The nature of working memory for Braille

Abstract

Blind individuals have been shown on multiple occasions to compensate for their loss of sight by developing exceptional abilities in their remaining senses. While most research has been focused on perceptual abilities per se in the auditory and tactile modalities, recent work has also investigated higher-order processes involving memory and language functions. Here we examined tactile working memory for Braille in two groups of visually challenged individuals (completely blind subjects, CBS; blind with residual vision, BRV). In a first experimental procedure both groups were given a Braille tactile memory span task with and without articulatory suppression, while the BRV and a sighted group performed a visual version of the task. It was shown that the Braille tactile working memory (BrWM) of CBS individuals under articulatory suppression is as efficient as that of sighted individuals' visual working memory in the same condition. Moreover, the results suggest that BrWM may be more robust in the CBS than in the BRV subjects, thus pointing to the potential role of visual experience in shaping tactile working memory. A second experiment designed to assess the nature (spatial vs. verbal) of this working memory was then carried out with two new CBS and BRV groups having to perform the Braille task concurrently with a mental arithmetic task or a mental displacement of blocks task. We show that the disruption of memory was greatest when concurrently carrying out the mental displacement of blocks, indicating that the Braille tactile subsystem of working memory is likely spatial in nature in CBS. The results also point to the multimodal nature of working memory and show how experience can shape the development of its subcomponents.

Figure 1. Results of the tactile task performed with and without articulatory suppression.

Both groups performed similarly with no significant difference in number of items recalled when the task was performed without articulatory suppression. However, when articulatory suppression was present, the CBS group performed better than the BRV group.

Figure 2. Results of the tactile task performed by the CBS subjects and of the visual task performed by BRV and sighted subjects.

Under their respective conditions, all groups performed equally well.

Figure 3. Results of the Braille task (Experiment 2).

The added tasks of mental arithmetic and mental displacement of blocks significantly affected performance for both groups. Additionally, the spatial task affected significantly more than the non-spatial one, again for both groups, indicating that the tactile module of working memory is more spatial in nature. Note that the error bar is 0 for the CBS group performing the Braille task alone as all of the subjects recalled the same number of items, possibly reflecting a ceiling effect.