Neural correlates associated with superior tactile symmetry perception in the early blind

Abstract

Symmetry is an organizational principle that is ubiquitous throughout the visual world. However, this property can also be detected through non-visual modalities such as touch. The role of prior visual experience on detecting tactile patterns containing symmetry remains unclear. We compared the behavioral performance of early blind and sighted (blindfolded) controls on a tactile symmetry detection task. The tactile patterns used were similar in design and complexity as in previous visual perceptual studies. The neural correlates associated with this behavioral task were identified with functional magnetic resonance imaging (fMRI). In line with growing evidence demonstrating enhanced tactile processing abilities in the blind, we found that early blind individuals showed significantly superior performance in detecting tactile symmetric patterns compared to sighted controls. Furthermore, comparing patterns of activation between these two groups identified common areas of activation (e.g. superior parietal cortex) but key differences also emerged. In particular, tactile symmetry detection in the early blind was also associated with activation that included peri-calcarine cortex, lateral occipital (LO), and middle temporal cortex, as well as inferior temporal and fusiform cortex. These results contribute to the growing evidence supporting superior behavioral abilities in the blind, and the neural correlates associated with crossmodal neuroplasticity following visual deprivation.

Symmetry Detection in Visual Impairment: Behavioral Evidence and Neural Correlates

“…On a behavioral level, in both the tactile memory task [36] and detection task [38], early blind participants were also found to outperform blindfolded sighted subjects. This result is in line with consistent evidence suggesting enhanced tactile discrimination abilities in the blind [55].…”

“…Matrices were presented either frontally (lower panel) or horizontally (upper panel). From left to right: examples of horizontally symmetric patterns, vertically symmetric patterns and non-symmetric patterns; (c) Custom made device used for the tactile symmetry detection task in Bauer et al [38]. The picture shows a vertically symmetric configuration.…”

“…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].…”

“…Moreover, in Cattaneo et al [36,37], we investigated whether symmetry facilitated memory, but we did not assess the performance of detecting symmetry explicitly. In a recent study [38], we addressed these limitations by testing early blind and blindfolded sighted participants in a tactile/haptic symmetry detection task using stimuli that resembled those typically used in investigating visual symmetry detection. Tactile stimuli consisted of a 32 by 36 tactile pin array (inter-pin spacing of 2.4 mm) that covered an area of 8.5 by 7.5 cm ( Figure 1C).…”

“…Our group has recently investigated the neural underpinnings of tactile symmetry detection [38]. In this study, early blind subjects and blindfolded sighted participants were presented with either symmetric (vertically or horizontally) or asymmetric tactile configurations (see above for methodological details and behavioral results).…”