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 WagstaffeRoom 453Office 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 conclusionsSome 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 PsychologyLooking for a specific object e.g. a RED LETTER BSearching for a TARGET amongst a number of DISTRACTERSBTARGETDISTRACTERS
6 What is FIT? Feature Integration Theory Treisman distinguished between features of objects and the objects themselvesE.g. A red letter B, is an object consisting of the colour red and the shape/form of a letter BThe letter T consists of a horizontal and a vertical lineFIT 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 distractersLooking 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 largerTarget not defined by a single feature!
10 Visual SearchSuggests that when target is defined by a combination of features search is slowerSearch requires serial processingi.e. must be carried out one item at a timeThis requires focused attention
11 Parallel vs. Serial Search Parallel Search – All objects inspected simultaneouslySerial 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)RTItemsRTItems
13 Assumptions of FITRapid initial parallel process – independent of attentionFollowed by slower serial process – features combinedFeatures 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 yellowWithout focused attention or schema info, features may be randomly combined (when attention is diverted)Illusory conjunctions (Treisman & Schmidt, 1982)28XTOI) report black digitsIi) report colour and shape of letters
14 Balint-Holmes Syndrome A brain-damaged condition in which some patients find it difficult to shift visual attentionOptic Ataxia: Misdirected movement- misreachingOcular Apraxia: Visual scanning deficitSimultanagnosia: Can see only one object
15 MRI Scan of KB’s brainLesions in Occipital & Parietal regions of brainNumbers are z-coordinates of transverse sections (horizontal plane). Parietal top back, occipital (vision) lower backL R
17 KB’s Serial SearchKB 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 Qs50010001500200025004812Reaction Time (ms)321130Target AbsentTarget PresentNumbers are % errorSet size
18 KB’s Parallel search is intact Find O among Qs50010001500200025004812Reaction Time (ms)321130Find Q among OsSet size15
19 KB’s caseEven 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 problemIssues arising when different kinds of information need to be integrated to produce object recognitionWhich features belongs to which objects?
20 Diagram Treisman’s Proposed model of Feature Integration Feature Maps Master Map (location)
21 Your experimental design… HypothesisIndependent variable(s)Dependent variable – reaction timesSubjects – who and how many?Which statistical test?Don’t go more complex than a 2 WAY analysis
22 Possible IdeasDo 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 IdeasDo 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
25 Week Summary Week 1 Mini lecture, example exp’ts, literature search Develop hypothesis, select projectWeek 3Pilot study, collect dataWeek 4Data analysis (Mini lecture)Week 5PresentationsWeek 6Hand in written report (Deadline Fri 10th Dec)
26 What you need to do before next week Get into groups of 3-4If you have any questions, ask the lecturer or demonstrator before you leaveLibrary searchDevise hypothesisDesign 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 atAccess to some Electronic JournalsWEB OF SCIENCE: wos.mimas.ac.uk/
28 Some BooksEysenck & 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!