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PubMed2006

Partition between volitional and induced forces in electrically augmented dynamic isometric muscle contractions.

Augmentation of force in partially deficient muscles can be achieved by combining electrical stimulation (ES) with their volitional activation (hybrid activation). However, while the overall torque results from the combination of the volitional and the electrically-induced torque components, the exact share between these components is not known. In a previous work, we described a method to resolve the share between the torque components under isometric static contractions. In this work, we extend our analysis to the case of isometric dynamic contractions. Five healthy subjects were instructed to contract their Tibialis Anterior (TA) muscles according to a typical gait-like dynamic torque pattern, that was visually displayed to them, while monitoring their actual ankle torque and TA electromyography (EMG). These experiments were done with and without augmented activation by means of ES. A computational algorithm was developed to dissociate the volitional from the overall torque, based on EMG signal processing and on precalibration of the dynamic system of the volitional torque versus EMG. The results indicated the quantitative relations between decrease in the volitional torque and the required increase in ES enhancement. The developed method also demonstrated what ES intensity profile is necessary to produce a desired overall torque output. This provides the means for designing an adaptive rehabilitation device for the hybrid activation of deficient muscles.

Adult↗
PubMed1998

Modeling the Mediating Role of Volition in the Learning Process.

According to action-control theory, volition plays a mediating role between the intention to learn (motivation) and goal-directed behavior (the use of learning strategies). Although extensive theoretical work has been done to document this flow of events, more empirical studies have been needed to identify the specific means by which volitional control protects the intention to learn and maintains the attempts to learn; our intention here was to address this gap in the literature. Using data from a sample of 487 college students in two different domains, we found that the positive effects of intrinsic goal orientation and self-efficacy on cognitive engagement were augmented by volitional control. We also found that the effects of volition differed by domain as well as by the type of learning strategy being considered. These results suggest that volitional control merits greater attention from those doing research in self-regulated learning. Copyright 1998 Academic Press.

Journal Article↗
PubMed2005

Interactions between volitional and automatic breathing during respiratory apraxia.

The sites and forms of interactions between voluntary breathing acts and automatic respiratory rhythm generation are the subject of considerable research interest. We report here observations of the control of breathing in a patient suffering from an advanced form of progressive supranuclear palsy (Steele-Richardson-Olszewski syndrome). This patient demonstrated a severely compromised ability to perform volitional respiratory acts upon command, despite exacerbated behavioural and automatic control of respiration. The presence of residual volitional control of breathing in this patient provided interesting insights concerning the interaction between the automatic and the voluntary control of respiration. We observed that (1) when the subjects was asked to inspire voluntarily he could at best mobilize a volume similar to spontaneous VT and only very slowly; (2) automatic breathing movements persisted, superimposed onto the active voluntary movements, with an amplitude that decreased when the inspiratory activity, albeit weak, reached its maximal level; (3) during breath holding both the amplitude and the frequency of the basal spontaneous rhythmic activity were depressed. This observation therefore supports the idea of a strong interaction between volitional and automatic breathing in the form of an inhibition of automatic activity during voluntary breathing. Although, the site of interaction (spinal versus supraspinal) could not be determined during volitional inspiration, the effect of breath holding on the frequency of the spontaneous breathing activity supports the view that a volitional breathing arrest has some inhibitory effects on the respiratory oscillator at the medullary level. Finally, in an attempt to reconcile the persistence of a rhythmic activity during voluntary inspiration and expiration with previous data from the literature, it is proposed that the normal suppression of the automatic activity during voluntary inspiration relies on cortical and sub-cortical structures involved in the planning, i.e. the praxic component, of a respiratory task rather than on projections originating from the primary motor cortex.

Aged↗
PubMed2006

Evaluation of methods for extraction of the volitional EMG in dynamic hybrid muscle activation.

BACKGROUND: Hybrid muscle activation is a modality used for muscle force enhancement, in which muscle contraction is generated from two different excitation sources: volitional and external, by means of electrical stimulation (ES). Under hybrid activation, the overall EMG signal is the combination of the volitional and ES-induced components. In this study, we developed a computational scheme to extract the volitional EMG envelope from the overall dynamic EMG signal, to serve as an input signal for control purposes, and for evaluation of muscle forces. METHODS: A "synthetic" database was created from in-vivo experiments on the Tibialis Anterior of the right foot to emulate hybrid EMG signals, including the volitional and induced components. The database was used to evaluate the results obtained from six signal processing schemes, including seven different modules for filtration, rectification and ES component removal. The schemes differed from each other by their module combinations, as follows: blocking window only, comb filter only, blocking window and comb filter, blocking window and peak envelope, comb filter and peak envelope and, finally, blocking window, comb filter and peak envelope. RESULTS AND CONCLUSION: The results showed that the scheme including all the modules led to an excellent approximation of the volitional EMG envelope, as extracted from the hybrid signal, and underlined the importance of the artifact blocking window module in the process. The results of this work have direct implications on the development of hybrid muscle activation rehabilitation systems for the enhancement of weakened muscles.

Journal Article↗
PubMed2003

Personality systems interactions theory and the theory of planned behaviour: evidence that self-regulatory volitional components enhance enactment of studying behaviour.

The role of volitional components specified by personality systems interactions theory in enhancing behavioural prediction was examined in a longitudinal investigation of students' studying. Participants completed measures specified by the theory of planned behaviour and questionnaire measures of 'conscious attention control', 'implicit attention control' and 'self-determination' from the volitional components inventory. Behaviour was assessed 2 weeks later. Regression analyses showed that volitional components increased variance explained in behaviour by 10-18%, after taking into account strength of motivation to study assessed by attitude, subjective norm, perceived behavioural control and intention from the theory of planned behaviour. Moreover, consistent with elements of personality systems interactions theory, moderator effects were obtained. Participants who reported self-determination, conscious attention control and implicit attention control were more likely to enact their intentions. Volitional components were also associated with increased studying among participants who perceived a low subjective norm for studying. Volitional components improved prediction of studying after accounting for past behaviour in the regression models.

Adolescent↗
PubMed2003

Volitional impairment and the sexually violent predator.

This article discusses psychiatry's limited conceptualization of volitional capacity and its application to sexually violent predator laws by exploring two legal opinions critical to predator case law (Kansas v. Hendricks and Kansas v. Crane). The author reviewed pertinent psychiatric literature on impaired volition to identify potential contributions and limitations that psychiatry may offer the legal field. Assessment of the ego dystonic nature of impaired self-regulation, utilization of recent advances in self-assessment and laboratory evaluation of impulsive behavior, and dimensional categorization of a volitional capacity construct are recommended as an approach to the assessment and understanding of an inability to control concept. This paper concludes that elements of volition may be psychiatrically evaluated in a way that contributes to the Court's understanding of that capacity. However, further study is needed to operationally define volitional capacity and address issues of assessment validity and reliability.

Criminal Law↗
PubMed1995

Volitional control of anticipatory ocular pursuit responses under stabilised image conditions in humans.

Ocular pursuit responses have been examined in humans in three experiments in which the pursuit target image has been fully or partially stabilised on the fovea by feeding a recorded eye movement signal back to drive the target motion. The objective was to establish whether subjects could volitionally control smooth eye movement to reproduce trajectories of target motion in the absence of a concurrent target motion stimulus. In experiment 1 subjects were presented with a target moving with a triangular waveform in the horizontal axis with a frequency of 0.325 Hz and velocities of +/- 10-50 degrees/s. The target was illuminated twice per cycle for pulse durations (PD) of 160-640 ms as it passed through the centre position; otherwise subjects were in darkness. Subjects initially tracked the target motion in a conventional closed-loop mode for four cycles. Prior to the next target presentation the target image was stabilised on the fovea, so that any target motion generated resulted solely from volitional eye movement. Subjects continued to make anticipatory smooth eye movements both to the left and the right with a velocity trajectory similar to that observed in the closed-loop phase. Peak velocity in the stabilised-image mode was highly correlated with that in the prior closed-loop phase, but was slightly less (84% on average). In experiment 2 subjects were presented with a continuously illuminated target that was oscillated sinusoidally at frequencies of 0.2-1.34 Hz and amplitudes of +/- 5-20 degrees. After four cycles of closed-loop stimulation the image was stabilised on the fovea at the time of peak target displacement. Subjects continued to generate an oscillatory smooth eye velocity pattern that mimicked the sinusoidal motion of the previous closed-loop phase for at least three further cycles. The peak eye velocity generated ranged from 57-95% of that in the closed-loop phase at frequencies up to 0.8 Hz but decreased significantly at 1.34 Hz. In experiment 3 subjects were presented with a stabilised display throughout and generated smooth eye movements with peak velocity up to 84 degrees/s in the complete absence of any prior external target motion stimulus, by transferring their attention alternately to left and right of the centre of the display. Eye velocity was found to be dependent on the eccentricity of the centre of attention and the frequency of alternation. When the target was partially stabilised on the retina by feeding back only a proportion (Kf = 0.6-0.9) of the eye movement signal to drive the target, subjects were still able to generate smooth movements at will, even though the display did not move as far or as fast as the eye. Peak eye velocity decreased as Kf decreased, suggesting that there was a continuous competitive interaction between the volitional drive and the visual feedback provided by the relative motion of the display with respect to the retina. These results support the evidence for two separate mechanisms of smooth eye movement control in ocular pursuit: reflex control from retinal velocity error feedback and volitional control from an internal source. Arguments are presented to indicate how smooth pursuit may be controlled by matching a voluntarily initiated estimate of the required smooth movement, normally derived from storage of past re-afferent information, against current visual feedback information. Such a mechanism allows preemptive smooth eye movements to be made that can overcome the inherent delays in the visual feedback pathway.

Conflict, Psychological↗
PubMed2006

Decision-making about volitional impairment in sexually violent predators.

The Kansas v. Hendricks (1997) decision, in which the Supreme Court authorized post-sentence civil commitment for certain sex offenders, appeared to be constitutionally legitimized by limiting the class of offenders eligible for this special form of civil commitment to those who are "unable to control" their dangerousness. Nowhere in the available record, however, did the Court elucidate what they meant by this notion of volitional impairment. This study sought to examine factors that legal professionals (n=43), psychologists (n=40), and mock jurors (n=76) deem most relevant to a determination of sex offender volitional impairment. Participants, who were randomly assigned to a sexual predator commitment or an insanity hearing context, read a series of 16 vignettes that described a pedophilic offender and included combinations of variables hypothesized to be related to judgments of volitional impairment. Results suggested that participants, who as a group made remarkably high estimates of likelihood of future sexual violence, considered verbalization of control, history of sexual violence, and the context of the hearing as highly relevant to determinations of volitional impairment. Implications for policy and practice are explored.

Adult↗
PubMed1995

Deglutitive tongue force modulation by volition, volume, and viscosity in humans.

BACKGROUND/AIMS: Deglutitive tongue biomechanics are complex, involving bolus containment, loading, and propulsion. This study aimed to quantify the modulation of deglutitive pulsive and clearing tongue forces in varied swallowing conditions. METHODS: Oropharyngeal pressure and force were recorded using sensing bulbs and strain-gauge manometry in 8 volunteers during swallows of varied volume and viscosity. Volitional modulation was explored with forceful and attenuated swallows. RESULTS: Temporal analysis confirmed that bulb recordings corresponded to tongue pulsive force, and the strain-gauge recordings measured tongue clearing pressure. Volition was the most potent modifier of both tongue pulsive force and clearing pressure with values showing a fourfold increase from attenuated to forceful swallows. Bolus viscosity also induced an increase of tongue pulsive force and clearing pressure by the oral tongue. Volitional control as well as adaptation to viscosity was greatest on the anterior and middle part of the oral tongue. There was no force adaptation with increased bolus volume. CONCLUSIONS: Tongue pulsive force and clearing pressure during swallow showed substantial modulation for bolus viscosity that can be reproduced by volitional control. The anterior two thirds of the tongue showed both greater forces and greater modulation than did the tongue base.

Adaptation, Physiological↗
PubMed2002

Nocturnal heart rate and volitional lifestyle in the elderly.

The relationship between the level of volitional lifestyle and nocturnal heart rate (HR) in the elderly was investigated. Twenty high- and low-volitional elderly individuals (n = 10 each; mean age 73.2 years) participated in the study. Heart rate during nocturnal sleep was recorded at their homes using an ambulatory polysomnographic system. High-volitional individuals showed a lower HR throughout the night and less variability during rapid eye movement sleep. These findings suggest that a volitional lifestyle of the elderly has a beneficial effect on autonomic activity during sleep.

Aged↗
PubMed2006

Extraretinal signals in MSTd neurons related to volitional smooth pursuit.

Smooth pursuit (SP)-related neurons in the dorsal-medial part of medial superior temporal cortex (MSTd) carry extraretinal signals that may play a role in maintenance of SP once eye velocity matches target velocity. For example, it has not been determined whether the extraretinal signals reflect volitional SP commands or proprioception. The aim of this study was to test some potential sources of extraretinal signals in MSTd pursuit neurons. We tested 40 MSTd neurons during step-ramp SP with target blink conditions to show that they carried an extraretinal signal. To examine potential contributions from eye movements that might reflect proprioceptive feedback from eye muscles, we tested MSTd neurons during rotational vestibular ocular reflex in complete darkness (VORd). Vestibular stimulation was delivered in the earth horizontal plane to elicit reflex driven smooth eye movements that matched the speed and frequency of volitional SP. We also tested VOR in the light (VOR x 1) and cancellation of the VOR (VOR x 0). Our neurons were modulated during both SP and cancellation of the VOR. In contrast, MSTd smooth pursuit neurons with extraretinal signals were not significantly modulated during VORd (sensitivity < or = 0.10 spike/s/ degrees /s). This combination of properties is compatible with classifying these neurons as gaze-velocity related. Absence of modulation during VORd testing could be caused by cancellation of head and eye movement sensitivity or dependence of neuronal firing on volitional SP commands. Our results support the suggestion that modulation of SP-related MSTd neurons reflects volitional SP commands rather then eye movements generated by reflex pathways.

Animals↗
PubMedDate not supplied

The Volitional Questionnaire: psychometric development and practical use.

This article describes the Volitional Questionnaire and presents recent empirical efforts to develop and validate this instrument. The Volitional Questionnaire is an observational method of gathering data on motivation that is designed for persons who are unable to self-report their own motives. Studies to date suggest that the instrument can provide a valid measure of volition, though a number of limitations of the tool are noted. Implications for use of the Volitional Questionnaire in practice and for further refinement and future research are discussed.

Humans↗
PubMed1995

Cortical control of human soleus muscle during volitional and postural activities studied using focal magnetic stimulation.

The surface-recorded electromyographic (EMG) responses evoked in the ankle musculature by focal, transcranial, magnetic stimulation of the motor cortex were studied in healthy human subjects. Such soleus evoked motor responses (EMRs) were characterised over a wide range of background levels of motor activity and using different stimulus intensities. EMRs were recorded during predominantly (1) volitional and (2) postural tasks. In the former task subjects were seated and voluntarily produced prescribed levels of soleus activation by reference to a visual monitor of EMG. In the latter task subjects assumed standing postures without EMG feedback. Comparison of the EMRs of soleus, traditionally considered a slow anti-gravity extensor muscle, during these tasks was used to evaluate its cortical control in primarily volitional versus primarily postural activities. The form of soleus EMRs produced by single magnetic cortical stimuli comprised an initial (approx. 30 ms) increase and subsequent (approx. 50 ms) depression of EMG. Cortical stimulation could elicit substantial excitatory soleus EMG responses; for example, responses evoked by mild, magnetic stimuli (125% threshold for inducing a response in the relaxed muscle) as subjects exerted full voluntary plantarflexor effort averaged almost 20% of the maximum M-wave which could be elicited by an electrical stimulus to the posterior tibial nerve. Excitatory EMRs could be elicited in the voluntarily relaxed soleus muscle of the majority of subjects during sitting. The amplitude of soleus responses, induced by threshold stimuli for the relaxed state or approximately 125% threshold intensity, increased approximately linearly with background EMG over a wide range of volitional contraction levels. By contrast, there was no systematic change in the latency of excitatory soleus EMRs with increasing voluntary effort. The excitatory responses evoked in the voluntarily relaxed soleus of seated subjects by magnetic stimulation were regularly facilitated by incremental, voluntary contraction of the contralateral ankle extensors in a graded manner. However, such facilitation of responses was not observed when subjects voluntarily activated the muscle in which EMRs were elicited. The pattern of the responses elicited in soleus by magnetic stimulation during the postural task generally resembled that found during the volitional task. The amplitudes of excitatory soleus EMRs at a given stimulus intensity, obtained when subjects stood quietly, leaned forwards or stood on their toes to produce differing levels of ankle extensor contraction, increased with background EMG.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2005

Practice of habitual and volitional health behaviors to prevent severe acute respiratory syndrome among Chinese adolescents in Hong Kong.

PURPOSE: To explore factors relating to the practice of habitual and volitional health behaviors against the severe acute respiratory syndrome (SARS) among Chinese adolescents in Hong Kong. METHODS: A community telephone survey was conducted with 230 Chinese adolescents. Random-digit dialing of the local residential telephone directory was used to select respondents, who were asked to provide information on their practice of SARS preventive health behaviors and associated factors as specified by the Health Belief Model. These factors included perceived threat of SARS, perceived benefits and barriers in practicing SARS preventive health behaviors, cues to action, knowledge of SARS, and self-efficacy. Hierarchical regression analyses were conducted to determine salient correlates of habitual and volitional health behaviors against SARS. RESULTS: About 54.8% of respondents reported practicing all three recommended habitual health behaviors. Another 47.8% indicated consistent practice of volitional health behavior of facemask-wearing to prevent SARS. Results of hierarchical regression analyses showed that habitual health behaviors against SARS were related to perceived health threat and environmental cues. For facemask-wearing, salient correlates were environmental cues, rates of SARS habitual health behaviors, younger age, and perceived health threat. CONCLUSIONS: The Health Belief Model is useful in understanding Chinese adolescents' practice of health behaviors, especially volitional health behaviors.

Adolescent↗
PubMed1991

Modulation of the stretch reflex during volitional sinusoidal tracking in Parkinson's disease.

Sinusoidal visually-guided wrist tracking, in normal and parkinsonian subjects, was perturbed by torque transients every 90 degrees throughout the movement. Long-latency stretch reflex and volitional EMG amplitude modulations were assessed as functions of the tracking phase. Reflex modulation during tracking, both in wrist flexor and extensor muscles, was found to differ significantly between parkinsonian and normal subjects. In the parkinsonian group, the abnormality consisted of an increased reflex activity during tracking phases in which the muscle was lengthening. At these phases the reflex generated torque is opposite in direction to the volitionally generated torque and the tracking movement. No differences in the unperturbed volitional EMG modulation were observed between groups for this error constrained tracking paradigm. Significant correlations were found between ratings of bradykinesia and the amount of abnormal reflex modulation in the wrist flexor. These data suggest that a component of bradykinesia results from a defective coordination of supraspinal reflex and volitional control systems.

Aged↗
PubMed1998

Effects of volitional lifestyle on sleep-life habits in the aged.

This study investigates the relationship between a volitional lifestyle and sleep-life habits in the aged. High volitional group (HVG: n=45, 26 men and 19 women, mean age 73.0 years) and low-volitional group (LVG: n=45, 27 men and 18 women, mean age 72.2 years) were grouped using the scale of self-confidence. It was found that high volitional aged individuals had a relatively well structured sleep, and that most had become accustomed to taking an appetitive nap (an individual with a mean wake time shorter than the average) in the mid-afternoon without experiencing insomniac problems.

Aged↗
PubMed2006

Computerized dynamic visual acuity with volitional head movement in patients with vestibular dysfunction.

OBJECTIVES: Patients with uncompensated vestibular dysfunction frequently report blurred vision during head movement, a symptom termed oscillopsia. One way to measure the functional deficit associated with an impaired vestibulo-ocular reflex is by comparing visual acuity from a baseline condition in which there is no head movement to visual acuity obtained during a dynamic condition with head movement. A previously described test incorporated a treadmill upon which patients walked during assessment of visual acuity. The objective of the current investigation was to evaluate an alternative method of assessing dynamic visual acuity that uses volitional head movement instead of walking on a treadmill. METHODS: Fifteen participants with normal vestibular function and 16 participants with impaired vestibular function were enrolled. All participants performed the visual acuity task under baseline conditions with no movement and also under dynamic conditions that included 1) walking on a treadmill and 2) volitionally moving their head in the vertical plane. RESULTS: No difference in performance was observed between the treadmill task and the volitional head movement task. Participants with impaired vestibular function performed more poorly under the dynamic conditions than did participants with normal vestibular function. CONCLUSIONS: The results suggest that the volitional head movement paradigm may be useful in identification of patients with functional deficits of the vestibulo-ocular reflex.

Adult↗
PubMed2002

Combining motivational and volitional interventions to promote exercise participation: protection motivation theory and implementation intentions.

OBJECTIVE: This study compared a motivational intervention based on protection motivation theory (PMT, Rogers, 1975, 1983) with the same motivational intervention augmented by a volitional intervention based on implementation intentions (Gollwitzer, 1993). DESIGN: The study had a longitudinal design, involving three waves of data collection over a 2-week period, incorporating an experimental manipulation of PMT variables at Time 1 and a volitional, implementation intention intervention at Time 2. METHOD: Participants (N=248) were randomly allocated to a control group or one of two intervention groups. Cognitions and exercise behaviour were measured at three time-points over a 2-week period. RESULTS: The motivational intervention significantly increased threat and coping appraisal and intentions to engage in exercise but did not bring about a significant increase in subsequent exercise behaviour. In contrast, the combined protection motivation theory/implementation intention intervention had a dramatic effect on subsequent exercise behaviour. This volitional intervention did not influence behavioural intention or any other motivational variables. CONCLUSIONS: It is concluded that supplementing PMT with implementation intentions strengthens the ability of the model to explain behaviour. This has implications for health education programmes, which should aim to increase both participants' motivation and their volition.

Clinical Trial↗