iterated learning and the cultural ratchet

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my presentation for cogsci 2009, as of 7/27

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  • 1.The Cultural Ratchet Iterated Learing and variationsResultsWhat does this mean? Iterated Learning and the Cultural Ratchet Aaron BeppuTom GrifthsDepartment of Psychology University of California BerkeleyCognitive Science, 2009Aaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet

2. The Cultural Ratchet Iterated Learing and variationsResultsWhat does this mean? Outline 1 The Cultural Ratchet2 Iterated Learing and variations3 Results4 What does this mean?Aaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet 3. The Cultural RatchetIterated Learing and variations Results What does this mean? What is the Cultural Ratchet?The process of cumulative cultural evolution requires not only creative invention but also . . . faithful social transmission that can work as a ratchet to prevent slippage backward so that the newly invented artifact or practice preserves its new and improved form at least somewhat faithfully until a further modication or improvement comes along. Michael Tomasello, The Cultural Origins of Human Cognition we do this other animals dontAaron Beppu, Tom Grifths Iterated Learning and the Cultural Ratchet 4. The Cultural RatchetIterated Learing and variations Results What does this mean? What are some existing explanations? We can try to explain this by focusing on individual teachers and learners : Were sophisticated learners (e.g. Tomasello 2001)We learn strategies and goals from each otherWe can follow each others attentionWe can faithfully reproduce behaviors we learn from others Were also good teachers (e.g. Gergeley & Csibra 2005)We understand which things are hard to learnTeachers call learners attention to the most relevant partsHuman learners benet from an enriched learningenvironmentAaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet 5. The Cultural Ratchet Iterated Learing and variations Iterated LearningResultsWhat does this mean? Modeling Cultural Evolution hypothesis hypothesis data data data... Learners are ordered into a sequence, and each agent learns from the output of the previous agent Can be used to study change in culture, (e.g. evolution of language Kirby 2001), or to examine peoples biases (e.g. Grifths, Christian & Kalish, 2006) Aaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet 6. The Cultural RatchetIterated Learing and variationsIterated Learning Results What does this mean? Analyzing Iterated LearningSpecics:Agents are Bayesian, and all have the same prior. Bayes Rule : p(h)p(d|h) p(h|d) =h p(h )p(d|h ) The data that a given agent passes on is sample according to his posterior beliefs. p(di |di1 ) = h p(di |h)p(h|di1 )The pure iterated learning model converges to the prior beliefs of its agents.Aaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet 7. The Cultural RatchetIterated Learing and variationsIterated Learning Results What does this mean? Cumulative Cultural EvolutionCumulative cultural evolution will require constantly bringing in new data from the world, in addition to some information passed from one generation to the next. We vary what kind of information is passed between agents.hypothesis hypothesis ?????? ??? ...newdata newdata Aaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet 8. The Cultural RatchetIterated Learing and variations Iterated Learning Results What does this mean? Observational Learninghypothesishypothesis... data data data ... newdatanewdataIn the Mixed Data case, each agent receives new data from the world, as well as data points sampled from the posterior distribution of the previous agent. This is similar to observational learning, achieved by observing the behavior of another. In this case, convergence is to d p(h|d )p (d ). Aaron Beppu, Tom Grifths Iterated Learning and the Cultural Ratchet 9. The Cultural RatchetIterated Learing and variationsIterated Learning Results What does this mean? Communicating Theories hypothesis hypothesistheorytheory theory ...newdata newdataIn the Posterior Passing case, each agent receives new data from the world. In addition, rather than receiving samples from the previous persons posterior distribution, each agent now receives the whole posterior distribution. Communicating theories might approximate how humans teach/learn. This chain converges to the truth. Aaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet 10. The Cultural RatchetIterated Learing and variationsIterated Learning Results What does this mean? Function learning is hard Why function learning? Strong bias towards positive linear functions; non-monotonic functions are hard (Busemeyer, Byun, DeLosh & McDaniel, 1997) The pure iterated learning case converges to a linear function (Kalish, Grifths, Lewandowsky, 2007) We can select a function that is too difcult for a single person to learn on their own, but which could plausibly be learned via cumulative cultural evolution. By using a difcult to learn parabola, we can separate out groups of people converging to the posterior from people converging to the prior. Aaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet 11. The Cultural Ratchet Iterated Learing and variationsResultsWhat does this mean? ApparatusAaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet 12. The Cultural Ratchet Iterated Learing and variationsResultsWhat does this mean? Examples from our results TrainingTestingPure iterated learning Aaron Beppu, Tom Grifths Iterated Learning and the Cultural Ratchet 13. The Cultural Ratchet Iterated Learing and variationsResultsWhat does this mean?TrainingTestingPure iterated learning Mixed data Aaron Beppu, Tom Grifths Iterated Learning and the Cultural Ratchet 14. The Cultural Ratchet Iterated Learing and variationsResultsWhat does this mean?TrainingTestingPure iterated learning Mixed data Posterior passing Aaron Beppu, Tom Grifths Iterated Learning and the Cultural Ratchet 15. The Cultural Ratchet Iterated Learing and variationsResultsWhat does this mean?0.6 pure iterated learning 0.6mixed dataposterior passing0.50.5 0.40.4 RMSERMSE0.30.3 0.20.2 0.10.1000 2 46 8 0 2 46 8Generation Generation Left : Cumulative average error (RMSE) for each chain for eachgeneration. Right : Same as left, but averaged by condition. Aaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet 16. The Cultural RatchetIterated Learing and variations Results What does this mean? What do we walk away with?Merely observing behavior of those around us isnt enough to have cumulative cultural evolution We need to communicate theories and beliefs about the world. Language is one way we can do this. This gives us an idea about the uniquely human characteristics that facilitate cultural evolution.What next? Can we adequately recover the posterior distributions from our teachers merely from observing their actions? What can we do with richer teacher/learner interactions? How can we reconcile this inference based perspective with other pressures on cultural evolution? Aaron Beppu, Tom GrifthsIterated Learning and the Cultural Ratchet

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