Startling Auditory Stimulus Research Articles

Startling stimuli increase maximal motor unit discharge rate and rate of force development in humans.

Maximal rate of force development in adult humans is determined by the maximal motor unit discharge rate, however, the origin of the underlying synaptic inputs remains unclear. Here, we tested a hypothesis that the maximal motor unit discharge rate will increase in response to a startling cue, a stimulus that purportedly activates the pontomedullary reticular formation neurons that make mono- and disynaptic connections to motoneurons via fast-conducting axons. Twenty-two men were required to produce isometric knee extensor forces "as fast and as hard" as possible from rest to 75% of maximal voluntary force, in response to visual (VC), visual-auditory (VAC; 80 dB), or visual-startling cue (VSC; 110 dB). Motoneuron activity was estimated via decomposition of high-density surface electromyogram recordings over the vastus lateralis and medialis muscles. Reaction time was significantly shorter in response to VSC compared with VAC and VC. The VSC further elicited faster neuromechanical responses including a greater number of discharges per motor unit per second and greater maximal rate of force development, with no differences between VAC and VC. We provide evidence, for the first time, that the synaptic input to motoneurons increases in response to a startling cue, suggesting a contribution of subcortical pathways to maximal motoneuron output in humans.NEW & NOTEWORTHY Motor unit discharge characteristics are a key determinant of rate of force development in humans, but the neural substrate(s) underpinning such output remains unknown. Using decomposition of high-density electromyogram, we show greater number of discharges per motor unit per second and greater rate of force development after a startling auditory stimulus. These observations suggest a possible subcortical contribution to maximal in vivo motor unit discharge rate in adult humans.

Auditory startle disrupts speech coordination

Abstract Speech production requires temporal coordination between the actions of different functional groupings of muscles in the human body. Crucially, such functionally organized units, or “modules”, may be susceptible to disruption by an external stimulus such as a startling auditory stimulus (SAS; >120dB), enabling a possible window into the internal structure of learned speech movements. Following on the observation that SAS is known to accelerate the release of pre-planned actions, the current study examines lip kinematics in SAS-induced responses during speech movements to test whether this accelerated release applies on the scale of entire syllables or on the scale of smaller functional units. Production measures show that SAS-elicited bilabial movements in [ba] syllables are prone to disruption as measured by discontinuity in velocity profiles. We use a 3D finite element method (FEM) biomechanical model to simulate the temporal interaction between muscle groupings in speech. Simulation results indicate that this discontinuity can be accounted for as an instance of temporally decoupled coordination across neuromuscular modules. In such instances, the muscle groupings controlling lip compression and jaw opening, which normally fire sequentially, appear more likely to be activated synchronously.

When reflex reactions oppose voluntary commands: The StartReact effect on eye opening.

A startling auditory stimulus (SAS) induces a reflex response involving, among other reactions, a strong contraction of the orbicularis oculi muscle (OOc) and subsequent eye closure. A SAS also induces the StartReact effect, a significant shortening of reaction time in subjects ready for task execution. We examined the obvious conflict appearing when a StartReact paradigm requires participants with eyes closed to open their eyes to look for a visual target. We recorded OOc EMG activity and eyelid movements in healthy volunteers who were instructed to open their eyes at perception of a somatosensory imperative stimulus (IS) and locate the position of a Libet's clock's hand shown on a computer screen at 80cm distance. In 6 out of 20 trials, we delivered a SAS simultaneously with the IS. The main outcome measures were reaction time at onset of eyelid movement and the time gap (TG) separating subjective assessment of the clock's hand position from real IS issuing. Control experiments included reaction time to eye closing and target location with eyes open to the same IS. Reaction time was significantly faster in SAS than in noSAS trials and slower for eye opening than for eye closing in both conditions. In the eye-opening task, TG was significantly shorter in SAS with respect to noSAS trials, despite the presence of the SAS-related burst in the OOc before EMG cessation. Our results indicate that the StartReact effect speeds up eye opening and location of a target in the visual field despite the startle reaction opposing the task.

The role of duration in speech plans uncovered by startling auditory stimulus

Abstract This study investigated how speech targets of different durations may be specified in speech plans and the release in response to startling auditory stimulus (SAS) triggering. In particular, we examined whether differentiated musical training background affects responses in terms of the preservation of duration. The results show that facilitated reaction time (RT) is only observed in SAS-induced responses shorter than 500 ms, suggesting that targets longer than 500 ms may not be as susceptible to SAS-induced rapid release. While both musically trained and untrained participants lacked accuracy in producing targets with fixed durations, they were able to differentiate syllable lengths, even though duration does not denote phonemic contrasts in Mandarin. The results also show a degree of compensation to elevated pitch level from musically trained participants, suggesting that they may have a higher sensitivity to pitch level even within a limited duration window.

BS24. Motor preparation in picture naming tasks

Introduction Utterance of a word may be an involuntary action. We hypothesize that, once pronunciation of a word is fully prepared it can be triggered as a reflex with no need for cortical processing. Methods We used modified protocols of picture naming tasks, with different levels of cognitive demands, to measure the reaction time of word pronunciation (RTWP). In test trials, picture presentation was accompanied by a startling auditory stimulus (SAS). Results When one and the same picture was repeatedly shown, SAS shortened RTWP by about 30% (StartReact effect), which did not occur when random pictures were shown. If subjects were led to learn which picture was to appear after repeated presentation of three pictures in sequence, they exhibited again the StartReact effect. Conclusion We conclude that, when fully prepared, pronunciation of words can be triggered as a SAS-induced subcortical motor reflex. However, the StartReact effect is inhibited during cognitive tasks.

Motor preparation in picture naming tasks

In certain circumstances, words can be uttered as an involuntary action. We hypothesize that, once pronunciation of a word is fully prepared it can be triggered as a reflex with no need for cortical processing. We used modified protocols of picture naming tasks, with different levels of cognitive demands, to measure reaction time to word pronunciation (RTWP). In test trials, picture presentation was accompanied by a startling auditory stimulus (SAS). When one and the same picture was repeatedly shown, SAS shortened RTWP by about 30% (StartReact effect), which did not occur when random pictures were shown. If subjects were led to learn which picture was to appear after repeated presentation of three pictures in sequence, they exhibited again the StartReact effect. We conclude that word pronunciation may be fully prepared for execution in absence of cognitive demands. However, the StartReact effect is inhibited during cognitive tasks.

Pitch height as part of speech plans: Evidence from response to auditory startle

In Mandarin, pitch contour denotes phonemic contrast while pitch height does not serve as a phonemic parameter. When triggered by a startling auditory stimulus (SAS, >120dB), prepared Mandarin CV syllable [ba] is elicited rapidly while its pitch contour remains unperturbed, suggesting that phonemic details are included in the speech plan and susceptible for rapid release under feedforward control [Chiu and Gick 2014, JASA-EL, 322-328]. Pitch height, however, is elevated in SAS-induced responses. It is not clear whether or not pitch height can be independently pre-specified in speech plans. The current study uses the startle paradigm to tackle this question by comparing general Mandarin speakers and Mandarin speakers with pitch training. Preliminary results show that specific pitch height can be prepared and is preserved in SAS-induced responses. More unperturbed pitch height is observed in pitch-trained speakers’ responses than in general Mandarin speakers’ responses. While slight and limited elevation may occur at the beginning of SAS-induced responses, the preservation of the absolute pitch height appears to interact with intended response durations. The results suggest that absolute pitch height, even when not acting as a phonemic parameter, can be pre-specified in speech plans and released by a SAS both rapidly and accurately.

An examination of the startle response during upper limb stretch perturbations

Unexpected presentation of a startling auditory stimulus (SAS>120 decibels) in a reaction time (RT) paradigm results in the startle reflex and an early release (<100ms) of the preplanned motor response (StartReact effect). Mechanical perturbations applied to the upper limbs elicit short- (M1) and long-latency (M2) stretch reflexes and have also been shown to initiate intended motor responses early (<100ms). Ravichandran et al. (2013) recently proposed that unexpected delivery of a perturbation could also elicit a startle response and therefore the StartReact effect may be responsible for the early trigger of a preplanned response. To investigate this further, we examined startle incidence, RT, and stretch reflex modulation for both expected and unexpected perturbations. In Experiment 1, participants performed active (ACT) and passive (DNI) conditions to an expected large perturbation (similar to previous studies examining M2). The startle response was not observed; however, the perturbation still elicited the voluntary response at short latency (<100ms) and goal-dependent modulation of the M2 response was observed. In Experiment 2, participants performed ACT and DNI conditions to a weak auditory stimulus or a small wrist perturbation. On unexpected trials we probed startle circuitry with a large perturbation or SAS. The SAS consistently elicited a startle response in both ACT and DNI conditions, but startle-like activity was only observed on 17.4% of ACT perturbation probe trials. Our findings suggest that while unexpected upper limb perturbations can be startling, startle triggering of the preplanned voluntary response is not the primary mechanism responsible for goal-dependent modulation of the M2 response.

Modulation of force and velocity for accurate tasks by a startle

Background Some skilfulfast activities require control of trajectory and force to fulfill the task. It is known that voluntary reactions can be speeded up by a startling auditory stimulus (SAS) delivered at the same time as the imperative signal (IS), a phenomenon termed Start-React (Valls-Sole et al., 1999). The aim of the present study was to examine how the performance of a task that demands accuracy, mainly in terms of velocity during the trajectory or force control when holding an object, is changed by a SAS timed to occur either at the time of IS or at a pre-determined time interval when movement has already begun and motor control of accurate reaching is expected. Methods Nine subjects performed an accurate elbow extension between two spots placed at an angular distance of 30° when holding with their right hand a pen that monitored, through two strain gauge systems, the force of the subject’s fingers during the hold, and the force at which pen-tip was exposed with table contact. According to block of trials, this end spot had three possible diameters: 5, 10, and 20 mm. Kinematic and force parameters were measured for three conditions, control, with SAS at IS or SAS delivered when movement has already started. Results In SAS trials, there were no evident differences with respect to control trials in the general outline but there were differences in the timing of the events. In SAS-IS trials time to peak velocity was 166 ms (SD = 41 ms), time to peak force was 95 ms (SD = 43 ms) both shorter than in control or SAS delivered when movement began. Peak velocity (315 ± 56 o/s) and peak force (8 ± 2 arbitr. units) were larger for SAS-IS trials than for control or SAS delivered when movement started. Conclusions Startle can advance a task that requires accuracy with velocity and force modulations, but when task onset is already launched there are not evident changes in velocity or force parameters, that seem already prepared.

Preparation for reaction time tasks in multiple sclerosis

Background Sensorimotor integration can be assessed using simple reaction time tasks to somatosensory stimuli (ssRT). Tasks performed to stimuli applied to the contralateral hemibody would reveal interhemispheric transfer of information (IHT) across corpus callosum, while tasks performed when a startling-auditory stimulus (SAS) is presented together with the somatosensory cue would reveal the level of subcortical motor preparation. We studied both preparation and IHT in MS patients in whom callosal pathways and subcortical structures may be particularly involved. Methods In 13 controls and 20 mildly disabled relapsing-remitting MS patients, we studied ssRT for voluntary wrist-extension to ipsilateral and contralateral low intensity electrical stimuli, applied to the index finger. Percentage delay (PD) of contralateral vs ipsilateral responses was calculated as a measure of IHT. StartReact trials were performed applying randomly a SAS in ssRT trials (20%). Percentage shortening (SAS-Short) with respect to ssRT was calculated as a measure of the effectiveness of preparation. Motor conduction time (MCT) was assessed by recording the motor-evoked potentials to TMS. Results In controls, mean PD of contralateral responses was 105.7% longer than for ipsilateral responses. In StartReact trials, the mean SAS-Short was 29.7% for ipsilateral and 23.3% for contralateral responses. With respect to controls, patients had no differences in PD (105.4%) but showed significantly lower SAS-Short for ipsilateral (23.4%; p = 0.02) and contralateral trials (10.9%; p = 0.005). Contralateral SAS-Short was inversely correlated with MCT (r = −0.294). Two patients had abnormally delayed orbiculari-oculi responses to SAS. Conclusions Patients with MS have defective subcortical motor preparation that is worse when IHT sensorimotor integration is required.

The StartReact effect in tasks requiring end-point accuracy

ObjectiveFast and accurate movements are often performed in response to a sensory signal. In reaction time tasks, execution of open loop movements is speeded up when a startling auditory stimulus (SAS) is applied together with the imperative signal (IS). In this study, we examined the effects of a SAS on the performance of a task that demands accuracy. MethodsNine subjects were asked to move a monitored pen to a target point located in a table at a fixed angular distance of 30 degrees from a start point. The target was a spot of three possible diameters: 5, 10, and 20mm. Finger force for pen holding, pen tip pressure against the table and kinematic variables of the forearm movement were measured for three conditions: control, SAS delivered at IS (SAS-IS trials) and SAS delivered during movement execution (SAS-MOV trials). ResultsTwo movement phases could be identified in the movement trajectory and force profile. The first phase, ballistic, was significantly shortened in SAS-MOV trials, with earlier and larger peak velocity and peak force with respect to control trials. The second phase, slow approach to target, was longer in SAS-IS trials but not in SAS-MOV trials. Accuracy was maintained throughout all conditions and stimulation modes. ConclusionsA SAS speeds up only the first (ballistic) part of the movement in an accuracy task. Slower target approach compensates for the accelerated initial movement. No changes in the last part of the movement are seen when a SAS is delivered after movement onset. SignificanceThe StartReact effect is restricted to the onset of a complex movement, when muscles are activated in a ballistic mode, without feedback.

Defective sensorimotor integration in preparation for reaction time tasks in patients with multiple sclerosis.

Slowness of voluntary movements in patients with multiple sclerosis (MS) may be due to various factors, including attentional and cognitive deficits, delays in motor conduction time, and impairment of specific central nervous system circuits. In 13 healthy volunteers and 20 mildly disabled, relapsing-remitting MS patients, we examined simple reaction time (SRT) tasks requiring sensorimotor integration in circuits involving the corpus callosum and the brain stem. A somatosensory stimulus was used as the imperative signal (IS), and subjects were requested to react with either the ipsilateral or the contralateral hand (uncrossed vs. crossed SRT). In 33% of trials, a startling auditory stimulus was presented together with the IS, and the percentage reaction time change with respect to baseline SRT trials was measured (StartReact effect). The difference between crossed and uncrossed SRT, which requires interhemispheric conduction, was significantly larger in patients than in healthy subjects (P = 0.021). The StartReact effect, which involves activation of brain stem motor pathways, was reduced significantly in patients with respect to healthy subjects (uncrossed trials: P = 0.015; crossed trials: P = 0.005). In patients, a barely significant correlation was found between SRT delay and conduction abnormalities in motor and sensory pathways (P = 0.02 and P = 0.04, respectively). The abnormalities found specifically in trials reflecting interhemispheric transfer of information, as well as the evidence for reduced subcortical motor preparation, indicate that a delay in reaction time execution in MS patients cannot be explained solely by conduction slowing in motor and sensory pathways but suggest, instead, defective sensorimotor integration mechanisms in at least the two circuits examined.

Subcortical visuomotor control of human limb movement.

It is generally accepted that cortical networks play a major role in the visual guidance of human limb movements. However, there is a growing body of evidence that points to subcortical visuomotor processes also having an important role to play. Behavioural evidence in man comes from studies on the very fast responses that occur when a target unexpectedly jumps to a new location during either an upper-limb reaching movement or a lower-limb stepping movement. In both cases, the target jump evokes a correction in the movement trajectory at a surprisingly short latency of 120–160 ms. These very fast reactions have a number of properties that are compatible with subcortical control: (1) they are not abolished by effort of will, (2) they can be made even faster by a startling auditory stimulus, (3) they do not obey Hick’s law. Further evidence comes from measurements of reach adjustment latencies in a subject with agenesis of the corpus callosum. Latencies are the same irrespective of whether the visual stimulus appears in contralateral or ipsilateral hemispace, a finding that is incompatible with cortical visuomotor control.

Are postural responses to backward and forward perturbations processed by different neural circuits?

Startle pathways may contribute to rapid accomplishment of postural stability. Here we investigate the possible influence of a startling auditory stimulus (SAS) on postural responses. We formulated four specific questions: (1) can a concurrent SAS shorten the onset of automatic postural responses?; and if so (2) is this effect different for forward versus backward perturbations?; (3) does this effect depend on prior knowledge of the perturbation direction?; and (4) is this effect different for low- and high-magnitude perturbations?Balance was perturbed in 11 healthy participants by a movable platform that suddenly translated forward or backward. Each participant received 160 perturbations, 25% of which were combined with a SAS. We varied the direction and magnitude of the perturbations, as well as the prior knowledge of perturbation direction. Perturbation trials were interspersed with SAS-only trials.The SAS accelerated and strengthened postural responses with clear functional benefits (better balance control), but this was only true for responses that protected against falling backwards (i.e. in tibialis anterior and rectus femoris). These muscles also demonstrated the most common SAS-triggered responses without perturbation. Increasing the perturbation magnitude accelerated postural responses, but again with a larger acceleration for backward perturbations.We conclude that postural responses to backward and forward perturbations may be processed by different neural circuits, with influence of startle pathways on postural responses to backward perturbations. These findings give directions for future studies investigating whether deficits in startle pathways may explain the prominent backward instability seen in patients with Parkinson’s disease and progressive supranuclear palsy.

The StartReact Effect on Self-Initiated Movements

Preparation of the motor system for movement execution involves an increase in excitability of motor pathways. In a reaction time task paradigm, a startling auditory stimulus (SAS) delivered together with the imperative signal (IS) shortens reaction time significantly. In self-generated tasks we considered that an appropriately timed SAS would have similar effects. Eight subjects performed a ballistic wrist extension in two blocks: reaction, in which they responded to a visual IS, and action, in which they moved when they wished within a predetermined time window. In 20–25% of the trials, a SAS was applied. We recorded electromyographic activity of wrist extension and wrist movement kinematic variables. No effects of SAS were observed in action trials when movement was performed before or long after SAS application. However, a cluster of action trials was observed within 200 ms after SAS. These trials showed larger EMG bursts, shorter movement time, shorter time to peak velocity, and higher peak velocity than other action trials (P < 0.001 for all), with no difference from Reaction trials containing SAS. The results show that SAS influences the execution of self-generated human actions as it does with preprogrammed reaction time tasks during the assumed building up of preparatory activity before execution of the willed motor action.

A Loud Auditory Stimulus Overcomes Voluntary Movement Limitation in Cervical Dystonia

BackgroundPatients with cervical dystonia (CD) present with an impaired performance of voluntary neck movements, which are usually slow and limited. We hypothesized that such abnormality could involve defective preparation for task execution. Therefore, we examined motor preparation in CD patients using the StartReact method. In this test, a startling auditory stimulus (SAS) is delivered unexpectedly at the time of the imperative signal (IS) in a reaction time task to cause a faster execution of the prepared motor programme. We expected that CD patients would show an abnormal StartReact phenomenon.MethodsFifteen CD patients and 15 age matched control subjects (CS) were asked to perform a rotational movement (RM) to either side as quick as possible immediately after IS perception (a low intensity electrical stimulus to the II finger). In randomly interspersed test trials (25%) a 130 dB SAS was delivered simultaneously with the IS. We recorded RMs in the horizontal plane with a high speed video camera (2.38 ms per frame) in synchronization with the IS. The RM kinematic-parameters (latency, velocity, duration and amplitude) were analyzed using video-editing software and screen protractor. Patients were asked to rate the difficulty of their RMs in a numerical rating scale.ResultsIn control trials, CD patients executed slower RMs (repeated measures ANOVA, p<0.10−5), and reached a smaller final head position angle relative to the midline (p<0.05), than CS. In test trials, SAS improved all RMs in both groups (p<0.10−14). In addition, patients were more likely to reach beyond their baseline RM than CS (χ2, p<0.001) and rated their performance better than in control trials (t-test, p<0.01).ConclusionWe found improvement of kinematic parameters and subjective perception of motor performance in CD patients with StartReact testing. Our results suggest that CD patients reach an adequate level of motor preparation before task execution.

Preparedness for landing after a self-initiated fall

A startling auditory stimulus (SAS) causes a faster execution of voluntary actions when applied together with the imperative signal in reaction time tasks (the StartReact effect). However, speeding up reaction time may not be the best strategy in all tasks. After a self-initiated fall, the program for landing has to be time-locked to foot contact to avoid damage, and therefore advanced execution of the program would not be convenient. We examined the effects of SAS on the landing motor program in 8 healthy subjects that were requested to let themselves fall from platforms either 50 or 80 cm high at the perception of a visual imperative signal and land on specific targets. In trials at random, SAS was applied either together with the imperative signal (SAS(IS)) or at an appropriate prelanding time (SAS(PL)). As expected, the latency of takeoff was significantly shortened in SAS(IS) trials. On the contrary, the timing of foot contact was not significantly different for SAS(PL) compared with control trials. No changes were observed in the size of the electromyograph bursts in the two experimental conditions with respect to the control condition. Our results indicate that the landing program after a self-initiated fall may in part be organized at the time of takeoff and involve precise information on timing of muscle activation. Once launched, the program is protected against interferences by external inputs.

Feed-forward control of phonetic gestures in consonant–vowel syllables: Evidence from responses to auditory startle.

Speech production like other limb movements relies on both feed-forward and feedback mechanisms. Use of a startling auditory stimulus (&amp;gt;90 dB) has been shown to trigger fast, accurate feed-forward performances in upper limb movements prior to access to feedback information [Valls-Solé et al. (1999), J. Physiol. 516: 931–938; Carlsen et al. (2004), J. Mot. Behav. 36: 253–264]. This startle paradigm is applied to test whether pre-programed, feed-forward speech production differs in phonetic detail from production with access to feedback. The experiment examined the production of the CV syllable [ba], starting with the mouth either open or closed. This speech production was triggered either by a control stimulus (82 dB) or by a startling stimulus (124 dB). Results from ten participants showed that lip compression occurred for both starting conditions (mouth open and mouth closed), and also indicated that the timing relationships of the articulators were stable across control trials and startle trials. The acoustics of syllables, formant values, and maximum amplitudes, were consistent across control trials and startle trials, suggesting that the production of pre-programmed gestural configurations in CV syllables may be executed under exclusively feed-forward control.

Speeding up gait initiation and gait-pattern with a startling stimulus

Human gait involves a repetitive leg motor pattern that emerges after gait initiation. While the automatic maintenance of the gait-pattern may be under the control of subcortical motor centres, gait initiation requires the voluntary launching of a different motor program. In this study, we sought to examine how the two motor programmes respond to an experimental manipulation of the timing of gait initiation. Subjects were instructed to start walking as soon as possible at the perception of an imperative signal (IS) that, in some interspersed trials was accompanied by a startling auditory stimulus (SAS). This method is known to shorten the latency for execution of the motor task under preparation. We reasoned that, if the two motor programmes were launched together, the gait-pattern sequence would respond to SAS in the same way as gait initiation. We recorded the gait phases and the electromyographic (EMG) activity of four muscles from the leg that initiates gait. In trials with SAS, latency of all gait initiation-related events showed a significant shortening and the bursts of EMG activity had higher amplitude and shorter duration than in trials without SAS. The events related to gait-pattern were also advanced but otherwise unchanged. The fact that all the effects of SAS were limited to gait initiation suggests that startle selectively can affect the neural structures involved in gait initiation. Additionally, the proportional advancement of the gait-pattern sequence to the end of gait initiation supports the view that gait initiation may actually trigger the inputs necessary for generating the gait-pattern sequence.

The effects of an auditory startle on obstacle avoidance during walking

Movement execution is speeded up when a startle auditory stimulus is applied with an imperative signal in a simple reaction time task experiment, a phenomenon described as StartReact. The effect has been recently observed in a step adjustment task requiring fast selection of specific movements in a choice reaction time task. Therefore, we hypothesized that inducing a StartReact effect may be beneficial in obstacle avoidance under time pressure, when subjects have to perform fast gait adjustments. Twelve healthy young adults walked on a treadmill and obstacles were released in specific moments of the step cycle. On average the EMG onset latency in the biceps femoris shortened by 20% while amplitude increased by 50%, in trials in which an auditory startle accompanied obstacle avoidance. The presentation of a startle increased the probability of using a long step strategy, enlarged stride length modifications and resulted in higher success rates, to avoid the obstacle. We also examined the effects of the startle in a condition in which the obstacle was not present in comparison to a condition in which the obstacle was visibly present but it did not fall. In the latter condition, the obstacle avoidance reaction occurred with a similar latency but smaller amplitude as in trials in which the obstacle was actually released. Our results suggest that the motor programmes used for obstacle avoidance are probably stored at subcortical structures. The release of these motor programmes by a startling auditory stimulus may combine intersensory facilitation and the StartReact effect.