Abstract
People suffering from neuromuscular disorders such as locked-in syndrome (LIS) are left in a paralyzed state with preserved awareness and cognition. In this study, it was hypothesized that changes in local hemodynamic activity, due to the activation of Broca’s area during overt/covert speech, can be harnessed to create an intuitive Brain Computer Interface based on Near-Infrared Spectroscopy (NIRS). A 12-channel square template was used to cover inferior frontal gyrus and changes in hemoglobin concentration corresponding to six aloud (overtly) and six silently (covertly) spoken words were collected from eight healthy participants. An unsupervised feature extraction algorithm was implemented with an optimized support vector machine for classification. For all participants, when considering overt and covert classes regardless of words, classification accuracy of 92.88 ± 18.49% was achieved with oxy-hemoglobin (O2Hb) and 95.14 ± 5.39% with deoxy-hemoglobin (HHb) as a chromophore. For a six-active-class problem of overtly spoken words, 88.19 ± 7.12% accuracy was achieved for O2Hb and 78.82 ± 15.76% for HHb. Similarly, for a six-active-class classification of covertly spoken words, 79.17 ± 14.30% accuracy was achieved with O2Hb and 86.81 ± 9.90% with HHb as an absorber. These results indicate that a control paradigm based on covert speech can be reliably implemented into future Brain–Computer Interfaces (BCIs) based on NIRS.
Highlights
Locked-in syndrome (LIS) is a neuromuscular disorder described as near-complete paralysis with preserved awareness and cognition [1]
With very minor chances of motor recovery and poor quality of life, healthy individuals and medical experts often find themselves wondering if such a life is worth fighting for [5]
Among several choices related to signal acquisition for speech classification that were made during this study, two aspects are worth mentioning: (1) Broca’s area was chosen as it plays an important role in speech processing [25] and as activation within this area is unavoidable during speech [26]; (2) Use of six directional words i.e., Up, Down, Right, Left, Forward, and Backward, since a navigational approach allows an intuitive control and it is commonly used in many Brain–Computer Interfaces (BCIs)
Summary
Locked-in syndrome (LIS) is a neuromuscular disorder described as near-complete paralysis with preserved awareness and cognition [1]. Patients with LIS are left with very few degrees of freedom ranging from restricted eye movement (classic LIS) to complete immobility (total LIS) [2]. The most common cause of LIS is a stroke or a traumatic brain injury (31%) or a cerebrovascular disease (52%) [3]. According to Blain et al [4], more than half a million people worldwide are affected by LIS. Sensors 2018, 18, 2989 patient has become medically stable, his/her life span can be significantly prolonged. With very minor chances of motor recovery and poor quality of life, healthy individuals and medical experts often find themselves wondering if such a life is worth fighting for [5].
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