Observers rely more on shadows than on shading and highlights when comparing illumination conditions S te Pas1, S C Pont2, E S Dalmaijer1, I T Hooge1 |
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1Experimental Psychology, Utrecht University - Helmholtz Institute, Netherlands |
| When comparing illumination conditions, human observers mostly extract the direction of the light source from low-level image cues. The question we ask here is whether they are able to distinguish other low-level aspects like diffuseness and number of light sources, and what kind of stimulus information is most important for this task. We use a teapot, an orange and a tennis ball from the ALOI database (Geusebroek et al., IJCV 2005) to create stimuli either with a single light source direction that varies in diffuseness or with two light source directions that vary in separation. Observers are presented with all three objects on every trial, and have to indicate which one is illuminated differently from the other two. We measured behavioural data as well as eye-movements to determine where our participants were looking. Results show that participants performed above chance for most combinations. Interestingly, eye-movement data show that participants primarily look at the shadows (60% of the fixations), in favour of shading (30%) and highlights (10%). This is in line with a model we presented at ECVP 2008 that shows that variance in performance for this task could best be modelled by using shadow information. |
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