Exploring Silent Speech Interfaces Based on Frequency-Modulated Continuous-Wave Radar

Speech is our most natural and efficient form of communication and offers a strong potential to improve how we interact with machines. However, speech communication can sometimes be limited by environmental (e.g., ambient noise), contextual (e.g., need for privacy), or health conditions (e.g., laryngectomy), preventing the consideration of audible speech. In this regard, silent speech interfaces (SSI) have been proposed as an alternative, considering technologies that do not require the production of acoustic signals (e.g., electromyography and video). Unfortunately, despite their plentitude, many still face limitations regarding their everyday use, e.g., being intrusive, non-portable, or raising technical (e.g., lighting conditions for video) or privacy concerns. In line with this necessity, this article explores the consideration of contactless continuous-wave radar to assess its potential for SSI development. A corpus of 13 European Portuguese words was acquired for four speakers and three of them enrolled in a second acquisition session, three months later. Regarding the speaker-dependent models, trained and tested with data from each speaker while using 5-fold cross-validation, average accuracies of 84.50% and 88.00% were respectively obtained from Bagging (BAG) and Linear Regression (LR) classifiers, respectively. Additionally, recognition accuracies of 81.79% and 81.80% were also, respectively, achieved for the session and speaker-independent experiments, establishing promising grounds for further exploring this technology towards silent speech recognition.

Scopolamine blocks context-dependent reinstatement of fear responses in rats

Return of fear poses a problem for extinction-based therapies of clinical anxiety. Experimental research has discovered several pathways to return of fear, one of which is known as reinstatement. Here, we evaluated in rats the potential of scopolamine, a non-selective muscarinic receptor antagonist that is also safe for use in humans, to prevent the reinstatement of extinguished fear. We conducted three experiments with a total sample of 96 female rats. All rats went through a fear acquisition session (tone-shock pairings, CS-US), followed by two extinction sessions (CS only) and a post-extinction fear memory test. Twenty-four hours later, rats were placed in the same or a different context from extinction and received two unsignaled foot shock (US) presentations. On the following day, CS-evoked freezing returned when the reinstating USs had occurred in the same context compared to a different context (context-dependent reinstatement, Experiment 1). Systemic administration of scopolamine before or after the reinstating USs blocked the return of CS-evoked freezing on the following day (Experiments 2 and 3). Our findings suggest that administering scopolamine around the time of an aversive experience could prevent relapse of extinguished fears in humans.

Retention of Adaptive Control Over Varying Intervals: Prevention of Slip- Induced Backward Balance Loss During Gait

Stability improvements made in a single acquisition session with merely five slips in walking are sufficient to prevent backward balance loss (BLOB) at the end of session, but not after 12 mo. The purpose of this study was to determine whether the effect of an enhanced single acquisition session would be retainable if tested sooner, at intervals of ≤4 mo. Twenty-four young subjects were exposed to blocks of slip, nonslip, and both types of trials during walking at their preferred speed in the acquisition session. In each of the four follow-up sessions around 1 wk, 2 wk, 1 mo, and 4 mo later, these same subjects experienced only a single slip after eight to 13 unperturbed walking trials in an otherwise identical setup. Gait stability was obtained as the shortest distance between the measured center of mass (COM) state (position and velocity) and the mathematically predicted threshold for BLOB at pre- and postslip, corresponding to the instants of touchdown of the slipping limb and liftoff of the contralateral limb, respectively. During the acquisition session, pre- and postslip stability improved significantly, resulting in a reduction of BLOB from 100% in the first slip (S1) to 0% in the last slip (S24), with improvements converging to a steady state, that enabled all of the subjects to avoid BLOB, regardless of whether a slip occurred. During retest sessions, subjects' preslip stability was not different from that in S24, but was greater than that in S1. Their postslip stability was also greater than that in S1 but less than that in S24, resulting in BLOB at a 40% level. No difference was found in any of these aspects between each follow-up session. These adaptive changes were associated with a range of individual differences, varying from no detectable deterioration in all aspects ( n = 8) to a consistent BLOB in all follow-ups ( n = 3). Our findings demonstrated the extent of plasticity of the CNS, characterized by rapid acquisition of a stable COM state under unpredictable slip conditions and retention of such improvements for months, resulting in a reduced occurrence of unintended backward falling.

Long-Term Retention of Gait Stability Improvements

Evidence of long-term modification of behavior—in particular, gait alterations in response to repeated exposure to slips—within the locomotor-balance control system is limited. The purpose of this study was to examine whether improvements in fall-resisting behavior as reflected by improvements in gait stability could be retained on a long-term basis. Eight healthy young subjects were exposed to a block of repeated slip trials during a single acquisition session consisting of five repeated slip exposures; the same subjects were then re-tested using the same protocol at a minimum of 12 mo later. Pre- and postslip gait stability for all slip trials was measured at touchdown (slipping limb) and liftoff (contralateral limb) based on the center of mass state (i.e., its instantaneous position and velocity) relative to the base of support (BOS) and the predicted thresholds for backward loss of balance. In the acquisition session, subjects were able to increase pre- and postslip stability, which significantly correlated with a decrease in the incidence of balance loss from 100% (1st slip) to 0% (5th slip). All subjects exhibited a similar balance loss on the first slip of the follow-up session. Nonetheless, subjects were able to retain the acquired preslip stability with feedforward control on the first slip but not the postslip stability related to the reactive response. Also, the subjects demonstrated a faster re-acquisition, with only one balance loss on the second slip of the follow-up session, as compared with seven balance losses on the acquisition session. Such rapid improvements were achieved by the significantly greater increase in post- compared with preslip stability; this increase was for the most part, a consequence of reductions in slip intensity (i.e., the peak BOS velocity). We concluded that a single acquisition session could only produce limited long-term retainable effects within the locomotor-balance control system. It appeared, however, that the CNS was still primed to more rapidly update its internal representation of gait stability during re-acquisition.

CASE-BASED REASONING FOR KNOWLEDGE ACQUISITION SUGGESTIONS

Case-based suggestion (CBS) is a general mechanism for system-driven interactive knowledge acquisition. CBS applies case-based reasoning to the task of knowledge acquisition. It utilizes previously acquired knowledge embodied in cases to assist the expert during the current knowledge acquisition session. In this work we describe the general CBS technique and illustrate its use during the acquisition of a specific kind of knowledge. A system utilizing CBS was implemented in the acquisition module of a prototype system called ODS, which structures acquired diagnostic knowledge in decision trees. The algorithm used for case-based suggestion by the ODS system and a description of how the decision tree knowledge was represented in the case base is presented. Several evaluation metrics are introduced, and the application of these measures to several experiences of acquiring knowledge with ODS is discussed.

Neuroendocrine and Behavioral Effects of Flunarizine in Young and Old Rats

Neuroendocrine and behavioral effects following an acute or chronic treatment with the calcium antagonist, flunarizine, have been studied in young and old rats. Both in young and old rats, acute administration of flunarizine (2 mg/kg) failed to modify plasma prolactin (PRL) levels, as measured at 8.00 a.m., 4.00 p.m. and 12.00 p.m. A chronic treatment with flunarizine (0.5 mg/kg/day, for 20 days) in young rats was followed by a relevant, albeit statistically not significant, increase in plasma PRL levels, as measured at 8.00 a.m. and 4.00 p.m., and by a significant decrease at 12.00 p.m. A shift of nocturnal peak of plasma PRL levels from 12.00 p.m. to 4.00 a.m. was observed in these animals. A chronic treatment with flunarizine in old rats was followed by a significant increase in plasma PRL levels, as measured at 12.00 p.m. The acquisition of active avoidance behavior was studied in a shuttle-box test. Acute administration of flunarizine failed to change the performance of young and old rats in acquiring the behavioral response, as measured by the total number of conditioned avoidance responses (CARs) and the percentage of learners. When flunarizine was administered chronically, a decrease in CARs and learners was observed both in young and old rats. This was accompanied by a significant increase in the percentage of animals that froze during the acquisition session. No significant effect was found in young and old rats tested in a “despair” test after a chronic treatment with flunarizine.