Psychophysically, it has been shown that humans can estimate their heading to within 1 deg of visual angle during simulated translation (Warren, Morris, & Kalish,
1988). However, good (i.e., accurate and precise) performance during pure translation and fixed gaze angle does not necessarily indicate 3D self-motion perception because the task could be easily performed by simply locating the FOE in the 2D flow field without any 3D interpretation. To determine if humans are capable of recovering 3D heading from combined translational and rotational retinal flow, a number of studies examined self-motion perception during simulated eye rotation and reported good performance when either the rotation rates were low (Warren & Hannon,
1988) or subjects had extraretinal information about rotation (Royden, Banks, & Crowell,
1992; Warren & Hannon,
1988) but poor performance at high rotation rates with retinal flow information alone (Royden et al.,
1992). However, the task used in these studies was to estimate future path with respect to an environmental reference point, which is quite different from estimating heading itself (Stone & Perrone,
1997) and is further confounded by ambiguity in the perceived depth of the reference point (Ehrlich, Beck, Crowell, Freeman, & Banks,
1998). Although Stone and Perrone (
1997), using a true heading-estimation task and simulating motion along a curved path, found that humans can indeed recover their heading accurately and precisely from optic-flow information alone (see also Cutting,
1986; Rieger & Toet,
1985), this finding does not fully resolve the question of whether humans can derive heading directly from the instantaneous velocity field as is done by the mathematical and neurophysiological models cited above. The accurate heading estimation observed could have resulted from an indirect reconstruction of heading by first estimating one's displacement over time with respect to a fixed rigid environment (one's path) and then working backward to infer heading as the path's tangent. While many recent studies have begun to address the question of heading versus path estimation during visual control of locomotion (e.g., Wann & Swapp,
2000; Warren, Kay, Zosh, Duchon, & Sahuc,
2001), the most direct way to resolve the issue unambiguously is to eliminate the visual cues beyond the velocity field that could allow one to recover one's path independent of heading (Li & Warren,
2000; Stone & Perrone,
1997). In this study, we investigate whether humans can precisely and accurately perceive and adjust their heading from a sequence of velocity fields by using dynamic random-dot optic-flow stimuli in which environmental points are periodically redrawn. This stimulus allowed us to generate a continuously available heading signal while eliminating path, displacement, and other visual cues beyond the velocity field from the optic flow.