Selective Visual Attention: Feature Integration Theory PS2009/10 Lecture 9

Feature Integration Theory (FIT) Visual Search tasks Visual Search tasks Illusory Conjunctions Illusory Conjunctions Texture Discrimination Texture Discrimination

Visual Search Task Triesman and Gelade (1980) Triesman and Gelade (1980) time to detect targets defined by a single feature is unaffected by the number of distracters time to detect targets defined by a single feature is unaffected by the number of distracters time to detect targets defined by multiple features is affected by the number of distracters time to detect targets defined by multiple features is affected by the number of distracters

Target defined by a single feature Time to detect Blue T unaffected by number of red S and T distracters

Target defined by multiple features Time to detect Blue T is effected by number of distracters - linear increase in search time.

Visual Search Times Targets defined by a single feature (e.g. Blue) Targets defined by a single feature (e.g. Blue) processing of features occurs in parallel (colour coded for all the items in the display independent of numbers. processing of features occurs in parallel (colour coded for all the items in the display independent of numbers. Targets defined by multiple features (e.g. Blue and T) Targets defined by multiple features (e.g. Blue and T) serial search process serial search process

Illusory Conjunctions Displayed for less than 200msec followed by a pattern mask Ss reported the digits and then details of the letters

Illusory Conjunctions Ss good at reporting digits Ss good at reporting digits Ss made errors reporting letters and colours Ss made errors reporting letters and colours more of the errors were conjunction errors more of the errors were conjunction errors conjunction error - Ss says the saw a red letter T and a blue X conjunction error - Ss says the saw a red letter T and a blue X

Texture Discrimination E.g. Beck (1966) Ss rate T as more similar to T Ss find it harder to discriminate the boundary between T and L

Texture Discrimination T and T can be discriminated on the basis of a single feature - orientation T and T can be discriminated on the basis of a single feature - orientation T and L only distinguishable when the features are combined T and L only distinguishable when the features are combined

Problems with FIT 1 Verzi & Egeth (1984) Ss showed evidence of illusory conjunctions report BIG but written in blue ink Colour Blue was not present

Problems with FIT 2 Illusory conjunctions influenced by the meaning of words in the display Illusory conjunctions influenced by the meaning of words in the display illusory conjunctions are not just a perceptual phenomenon illusory conjunctions are not just a perceptual phenomenon

Problems with FIT 3 Humphreys et al (1985) Time taken to detect target not influenced by the number of distracters.

Attentional Engagement Theory Similarity between targets and distracters increases search time. Similarity between targets and distracters increases search time. Similarity between distracters reduces search time. Similarity between distracters reduces search time.