R 3.0 model of the visual enumeration task that 
demonstrates emergence of the subitizing phenomenon.  The model is fully 
described in a paper I have written with Tony Simon titled 
"Computational Evidence for the Subitizing Phenomenon as an Emergent 
Property of the Human Cognitive Architecture," which is in the queue for 
publication in Cognitive Science.  The abstract for our paper is 
appended below.  An earlier version of the model (Peterson, Simon, & 
Morton, 1997) was published in the Proceedings of the Cognitive Science 
Society.  Your comments are welcomed and appreciated; we hope to make 
many improvements as we upgrade the model for ACT-R version 4.

Abstract
--------
A computational modeling approach was used to test one possible 
explanation for the limited capacity of the subitizing phenomenon.  Most 
existing models of this phenomenon associate the subitizing span with an 
assumed structural limitation of the human information processing 
system.  In contrast, we show how this limit might emerge as the 
combinatorics of the space of enumeration problems interacts with the 
human cognitive architecture in the context of an enumeration task.  
Subitizing-like  behavior was generated in two different models of 
enumeration, one based on the ACT-R cognitive architecture and the other 
based on the principles of parallel distributed processing (PDP).  Our 
results provide good qualitative fits to results obtained in a variety 
of empirical studies.

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Scott Peterson
School of Psychology
Georgia Institute of Technology
Atlanta, GA  30332-0170

phone:  (404) 894-7314
e-mail: gt4747c at prism.gatech.edu
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