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.