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Accordingly the evidence that accumulates during a

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Unformatted text preview: nt (this quantity will tend to overestimate the evidence from weak stimuli and underestimate the evidence from strong stimuli). Accordingly, the evidence that accumulates during a trial can be interpreted as a fraction of this quantity and thus in units of natural bans—even when the scaling between the decision variable and the weight of evidence is not known (e.g., if the brain does not know the shapes of the sensory response distributions). 1 is a constant that represents the barrier height f h . For two mutually exclusive hypotheses 1 Pr(h |m) or, equivalently, Pr(h ) 1 nd assuming the weight of evidence is exin bans, this rearranges to: Review 303 Pr(h |m) 1 1 . 10 (4) LIP neurons? 4 indicates that the posterior probability of h 1 only on the value of the barrier, B, and not on ular samples of evidence, m, encountered. In rds, as long as the weight of evidence reaches he probability that h is correct is a fixed value. Figure 2. Decision Model 1 logarithm of the ratio of the equal to the between x and y. Solving for the weight of evidence (in nically related obabilities. Incommon variance, this case, for a given bans)are the versus h yields: weightfor h means of 2 is the units of natural 1966). Briefly, 1 and 0 1 0 (e.g., the stopping pointExperimentalsEvidence in Banburismus): the covariance Turing’s and y, of x Weight respectively, under h1, and i is case, a rate Evidence Pr(x For Neurophysiology: Banburismus |h ) the Brain s from a pair of sensory neurons whenfor or h1 is true, asof evidence 1(in h0evidence indicated.,y in between x Solving thought of as and y. weight of the weight log Pr(h1|m) neuron that prefers upward motion. The lower curve would tion-selective ofweight of evidence versus h (3) units natural bans) for h1 B 0 yields:Pr(x,y|h0) lushconditions Pr( 0|m) fers downward motion. Here we make the simplifying assumption that the value but can d equal variances ( 2 ). Note that other forms x,y|h distribution, including of the ) 1 (1 Pr( 0) 1 · · (x y) (6) adlen, 2001). thatpanel on the rightlog shows Turing’s weight constant The...
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This note was uploaded on 09/15/2011 for the course COGS 1 taught by Professor Lewis during the Spring '08 term at UCSD.

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