[lingtalks] Angela Yu Talk, Monday Jan. 28th 12pm

[Steven Ford]

The UCSD Department of Cognitive Science is pleased to announce a talk by

Angela Yu Ph.D.


Center for the Study of Brain, Mind, and Behavior

Princeton University


Monday, January 28, 2008 at 12pm
Cognitive Science Building, room 003


"Sequential Effects: Irrational Superstition or Sophisticated Computation?"

Just as visual illusions hint at the principles and mechanisms underlying 
natural visual processing, "cognitive illusions" provide similar insight 
into the computations underlying decision-making.  In a variety of 
behavioral tasks, subjects exhibit a sequential effect: they respond more 
rapidly and accurately to a stimulus if it reinforces a local pattern in 
stimulus history, such as a string of repetitions or alternations, compared 
to when it violates such a pattern. This is often the case even if the 
local trends arise by chance in the context of a randomized design, such 
that stimulus history has no predictive value. In this work, we use a 
normative Bayesian framework to show that such idiosyncrasies may reflect 
the engagement of mechanisms critical for changing environments, though not 
necessarily appropriate for the randomized 2AFC task. We show that prior 
belief in non-stationarity can induce experimentally observed sequential 
effects in an otherwise Bayes-optimal algorithm. The Bayesian algorithm is 
shown to be well approximated by linear-exponential filtering of past 
observations, something also observed in human and monkey behavior.  We 
show that linear-exponential filtering can be implemented by standard leaky 
integrating neuronal dynamics, and that optimal parameters of the process 
can be learned without explicit representation of probabilities.  Our work 
provides a normative account of how decision-making should adapt to a 
changing environment, a functional theory for WHY subjects exponentially 
discount the past, as well as a principled hypothesis of how neurons can
implement the necessary computations.
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