Attention & Scene Analysis 1 PSY 295 – Sensation & Perception Christopher DiMattina, PhD
Attention PSY 295 - Grinnell College - Fall 2012
Attention “Everyone knows what attention is. It is the taking possession by the mind, in clear and vivid form, one out what seem several simultaneously possible objects or trains of thought.” - William James (1890) PSY 295 - Grinnell College - Fall 2012
Attention • Over 100 years later, we don’t have a much better definition • Defined roughly in the book as “any of the large set of selective processes in the brain which restrict processing to a subset of things” PSY 295 - Grinnell College - Fall 2012
General characteristics • Visual attention can be overt or covert • Can be divided (being aware of music while reading) • Can be bottom-up or top-down • Selective attentionis where we attend to one of a variety of different possible stimuli PSY 295 - Grinnell College - Fall 2012
Attention is limited PSY 295 - Grinnell College - Fall 2012
Visual search Often we shift attention to search a crowded scene PSY 295 - Grinnell College - Fall 2012
Eye movements • Overt attention measured by recording eye movements • Depend on both bottom-up and top-down information PSY 295 - Grinnell College - Fall 2012
Salience • An important concept for studying bottom-up attention is that of salience which is vivid a stimulus is relative to its neighbors PSY 295 - Grinnell College - Fall 2012
Saliency map • Neural modeling have been developed to determine which part of a visual image are the most salient • Do good job of predicting human eye movements PSY 295 - Grinnell College - Fall 2012
Attention in space PSY 295 - Grinnell College - Fall 2012
Selective attention in space • Subject fixates central location and simply hits a key as fast as possible when test probe appears PSY 295 - Grinnell College - Fall 2012
Selective attention in space • Prior to appearance of probe, subject cued to probe location • Cue is either valid (matching) or invalid (opposite) PSY 295 - Grinnell College - Fall 2012
Symbolic cues • Instead of spatial cues, Posner also tried symbolic cues • Red spot means right, green spot means left PSY 295 - Grinnell College - Fall 2012
Results • Valid cues reduced reaction times • Invalid cues increased reaction times PSY 295 - Grinnell College - Fall 2012
Results PSY 295 - Grinnell College - Fall 2012
More results PSY 295 - Grinnell College - Fall 2012
Spotlight metaphor • One popular metaphor for top-down attention is a spotlight which focuses on different parts of the visual scene • Things outside of this spotlight are harder to detect – you might be completely oblivious to huge changes in scene! PSY 295 - Grinnell College - Fall 2012
What is changing? NRS 495 - Grinnell College - Fall 2012
What is changing? PSY 295 - Grinnell College - Fall 2012
Spot four differences PSY 295 - Grinnell College - Fall 2012
Spot four differences PSY 295 - Grinnell College - Fall 2012
Change blindness • When you a scene changes with an intervening blank image (or eye movement) you often can miss large changes • This is called change blindness PSY 295 - Grinnell College - Fall 2012
Web activity • http://sites.sinauer.com/wolfe3e/chap7/changeblindF.htm PSY 295 - Grinnell College - Fall 2012
Attention experiment DJ Simons NRS 495 - Grinnell College - Fall 2012
Inattentional blindness • We can literally be blind to aspects of a scene we are not attending to or expecting • In the original experiments by Simons and colleagues, about half of the subjects did not see the gorilla • More difficult attention task caused more people to miss the gorilla, easier task and more people say the gorilla PSY 295 - Grinnell College - Fall 2012
Door experiment • Simons and Levin (1997) on the streets of Ithaca, NY • Asked a stranger for directions • Two construction workers (actually experimenters) carrying a door went between the experimenter and the subject, but one of them switched places with the experimenter • Quite often the subject did not realize the person they were talking to was different!! PSY 295 - Grinnell College - Fall 2012
Visual search and bottom up attention PSY 295 - Grinnell College - Fall 2012
Visual search PSY 295 - Grinnell College - Fall 2012
Vertical red bar ‘pops out’ Time needed to find red bar does not depend on number of distractors PSY 295 - Grinnell College - Fall 2012
Parallel search PSY 295 - Grinnell College - Fall 2012
Conjunction search PSY 295 - Grinnell College - Fall 2012
Conjunction search • Conjunction search is serial instead of parallel • Time to detect target increases with set size PSY 295 - Grinnell College - Fall 2012
Spatial configuration search PSY 295 - Grinnell College - Fall 2012
Feature versus conjunction • Feature searches are parallel and efficient • Conjunction searches are serial and inefficient PSY 295 - Grinnell College - Fall 2012
High level features PSY 295 - Grinnell College - Fall 2012
Web activity • http://sites.sinauer.com/wolfe3e/chap7/vissearchF.htm PSY 295 - Grinnell College - Fall 2012
Finding arbitrary objects is inefficient Find the faucet PSY 295 - Grinnell College - Fall 2012
Scene based guidance Find the faucet PSY 295 - Grinnell College - Fall 2012
Treisman’s feature integration theory • A major problem in sensory neuroscience is the binding problem – different brain areas process different features. How do we put them together? • One proposed solution offered by Treisman is that attention binds features together • Many other possible solutions not involving attention proposed by other scientists PSY 295 - Grinnell College - Fall 2012
Feature integration theory • Limited set of features can be processed pre-attentively • Correct binding requires attention PSY 295 - Grinnell College - Fall 2012
Illusory conjunctions PSY 295 - Grinnell College - Fall 2012
