[ACT-R-users] Baseline activation strengthening and decay

[Niels Taatgen]

On 15 Feb 2006, at 22:30, ben.willems at faa.gov wrote:

>
> Please excuse my ignorance, but I am working on the other side of  
> the cognitive modelers.  That is, I run simulations using human  
> experts in Air Traffic Control and create records of human activity  
> quite similar to what you call a simulation trace.  Ignoring for a  
> moment that the visual system may be able to process several things  
> within the foveal area simultaneously, how would you interpret a  
> single 1500msec fixation on an object in terms of number of  
> retrievals?  Does that include a single retrieval or does it  
> involve cyclic retrievals with a time constant of 50msec for the  
> retrieval and another 50msec to push the chunk to the goal stack?   
> Or do you assume that initially there is a retrieval followed by  
> maintaining activation at a faster cycle time?  Do you assume that  
> activation strengthening occurs independent of the perceptual or  
> motor event that triggers activation of the chunk?  E.g., seeing an  
> aircraft representation vs. listening to a reference to an aircraft  
> or typing in an identifier for that aircraft.


Something to keep in mind here is that the perception of a stimulus  
does not mean anything is retrieved from memory. Memory retrieval may  
well be a result of perceiving something, but in the case of a  
complex aircraft icon that is not necessarily the case. 1500 ms is  
pretty long for an eye-fixation (ACT-R's default assumption is that a  
stimulus can be perceived in 85ms), so either it is a really complex  
stimulus with multiple features to attend to, or indeed some  
reasoning on the basis of that fixation is going on, and keeping the  
eyes fixated on the stimulus keeps the information active. This may  
involve memory retrieval, i.e., retrieving previous interactions with  
that particular aircraft, but also possibly planning steps which do  
not necessarily involve retrieval.
Retrieval time is very variable: retrieving general knowledge about  
for example an airplane time should be pretty fast (<100ms), or might  
be compiled into productions rules, but episodic memory retrieval  
(what did I tell this guy to do 10 minutes ago) is potentially much  
slower, and could take up to 1500ms.

===================================================
Niels Taatgen - Carnegie Mellon University, Psychology, BH 345E
Also (but not now): University of Groningen, Artificial Intelligence
web: http://www.ai.rug.nl/~niels     email: taatgen at cmu.edu
Telephone: +1 412-268-2815
===================================================

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