Velocity constancy for familiar and unfamiliar objects

MARTÍN, ANDRÉS; BARRAZA, JOSÉ F.

Naples, Florida

Encuentro; 13a annual meeting Vision Science Society (VSS); 2013

VSS

To explain that people can easily perceive physical instead of retinal speed, psychophysicists have proposed the temporal frequency hypothesis. The hypothesis is well suited to answer why an observer does not use the raw retinal speed measurement to decide about the velocity of objects in its field of vision. It also explains how the retinal speed signal can be processed to obtain an estimation of the object?s physical speed, and why the distance does not matter in this processing. However, the hypothesis cannot explain why the algorithm seems to work well for cases in which distance and size vary coherently between them, and why object?s familiarity biases the estimation of speed. In this work we present a conceptual model that captures the features mentioned above, and it is qualitatively capable to account for most psychophysical data, including a new experiment in which the observers had to compare the motion of familiar (basketballs and tennis balls) and unfamiliar objects. The experiment consisted in presenting to the observers movies containing basket and tennis balls and a white circle of the same size of the balls (control condition). The movies were presented on two CRT monitors. There were two main conditions namely, the one in which test and reference were displayed at the same distance, and the other, in which the test was displayed 3.6 times further away than the reference. 3.6 corresponds to the size relation between a basket and a tennis balls. A 2IFC paradigm with the method of constant stimuli was used to measure the point of subjective equality (PSE). Results show that the temporal frequency hypothesis cannot explain the perception of speed of familiar objects. In this case, speed seems to be scaled by using the prototypical size of the objects.