PSYC 330: Perception

1. PSYC 330: Perception Attention

2. http://www.youtube.com/watch?v=IGQmdoK_ZfY

3. What is Attention? • Definition – SET of processes that guide and select processing of subset(s) of stimuli based on objects, ideas, places, or times. • Types of attention • Overt – Covert • Divided – Singular • External - Internal • Selective – Nonselective • Are there special kinds of attention for different sensory systems?

4. Measuring Attention • Basic features of an attention experiment • Test stimuli (subdivision = target/distractor) • Attentional stimulus (cue) • Performance measure • Simple example: Posner Cueing Task (place priming) • Hit button when stimulus appears (RT measure) • Can appear on left or right of screen • Cueing • IV = absent (control), valid cue, invalid cue • DV baseline, decrease, increase RT

5. Attentional “Spotlight” • Spotlight analogy – attention moves from one fixation to the next (like a flashlight beam) • Alternative = Attentional lens • Focus shifts not only in space but in level of detail • Camera example • Empirical support? • Range effects • Dimensional contrast effects

6. Measuring Attention • Visual Search Paradigm (Anne Triesmanpg 191) • Find target amidst a background of distractors • Measure how long it takes to locate feature (RT) • IV = set size • IV = stimulus composition (simple feature, conjunction, configural) • DV = RT to find item increases across three tasks)

7. Search Strategies (in Triesman Tasks) • Feature search, with “salient” feature  POPOUT • RT unaffected by set size • Indicates search occurring in parallel • Search can be accomplished with pre-attentive processes • What makes a feature “salient”? • More complex searches (configural)  slow search • RT affected by set size (conjunction/spatial configuration conditions) • Indicates serial self-terminating search • Also may indicate serial exhaustive search • Combination strategies (guided search) • Use simple features to narrow possibilities quickly, then find conjuctive features

8. The Binding Problem • How do we put features together to understand objects in the environment? • Recall processing of simple features in striate cortex • Where, how does this process occur? • How do we NOT bind?

9. Triesman’s Feature Integration Theory • Visual processing is a two-stage process • Simple features collected via pre-attentive processes • But to recognize object (integrate multidimensional features - BINDING) requires attention and is much slower, more limited process • Evidence • Visual search data described • Illusory conjunctions • Which features do we bind? How do the dimensions of multidimensional stimuli interact?

10. All Stimuli are Not Created Equally • Garner and Separable and Integral Stimuli • Example: rectangles have two dimensions (height, width) • SIMPLE: attend to height differences while width is held constant • CORRELATED: attend to height differences while width also varies in the same way (taller/wider…. shorter/narrower)(taller/narrower…. shorter/wider) • ORTHOGONAL: attend to height differences while width also varies unsystematically (must ignore width)

11. Garner’s Converging Operations • Speeded classification • Free classification • Magnitude estimation (euclidean, city-block) • Integral  holistic processing • Separable  dimensional processing

12. Learning to separate? • Comparison of separable and integral stimuli • With range effects, dimensional contrast, and other paradigms… • Age • Species • Experience (expertise?)

13. The Neurology of Attention • What IS attention (from neurological POV)? • Features: At relatively low level (striate cortex) (pg 200) • Posner task – shift in “spotlight” to expected receptive field • Triesman task – shift to specific features or conjunctions. Example in book (7.18) note how global features emerge from focusing on different local features. • Objects: O’Craven & Kanwisher (2000) • Differences in face and house processing locations (fusiform face area and parahippocampal place area) • Combined stimuli (instructed to attend to face or house)

15. Temporal Effects • Attentional “BLINK” • When attending to a serial presentation, brief period of time after target identification when subject is relatively inattentive (will miss subsequent targets) • 200-300 ms • Repetition blindness • Also with serial presentation, participants tend to not notice hen the target is repeated more than once in the list.

16. Scene Perception • http://www.youtube.com/watch?v=6JONMYxaZ_s&feature=player_embedded • What is our task? • MANY features (all possible combinations) • CHANGE (scene, perspective, etc.) • Must bind some • Must select/analyze others • Must attend to global features and local features • Which is primary (do we construct global from local or other way around?) Example of kitchen – look for faucet because we are in kitchen, but how do we know we are in the kitchen without noting the faucet?

17. The Paradox of Scenes How can we be so bad, when we are so good????? Scene perception research – representative studies • Roger Shepard (1967) Showed participants 612 pictures- When tested for recognition of pictures (amongst foils) participants were 98% correct! - 90% correct a week later! • Intraub (1981) showed images for 125 ms and asked participants to monitor them for image that was NOT an animal. Again, participants performed very well.- 8 images per second! • Change blindness – we suck!

18. Global and Local Affordances • Selective and non-selective pathways • Global • Oliva & Torralba (2001) Spatial frequency analysis of scenes. What information is available in the stimulus? • Scene analyses (via spatial frequency) revealed common patterns reflecting scenes that were meaningfully interpreted similarly. • Wide open scenes (beaches, prairies, parking lots, etc.) have lots of strong horizontal components to spatial frequency analysis. Dimension = “openness” • “Naturalness”, “roughness” • Take novel scenes and organize them along these dimensions they cluster in meaningful ways that the visual system could use to make global assessment of scene • DEVOID of specifics – classification based upon overall image • Note interesting pigeon parallel

19. Local - details • Must move our eyes to see local details • Eye movements • Preattentive processing • Covert attentional shifts No eye movements • Overt attentional shifts Eye movements – saccadesVoluntary fast jumps (ballistic movements)Processing ceases during movementNOT random

20. Eye tracking

21. Two Step hypothesis? • Broad, spatial layout extracted preattentively? • Focused, overt attention (via saccades) to predicted meaningful regions of the layout for further identifying information • Then GUESS (if you don’t have much time) • Why does this work so well in the real world?

22. A summary of Vision • Sensation • Transduction, rods and cones • Coding patterns for color, form, movement, location • Midlevel Feature Processing • Parvocellular and magnocellular paths • Primary visual cortex and features • Perception • “Where?” “What?”

23. Take-home messages…. • Vision is not a “picture” of the “real world” • Vision is a constructive process • Back to Gibson….. • Vision occurs at the ECOLOGICAL LEVEL • Mountains, hills, oceans • Boulders, cliffs, trees • Pebbles, blades of grass, insects • Extract invariances from the stimulus flux • Information becomes AFFORDANCES when we interact with it to extract meaning

24. What is Louie Missing? • What important information do we encode from the visual world? • How do we encode that information? • How does the information get organized so that we can interact with it in meaningful/useful ways?