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

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Presentation on theme: "2nd Year Practical Feature Integration Theory (FIT) & Visual Search"— Presentation transcript:

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

2 Contact Details Dr Jonathan Stirk Room: 438 Phone Extn: 15330
Web: Demonstrator: Joanna Wagstaffe Room 453 Office hour: Contact Joanna to make an appointment

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 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 B 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 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 8 X T O 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 Numbers are z-coordinates of transverse sections (horizontal plane). Parietal top back, occipital (vision) lower back L R

16 Occipital & 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 11 30 Target Absent Target Present Numbers are % error Set size

18 KB’s Parallel search is intact
Find O among Qs 500 1000 1500 2000 2500 4 8 12 Reaction Time (ms) 3 2 11 30 Find Q among Os Set size 1 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
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
A very good summary of FIT can be found at Access to some Electronic Journals WEB OF SCIENCE:

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 Remember to search for further information!
Treisman, A. (1988). Features and Objects”, Q. J. of Exp. Psychology, 40A, Treisman, A. (1986). Features and Objects in visual processing, Scientific American, 255, Friedman-Hill, SR, Robertson LC, Treisman, A. (1995). Parietal contributions to visual feature binding: evidence from a patient with bilateral lesions. Science, 269, 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, Remember to search for further information!

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