Empirical studies consistently show that judgments of the speed of self-motion are influenced by changes in the altitude of an observer. In general, a given actual speed is judged to be relatively faster from a lower altitude and relatively slower from a higher altitude. Similarly, loss of altitude can be accompanied by a false perception of increasing speed, while increases in altitude can be accompanied by a false perception of loss in speed. The direction of these effects is consistent with the Global Optical Flow Rate (GOFR) Hypothesis. However, the pattern of effects is not proportional to the ratio of velocity to altitude as predicted by the GOFR Hypothesis. An alternative model is presented that predicts additive effect of speed and altitude changes on speed perception.
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