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Charlie Burlingham, David Heeger; Heading Perception Depends on Time-Varying Evolution of Optic Flow. Journal of Vision 2018;18(10):47. doi: 10.1167/18.10.47.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Is heading perception computed from instantaneous optic flow? Background: For observer translation, heading direction is indicated by a singularity in the optic flow field, the point in the image at which optic flow is zero. When an observer rotates while translating, the singularity is displaced and no longer corresponds to heading. Methods: Observers viewed moving patterns and made forced-choice heading judgements. Each moving pattern consisted of a collection of grating patches. Each patch was a plaid composed of two orthogonal gratings (sf = 3 cycles/°; overall contrast = 100%) multiplied by a raised cosine envelope (diameter = .25°). No patches were presented within a central rectangular region, ensuring that observers could not directly track the singularity of the flow field. There were three stimulus conditions: envelope motion, phase motion, and time-varying phase motion. For envelope motion, each patch (both the envelope and the plaid) was displaced on each frame. This stimulus contained two cues that could potentially compensate for rotation: the trajectories of the patches and time-varying optic flow. For phase motion and time-varying phase motion, the plaid envelopes remained stationary while the phases of the gratings shifted over time. The phase velocity of the plaid patches corresponded to either a single optic flow field (phase motion) or a sequence of flow fields (time-varying phase motion). Phase motion conveyed only instantaneous optic flow. Time-varying phase motion conveyed time-varying optic flow, but not patch trajectories. Results: Heading judgements were strongly biased for phase motion, indicating that observers misinterpreted rotation as additional translation. Observers were able to compensate for the rotation in the envelope motion and time-varying phase motion conditions, removing more than 50% of the bias. Conclusion: Instantaneous optic flow is insufficient for accurate heading perception. Time-varying optic flow is needed.
Meeting abstract presented at VSS 2018
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