1What is Cognitive Science?… is the interdisciplinary study of mind and intelligence, embracing philosophy, psychology, artificial intelligence, neuroscience, linguistics, and anthropology(Stanford Encyclopedia of Philosophy)http://plato.stanford.edu/entries/cognitive-science/Practical Value• Education: – Intelligent tutoring systems– Automatically grading exams • Legal: – Distinguishing between true and false memories– Evaluating line-ups• Sales– Understanding beliefs and desires• Information technology:– Search engines– Building intelligent systemsC iti i ti t i ht h thi tMost cognitive scientists are cognitive psychologists, computer scientists, or cognitive neuroscientists(from: Schunn et al. 2005)Cognitive ScienceComputer Science/ Artificial IntelligenceNeurosciencePhilosophyExperimentalCognitive PsychologyLinguisticsUnderstanding ComputationTo understand limits of theoriesTo understand structure of languageTo understand howthe brain worksFor human data in various tasksWe will focus mostly on insights from Cognitive PsychologyInterdisciplinarystudy of intelligentbehaviorAreas of Study• Cognition is about internal processes that are often unobservable, e.g.:Perception, Attention, Memory, Visual Imagery, Language, Concept Learning, Reasoning• Need converging evidence from different perspectives to really understand cognitive processes ?Levels of Analysis• Implementation:– Where does mental activity take place in the brain?–Howis processing actually done with neural activity? • Algorithm: – What is the abstract representation for input and output?– What stages are used to process information? – (Information processing level) • Computation: –Whydoes the algorithm work well?– What is the goal or purpose of the computation?(Marr, 1982)2Levels of Analysis ExampleInformation Processing• Information processing models resemble processing in computers – made cognitive psychology popular• Information made available by the environment is processed by a series of processing systems• Processing system is a set of processes that work together to accomplish a type of task, using and producing representations as appropriate• The major goal of research is to specify these processes and representationsTypes of Processing• Bottom-up processing• Top-down processing• Parallel processing• Serial processingAn early version of the information-processing approachÆ purely bottom up or stimulus-drivenA Demonstration of Top-Down Processing(Kleffner & Ramachandran, ’92)Why do we seem to have a fairly robust interpretation of which shapes are concave and convex when the perceptual information is perfectly ambiguous? -> perception affected by knowledge Top-down processing: perception affected by knowledge of world3Top down processing: perception affected by memory• First time, sine wave speech sounds incomprehensible (to most)• After hearing the natural utterance, perception of sine-wave speech seems to be quite different"The steady drip is worse than a drenching rain."(for more info: http://www.haskins.yale.edu/haskins/MISC/SWS/SWS.html)http://psiexp.ss.uci.edu/research/teachingP140C/demos/sinewavespeech.aifhttp://psiexp.ss.uci.edu/research/teachingP140C/demos/naturalutterance.aifSound Induced Illusory Flashes• Example of parallel and interactive processing: visual perception affected by auditory perception• http://www.cns.atr.jp/~kmtn/soundInducedIllusoryFlash2/Top-down processingLater stages of processing affect earlier stagesÆ can explain effects of Knowledge, memory, expectations and contextParallel vs. Serial Processing• To illustrate the difficulty of distinguishing between serial and parallel processing, consider the Sternberg task• Goal: what steps are involved in comparing information to memory? How long do these steps take?• Task: – give subjects memory sets. E.g. 3 9 7– Probe memory with targets and foil digits: 9 = “yes”, 6=“no”. Measure reaction time. – Vary the size of these memory setsTypical Sternberg Results• Plot reaction time as function of memory set size and type of trial (targets/foils)• What are the implications of seeing a linear increase in reaction time as a function of memory set?A serial information processing model for Sternberg taskPerceive StimulusIs it a 3?Is it a 9?9Is it a 7?Make DecisionyesThis serial information processing model predicts a linear increase4A parallel information processing model for Sternberg taskPerceive StimulusIs it a 3?Is it a 9?9Is it a 7?Make DecisionyesThis parallel information processing model also predicts a linear increaseIdentifiability• Identifiability refers to the ability to specify the correct combination of representations and processes used to accomplish a task• Sometimes, behavioral results do not allow processes and representations to be uniquely identified (e.g. Sternberg task)• Need converging evidence to tell theories apart– More behavioral data– Data from cognitive neuroscience– Data from