2nd Year Practical Feature Integration Theory (FIT) & Visual Search

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: 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)

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

4. 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)

5. B B B B B B B B 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

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) RT Items RT Items

13. 2 X T O 8 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

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 Lesions in Occipital & Parietal regions of brain L R

16. Occipital & Parietal Cortex Parietal Cortex Occipital Cortex

17. Find O among Qs 2500 2 3 2000 8 Reaction Time (ms) 1500 30 11 3 1000 500 4 8 12 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. Target Absent Target Present Numbers are % error Set size

18. Find Q among Os Find O among Qs 2500 2500 2 3 2000 2000 Reaction Time (ms) 8 Reaction Time (ms) 1500 1500 2 0 30 11 1 3 1000 1000 2 5 3 500 500 4 8 12 4 8 12 Set size KB’s Parallel search is intact

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

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!