Organizational Notes

• no study guide• no review session• not sufficient to just read book and glance at

lecture material• midterm/final is considered hard by some

students• questions will relate to both book and lecture

material

What 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 systems

Cognitive scientists might have some things to say about these issues.

Most cognitive scientists are cognitive psychologists, computer scientists, or cognitive neuroscientists

(from: Schunn et al. 2005)

Cognitive Science

Computer Science/ Artificial Intelligence

Neuroscience

Philosophy

Cognitive Psychology Linguistics

Understanding ComputationBuilding computer models that learn from the environment

To understand limits of theories

To understand structure of language

To understand howthe brain works

For behavioral data in various tasks; mental representations and processes

We will focus mostly on insights from Cognitive Psychology

Interdisciplinarystudy of intelligentbehavior

Areas of Study

• Cognitive psychology/science is about studying 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

• Implementational:– Where does mental activity take place in the brain?– How is processing actually done with neural activity?

• Algorithmic: – What is the abstract representation for input and output?– What stages are used to process information? – (also known as information processing level)

• Computational: – Why does the algorithm work well?– What is the goal or purpose of the computation?

(Marr, 1982)

Levels of Analysis Example

Cognitive Neuroscience

• the study of the relation between cognitive processes and brain activities

• Potential to measure some “hidden” processes that are part of cognitive theories (e.g. memory activation, attention, “insight”)

• Measuring when and where activity is happening. Different techniques have different strengths: tradeoff between spatial and temporal resolution

Information Processing

• Information processing models resemble processing in computers – made cognitive psychology popular

• Idea is that information is processed in a number of stages

• The major goal of information processing research is to– identify those processes – identify how information is represented

Types of Processing

• Bottom-up processing• Top-down processing• Parallel processing• Serial processing

An early version of the information-processing

approach

purely bottom up or stimulus-driven

A 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 world

Top 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.aif

http://psiexp.ss.uci.edu/research/teachingP140C/demos/naturalutterance.aif

Sound Induced Illusory Flashes

• Example of parallel and interactive processing:– processing of perceptual information in one modality is

often affected by processing in another modality

• Demo of sound induced illusory flashes:– http://shamslab.psych.ucla.edu/demos/– http://www.cns.atr.jp/~kmtn/soundInducedIllusoryFlash/index.html– http://www.cns.atr.jp/~kmtn/soundInducedIllusoryFlash2/– For more information on this effect see:

http://shamslab.psych.ucla.edu/publications/SCR-reprint.pdf– note: demo might not work on your particular computer

• Demo shows that visual perception affected by auditory perception

Top-down processing

Later stages of processing affect

earlier stages

can explain effects of Knowledge, memory,

expectations and context

Parallel 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 sets

Typical 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 task

Perceive Stimulus

Is it a 3?

Is it a 9?9

Is it a 7?

Make Decision yes

This serial information processing model predicts a linear increase

A parallel information processing model for Sternberg task

Perceive Stimulus

Is it a 3?

Is it a 9?

9

Is it a 7?

Make Decision yes

This parallel information processing model also predicts a linear increase

Identifiability

• Sometimes, behavioral results do not allow processes and representations to be uniquely identified (e.g. Sternberg task)

• Identifiability refers to the ability to specify the correct combination of representations and processes used to accomplish a task

How can we tell models/theories apart?

• Need converging evidence to tell theories apart– More behavioral data– Data from cognitive neuroscience– Data from neuropsychology

Note

• Please read book – to review major brain structures and their functions– to review brain imaging techniques

• See also additional PowerPoint slides available on class website– cogneuro review slides