[Abstract Title]. - Society for Neuroscience

ACC projects to locus coeruleus (LC), an area that sends diffuse noradrenergic projections
throughout the brain and is thought to influence pupil diameter. To test for a role of the LC in
belief updating we developed an isoluminent version of the task and measured pupil diameter
after each presentation of new information. We found that pupillary response correlated with
relative errors made by subjects. This pupillary response was also predictive of the extent to
which subjects would use new information in a subsequent opportunity to update their belief.
These data suggest that human subjects approximate optimal belief updating by using error size
as a heuristic for volatility, and that a reflection of this measurement is seen in the pupillary
response. We propose that LC may mediate an increased weighting of sensory information
relative to previously established beliefs in response to volatile changes.
Disclosures: M.R. Nassar, None; J.I. Gold, None; B. Heasly, None.
Poster
289. Human Decision Making
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 289.4/RR40
Topic: F.01.g. Decision making and reasoning
Support: AFRL Grant FA9550-07-1-0537
Title: Integrating reward and stimulus information in a perceptual decision making task
Authors: *J. GAO, R. TORTELL, J. L. MCCLELLAND;
Dept. of Psychology, Stanford Univ., Stanford, CA
Abstract: When observers must identify ambiguous stimuli, they adjust their decision toward
the alternative offering a larger reward. Working in the context of dynamical models of decision
making (Ratcliff, R., 1978, Psychological Review; Usher, M. & McClelland, J. L., 2001,
Psychological Review), we consider how this reward bias effect might be incorporated. Previous
investigations have considered the possibility that reward may affect the starting point of an
evidence accumulation process, or that it may act like a constant input to this process. However,
neither of these policies is necessarily optimal, especially if the time that will be available for
evidence accumulation is uncertain. We investigated this situation. Human observers saw a
rectangle offset 1, 3, or 5 pixels to the left or right of fixation, and were required to indicate the
direction of shift within 250 msec of a response signal that could occur at any one of 10 different
lags (0 to 2000 msec) relative to stimulus onset. 750 msec prior to stimulus onset, a cue indicated
which response would, if correct, receive a larger reward (2 points vs 1 point). Previous research
with similar stimuli has shown that accuracy identifying the direction of shift is at chance at early