The effects of dot density on the metric estimation of rotation and expansion

WURFEL J.D.; BARRAZA J.F.; GRZYWACZ N.M.

Sarasota, Florida, USA

Congreso; 4th Annual Meeting of the Vision Sciences Society; 2004

Vision Sciences Society

Optic flow generated by rigid surface patches can be decomposed into four elementary motion types, translation, rotation, expansion, and deformation1. We have shown that the human visual system can metrically estimate two of these motion types, rotation2 and expansion3, by angular velocity and rate of expansion respectively. However, the use of angular velocity to metrically estimate rotation contradicts previous work that reported linear velocity to be the parameter estimated4. This discrepancy was caused by a difference in experimental methods. There were very few dots used in the previous experiments compared to the amount used in our own experiments. Experimental evidence shows that the visual system uses linear velocity when there are a small number of dots in the stimuli and angular velocity when there are greater number5. We’ve modeled this systematic switchover in information utilized in a probabilistic manner. Specifically, low information motion stimuli have a higher probability of being estimated by linear velocity than high information motion stimuli. We found that a similar switchover occurs in the metric estimation of expansion and that the data fits the probabilistic model developed for rotation. Previous studies have shown the importance of the number of dots in estimating expansion6, however the scope of their work did not include this exact switchover from linear velocity to rate of expansion.