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The Cultural Ratchet
      Iterated Learing and variations
                             Results
               What does t...
The Cultural Ratchet
                Iterated Learing and variations
                                       Results
      ...
The Cultural Ratchet
               Iterated Learing and variations
                                      Results
        ...
The Cultural Ratchet
               Iterated Learing and variations
                                      Results
        ...
The Cultural Ratchet
                Iterated Learing and variations
                                                  Ite...
The Cultural Ratchet
               Iterated Learing and variations
                                                   Ite...
The Cultural Ratchet
               Iterated Learing and variations
                                                 Itera...
The Cultural Ratchet
               Iterated Learing and variations
                                                      ...
The Cultural Ratchet
                 Iterated Learing and variations
                                                   I...
The Cultural Ratchet
               Iterated Learing and variations
                                                 Itera...
The Cultural Ratchet
            Iterated Learing and variations
                                   Results
              ...
The Cultural Ratchet
                            Iterated Learing and variations
                                         ...
The Cultural Ratchet
                          Iterated Learing and variations
                                           ...
The Cultural Ratchet
                          Iterated Learing and variations
                                           ...
The Cultural Ratchet
                        Iterated Learing and variations
                                             ...
The Cultural Ratchet
               Iterated Learing and variations
                                      Results
        ...
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Iterated learning and the Cultural Ratchet

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my presentation for cogsci 2009, as of 7/27

Published in: Technology
  • It appears the iterate learning example model is an iteration function or orbit. It doesn't seem to portend toward a new step in evolution, merely maintenance of the status quo or a ratchet step along a given progression of the system. It would seem absent outside stimuli there is no need to progress toward a new step merely a ratchet step that tends toward stagnation. While it makes for a smooth system it would seem that it doesn't allow without for the possibility that the system is being directed necessarily toward progress so much as responding to the easiest path through a given set of variables which may be subject to change due to variables in the greater ecological system in which human culture system functions. The iterate function also tends to be a measure of specialization rigidity in a system that tends to make it less capable of adjusting to major changes in its environment. The thing that seems to be absent from the model is the storehouse of earlier experiences and the solutions to them, much like the seeming random RNA in the cell nucleus. I believe in human culture system this is called the library or data bank.
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  • Wow. You mean this idea I had has real application. I have long suspected that all systems are governed by these two principles including evolution and the origin of the universe.the two effects apply to all systems and invariably dictate progress away from a finite origin or base point of 0+ such that any subsequent event behaves as a ratchet step limiting the base point of the next event and that the cumulative effect (which seems to correspond to a Fibonacci series tends to define the rules that govern any system that evolves from the original progression.
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Iterated learning and the Cultural Ratchet

  1. 1. The Cultural Ratchet Iterated Learing and variations Results What does this mean? Iterated Learning and the Cultural Ratchet Aaron Beppu Tom Griffiths Department of Psychology University of California Berkeley Cognitive Science, 2009 Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  2. 2. The Cultural Ratchet Iterated Learing and variations Results What does this mean? Outline 1 The Cultural Ratchet 2 Iterated Learing and variations 3 Results 4 What does this mean? Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  3. 3. The Cultural Ratchet Iterated 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 modification or improvement comes along. – Michael Tomasello, The Cultural Origins of Human Cognition we do this other animals don’t Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  4. 4. The Cultural Ratchet Iterated 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 : We’re sophisticated learners (e.g. Tomasello 2001) We learn strategies and goals from each other We can follow each others attention We can faithfully reproduce behaviors we learn from others We’re also good teachers (e.g. Gergeley & Csibra 2005) We understand which things are hard to learn Teachers call learner’s attention to the most relevant parts Human learners benefit from an enriched learning environment Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  5. 5. The Cultural Ratchet Iterated Learing and variations Iterated Learning Results What 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 people’s biases (e.g. Griffiths, Christian & Kalish, 2006) Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  6. 6. The Cultural Ratchet Iterated Learing and variations Iterated Learning Results What does this mean? Analyzing Iterated Learning Specifics: 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 |di−1 ) = h p(di |h)p(h|di−1 ) The pure iterated learning model converges to the prior beliefs of its agents. Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  7. 7. The Cultural Ratchet Iterated Learing and variations Iterated Learning Results What does this mean? Cumulative Cultural Evolution Cumulative 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 ??? ??? ??? ... new data new data Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  8. 8. The Cultural Ratchet Iterated Learing and variations Iterated Learning Results What does this mean? Observational Learning hypothesis hypothesis ... data data data ... new data new data In 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 Griffiths Iterated Learning and the Cultural Ratchet
  9. 9. The Cultural Ratchet Iterated Learing and variations Iterated Learning Results What does this mean? Communicating Theories hypothesis hypothesis theory theory theory ... new data new data In the “Posterior Passing” case, each agent receives new data from the world. In addition, rather than receiving samples from the previous person’s 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 Griffiths Iterated Learning and the Cultural Ratchet
  10. 10. The Cultural Ratchet Iterated Learing and variations Iterated 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, Griffiths, Lewandowsky, 2007) We can select a function that is too difficult for a single person to learn on their own, but which could plausibly be learned via cumulative cultural evolution. By using a difficult to learn parabola, we can separate out groups of people converging to the posterior from people converging to the prior. Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  11. 11. The Cultural Ratchet Iterated Learing and variations Results What does this mean? Apparatus Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  12. 12. The Cultural Ratchet Iterated Learing and variations Results What does this mean? Examples from our results Training Testing Pure iterated learning Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  13. 13. The Cultural Ratchet Iterated Learing and variations Results What does this mean? Training Testing Pure iterated learning Mixed data Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  14. 14. The Cultural Ratchet Iterated Learing and variations Results What does this mean? Training Testing Pure iterated learning Mixed data Posterior passing Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  15. 15. The Cultural Ratchet Iterated Learing and variations Results What does this mean? 0.6 pure iterated learning 0.6 mixed data posterior passing 0.5 0.5 0.4 0.4 RMSE RMSE 0.3 0.3 0.2 0.2 0.1 0.1 0 0 0 2 4 6 8 0 2 4 6 8 Generation Generation Left : Cumulative average error (RMSE) for each chain for each generation. Right : Same as left, but averaged by condition. Aaron Beppu, Tom Griffiths Iterated Learning and the Cultural Ratchet
  16. 16. The Cultural Ratchet Iterated Learing and variations Results What does this mean? What do we walk away with? Merely observing behavior of those around us isn’t 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 Griffiths Iterated Learning and the Cultural Ratchet

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