2nd Year Practical Feature Integration Theory FIT

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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_at_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_at_psychology.nottingham.ac.uk)

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Overview of lecture

• What is Visual Search?
• What is FIT?
• Evidence from visual search.
• Evidence from simultanagnosia.
• Some conclusions
• Some new questions

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Visual Search Paradigm

• 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)

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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

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)

RT
Items
RT
Items
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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)

I) report black digits Ii) 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 KBs brain
Lesions in Occipital Parietal regions of brain
L R
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Occipital Parietal Cortex
Parietal Cortex
Occipital Cortex
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KBs Serial Search

• KB is very slow (worse than normals) finding an
  O surrounded by Qs.
• Serial search time to find O is linearly
  related to number of distracters.

Target Absent
Target Present
Numbers are error
Set size
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KBs Parallel search is intact
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KBs 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

• Treismans 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?
• Dont 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/Distracte
  r 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
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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 IVs (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/Psycholog
  y/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!