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Kobe Bryant LA Lakers 31.6 PPG (2006-7). Chris Bosh Toronto Raptors 26.3 PPG (2006-7). 3P attempts: 398 (23%) 2P attempts: 1,359 (77%). 35 (3%) 1,059 (97%). 3P success: 34% 2P success : 50%. 34% 50%. Decision making in basketball.
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Kobe Bryant LA Lakers 31.6 PPG (2006-7) Chris Bosh Toronto Raptors 26.3 PPG (2006-7) 3P attempts: 398 (23%) 2P attempts: 1,359 (77%) 35 (3%) 1,059 (97%) 3P success:34% 2P success : 50% 34% 50% Decision making in basketball • 2-point shot: easier, fewer points • 3-point shot: more difficult, more points
The matching law NBA best 100 players (2006-2007) Bryant N2,3 = # of 2,3 points shots I2,3= # 2,3 points earned Bosh
The matching law 1 1 Herrnstein, JEAB, 1961
The matching law Sugrue, Corrado & Newsome, Science,2004
The matching law Gallistel et al., unpublished
The matching law Nj = # of attempts at alternative j investment inj Ij = # of points earned from alternative j income fromj equal returns
The matching law is very general. It is found in many animal types as well as humans, under very different experimental conditions.
Example: addiction model E[R|A=drugs] freq [drugs] 1–freq [work] after Herrnstein and Prelec, J Econ Perspect, 1991
matching Example: addiction model E[R|A=drugs] E[R|A=work] freq [drugs] 1–freq [work] after Herrnstein and Prelec, J Econ Perspect, 1991
Example: addiction model E[R|A=drugs] E[R|A=work] E[R] maximizing matching freq [drugs] 1–freq [work] after Herrnstein and Prelec, J Econ Perspect, 1991
Question: What is the neural basis of the matching law?
0.4 μm It is generally believed that learning is due to changes in the efficacy of synapses Kennedy, Science, 2000
Question: What is the neural basis of the matching law? Question: What microscopic plasticity rules underlie adaptation to matching behavior?
Question: What is the neural basis of the matching law? Hypothesis: the matching law results from synaptic plasticity that is driven by the covariance of reward and neural activity
Question: What is the neural basis of the matching law? Hypothesis: the matching law results from synaptic plasticity that is driven by the covariance of reward and neural activity
Covariance is a measure of dependence • two random variables X, Y • covariance: • correlation coefficient:
Hypothesis:the matching law results from synaptic plasticity that is driven by the covarianceof reward and neural activity
Synaptic plasticity • Local signals affect synaptic efficacies. Popular theory: Hebbain plasticity • Global signals affect synaptic efficacies. Popular theory: dopamine gates Hebbian plasticity (Wickens)
Synaptic plasticity • Local signals affect synaptic efficacies. Popular theory: Hebbain plasticity • Global signals affect synaptic efficacies. Popular theory: dopamine gates Hebbian plasticity (Wickens) • Popular theory: dopamine codes the mismatch between reward and expected reward (Schultz)
Average trajectory approximation Synaptic plasticity
Covariance-based plasticity rules N=Spre , N=Spost , N=SpreSpost Average trajectory approximation:
Hypothesis: covariance-based synaptic plasticity The matching law outline: Stationary state of covariance-based plasticity The matching law
Assumptions neurons N1 1. E[N|A=i] ≠E[N|A≠i] 2. The dependence of the reward R on neural activity N is through the action A. action reward N2 A R N3 N5 N4 hidden variables
Theorem Suppose that Assumptions 1 and 2 are satisfied The matching law
neuron action reward N A R Intuition • In general R depends on A • If, as a result of the policy used by the subject, R becomes independent of A then R also becomes independent of N
Summary Hypothesis: Covariance based synaptic plasticity underlies the matching law Theorem: The matching law Loewenstein & Seung, PNAS, 2006 Loewenstein, PLoS Comp Biol, 2008 Disclaimer: There are learning rules that converge to Cov[R,N]=0 that are not driven by covariance