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1
2nd Year PracticalFeature Integration Theory (FIT) &
Visual Search
Dr Jonathan Stirk
2
Contact Details
Dr Jonathan Stirk
Room: 438
Phone Extn: 15330
E-mail: [email protected]
Web: www.psychology.nottingham.ac.uk/staff/jas
Demonstrator: Joanna Wagstaffe
– Room 453
– Office hour: Contact Joanna to make an appointment
3
What is Visual Search?
What is FIT?
Evidence from visual search.
Evidence from simultanagnosia.
Some conclusions
Some new questions
Overview of lecture
4
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
5
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
6
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
7
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
8
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
9
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!
10
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
11
Parallel vs. Serial Search
Parallel Search – All objects inspected simultaneously
Serial Search – Objects inspected one at a time
12
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
13
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
14
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
15
MRI Scan of KB’s brain
L R
Lesions in Occipital & Parietal regions of brain
16
Occipital & Parietal Cortex
Parietal Cortex
Occipital Cortex
17
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
18
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
19
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?
20
Diagram
Treisman’s Proposed model of Feature Integration
•Feature Maps
•Master Map (location)
21
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
22
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.
23
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
24
Summary
Develop hypothesis Choose independent variable(s) Choose stimuli Create the design / Create stimuli Pilot study Test subjects Analyze data, write report, present findings
25
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)
26
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)
27
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/
28
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.
29
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!