Page 239 - Control Theory in Biomedical Engineering

220 Control theory in biomedical engineering

conditions: no feedback, visual feedback, feedback through vibrotactile or
electrotactile stimulation, and addition of an extra stimulator for touch
feedback.
As a result, vibrotactile stimulation had much better performance com-
pared to the nonfeedback conditions; and the addition of touch feedback
further increased the performance but at the cost of increasing the duration.
A benefit of electrocutaneous systems is that they often require less power
than mechanical systems (e.g., vibrotactile devices). However, the contam-
ination of EMG signals is probably due to the electrical stimulation of
muscles.

Others
There are other substitution techniques such as vision substitution (Bach-y-
Rita et al., 1969), auditory substitution (Lundborg et al., 1999), and others.
These techniques currently open the paradigm of associating an external
stimulus as sensory feedback called synesthesia (Cytowic, 2002). Two types
of synesthesia can be distinguished: strong synesthesia is characterized by a
vivid image in one sensory modality in response to stimulation in another
one, and weak synesthesia is characterized by cross-sensory correspondences
expressed through language, perceptual similarity, and perceptual interac-
tions during information processing (Martino and Marks, 2001). Synesthetic
learning can also be present in vibrotactile stimuli, for instance, Huaroto
et al. (2018) reported, after 2 days of training, WD adherence and synesthetic
learning due to a pressure stimulus on healthy individuals using a soft vibro-
tactile device.

4.5.2 Modality-matched feedback
In modality-matched methods, the information from the user is matched
with sensations, for example, touch with a prosthesis is felt as touch on
the user’s skin although with mismatched locations. As a result, the user must
still dedicate attention to interpret the feedback signal. In some applications,
modality-matched feedback is preferred to sensory substitution because it
does not require a significant interpretation by the user (Schofield et al.,
2014). For instance, Meek et al. (1989) explored grip pressure feedback with
a myoelectric-controlled prosthetic arm. They mounted a servo-controlled
“pusher” on a socket. The pusher pressed into the skin an amount propor-
tional to the force in the terminal device, a method that the authors termed
“Extended Physiologic Taction” (EPT). Additionally, to achieve intuitive
haptic feedback it is beneficial to satisfy two conditions: (1) somatotopic