Effects of muscle fatigue on the usability of a myoelectric human-computer interface.

Electromyography-based human-computer interface development is an active field of research. However, knowledge on the effects of muscle fatigue for specific devices is limited. We have developed a novel myoelectric human-computer interface in which subjects continuously navigate a cursor to targets by manipulating a single surface electromyography (sEMG) signal. Two-dimensional control is achieved through simultaneous adjustments of power in two frequency bands through a series of dynamic low-level muscle contractions. Here, we investigate the potential effects of muscle fatigue during the use of our interface. In the first session, eight subjects completed 300 cursor-to-target trials without breaks; four using a wrist muscle and four using a head muscle. The wrist subjects returned for a second session in which a static fatiguing exercise took place at regular intervals in-between cursor-to-target trials. In the first session we observed no declines in performance as a function of use, even after the long period of use. In the second session, we observed clear changes in cursor trajectories, paired with a target-specific decrease in hit rates.

Learning to modulate the partial powers of a single sEMG power spectrum through a novel human-computer interface.

New human-computer interfaces that use bioelectrical signals as input are allowing study of the flexibility of the human neuromuscular system. We have developed a myoelectric human-computer interface which enables users to navigate a cursor to targets through manipulations of partial powers within a single surface electromyography (sEMG) signal. Users obtain two-dimensional control through simultaneous adjustments of powers in two frequency bands within the sEMG spectrum, creating power profiles corresponding to cursor positions. It is unlikely that these types of bioelectrical manipulations are required during routine muscle contractions. Here, we formally establish the neuromuscular ability to voluntarily modulate single-site sEMG power profiles in a group of naïve subjects under restricted and controlled conditions using a wrist muscle. All subjects used the same pre-selected frequency bands for control and underwent the same training, allowing a description of the average learning progress throughout eight sessions. We show that subjects steadily increased target hit rates from 48% to 71% and exhibited greater control of the cursor's trajectories following practice. Our results point towards an adaptable neuromuscular skill, which may allow humans to utilize single muscle sites as limited general-purpose signal generators. Ultimately, the goal is to translate this neuromuscular ability to practical interfaces for the disabled by using a spared muscle to control external machines.

Immediate judgments of learning predict subsequent recollection: evidence from event-related potentials.

Judgments of learning (JOLs) are assessments of how well materials have been learned. Although a wide body of literature has demonstrated a reliable correlation between memory performance and JOLs, relatively little is known about the nature of this link. Here, we investigate the relationship between JOLs and the memory retrieval processes engaged on a subsequent memory test. Participants first studied cue-target word pairs and assigned JOLs to each. Later, memory for the cue word in each pair was assessed using an old/new recognition memory task, and electrophysiological measures of familiarity and recollection were examined. Recognition accuracy was superior for materials given high rather than low JOLs. Analysis of event-related potentials (ERPs) revealed that for both high and low JOL items, successful recognition elicited correlates of familiarity (the mid-frontal effect) and recollection (the left-parietal effect). Importantly, however, the magnitude of the familiarity correlate was equal for high and low JOL items, whereas the magnitude of the recollection correlate was significantly larger for items given high JOLs. These findings demonstrate that JOLs made at study correlate with memory retrieval at test-but that this correlation is specific to recollection. The electrophysiological data support the broader view that participants focus on contextual cues when making JOLs, which may later aid recollection.

Pilot study for a Brain-Muscle-Computer Interface using the Extensor Pollicis Longus with preselected frequency bands.

We are developing a new class of Brain-Computer Interface that we call a Brain-Muscle-Computer Interface, in which surface electromyography (sEMG) recordings from a single muscle site are used to control the movement of a cursor. Previous work in our laboratory has established that subjects can learn to navigate a cursor to targets by manipulating the sEMG from a head muscle (the Auricularis Superior). Subjects achieved two-dimensional control of the cursor by simultaneously regulating the power in two frequency bands that were chosen to suit the individuals. The purposes of the current pilot study were to investigate (i) subjects' abilities to manipulate power in separate frequency bands in other muscles of the body and (ii) whether subjects can adapt to preselected frequency bands. We report pilot study data suggesting that subjects can learn to perform cursor-to-target tasks on a mobile phone by contracting the Extensor Pollicis Longus (a muscle located on the wrist) using frequency bands that are the same for every individual. After the completion of a short training protocol of less than 30 minutes, three subjects achieved 83%, 60% and 60% accuracies (with mean time-to-targets of 3.4 s, 1.4 s and 2.7 s respectively). All three subjects improved their performance, and two subjects decreased their time-to-targets following training. These results suggest that subjects may be able to use the Extensor Pollicis Longus to control the BMCI and adapt to preselected frequency bands. Further testing will more conclusively investigate these preliminary findings.

Judgments of learning do not reduce to memory encoding operations: event-related potential evidence for distinct metacognitive processes.

To examine how judgments of learning (JOLs) are made, we used event-related potentials (ERPs) to compare neural correlates of JOLs and successful memory encoding. Participants saw word pairs, and for each made a JOL indicating how confident they were that they would remember the pairing on a later cued recall task. ERPs were recorded while JOLs were made and were separated according to whether items were: (i) remembered or forgotten on the subsequent test, and (ii) rated likely or unlikely to be remembered. An early positive-going ERP effect was associated with both of these comparisons, whereas a later negative-going effect was present only in the separation based upon JOL ratings. ERP data therefore indicate that JOLs do not reduce to encoding processes that predict the accuracy of memory judgments.