Sergei Gepshtein, RIKEN BSI, Japan
Michael Kubovy, University of Virginia, USA

Visual apparent motion is the experience of motion from the successive stimulation of separate spatial locations. How spatial and temporal distances interact to determine the strength of apparent motion has been controversial.

Some studies report space-time coupling: If we increase spatial or temporal distance between successive stimuli, we must also increase the other distance between them to maintain a constant strength of apparent motion (Korte's third law of motion).

Other studies report space-time tradeoff: If we increase one of these distances we must decrease the other to maintain a constant strength of apparent motion.

We resolve the controversy. Starting from a normative theory of motion measurement and data on human spatiotemporal sensitivity, we conjecture that both coupling and tradeoff should occur, but at different speeds.

We confirm the prediction in two experiments, using suprathreshold multistable apparent-motion displays called motion lattices. Our results show a smooth transition between the tradeoff and coupling as a function of speed: Tradeoff occurs at low speeds and coupling at high speeds. From our data we reconstruct the suprathreshold equivalence contours that are analogous to isosensitivity contours obtained at the threshold of visibility.

Local References

Gepshtein, S., & Kubovy, M. (2007). The lawful perception of apparent motion. Journal of Vision, 7(8):9, 1-15, http://journalofvision.org/7/8/9/, doi:10.1167/7.8.9. [local pdf]

S. Gepshtein and M. Kubovy. Korte's law, the spatiotemporal sensitivity of vision, and the failure of the proximity principle in apparent motion. In Perception, Supp., volume 32. Pion, 2003.\

Other References

Gepshtein, S., Tyukin, I., & Kubovy, M. (2007). The economics of motion perception and invariants of visual sensitivity. Journal of Vision, 7(8):8, 1-18, http://journalofvision.org/7/8/8/, doi:10.1167/7.8.8. [local pdf]