A hat trick for decay

[Erik M. Altmann]

Tower of Hanoi, task switching, and the Stroop effect...

Erik.


Altmann, E. M. & Trafton, J. G. (in press).  Memory for goals: An 
activation-based model.  Cognitive Science.

Goal-directed cognition is often discussed in terms of specialized 
memory structures like the "goal stack." The goal-activation model 
presented here analyzes goal-directed cognition in terms of the 
general memory constructs of activation and associative priming. The 
model embodies three predictive constraints: (1) the interference 
level, which arises from residual memory for old goals; (1) the 
strengthening constraint, which makes predictions about time to 
encode a new goal; and (3) the priming constraint, which makes 
predictions about the role of cues in retrieving pending goals. These 
constraints are formulated algebraically and are tested through 
simulation of latency and error data from the Tower of Hanoi, a 
means-ends puzzle that depends heavily on suspension and resumption 
of goals. Implications of the model for understanding intention 
superiority, post-completion error, and effects of task interruption 
are discussed.  (http://www.msu.edu/~ema/goals)


Altmann, E. M. & Gray, W. D.  (in press). Forgetting to remember: The 
functional relationship of decay and interference.  Psychological 
Science.

Functional decay theory proposes that decay and interference, 
historically viewed as competing accounts of forgetting, are instead 
functionally related. The theory posits (1) that when an attribute 
must be updated frequently in memory, its current value decays to 
prevent interference with later values, and (2) the decay rate adapts 
to the rate of memory updates. Behavioral predictions of the theory 
were tested in a task-switching paradigm in which memory for the 
current task had to be updated every few seconds, hundreds of times. 
RT and error both increased gradually between updates, reflecting 
decay of memory for the current task. This performance decline was 
slower when updates were less frequent, reflecting a decrease in the 
decay rate following a decrease in the update rate. A candidate 
mechanism for controlled decay is proposed, the data are reconciled 
with practice effects, and implications are discussed for models of 
executive control.  (http://www.msu.edu/~ema/forget)


Altmann, E. M. & Davidson, D. J. (2001).  An integrative approach to 
Stroop: Combining a language model and a unified cognitive theory. 
To appear in Proceedings of the twenty second annual conference of 
the Cognitive Science Society (Edinburgh, August 2001).

The rich empirical puzzle of the Stroop effect has traditionally been 
approached with narrowly focused and somewhat atheoretical models. A 
recent exception is a simulation model based on the WEAVER++ language 
theory. The present model, WACT, combines components of WEAVER++ with 
the memory and control processes of the ACT-R cognitive theory. WACT 
accounts for the time course of inhibition from incongruent word 
distractors, facilitation from congruent word distractors, the lack 
of effect of color distractors, and the semantic gradient in 
inhibition. WACT goes beyond WEAVER++ to account for Stroop 
performance errors as well as latencies, and its implementation in a 
unified cognitive theory opens doors to broader coverage of Stroop 
phenomena than standalone models are likely to attain. Documented and 
executable code for WACT is available for inspection and comment at 
www.msu.edu/~ema/stroop.  (http://www.msu.edu/~ema/stroop)
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Erik M. Altmann
Department of Psychology
Michigan State University
East Lansing, MI  48824
517-353-4406 (voice)
517-353-1652 (fax)
ema at msu.edu
http://www.msu.edu/~ema
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