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Measuring the sensitivity of tactile temporal order judgments in sighted and blind participants using the adaptive psi method
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Description: Spatial locations of somatosensory stimuli are coded according to somatotopic and spatiotopic reference frames, representing somatic sensations according to the anatomical distribution of the sensory receptors on the skin surface, and according to the relative position of the body parts in external space, respectively. This was mostly evidenced by means of temporal order judgment (TOJ) tasks in which participants discriminate the temporal order of two tactile stimuli applied on the two hands. Because crossing the hands generates a conflict between anatomical and spatial responses, TOJ performance is typically decreased in such posture, except for congenitally blind people, suggesting a role of visual experience in somatosensory perception. In most previous TOJ studies, stimuli were presented using the method of constant stimuli, i.e. the constant repetition of a predefined sample of stimulus-onset asynchronies (SOA) separated the two stimuli. This method has the disadvantage that an important number of trials is needed to obtain reliable data, and to dissociate performances of distinct groups characterized by different cognitive abilities. Therefore, this study aimed to replicate previous tactile TOJ data with the adaptive psi method. Such method adapts the SOA presented in each trial according to the participant’s performance in all the previous trials, allowing to precisely estimate the temporal sensitivity of each participant while the presented stimuli are adapted to the participant’s individual discrimination threshold. We successfully replicated previous findings in both sighted and blind participants, corroborating previous data on spatial representations of somatosensory inputs using a more robust psychophysical tool.