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SUMMARY:Seeing Patterns in Randomness: Irrational Superstition or Adaptive
  Behavior? - Dr Angela Yu (Princeton)
DTSTART:20080612T150000Z
DTEND:20080612T160000Z
UID:TALK12351@talks.cam.ac.uk
CONTACT:Zoubin Ghahramani
DESCRIPTION:Just as visual illusions reveal principles and mechanisms unde
 rlying\nnatural visual processing\, "cognitive illusions" can provide simi
 lar\ninsight into the computations underlying decision-making.  In a varie
 ty\nof behavioral tasks involving randomized sequences of stimuli\, subjec
 ts\nexhibit an odd "sequential effect": their responses are facilitated by
 \nchance runs of repetitions and alternations in stimulus identity\, and\n
 are hampered by violations of such transient local patterns.  Such\nbehavi
 or is sub-optimal in the context of the task\, since these\ntransient patt
 erns are spurious and have no true predictive power of\nfuture stimuli.  W
 e hypothesize that this apparently superstitious\nbehavior may in fact ref
 lect the engagement of adaptive mechanisms that\nare critical for respondi
 ng to environments containing statistics that\nchange over time.  We use a
  normative Bayesian framework to show that a\nprior belief in changing sta
 tistics is sufficient to produce the type of\nsequential effects observed 
 in subjects' behavior.  The Bayesian\nalgorithm is shown to have an approx
 imately linear dependence on the\nhistory of past observations\, where the
  dependence decays exponentially\ninto the past\; this exponential decay i
 s also apparent in human and\nmonkey behavior\, as we found by re-analyzin
 g data from published\nstudies.  We show that the necessary computations c
 an be implemented by\nneurons with dynamics previously thought to underlie
  a variety of\nsensory processing and decision making computations.  Our w
 ork provides\na unifying account of how decision-making SHOULD adapt to a 
 changing\nenvironment\, a functional theory for WHY subjects exponentially
  discount\nthe past\, as well as a principled hypothesis of HOW neurons ca
 n\nimplement the necessary computations.\n
LOCATION:Engineering Department\, CBL Room 438
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