Abstract
In a previous behavioral study, it was shown that early blind individuals were superior to sighted ones in discriminating two-dimensional (2D) tactile angle stimuli. The present study was designed to assess the neural substrate associated with a haptic 2D angle discrimination task in both sighted and blind individuals. Subjects performed tactile angle size discriminations in order to investigate whether the pattern of crossmodal occipital recruitment was lateralized as a function of the stimulated hand. Task-elicited activations were also compared across different difficulty levels to ascertain the potential modulatory role of task difficulty on crossmodal processing within occipital areas. We show that blind subjects had more widespread activation within the right lateral and superior occipital gyri when performing the haptic discrimination task. In contrast, the sighted activated the left cuneus and lingual gyrus more so than the blind when performing the task. Furthermore, activity within visual areas was shown to be predictive of tactile discrimination thresholds in the blind, but not in the sighted. Activity within parietal and occipital areas was modulated by task difficulty, where the easier angle comparison elicited more focal occipital activity along with bilateral posterior parietal activity, whereas the more difficult comparison produced more widespread occipital activity combined with reduced parietal activation. Finally, we show that crossmodal reorganization within the occipital cortex of blind individuals was primarily right lateralized, regardless of the stimulated hand, supporting previous evidence for a right-sided hemispheric specialization of the occipital cortex of blind individuals for the processing of tactile and haptic inputs.
Highlights
Previous work has shown the blind to possess superior auditory abilities, in the spatial hearing (Lessard et al, 1998; Voss et al, 2004) and in the pitch domains (Gougoux et al, 2004)
To further investigate the issue of superior tactile processing in the blind, we recently explored both tactile and haptic perception using a two-dimensional (2D) angle size discrimination task that was developed by Voisin et al (2002), and shown to be dependent on cutaneous, and on proprioceptive feedback (Voisin et al, 2002)
We found that the BOLD activity observed in several visual areas is predictive of the IPT for blind subjects; though this was only true for right-hand angle explorations
Summary
Previous work has shown the blind to possess superior auditory abilities, in the spatial hearing (Lessard et al, 1998; Voss et al, 2004) and in the pitch domains (Gougoux et al, 2004). The primary goal of this study was to address these questions by exploring the pattern of brain activation elicited by an adapted version of the 2D angle discrimination task, designed to be compatible with the physical constraints of functional magnetic resonance imaging (fMRI). This enabled a novel proprioceptive element to the study, as most prior imaging studies of blind individuals focusing on the somatosensory system used passive tactile tasks. This approach is in line a growing body of literature establishing the importance of studying cognitive processes and their underlying neural activity in more action-oriented paradigms to better mimic how individuals interact with the environment (Engel et al, 2013)
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