Asynchronous, online spaced-repetition training alleviates word-finding difficulties in aphasia.

Word-finding difficulties for naming everyday objects are often prevalent in aphasia. Traditionally, treating these difficulties has involved repeated drilling of troublesome items with a therapist. Spaced repetition schedules can improve the efficiency of such training. However, spaced repetition in a therapy environment can be both difficult to implement and time-consuming. The current study evaluated the potential utility of automated, asynchronous, online spaced repetition training for the treatment of word-finding difficulties in individuals with aphasia. Twenty-one participants completed a two-week training study, completing approximately 60 minutes per day of asynchronous online drilling. The training items were identified using a pretest, and word-finding difficulties were evaluated both at the end of training (i.e., a post-test) and four weeks later (i.e., a retention test). The trained items were separated into three different spaced-repetition schedules: (1) Short-spacing; (2) Long-spacing; and (3) Adaptive-spacing. At the retention-test, all trained items outperformed non-trained items in terms of accuracy and reaction time. Further, preliminary evidence suggested a potential reaction time advantage for the adaptive-spacing condition. Overall, online, asynchronous spaced repetition training appears to be effective in treating word-finding difficulties in aphasia. Further research will be required to determine if different spaced repetition schedules can be leveraged to enhance this effect.

Music-based intervention drives paretic limb acceleration into intentional movement frequencies in chronic stroke rehabilitation.

This study presented a novel kinematic assessment of paretic limb function "online" during the actual therapeutic exercisers rooted within the acceleration domain. Twenty-eight patients at chronic stroke stages participated in an auditory-motor intervention mapping reaching movements of the paretic arm unto surfaces of large digital musical instruments and sound tablets that provided rhythmic entrainment cues and augmented auditory feedback. Patients also wore a tri-axial accelerometer on the paretic limb during the nine-session intervention. The resulting acceleration profiles were extracted and quantified within the frequency domain. Measures of peak power and peak width were leveraged to estimate volitional control and temporal consistency of paretic limb movements, respectively. Clinical assessments included the Wolf Motor Function Test and Fugl-Meyer - Upper Extremity subtest. The results showed that peak power increased significantly from Session 1 to Session 9 within oscillatory frequency ranges associated with intentional movement execution (i.e., 4.5 Hz). Decreases in peak width over time provided additional evidence for improved paretic arm control from a temporal perspective. In addition, Peak width values obtained in Session 1 was significantly correlated with pre-test Fugl-Meyer - Upper Extremity scores. These results highlighted improvements in paretic limb acceleration as an underlying mechanism in stroke motor recovery and shed further light on the utility of accelerometry-based measures of paretic limb control in stroke rehabilitation. The data reported here was obtained from a larger clinical trial: https://clinicaltrials.gov/ct2/show/NCT03246217 ClinicalTrials.gov Identifier: NCT03246217.

Temporospatial Alterations in Upper-Limb and Mallet Control Underlie Motor Learning in Marimba Performance.

Sound-producing movements in percussion performance require a high degree of fine motor control. However, there remains a relatively limited empirical understanding of how performance level abilities develop in percussion performance in general, and marimba performance specifically. To address this issue, nine percussionists performed individualised excerpts on marimba within three testing sessions spaced 29 days apart to assess early, intermediate, and late stages of motor learning. Motor learning was quantified via analyses of both the temporal control of mallet movements, and the spatial variability of upper-limb movements. The results showed that temporal control of mallet movements was greater in the intermediate compared to the early learning session, with no significant additional improvements revealed in the late learning session. In addition, spatial variability in the left and right elbows decreased within the intermediate compared to the early learning session. The results suggest that temporal control of mallet movements may be driven by reductions in spatial variability of elbow movements specifically. As a result, this study provides novel evidence for kinematic mechanisms underlying motor learning in percussion which can be applied towards enhancing musical training.

Auditory cues for somatosensory targets invoke visuomotor transformations: Behavioral and electrophysiological evidence.

Prior to goal-directed actions, somatosensory target positions can be localized using either an exteroceptive or an interoceptive body representation. The goal of the present study was to investigate if the body representation selected to plan reaches to somatosensory targets is influenced by the sensory modality of the cue indicating the target's location. In the first experiment, participants reached to somatosensory targets prompted by either an auditory or a vibrotactile cue. As a baseline condition, participants also performed reaches to visual targets prompted by an auditory cue. Gaze-dependent reaching errors were measured to determine the contribution of the exteroceptive representation to motor planning processes. The results showed that reaches to both auditory-cued somatosensory targets and auditory-cued visual targets exhibited larger gaze-dependent reaching errors than reaches to vibrotactile-cued somatosensory targets. Thus, an exteroceptive body representation was likely used to plan reaches to auditory-cued somatosensory targets but not to vibrotactile-cued somatosensory targets. The second experiment examined the influence of using an exteroceptive body representation to plan movements to somatosensory targets on pre-movement neural activations. Cortical responses to a task-irrelevant visual flash were measured as participants planned movements to either auditory-cued somatosensory or auditory-cued visual targets. Larger responses (i.e., visual-evoked potentials) were found when participants planned movements to somatosensory vs. visual targets, and source analyses revealed that these activities were localized to the left occipital and left posterior parietal areas. These results suggest that visual and visuomotor processing networks were more engaged when using the exteroceptive body representation to plan movements to somatosensory targets, than when planning movements to external visual targets.

The influence of robotic guidance on error detection and correction mechanisms.

New technologies have expanded the available methods to help individuals learn or re-learn motor skills. Despite equivocal evidence for the impact of robotic guidance for motor skill acquisition (Marchal-Crespo, McHughen, Cramer, & Reinkensmeyer, 2010), we have recently shown that robotic guidance mixed with unassisted practice can significantly improve the learning of a golf putting task (Bested & Tremblay, 2018). To understand the mechanisms associated with this new mixed approach (i.e., unassisted and robot-guided practice) for the learning of a golf putting task, the current study aimed to determine if such mixed practice extends to one's ability to detect errors. Participants completed a pre-test, an acquisition phase, as well as immediate, delayed (24-h), and transfer post-tests. During the pre-test, kinematic data from the putter was converted into highly accurate, consistent, and smooth trajectories delivered by a robot arm. During acquisition, 2 groups performed putts towards 3 different targets with robotic guidance on either 0% or 50% of acquisition trials. Only the 50% guidance group significantly reduced ball endpoint distance and variability, as well as ball endpoint error estimations, between the pre-test and the post-tests (i.e., immediate retention, 24-h retention, and 24-h transfer). The current study showed that allowing one to experience both robotic guidance and unassisted (i.e., errorful) performances enhances one's ability to detect errors, which can explain the beneficial motor learning effects of a mixed practice schedule.

Accuracy instructions differently modulate visual and nonvisual contributions to ongoing reaches.

The control of ongoing goal-directed reaches is influenced by both visual and nonvisual sensorimotor processes. Notably, intentions to produce accurate movements also influence reaching performance. However, it is not known whether these improvements associated with accuracy-based intentions can be attributed to changes in movement planning and/or online control. Notably, such improvements may come about via both visual and nonvisual online control processes. Using frequency domain analyses, the relative online contributions of visual and nonvisual subprocesses to reaching performance have been previously identified (e.g., de Grosbois & Tremblay, 2018a, 2018b). Thus, the current study tested whether the relative contributions of these online control subprocesses are influenced by instructions to be accurate. Reaching movements were completed in the presence of 3 experimental manipulations. First, vision during voluntary reaches was either provided or occluded. Second, high- and low-accuracy instruction sets were provided. And third, the predictability of visual information was manipulated through blocked and randomized feedback scheduling. The results indicated that the contribution of online visuomotor processes (i.e., visual subprocess) was increased by the availability of online vision and instructions to be accurate. In contrast, the nonvisual subprocess was promoted in the absence of online vision, but suppressed when a randomized feedback schedule was implemented with instructions to be accurate. Ultimately, instructions to be accurate increase the relative contribution of vision-based online sensorimotor processes and can decrease the contributions of nonvisual online sensorimotor processes. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Which Measures of Online Control Are Least Sensitive to Offline Processes?

A major challenge to the measurement of online control is the contamination by offline, planning-based processes. The current study examined the sensitivity of four measures of online control to offline changes in reaching performance induced by prism adaptation and terminal feedback. These measures included the squared Z scores (Z2) of correlations of limb position at 75% movement time versus movement end, variable error, time after peak velocity, and a frequency-domain analysis (pPower). The results indicated that variable error and time after peak velocity were sensitive to the prism adaptation. Furthermore, only the Z2 values were biased by the terminal feedback. Ultimately, the current study has demonstrated the sensitivity of limb kinematic measures to offline control processes and that pPower analyses may yield the most suitable measure of online control.

Better together: Contrasting the hypotheses explaining the one-target advantage.

Movement times are significantly shorter when moving from a start position to a single target, compared to when one has to continue onto a second target (i.e., the one-target advantage [OTA]). To explain this movement time difference, both the movement integration and the movement constraint hypotheses have been proposed. Although both hypotheses have been found to have explanatory power as to why the OTA exists, the support for each has been somewhat equivocal. The current review evaluated the relative support in the literature for these two hypotheses. Ultimately, preferential support for each theoretical explanation was found to be related to the higher indices of difficulty (IDs: Fitts, 1954) employed. That is, studies that included higher IDs (i.e., 6-8 bits) were more likely to provide more support for the movement constraint hypothesis, whereas studies employing lower IDs (i.e., 1-4 bits) were more likely to provide more support for the movement integration hypothesis. When the IDs employed were relatively intermediate (i.e., 5 bits), both hypotheses were mostly supported. Thus, task difficulty is crucial when determining which hypothesis better explains the planning and control of sequential goal-directed movements. Critically, the OTA most likely always involves integration but may also involve constraining if the accuracy demands are sufficiently high.

Distinct and flexible rates of online control.

Elliott et al. (Hum Mov Sci 10:393-418, 1991) proposed a pseudocontinuous model of online control whereby overlapping corrections lead to the appearance of smooth kinematic profiles in the presence of online feedback. More recently, it was also proposed that online control is not a singular process [see Elliott et al. (Psychol Bull 136(6):1023-1044, 2010)]. However, support for contemporary models of online control were based on methodologies that were not designed to be sensitive to different online control sub-processes. The current study sought to evaluate the possibility of multiple distinct (i.e., visual and non-visual) mechanisms contributing to the control of reaching movements completed in either a full-vision, a no-vision, or a no-vision memory-guided condition. Frequency domain analysis was applied to the acceleration traces of reaching movements. In an attempt to elicit a modulation in the online control mechanisms, these movements were completed at two levels of spatio-temporal constraint, namely with 10 and 30 cm target distances. One finding was that performance in the full-vision relative to both no-vision conditions could be distinguished via two distinct frequency peaks. Increases in the peak magnitude at the lower frequencies were associated with visuomotor mechanisms and increases in the peak magnitude at the higher frequencies were associated with non-visual mechanisms. In addition, performance to the 30-cm target led to a lower peak at a lower frequency relative to the 10 cm target, indicating that the iterative rates of visuomotor control mechanisms are flexible and sensitive to the spatio-temporal constraints of the associated movement.

Amending Ongoing Upper-Limb Reaches: Visual and Proprioceptive Contributions?

In order to maximize the precise completion of voluntary actions, humans can theoretically utilize both visual and proprioceptive information to plan and amend ongoing limb trajectories. Although vision has been thought to be a more dominant sensory modality, research has shown that sensory feedback may be processed as a function of its relevance and reliability. As well, theoretical models of voluntary action have suggested that both vision and proprioception can be used to prepare online trajectory amendments. However, empirical evidence regarding the use of proprioception for online control has come from indirect manipulations from the sensory feedback (i.e., without directly perturbing the afferent information; e.g., visual-proprioceptive mismatch). In order to directly assess the relative contributions of visual and proprioceptive feedback to the online control of voluntary actions, direct perturbations to both vision (i.e., liquid crystal goggles) and proprioception (i.e., tendon vibration) were implemented in two experiments. The first experiment employed the manipulations while participants simply performed a rapid goal-directed movement (30 cm amplitude). Results from this first experiment yielded no significant evidence that proprioceptive feedback contributed to online control processes. The second experiment employed an imperceptible target jump to elicit online trajectory amendments. Without or with tendon vibration, participants still corrected for the target jumps. The current study provided more evidence of the importance of vision for online control but little support for the importance of proprioception for online limb-target regulation mechanisms.

Index of difficulty and side of space are accommodated during the selection and planning of a joint action.

Co-actors can facilitate the achievement of a shared goal by accurately anticipating each other's needs and subsequently planning actions to accommodate those needs. The purpose of the present study was to determine if co-actors plan and execute their movements to accommodate the difficulty of their partners' action. We hypothesized that information derived from shared task representations could influence the simulation of other's actions and that motor experience would enhance the ability of co-actor's to anticipate their co-actor's needs. Partners performed a sequential aiming task. The initiator of the sequential action placed a dowel on a line between two potential targets that varied in size across trials. The initiator did not know the actual target location prior to placing the dowel. The finisher then grasped the dowel and moved it to whichever target was signaled, from wherever their partner had placed the dowel. Participants completed the partner task before and after completing an individual task in which they completed both the initiating and the finishing movements. Consistent with the prediction that co-actors represent the difficulty of their partners' actions, the dowel was placed closer to the smaller target of a pair. Further, it was found that motor experience influenced dowel placement - there was a shift in dowel placement following the completion of the individual task. These results indicate that co-actors plan their movements based on features of their co-actor's movements and that motor experience provides information that allows people to better plan movements for their partners.

An optimal velocity for online limb-target regulation processes?

The utilization of visual information for the control of ongoing voluntary limb movements has been investigated for more than a century. Recently, online sensorimotor processes for the control of upper-limb reaches were hypothesized to include a distinct process related to the comparison of limb and target positions (i.e., limb-target regulation processes: Elliott et al. in Psychol Bull 136:1023-1044. doi: 10.1037/a0020958 , 2010). In the current study, this hypothesis was tested by presenting participants with brief windows of vision (20 ms) when the real-time velocity of the reaching limb rose above selected velocity criteria. One experiment tested the perceptual judgments of endpoint bias (i.e., under- vs. over-shoot), and another experiment tested the shifts in endpoint distributions following an imperceptible target jump. Both experiments revealed that limb-target regulation processes take place at an optimal velocity or "sweet spot" between movement onset and peak limb velocity (i.e., 1.0 m/s with the employed movement amplitude and duration). In contrast with pseudo-continuous models of online control (e.g., Elliott et al. in Hum Mov Sci 10:393-418. doi: 10.1016/0167-9457(91)90013-N , 1991), humans likely optimize online limb-target regulation processes by gathering visual information at a rather limited period of time, well in advance of peak limb velocity.

Eye movements may cause motor contagion effects.

When a person executes a movement, the movement is more errorful while observing another person's actions that are incongruent rather than congruent with the executed action. This effect is known as "motor contagion". Accounts of this effect are often grounded in simulation mechanisms: increased movement error emerges because the motor codes associated with observed actions compete with motor codes of the goal action. It is also possible, however, that the increased movement error is linked to eye movements that are executed simultaneously with the hand movement because oculomotor and manual-motor systems are highly interconnected. In the present study, participants performed a motor contagion task in which they executed horizontal arm movements while observing a model making either vertical (incongruent) or horizontal (congruent) movements under three conditions: no instruction, maintain central fixation, or track the model's hand with the eyes. A significant motor contagion-like effect was only found in the 'track' condition. Thus, 'motor contagion' in the present task may be an artifact of simultaneously executed incongruent eye movements. These data are discussed in the context of stimulation and associative learning theories, and raise eye movements as a critical methodological consideration for future work on motor contagion.

Can You Hear That Peak? Utilization of Auditory and Visual Feedback at Peak Limb Velocity.

PURPOSE: At rest, the central nervous system combines and integrates multisensory cues to yield an optimal percept. When engaging in action, the relative weighing of sensory modalities has been shown to be altered. Because the timing of peak velocity is the critical moment in some goal-directed movements (e.g., overarm throwing), the current study sought to test whether visual and auditory cues are optimally integrated at that specific kinematic marker when it is the critical part of the trajectory. METHODS: Participants performed an upper-limb movement in which they were required to reach their peak limb velocity when the right index finger intersected a virtual target (i.e., a flinging movement). Brief auditory, visual, or audiovisual feedback (i.e., 20 ms in duration) was provided to participants at peak limb velocity. Performance was assessed primarily through the resultant position of peak limb velocity and the variability of that position. RESULTS: Relative to when no feedback was provided, auditory feedback significantly reduced the resultant endpoint variability of the finger position at peak limb velocity. However, no such reductions were found for the visual or audiovisual feedback conditions. Further, providing both auditory and visual cues concurrently also failed to yield the theoretically predicted improvements in endpoint variability. CONCLUSIONS: Overall, the central nervous system can make significant use of an auditory cue but may not optimally integrate a visual and auditory cue at peak limb velocity, when peak velocity is the critical part of the trajectory.

Quantifying online visuomotor feedback utilization in the frequency domain.

The utilization of sensory information during activities of daily living is ubiquitous both prior to and during movements (i.e., related to planning and online control, respectively). Because of the overlapping nature of online corrective processes, the quantification of feedback utilization has proven difficult. In the present study, we primarily sought to evaluate the utility of a novel analysis in the frequency domain for identifying visuomotor feedback utilization (i.e., online control). A second goal was to compare the sensitivity of the frequency analysis to that of currently utilized measures of online control. Participants completed reaching movements to targets located 27, 30, and 33 cm from a start position. During these reaches, vision of the environment was either provided or withheld. Performance was assessed across contemporary measures of online control. For the novel frequency analysis presented in this study, the acceleration profiles of reaching movements were detrended with a 5th-order polynomial fit, and the proportional power spectra were computed from the residuals of these fits. The results indicated that the use of visual feedback during reaching movements increased the contribution of the 4.68-Hz frequency to the residuals of the acceleration profiles. Comparisons across all measures of online control showed that the most sensitive measure was the squared Fisher transform of the correlation between the positions at 75 % and 100 % of the movement time. However, because such correlational measures can be contaminated by offline control processes, the frequency-domain analysis proposed herein represents a viable and promising alternative to detect changes in online feedback utilization.

Augmented feedback influences upper limb reaching movement times but does not explain violations of Fitts' Law.

Fitts' (1954) classic theorem asserts that the movement time (MT) of voluntary reaches is determined by amplitude and width requirements (i.e., index of difficulty: ID). Actions associated with equivalent IDs should elicit equivalent MTs regardless of the amplitude and/ or width requirements. However, contemporary research has reported that amplitude-based contributions to IDs yield larger increases in MTs than width-based contributions. This discrepancy may relate to the presence of augmented terminal feedback in Fitts' original research, which has not been provided in more recent investigations (e.g., Heath et al., 2011). To address this issue, participants performed reaching movements during two sessions wherein feedback regarding terminal accuracy was either provided or withheld. It was hypothesized that the absence of augmented terminal feedback would result in a stereotyped performance across target widths and explain the violation of Fitts' theorem. Yet, the results revealed distinct influences of amplitude- and width-based manipulations on MT, which also persisted across feedback conditions. This finding supports the assertion that the unitary nature of Fitts' theorem does not account for a continuous range of movement amplitudes and target widths. A secondary analysis was competed in an attempt to further investigate the violation of Fitts' Law. Based on error rates, participants were segregated into accuracy- and speed-prone groups. Additionally, target's IDs were recalculated based on each participant's performance using the effective target width (i.e., IDWe) instead of the nominal target width. When using MT data from the accuracy-prone group with this IDWe, the aforementioned violation was alleviated. Overall, augmented terminal feedback did not explain the violation of Fitts' theorem, although one should consider using the effective target width and participant's strategy in future investigations.

Preceding movement effects on sequential aiming.

In this study, two experiments were devised to examine the control strategy used by individuals when performing sequential aiming movements. Of particular interest was the aiming behavior displayed when task difficulty was changed midway through a sequence of movements. In Experiment 1, target size was manipulated, as the targets were made either larger or smaller, between the 8th and 12th movement of the sequence. In Experiment 2, the amplitude between the two targets was similarly changed while the target size remained constant. Results revealed that in Experiment 1, individuals took two movements following the perturbation to target size, to re-tune their movement times in order to correspond with the new task difficulty. Conversely for Experiment 2, movement time changed immediately and in correspondence with the new target amplitude. These findings demonstrate that participants can use information from the preceding movement to prepare and guide subsequent movements--but only when target size is changed. When response amplitude changes mid-sequence, it seems individuals rely more on immediate, target-derived information. Therefore, counter to some current accounts of visual movement control, it appears that memory representations of the preceding movement can guide subsequent movements; however, this information appears selectively accessed in a context-dependent fashion.