Xref: utzoo comp.ai:2171 sci.lang:2990 Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!uflorida!gatech!udel!princeton!mind!harnad From: harnad@mind.UUCP (Stevan Harnad) Newsgroups: comp.ai,sci.lang Subject: Pinker & Prince Reply (short version) Keywords: connectionism, symbolic rules, learnability, past tense formation Message-ID: <2816@mind.UUCP> Date: 1 Sep 88 19:05:36 GMT Followup-To: comp.ai Organization: Cognitive Science, Princeton University Lines: 93 Posted for Pinker & Prince by S. Harnad ----------------------------------------------------------- From: Steve Pinker Site: MIT Center for Cognitive Science Subject: answers to S. Harnad's questions, short version Alluding to our paper "On Language and Connectionism: Analysis of a PDP model of language acquisition", Stevan Harnad has posted a list of questions and observations as a 'challenge' to us. His remarks owe more to the general ambience of the connectionism / symbol-processing debate than to the actual text of our paper, in which the questions are already answered. We urge those interested in these issues to read the paper or the nutshell version published in Trends in Neurosciences, either of which may be obtained from Prince (address below). In this note we briefly answer Harnad's three questions. In another longer message to follow, we direct an open letter to Harnad which justifies the answers and goes over the issues he raises in more detail. Question # 1: Do we believe that English past tense formation is not learnable? Of course we don't! So imperturbable is our faith in the learnability of this system that we ourselves propose a way in which it might be done (OLC, 130-136). Question #2: If it is learnable, is it specifically unlearnable by nets? No, there may be some nets that can learn it; certainly any net that is intentionally wired up to behave exactly like a rule-learning algorithm can learn it. Our concern is not with (the mathematical question of) what nets can or cannot do in principle, but with which theories are true, and our conclusions were about pattern associators using distributed phonological representations. We showed that it is unlikely that human children learn the regular rule the way such a pattern associator learns the regular rule, because it is simply the wrong tool for the job. Therefore it's not surprising that the developmental data confirm that children do not behave in the way that such a pattern associator behaves. Question # 3: If past tense formation is learnable by nets, but only if the invariance that the net learns and that causally constrains its successful performance is describable as a "rule", what's wrong with that? Absolutely nothing! --just like there's nothing wrong with saying that past tense formation is learnable by a bunch of precisely-arranged molecules (viz., the brain) but only if the invariance that the molecules learn, etc. etc. etc. The question is, what explains the facts of human cognition? Pattern associator networks have some interesting properties that can shed light on certain kinds of phenomena, such as *irregular* past tense forms. But it is simply a fact about the *regular* past tense alternation in English that it is not that kind of phenomenon. You can focus on the interesting empirical predictions of pattern associators, and use them to explain certain things (but not others), or you can generalize them to a class of universal devices that can explain nothing without an appeal to the rules that they happen to implement. But you can't have it both ways. Alan Prince Program in Cognitive Science Department of Psychology Brown 125 Brandeis University Waltham, MA 02254-9110 prince@brandeis.bitnet Steven Pinker Department of Brain and Cognitive Sciences E10-018 MIT Cambridge, MA 02139 steve@cogito.mit.edu References: Pinker, S. & Prince, A. (1988) On language and connectionism: Analysis of a parallel distributed processing model of language acquisition. Cognition, 28, 73-193. Reprinted in S. Pinker & J. Mehler (Eds.), Connections and symbols. Cambridge, MA: Bradford Books/MIT Press. Prince, A. & Pinker, S. (1988) Rules and connections in human language. Trends in Neurosciences, 11, 195-202. Rumelhart, D. E. & McClelland, J. L. (1986) On learning the past tenses of English verbs. In J. L. McClelland, D. E. Rumelhart, & The PDP Research Group, Parallel distributed processing: Explorations in the microstructure of cognition. Volume 2: Psychological and biological models. Cambridge, MA: Bradford Books/MIT Press. ---------------------------------------------------------------- Posted for Pinker & Prince by: -- Stevan Harnad ARPANET: harnad@mind.princeton.edu harnad@princeton.edu harnad@confidence.princeton.edu srh@flash.bellcore.com harnad@mind.uucp BITNET: harnad%mind.princeton.edu@pucc.bitnet UUCP: princeton!mind!harnad CSNET: harnad%mind.princeton.edu@relay.cs.net