Changes in predictive motor control in drop-jumps based on uncertainties in task execution

Drop-jumps are controlled by predictive and reactive motor strategies which differ with respect to the utilization of sensory feedback. With reaction, sensory feedback is integrated while performing the task. With prediction, sensory information may be used prior to movement onset. Certainty about upcoming events is important for prediction. The present study aimed at investigating how uncertainties in the task execution affect predictive motor control in drop-jumps. Ten healthy subjects (22±1 years, M±SD) participated. The subjects performed either (i) drop-jumps by knowing that they might had to switch to a landing movement upon an auditory cue, which was sometimes elicited prior to touch-down (uncertainty). In (ii), subjects performed drop-jumps by knowing that there would be no auditory cue and consequently no switch of the movement (certainty). The m. soleus EMG prior to touch-down was higher when subjects knew there would be no auditory cue compared to when subjects performed the same task but switching from drop-jump to landing was possible (uncertainty). The EMG was reversed in the late concentric phase, meaning that it was higher in the high uncertainty task. The results of the present study showed that the muscular activity was predictively adjusted according to uncertainties in task execution. It is argued that tendomuscular stiffness was the variable responsible for the adjustment of muscular activity. The required tendomuscular stiffness was higher in drop-jumps than in landings. Consequently, when it was not certain whether to jump or to land, muscular activity and therefore tendomuscular stiffness was reduced.     

Task performance and electromyopotential as functions of task difficulty and EMG feedback

The dearth of empirical research in the application of biofeedback is discussed. Exp. 1 assessed relationships among biofeedback EMG training, EMG levels, cognitive task performance, and task difficulty. 72 subjects (male or female college students) were administered 1 trial on an iconic memory task with either EMG audio feedback, sham EMG audio feedback, or no feedback. Three levels of task difficulty were used. One 20-min. training session significantly lowered EMG responses, and task performance was inversely related to task difficulty. No relationship between EMG level and task performance was observed. Exp. 2 investigated the effect of increased EMG responses on cognitive task performance for one level of difficulty. One biofeedback training session did not significantly increase frontalis EMG, and there was no relationship between increased EMG and task performance.     

An examination of methods for producing relaxation during short-term laboratory sessions

Reductions in psychological and physiological correlates of tension produced by various muscle relaxation training techniques were examined during a short-term laboratory session. Two studies are described involving a combined total of one hundred subjects receiving either abbreviated progressive relaxation, visual, auditory, or tactile electromyographic (EMG) biofeedback procedures. The Anxiety Differential was administered before and after the laboratory session. Heart rate, respiratory rate, skin conductance, systolic blood pressure, and frontalis and dominant forearm extensor EMG measures were obtained before, during, and after administration of relaxation training. Results indicated feedback in the tactile modality to produce overall reductions in tension comparable to those produced by progressive relaxation. Overall reductions in tension displayed by both progressive relaxation and tactile feedback were generally greater than reductions shown by visual or auditory feedback procedures. Interpretations suggest that certain forms of EMG feedback may offer an alternative to progressive relaxation techniques for producing short-term reductions in tension. Feedback modality is further indicated as a potentially important variable during relaxation training using the EMG feedback technique.     

Sensory feedback in the learning of a novel motor task

The role of different forms of feedback is examined in learning a novel motor task. Five groups of ten subjects had to learn the voluntary control of the abduction of the big toe, each under a different feedback condition (proprioceptive feedback, visual feedback, EMG feedback, tactile feedback, force feedback). The task was selected for two reasons. First, in most motor learning studies subjects have to perform simple movements which present hardly any learning problem. Second, studying the learning of a new movement an provide useful information for neuromuscular reeducation, where patients often also have to learn movements for which no control strategy exists. The results show that artificial sensory feedback (EMG feedback, force feedback) is more powerful than "natural" (proprioceptive, visual, and tactile) feedback. The implications of these results for neuromuscular reeducation are discussed.     

Studies on sensory feedback: III the effects of display gain on tracking performance

Instrumentation is described which permits study of the effects of different forms of visual feedback display on the patterns of fine movement obtained from the extended human index finger when the subject is attempting to keep his finger at a fixed point in space. The task is a compensatory tracking task in which the only source of input to the system is the subject's own finger movement. The effects of increasing the gain (or amplification) of a proportional error signal on the pattern of finger movement was studied. Gains of 1, 2, 4, 10, 20 and 40 were studied with a group of 24 subjects. Increasing the gain of a proportional error signal resulted in a marked improvement in the ability of subjects to maintain their extended finger at a fixed point in space. As the gain of the error signal was increased, the subject's high-amplitude, low frequency errors were reduced, and there was a progressive appearance of high-frequency activity of low-amplitude, more accurately centred about the reference position in space. A total off-target area measure (integrated absolute error) showed marked decrease in scores as the amplification of the error signal was increased from 1 through 10. Beyond this gain there was no appreciable additional improvement in motor control, however no degradation of control was noted to characterize the group performance.

Exploratory studies were undertaken to permit comparison of the effects of increasing the gain of a proportional visual display with the effects of increasing the gain of non-proportional visual and auditory displays. An increase in the dominant-energy frequency was noted as the error signal gain was increased, independent of whether a proportional visual, or non-proportional visual or auditory display was used. This observation suggests that common mechanisms mediate the processing of the gain parameters of feedback displays, in some measure independent of the display form or the sensory modality used for presentation.     

Sensory Feedback in the Learning of a Novel Motor Task

The role of different forms of feedback is examined in learning a novel motor task. Five groups of ten subjects had to learn the voluntary control of the abduction of the big toe, each under a different feedback condition (proprioceptive feedback, visual feedback, EMG feedback, tactile feedback, force feedback). The task was selected for two reasons. First, in most motor learning studies subjects have to perform simple movements which present hardly any learning problem. Second, studying the learning of a new movement can provide useful information for neuromuscular reeducation, where patients often also have to learn movements for which no control strategy exists. The results show that artificial sensory feedback (EMG feedback, force feedback) is more powerful than “natural” (proprioceptive, visual, and tactile) feedback. The implications of these results for neuromuscular reeducation are discussed.     

MODIFICATION OF COMBINED MIGRAINE-MUSCLE CONTRACTION HEADACHES USING BVP AND EMG FEEDBACK

The effect of blood volume pulse (BVP) and frontalis muscle action potential (EMG) feedback on control of vasoconstriction of the temporal artery and frontalis muscle activity in combined migraine-muscle tension subjects was investigated in a multiple baseline design (across subjects and responses). The data indicated: (a) both subjects obtained an ability to control BVP during BVP feedback and EMG during EMG feedback; (b) there were decreases in frequency of migraine headaches during BVP feedback and decreases in muscle contraction headaches during EMG feedback. The results of this study supported the theoretical explanation of two pain mechanisms involved in combined muscle contraction-migraine headaches as well as the effectiveness of biofeedback procedures that target directly the specific pain mechanism in the elimination of the two types of head pain.     

Some effects of progressively lowering electromyographic levels with feedback procedures on the frequency of stuttered verbal behaviors

Feedback procedures were used to progressively decrease the EMG activity of three stutterers during connected speech tasks. Single subject experimental designs were used which allowed for procedural changes as dictated by each subject's performance. All three subjects demonstrated clinically significant decreases in disfluencies and generalization of the treatment effects for an oral reading task, while one of the subjects also showed this effect for a conversational speech task. The subjects' strategies for manipulating the feedback tone seemed to be related to reduction in many of the motoric and prosodic complexities of speech which may have been importantly related to enhancing and maintaining fluency.     

Effects of false increasing,decreasing, and true electromyographic biofeedback on the frequency of stuttering

Adult stutterers received auditory feedback of laryngeal area muscle activity while reading aloud under three conditions: (1) False Increasing Feedback, (2) False Decreasing Feedback, and (3) True Feedback. The subjects were unaware that the feedback in two conditions was being altered and were instructed not to manipulate the feedback signal. Decreases in the frequency of stuttering were observed for both the false increase and true feedback conditions. Factors contributing to the effectiveness of biofeedback techniques with stutterers are discussed.     

Comparisons of some learning models for response bias in signal detection

The effects of variations in signal probability and varying degrees of correct feedback on response bias were studied in a yes-no auditory signal detection task. The main finding was that the bias towards saying yes was an increasing function of the frequency of signal feedback events, but did not depend on the correctness of the feedback. Several learning models coupled with a simple psychophysical and decision model yielded predictions about overall biases and certain sequential statistics. Only one model, which can be decribed as an “informational” model, gave a good account of both observed overall biases and sequential statistics. This model assumes the observer’s response bias is strengthened for the feedback-reinforced response when the observer’s sensory information is ambiguous or is contradicted by the feedback information.     

Prior task failure as a determinant of biofeedback and cognitive task performance

In a study of the effects of controllability of outcomes upon behavior in a biofeedback context, 40 college students were assigned to four groups differing in pretreatment: (1) a success-failure group, given false feedback in a fictitious blood-vessel control task for two sessions designed to convey success followed by two sessions of failure feedback; (2) a failure-failure group, given false failure feedback throughout pretreatment; (3) a contingent failure group, receiving actual feedback in a temperature biofeedback task with criteria that assured failure throughout pretreatment; and (4) a control group, given no specific task during this phase. In a subsequent phase, all subjects received actual frontal (forehead) electromyographic (EMG) response training with biofeedback. In analyses of the results, during EMG training, the contingent failure group attained lower levels than the other three groups. By contrast, on a cognitive (anagram) task, interpolated between pretreatment and EMG training, the contingent failure group demonstrated relatively poorer performance than the other groups. The results are discussed in terms of reactance and learned helplessness theories of perceived loss of control in this context.Some of the data reported here were included in a thesis submitted by the second author in partial fulfillment of requirements for the master's degree in psychology, University of Hawaii, 1981. The entire paper was the basis for a presentation at the annual meeting of the Biofeedback Society of America, Albuquerque, 1984.     

On the role of reduced auditory feedback and kinesic self-stimulation during Stroop Color-Word performance1

Feedback from one's own voice provides important vocal–motor cues for effective cognitive processing. Reduction of such feedback is known to disturb such functioning. Work in our laboratory has shown that kinesic self-stimulation also plays an important role in cognition, and appears to regulate the focusing of attention under conditions of distraction. The present study investigated the effects of both auditory feedback and kinesic self-stimulation in the regulation of cognitive interference during performance of the Stroop Color-Word Task. Twelve subjects were tested on the Stroop task under conditions of normal and occluded hearing. Kinesic self-stimulation and response errors during color-word performance were recorded on video tape. The findings indicated that not only did self-stimulation increase when voice feedback was reduced, but that this increase was associated with a reduction in specific types of color-word performance errors. Individual differences revealed that high kinesic responders made significantly fewer errors in task performance than did low kinesic responders. Results were interpreted as revealing a kinesic feedback mechanism which has adaptive significance in regard to self-editing when auditory feedback is reduced.     

Motor learning of cue-dependent pull-force changes during an isometric precision grip task

The “raspberry task” represents a precision grip task that requires continuous adjustment of grip and pull forces. During this task subjects grip a specialized grip rod and have to increase the pull force linearly while the rod is locked. The aim of this study was to determine whether an associated, initially neutral cue is able to evoke pull-force changes in the raspberry task. A standard delay paradigm was used to study cued pull-force changes during an ongoing movement resulting in unloading. Pull force and EMG activity of hand and arm muscles were recorded from 13 healthy, young subjects. The cue was associated with a complex change in motor behavior.In this task, cued force changes take place more rapidly than in protective reflex systems (in median after the second presentation of the cueing stimulus). A cued force change was detectable in two-thirds of paired trials. Although the force change is produced by a decrease of the EMG activity in several grip- and pull-force-producing muscles, the most significant effect in the majority of the subjects was an increase of the activity of the flexor carpi ulnaris muscle which antagonises corresponding pull-force-producing muscles. Cued force changes require adequately and precisely controlled activation of the muscle groups involved in the movement.     

Influence of speed-related auditory feedback on braking in a 3D-driving simulator

Although discrete auditory stimuli have been found useful for emergency braking, the role of continuous speed-related auditory feedback has not been investigated yet. This point may though be of importance in electric vehicles in which acoustic cues are drastically changed. The present study addressed this question through two experiments. In experiment 1, 12 usual drivers were exposed to naturalistic auditory feedback mimicking those issued from electric cars, while facing dynamic visual scenes in a 3D driving simulator. After being passively travelled up to a sustained constant speed, subjects had to stop their car in front of a traffic light that unexpectedly turned to red. Modifications of the speed-related auditory feedback did not impact braking initiation and regulation. In experiment 2, synthesized auditory feedback based on the Shepard-Risset glissando was provided to a new sample of 15 usual drivers in the same task. Pitch variations of this acoustic stimulus, although not scaled to an absolute speed, were manipulated as a function of visual speed changes. Changing the mapping between pitch variations of the synthesized auditory feedback and visual speed changes induced adjustments on braking which depended on acceleration/deceleration feedback. These findings stressed the importance of the acoustic content and its dynamics for car speed control.     

Emotional responsivity to nonveridical heart rate feedback as a function of anxiety

The purpose of the present investigation was to examine the effects of nonveridical heart rate feedback and anxiety on electrodermal responses and verbal reports to emotionally laden stimuli. Forty-eight female subjects were divided into high and low anxious groups on the basis of their Taylor Manifest Anxiety Scale scores and resting level electrodermal activity. All subjects viewed 10 autopsy slides while hearing continuous auditory tones supposedly representing their own heartbeats. Twenty-four subjects heard the tones increase in rate with slide onset. The other 24 subjects heard no change in rate with slide onset. The high resting autonomic activity group responded with significantly larger electrodermal responses to the heart rate feedback-slide combination than the low resting level autonomic activity group. The high autonomic activity group also reported that the slides were significantly more unpleasant than the low autonomic activity group, particularly those slides accompanied by an increase in heart rate feedback. Implications of these findings for a cognitive-visceral model of emotion are discussed.     

Rapid error correction during human arm movements: evidence for central monitoring

Studies were made of rapid error correction movements in eight subjects performing a visually guided tracking task involving flexion-extension movements about the elbow. Subjects were required to minimize reaction times in this two-choice task. Errors in initial movement direction occurred in about 3% of the trials. Error correction times (time from initiation to reversal of movement in incorrect direction) ranged from 30-150 ms. The first sing of correction of the error movement was a suppression of the electromyographic (EMG) activity in the muscle producing the error movement. This suppression started as early as 20-40 ms after the initiation of the error-related EMG activity and as much as 50 ms before any overt sign of limb movement. The correction of the error movement was also accompanied by an increase in the drive to the muscle which moved the arm in the correct direction. This increased activity always occurred after the initiation of the error movement. it is concluded that the first step in the error correction, suppression of drive to the muscle producing the error movement, cannot be based on information from the moving limb. It is thus suggested that this earliest response to the error movement is based on central monitoring of the commands for movement.     

Rapid Error Correction During Human Arm Movements

Studies were made of rapid error correction movements in eight subjects performing a visually guided tracking task involving flexion-extension movements about the elbow. Subjects were required to minimize reaction times in this two-choice task. Errors in initial movement direction occurred in about 3% of the trials. Error correction times (time from initiation to reversal of movement in incorrect direction) ranged from 30-150 ms. The first sign of correction of the error movement was a suppression of the electromyographic (EMG) activity in the muscle producing the error movement. This suppression started as early as 20-40 ms after the initiation of the error-related EMG activity and as much as 50 ms before any overt sign of limb movement. The correction of the error movement was also accompanied by an increase in the drive to the muscle which moved the arm in the correct direction. This increased activity always occurred after the initiation of the error movement. It is concluded that the first step in the error correction, suppression of drive to the muscle producing the error movement, cannot be based on information from the moving limb. It is thus suggested that this earliest response to the error movement is based on central monitoring of the commands for movement.     

Neural Processing to Visual Stimuli in a Three-Choice Reaction-Time Task

Some authors have suggested that certain components of the event-related potentials (ERPs) reflect underlying stages in the discrimination process. Previous studies have shown that in an auditive three-choice reaction-time task the discrimination is accomplished as a two-stage process, with the more frequently occurring stimulus discriminated at an earlier point than the rarer stimulus and the subjects could be classified as fast and slow responders in function of their response to the most frequent of the three tones. We continuously recorded the electrocerebral activity (EEG) from the scalp and the electromyographic activity (EMG) from the responding muscles in a visual three-choice reaction-time task in 10 strictly right-handed subjects. EEG and EMG responses were subsequently analyzed off-line by aligning them by the onset of either the stimulus (stimulus-synchronized) or the response (response-synchronized). The results suggest that processes of visual stimuli evaluation and response execution are continuously integrated. The discrimination and response systems to visual stimuli is accomplished as a three-stage process, one to frequent tone, another for rare 1, and the last for rare 2. The subjects were classified as fast and slow responders in function of their response to the most frequent of the three tones.     

Adaptation to delayed auditory feedback

Delayed auditory feedback disrupts the production of speech, causing an increase in speech duration as well as many articulatory errors. To determine whether prolonged exposure to delayed auditory feedback IDAFI leads to adaptive compensations in speech production, 10 subjects were exposed in separate experimental sessions to both incremental and constantdelay exposure conditions. Significant adaptation occurred for syntactically structured stimuli in the form of increased speaking rates. After DAF was removed, aftereffects were apparent for all stimulus types in terms of increased speech rates. A carry-over effect from the first to the second experimental session was evident as long as 29 days after the first session. The use of strategies to overcome DAF and the differences between adaptation to DAF and adaptation to visual rearrangement are discussed.     

The immediate processing of sentences

Two independent groups of subjects, under instruction orienting them towards understanding or towards memorizing sentences were timed to respond to a brief auditory signal which occurred at some point during the course of a sentence. Latency appeared to be primarily a function of the task, such that the deeper the semantic processing of the sentence the longer the reaction time. Together with other aspects of the data, it is argued that such tasks affect the extent to which a subject retrieves the meanings of the words in a sentence and integrates them at the end of it. Concrete and abstract sentences were processed in fundamentally the same way. The conclusion drawn is that speech comprehension is an integrative process, under voluntary control, which collates together different aspects of the speech signal.