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CS 764 Seminar in Computer Vision

CS 764 Seminar in Computer Vision. Attention in visual tasks. Two different tasks. Perception of motion Experiments indicate systems similar to the ones used in computer vision Object representations and visual memory Results indicate systems different from anything we implement.

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CS 764 Seminar in Computer Vision

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  1. CS 764 Seminar in Computer Vision Attention in visual tasks

  2. Two different tasks • Perception of motionExperiments indicate systems similar to the ones used in computer vision • Object representations and visual memoryResults indicate systems different fromanything we implement

  3. Attention and motion • Todd Horowitz and Anne TreismanSpatial Vision Vol. 8, No. 2, 1994 • Apparent x Real motion • Short range x Long range system

  4. Short range x Long range system • Short rangeSmall displacement Small time interval between stimuliConstant contrast • Long rangeEverything else

  5. Theoretical framework • Short range motionArray of simple motion detectors operating in parallel. (like optical flow computation) • Long range motionDepends on linking stimuli separated in space and time. Requires attention(like shape matching)

  6. Experiment 1 • Detection of long and short range motion with unicontrast and bicontrast stimuli • Measure response time as a function of number of distractors.Parallel search => constant timeSerial search => linear time

  7. Experiment 2 - Motion Aftereffect • The effects of adaptation are reversed between short and long range motion. • Short range system becomes less sensitive to adapted motion • Long range system benefits from ‘practice’ stimuli

  8. Summary • Two different systems for motion perception We have decent models for both systems • Short range motion seems much like optical flow computation • Long range motion seems much like shape matching

  9. Object Tokens, Attention, and Visual Memory • Anne Treisman and Brett DeSchepperAttention and Performance XVI, 1996 • Probe bottom-up registration of unattended objects • Specially novel objects, for which new representations may be constructed

  10. Introduction • On recognition tasks, we can’t remember novel unattended shapes • But indirect measures (i.e. priming) reveal memory beyond conscious level • How much processing and learning happens without attention?

  11. Experiment 1 • Tests indicate unattended shapes cause negative primingFew subjects show facilitation • Very long duration of effect (> weeks) • No explicit memory of unattended shapes

  12. Experiment 2 • Are there differences between representations built for attended and unattended shapes? • Maybe attended shapes are processed to a higher level and representations reflect this

  13. Summary • No explicit memory of unattended novel shapes • Priming indicates implicit memory • Implicit memory “learns” with one example and repetition is irrelevant. • Effects last for long periods (novel shapes) • When attended, novel shapes are processed to a higher level.

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