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

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?

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

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

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

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

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

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

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

Terms Slant discrimination bias -st dev Slant discrimination threshold -mean

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

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

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

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

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

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

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

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.