Abstract
Stroke patients suffer from impairments of both motor and somatosensory functions. The functional recovery of upper extremities is one of the primary goals of rehabilitation programs. Additional somatosensory deficits limit sensorimotor function and significantly affect its recovery after the neuromotor injury. Sensory substitution systems, providing tactile feedback, might facilitate manipulation capability, and improve patient's dexterity during grasping movements. As a first step toward this aim, we evaluated the ability of healthy subjects in exploiting electrotactile feedback on the shoulder to determine the number of perceived stimuli in numerosity judgment tasks. During the experiment, we compared four different stimulation patterns (two simultaneous: short and long, intermittent and sequential) differing in total duration, total energy, or temporal synchrony. The experiment confirmed that the subject ability to enumerate electrotactile stimuli decreased with increasing the number of active electrodes. Furthermore, we found that, in electrotactile stimulation, the temporal coding schemes, and not total energy or duration modulated the accuracy in numerosity judgment. More precisely, the sequential condition resulted in significantly better numerosity discrimination than intermittent and simultaneous stimulation. These findings, together with the fact that the shoulder appeared to be a feasible stimulation site to communicate tactile information via electrotactile feedback, can serve as a guide to deliver tactile feedback to proximal areas in stroke survivors who lack sensory integrity in distal areas of their affected arm, but retain motor skills.
Highlights
The sense of touch is the basis of interaction with other human beings and with the environment around us
The distribution of electrotactile intensity thresholds was submitted to two Friedman Tests with electrodes location and electrotactile code as factors
The first analysis revealed the main effect of the electrodes location on the current intensity (χ 2 = 45.8, p < 0.001)
Summary
The sense of touch is the basis of interaction with other human beings and with the environment around us. The tactile sensation provides information about contact with objects, which is essential to grasp and to manipulate them Neurological diseases such as stroke can interrupt or damage sensory feedback pathways that normally play a key role in the coordination and Electrotactile Code in Numerosity Judgment accuracy of movements. Due to the impaired motor control and the long processing delays of the visual system, even the simplest movements require great concentration and can become nearly impossible (Cameron et al, 2014). This condition limits the independence of patients, their safety and often prolongs hospital stay (Carey, 1995; Sommerfeld and von Arbin, 2004; Tyson et al, 2008). Feedback of tactile information has the potential to improve hand function in patients with sensory loss since it provides additional information that would otherwise be unavailable, countering the learned non-use phenomenon and favoring functional recovery
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