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When estimating ego-motion in environments (e.g., tunnels, streets) with varying depth, human subjects confuse ego-acceleration with environment narrowing and ego-deceleration with environment widening. Festl, Recktenwald, Yuan, and Mallot (2012) demonstrated that in nonstereoscopic viewing conditions, this happens despite the fact that retinal measurements of acceleration rate-a variable related to tau-dot-should allow veridical perception. Here we address the question of whether additional depth cues (specifically binocular stereo, object occlusion, or constant average object size) help break the confusion between narrowing and acceleration. Using a forced-choice paradigm, the confusion is shown to persist even if unambiguous stereo information is provided. The confusion can also be demonstrated in an adjustment task in which subjects were asked to keep a constant speed in a tunnel with varying diameter: Subjects increased speed in widening sections and decreased speed in narrowing sections even though stereoscopic depth information was provided. If object-based depth information (stereo, occlusion, constant average object size) is added, the confusion between narrowing and acceleration still remains but may be slightly reduced. All experiments are consistent with a simple matched filter algorithm for ego-motion detection, neglecting both parallactic and stereoscopic depth information, but leave open the possibility of cue combination at a later stage.

The formation of a hierarchical representation of space can be induced by the spatial adjacency of places marked by landmark objects from the same semantic category, as was demonstrated by a route-planning experiment (Wiener and Mallot in Spat Cogn Comput 3(4):331-358, 2003). Using the same paradigm, we tested the efficiency of linguistic cues with various hierarchical categorization principles in regional structuring. In five different conditions, places of the experimental environment were characterized (1) by landmark objects, (2) by arbitrary proper names on region level, (3) by prototypical names on region level, (4) by nouns from different semantic categories, and (5) by groups of nouns with intrinsic whole-part relation. A region effect comparable to the landmark object condition was found only for the whole-part relations, which combine spatial proximity with a shared context. A linguistic analysis revealed a correspondence to the intended regional subdivision only for the cues of this condition.

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