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

Abstract

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.

Symmetry Detection in Visual Impairment: Behavioral Evidence and Neural Correlates

“…Given that symmetry affords grouping, the effect may arise because the presence of paired structures increases the perceptual salience of the haptically explored pattern [36,37]. Our findings indicate that symmetry facilitates the tactile processing of stimuli, even when it is an incidental encoding property and participants' attention is not focused on this property, because participants were not informed that some configurations would be symmetric.…”

“…Although haptic object and picture recognition have been extensively studied in the blind, only recently has symmetry detection been specifically investigated in early and late blind individuals [36][37][38].…”

“…In a set of studies by the co-authors of this review, Cattaneo et al [36,37] presented blind participants with a short-term memory task in which they were required to memorize and retrieve a number of target-positions on a 2D matrix that was explored haptically (see details below). Using a similar task in the visual modality, Rossi-Arnaud and colleagues [51,52] found that the presence of symmetry (although irrelevant for the purpose of their task), facilitated the memory retrieval of target patterns.…”

“…Although symmetry can still be perceived by individuals lacking binocular input (or with a deficit in binocular vision), processing appears to be less efficient than observed for individuals possessing a normally developed binocular vision system. [25] and Cattaneo et al [35], to assess visual symmetry detection: a vertically symmetric pattern (left) and a random non-symmetrical pattern (right) are shown here; (b) Example of haptic matrices used in Cattaneo et al [36,37]. Matrices were presented either frontally (lower panel) or horizontally (upper panel).…”

“…Our aim was to determine whether this was also the case in blind individuals when perceiving similar configurations in the haptic domain. In particular, we presented blind participants with wooden 2D matrices consisting of 25 tactilely perceivable cells, seven of which were covered with sandpaper, so that they could be easily recognized by touch [36,37]. Target cells could either form a symmetric configuration (either along the vertical or the horizontal axis) or be placed in a random non-symmetrical order (see Figure 1B).…”