When Texture takes precedence over Motion

1. When Texture takes precedence over Motion By Justin O’Brien and Alan Johnston

2. Focus • Slant can be calculated from both texture and motion information using similar methods • Texture or motion cue- which one is stronger in slant perception?

3. Background • Separate -Gibson(1950), Rogers and Graham (1979)…Braunstein et al(1993) • Combined -Braunstein(1968) and Young et al (1993) • Usually motion is a stronger cue

4. Their work • Differs from Braunstein and Young et al • Interaction of texture and motion cues when they both provide similar info

5. Experiments • Four experiments -Identical motion and regular texture -Disparity between motion and regular texture -Disparity between motion and irregular texture pattern -Changing spatial-frequency of texture and velocity gradient of motion

6. Set-up • Sun Sparc or Silicon Graphics Indigo • Viewed monocularly through a circular aperture 50 cm from the display • Aperture 25cm from the display

7. Set-up • Textures were generated using spatial frequency information • Motion velocity is inversely proportional to the spatial frequency • Images were ray-traced

8. Method • Relative slant- use of standard stimulus and test stimuli • Standard stimulus shown 5 times for 1s • Test stimuli shown with different slants with intervals of 2s • Asked to compare with standard

9. Method (pg 439) • Standard stimulus -plaid textured surface slanted at 45 deg with a diagonal motion • Test Stimuli -Horizontal texture and horizontal/no motion -Vertical texture and vertical/no motion -Plaid texture and both/no Each test stimulus was shown 8 times at nine levels 72 measurements

10. Terms • Slant discrimination bias -st dev • Slant discrimination threshold -mean

11. Experiment 1 • Effect of motion and texture on perceived slant • Stimuli- pictures similar to Pg 439 • Procedure • 8 Subjects

12. Results-Experiment 1 • The graphs show the mean of the observers median bias and median threshold • 1D texture- less slant (more error) • 2D texture- more slant (less error) • Obervers are accurate to 1 deg • Texture more important than motion

13. Experiment 2 • Interaction of texture and motion when they differ • Procedure -Standard stimuli 1. Texture slant constant at 45 deg motion was varied 2. Motion slant constant at 45 deg texture was varied Then previous method was used • 2 Subjects

14. Results-Experiment 2 • The bias was less for varying motion • The bias was more for varying texture

15. Experiment 3 • Regular texture vs Irregular texture • Standard stimulus- plaid texture with diagonal motion set at 45 deg • Procedure • 2 subjects • Result -irregular texture did not make much of a difference

16. Experiment 4 • Sensitivity to changes in spatial-frequency gradients vs changes in velocity gradients • Motion is a strong cue then is it the velocities used?? • Procedure 1. Spatial frequency gradient discrimination 2. Velocity gradient discrimination - 3 test stimulus types, 10 deg interval • Bias not calculated • 2 Subjects

17. Results-Experiment 4 • Motion – a strong cue • Most discriminable cue for slant estimation

18. Conclusion • Motion cue did not affect slant perception when texture and motion both provided similar info • When there was a disparity, texture cue dominated • Type of texture did not matter • Changes to velocity gradient was harder to discriminate.