CS 764 Seminar in Computer Vision

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.