1 2nd Year Practical Feature Integration Theory (FIT) & Visual Search Dr Jonathan Stirk.

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2nd Year PracticalFeature Integration Theory (FIT) &

Visual Search

Dr Jonathan Stirk

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Contact Details

Dr Jonathan Stirk

Room: 438

Phone Extn: 15330

E-mail: jas@psychology.nottingham.ac.uk

Web: www.psychology.nottingham.ac.uk/staff/jas

Demonstrator: Joanna Wagstaffe

– Room 453

– Office hour: Contact Joanna to make an appointment

(lpxjkw@psychology.nottingham.ac.uk)

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What is Visual Search?

What is FIT?

Evidence from visual search.

Evidence from simultanagnosia.

Some conclusions

Some new questions

Overview of lecture

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What is visual search?– E.g. a specific book on a shelf of the library or a friend in a

crowded room

– “From the time we wake in the morning until we go to bed at

night, we spend a god deal of each day searching the

environment …in the office, we may look for a coffee cup,

the manuscript we were working on several days ago, or a

phone number of a colleague that we wrote down on a

scrap of paper.” – Peterson, Kramer, Wang, Irvin &

McCarley (2001)

Visual Search Paradigm

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Visual Search Paradigm

In Psychology– Looking for a specific

object e.g. a RED LETTER B

– Searching for a TARGET amongst a number of DISTRACTERS

BB

BB B

B

BB

TARGET DISTRACTERS

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What is FIT?

Feature Integration Theory Treisman distinguished between features of objects

and the objects themselves E.g. A red letter B, is an object consisting of the

colour red and the shape/form of a letter B The letter T consists of a horizontal and a vertical

line FIT suggests that the features are independently

coded by the visual system. E.g. Colour, motion, orientation, etc each have

dedicated processing. Evidence comes from visual search tasks

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Visual Search Examples (feature search)

Looking for the white rectangle is easy because it consists of a single unique feature (Colour white) compared to the distracters

Looking for the horizontal rectangle is also easy

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Visual Search

Both are single feature searches. The oddball ‘pops out’

Detection speed unrelated to set size (number of distracters)

Suggests that feature of colour and orientation are processed in parallel (all at the same time)

This process is pre-attentive

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Visual Search Examples (conjunction search)

However: If the target is not defined by a single feature but by a combination of features, then processing is slower (white AND horizontal)

In these cases, response time is related to set size (number of distracters). Slower when set size is larger

Target not defined by a single feature!

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Visual Search

Suggests that when target is defined by a combination of features search is slower

Search requires serial processing– i.e. must be carried out one item at a time– This requires focused attention

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Parallel vs. Serial Search

Parallel Search – All objects inspected simultaneously

Serial Search – Objects inspected one at a time

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Parallel vs. Serial Search

Parallel Search Time: independent of distracters.

Serial Search Time: correlated with num items, target absent especially slow. (Target present)

Items

RT

Items

RT

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Assumptions of FIT

Rapid initial parallel process – independent of attention Followed by slower serial process – features combined Features are combined using focused attention to the location

of an object– “glue”

Feature combination is influenced by stored knowledge (schemas)

– E.g. Bananas are usually yellow Without focused attention or schema info, features may be

randomly combined (when attention is diverted)– Illusory conjunctions (Treisman & Schmidt, 1982)

2 8X T O I) report black digitsI) report black digitsIi) report colour and shape of lettersIi) report colour and shape of letters

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Balint-Holmes Syndrome

A brain-damaged condition in which some patients find it difficult to shift visual attention

Optic Ataxia: Misdirected movement- misreaching

Ocular Apraxia: Visual scanning deficit

Simultanagnosia: Can see only one object

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MRI Scan of KB’s brain

L R

Lesions in Occipital & Parietal regions of brain

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Occipital & Parietal Cortex

Parietal Cortex

Occipital Cortex

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KB’s Serial Search

KB is very slow (worse than normals) finding an ‘O’ surrounded by ‘Q’s.

‘Serial search’: time to find ‘O’ is linearly related to number of distracters.

Find O among Qs

500

1000

1500

2000

2500

4 8 12

Reaction Time (ms)

3

2

8

11 30

3

Set size

Target AbsentTarget Present

Numbers are % error

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KB’s Parallel search is intact

Find O among Qs

500

1000

1500

2000

2500

4 8 12

Reaction Time (ms)

3

2

8

11 30

3

Find Q among Os

500

1000

1500

2000

2500

4 8 12Set size

Reaction Time (ms)

01 2

32 5

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KB’s case

Even though KB is only consciously aware of one item at a time, parts of her brain are still perceiving the entire visual scene. (Feature maps intact).

KB seems to have a binding problem– Issues arising when different kinds of information

need to be integrated to produce object recognition

– Which features belongs to which objects?

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Diagram

Treisman’s Proposed model of Feature Integration

•Feature Maps

•Master Map (location)

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Your experimental design…

Hypothesis Independent variable(s) Dependent variable – reaction times Subjects – who and how many? Which statistical test?

– Don’t go more complex than a 2 WAY analysis

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Possible Ideas

Do items pop out if we do not know which feature to expect?– Every trial has new single feature (e.g. colour

[red], diagonal). Subjects are asked if oddball is present.

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Further Ideas

Do items pop out if we do not know whether we will make a feature or conjunction search (always same target, random conjunction or feature searches).

Presentation time (vary display time, add masks). Practice effects?

– Does practise effect ability?– Does it effect both types of search?

Target/Distracter similarity? Distracter/Distracter similarity? Figure-background effects

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Summary

Develop hypothesis Choose independent variable(s) Choose stimuli Create the design / Create stimuli Pilot study Test subjects Analyze data, write report, present findings

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Week Summary

Week 1 Mini lecture, example exp’ts, literature search

Week 2 Develop hypothesis, select project

Week 3 Pilot study, collect data

Week 4 Data analysis (Mini lecture)

Week 5 Presentations

Week 6 Hand in written report (Deadline Fri 10th Dec)

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What you need to do before next week

Get into groups of 3-4 If you have any questions, ask the lecturer or

demonstrator before you leave Library search Devise hypothesis Design experiment – manipulate 2 IV’s (2x2)

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Some Web Information

psychology.uww.edu/305WWW/FIT/FIT.htm

A very good summary of FIT can be found at www.stir.ac.uk/Departments/HumanSciences/Psychology/46ac/attention3/

Access to some Electronic Journals www.nottingham.ac.uk/library/ejournals/index.html

WEB OF SCIENCE: wos.mimas.ac.uk/

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Some Books

Eysenck & Keane (2000). Cognitive Psychology: A Student's Handbook. Psychology Press.

Eysenck, M.W. (2001). Principles of cognitive psychology (2nd Ed). Psychology Press.

Eysenck, M.W. (2004). Psychology: an international perspective. Psychology Press.

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Some Articles

Treisman, A. (1988). Features and Objects”, Q. J. of Exp. Psychology, 40A, 201-237.

Treisman, A. (1986). Features and Objects in visual processing, Scientific American, 255, 106-111.

Friedman-Hill, SR, Robertson LC, Treisman, A. (1995). Parietal contributions to visual feature binding: evidence from a patient with bilateral lesions. Science, 269, 853-855.

Wolfe, J, Cave, KR, Franzel, S. (1989). Guided search: an alternative to the feature integration model for visual search. J. of Experimental Psychology: Human Perception and Performance, 15, 419-433.

Remember to search for further information!