MONOCULAR EGOCENTRIC DISTANCE INFORMATION GENERATED BY HEAD MOVEMENT

How might definite spatial scale be determined on the basis of monocular optic flows? The evidence for the perception of distances in depth from optic flow indicates that head motion is essential for accurate performance. Accordingly, we propose a solution that entails the use of symmetries in the physically determined form of oscillatory head trajectories. The hypothesized solution is notable in two other respects. The first is the use of a time-dimensioned optic variable, tau (Lee, 1974). This strategy takes advantage of the fact that metric temporal scaling is preserved in optic flow. Second, somatosensory information about the amplitude of head motion is used to scale distance in intrinsic units. An alternative multimodal solution would require somatosensory information about velocity of head motion, but the evidence from studies of vestibulo-ocular reflex indicate that adequate velocity information may not be available. Finally, we discuss means for testing the proposed solution.