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Harald Frenz, Markus Lappe; Travel distance estimation from optic flow. Journal of Vision 2002;2(7):638. doi: 10.1167/2.7.638.
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© ARVO (1962-2015); The Authors (2016-present)
Can optic flow be used to estimate travel distance? In principle this is impossible because optic flow speeds scale with the dimensions of the environment. Distance estimation from optic flow therefore needs calibration from other sources of depth information. Previously we have shown, however, that discrimination of the distances of simulated self-motions of different speed and duration is reliably possible from optic flow if the visual environment is the same for both motions. In this case, independent scaling information is not necessary. Here we ask whether a distance estimate obtained from optic flow can be transformed into a spatial interval in the same visual environment.
Subjects viewed a simulated self-motion sequence on a large (90 by 90 deg) projection screen. The sequence depicted self-motion over a textured ground plane. Simulated distances ranged from 1.5 to 9 meters with variable speed and duration of the movement. After the movement stopped, the screen depicted a stationary view of the scene and two horizontal lines appeared on the ground in front of the observer. The subject had to adjust one of these lines such that the spatial interval between the lines matched the distance traveled during the movement simulation.
Adjusted interval size was linearly related to simulated travel distance, suggesting that observers were able to obtain a measure of distance from the optic flow. The slope of the regression was 0.7. Thus subjects underestimated distance by 30%. We conclude that optic flow can be used to derive an estimate of travel distance, but this estimate is subject to scaling when compared to static intervals in the environment.
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