Reference Frame Preferences in Haptics Differ for the Blind and Sighted in the Horizontal but Not in the Vertical Plane

The effect of vertical and horizontal symmetry on memory for tactile patterns in late blind individuals

Visual stimuli that exhibit vertical symmetry are easier to remember than stimuli symmetric along other axes, an advantage that extends to the haptic modality as well. Critically, the vertical symmetry memory advantage has not been found in early blind individuals, despite their overall superior memory, as compared with sighted individuals, and the presence of an overall advantage for identifying symmetric over asymmetric patterns. The absence of the vertical axis memory advantage in the early blind may depend on their total lack of visual experience or on the effect of prolonged visual deprivation. To disentangle this issue, in this study, we measured the ability of late blind individuals to remember tactile spatial patterns that were either vertically or horizontally symmetric or asymmetric. Late blind participants showed better memory performance for symmetric patterns. An additional advantage for the vertical axis of symmetry over the horizontal one was reported, but only for patterns presented in the frontal plane. In the horizontal plane, no difference was observed between vertical and horizontal symmetric patterns, due to the latter being recalled particularly well. These results are discussed in terms of the influence of the spatial reference frame adopted during exploration. Overall, our data suggest that prior visual experience is sufficient to drive the vertical symmetry memory advantage, at least when an external reference frame based on geocentric cues (i.e., gravity) is adopted.

Language as a Source of Evidence for Theories of Spatial Representation

David Marr's metatheory emphasized the importance of what he called the computational level of description—an analysis of the task the visual system performs. In the present article I argue that this task should be conceived of not just as object recognition but as spatial understanding, and that the mental representations responsible for spatial understanding are not exclusively visual in nature. In particular, a theory of the visual system must interact with a theory of the language faculty to explain how we talk about what we see—and how we see all the things we talk about as though they are part of the perceived world. An examination of spatial language both raises the bar for theories of vision and provides important hints for how spatial understanding is structured.