The relative contributions of global and local acceleration components on speed perception and discriminability following adaptation

- Speed adaptation was biased towards local and global components of random dot fields.
- Perceived speed and speed sensitivity were measured following adaptation.
- Perceived speed was dependent on the ratio of adaptation speed to test.
- Changes in perceived speed and sensitivity were dominated by local motion.
- Only perceived speed showed some small modulation due to global motion.

The perception of speed is dependent on the history of previously presented speeds. Adaptation to a given speed regularly results in a reduction of perceived speed and an increase in speed discriminability and in certain circumstances can result in an increase in perceived speed. In order to determine the relative contributions of the local and global speed components on perceived speed, this experiment used expanding dot flow fields with accelerating (global), decelerating (global) and mixed accelerating/decelerating (local) speed patterns. Profound decreases in perceived speed are found when viewing low test speeds after adaptation to high speeds. Small increases in the perceived speed of high test speeds occur following adaptation to low speeds. There were small but significant differences in perceived stimulus speed after adaptation due to different acceleration profiles. No evidence for global modulation of speed discriminability following adaptation was found.