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Chapter 7 - Visual Attention

Chapter 7 - Visual Attention. Cognitive overview of the problem of attention. What is Attention?.

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Chapter 7 - Visual Attention

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  1. Chapter 7 - Visual Attention Cognitive overview of the problem of attention

  2. What is Attention? “Everybody knows what attention is. It is taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others , and is a condition which has a real opposite in the confused, dazed scatterbrain state … “ William James (1890)

  3. What is Attention? • ‘Taking possession of the mind’ • Controlling the focus of attention; intentionality; “Please pay attention …” • ‘one out of what seem several simultaneously possible objects’ • Our apparent inability to attend to multiple things at once • ‘It implies withdrawal from some things in order to deal effectively with others’ • Attending has a cost • Attending is a limited capacity process • ‘has a real opposite in the confused, dazed scatterbrain state’ • Attending is the glue that keeps perception together

  4. Attention: Selecting some stimuli over others for further processing • Why select? Why not process all visual input? • Limited processing capacity • Limited processing capacity of what? • Response systems: Two hands, one mouth, etc. • Input: One pair of foveas • Use of distributed representations: When more than one pattern is activated simultaneously, interference or cross-talk may occur.

  5. Coping with the problem of interference and cross talk • Reducing the degree of distributedness at higher levels of visual representation • Evidence of sparse population codes (e.g., IT face representations) • Binding attributes via synchronized oscillations • Selective Attention: Focusing processing on a selected portion of the scene • Reduces information overload

  6. Selective Attention • Selective attention: Limits the processing to one portion of the scene at a time. • Stimulus selection could be based on: • location in a (retinotopic map) • object representation

  7. Spatial-based Selection Posner’s Spatial Cuing Procedure. - See fixation cross - Brightness change - Respond to target onset Fastest response to a target that occurs on the cued side (valid) and slowest when target occurs on the non-cued side (invalid).

  8. Object-based Selection • Task • Told what dimension(s) to report • Fixation point • See target (~79 ms) • Pattern mask • Report • Target: Two overlapping objects, each with 2 dimensions: • Box: Height; Gap • Line: Texture; Orientation • Equally accurate reporting one or two dimensions from the same object • More accurate reporting two dimensions from the same object than one dimension from each of two objects. (Vecera & Farah, 1994, E1: 86% > 80%) After Duncan (1980)

  9. Visual Attention: The Glue that Binds • We normally experience our complex environments as a coherent world of integrated objects. • Remember: Sensory information (i.e., shape, color, motion) arrives in parallel and is processed by different pathways in brain. • To create useful mental representations of objects, we collect their features, bind them into the correct temporal and spatial bundles, and interpret these bundles to specify their real world origins. • This process depends upon focused attention. • If focused attention fails, binding may fail and we perceive illusory conjunctions (i.e., upon seeing two cars (red Focus and black Echo, may falsely report a red Echo).

  10. Feature Integration Theory: Treisman (1998)

  11. Limited Visual Input • Although we seem to have a detailed, highly veridical and continuous mental representation of visual world about us, visual input is limited. • Visual acuity is good only for foveal focus. • Eyes movement from one fixation point to another while viewing a scene. • Saccades: 3-5 saccades/sec, 40 – 50 msec each. • Fixations: ~300 msec, during which we pick up visual information.

  12. Eye Movements: Saccades and Fixations

  13. Change Blindness • Failure to detect supraliminal changes in a visual scene. (i.e., editing discontinuities in movies). • Flicker technique: In your demonstration, changes involved: color, size, location, presence/absence of objects in scene. Winter 2006 data (Psych 3450) Accuracy Latency Central Interest 96% 5.5 sec Marginal Interest 84% 13.5 sec

  14. Two Empirical Issues to be Addressed from the Neuroscience Perspective • How does attention affect visual information processing at different stages? • What neural systems control the allocation of attention?

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