Acoustic Warning Signals Research Articles

Effects of acoustic warning signal intensity in the control of visuospatial interference

Abstract Previous studies have reported increased interference when a task-irrelevant acoustic warning signal preceded the target presentation in cognitive tasks. However, the alerting-congruence interaction was mostly observed for tasks measuring Flanker and Simon interferences but not for Stroop conflict. These findings led to the assumption that warning signals widen the attentional focus and facilitate the processing of irrelevant spatial characteristics. However, it is not clear whether these effects are because of the temporal information provided by the warning signal or because of their alerting effects. Based on these findings, and on the open question about the nature of the warning signal intervention on visuospatial interferences, we decided to test the impact of the warning signal on the processing of irrelevant spatial features, by using a procedure suitable for measuring both Simon and spatial Stroop interferences. We also manipulated the intensity of the warning signal to study the effect of the task-irrelevant characteristics of warning signals in visuospatial interferences. For the Simon conflict, results demonstrated an increased interference provoked by the presence (Experiment 1) and intensity (Experiment 2) of warning signals. In contrast, neither the presence nor the intensity of warning signals affected the spatial Stroop interference. Overall, these findings suggest that the impact of warning signals primarily depends on the processing of irrelevant spatial attributes and on the type of conflict (e.g., spatial stimulus-response interference in Simon vs. stimulus-stimulus interference in spatial Stroop). In general, acoustic warning signals facilitate the automatic response activation, but their modulatory effect depends on the task setting involved.

Cerebral blood flow modulations during proactive control in major depressive disorder.

In addition to mood disturbance, as well as motivational and somatic symptoms, patients with major depressive disorder (MDD) frequently experience impairments in attention and cognitive control. This study investigated cerebral blood flow modulations during proactive control in MDD, which refers to cognitive processes occurring during anticipation of a behaviourally relevant event. Using functional transcranial Doppler sonography, blood flow velocities in the middle cerebral arteries of both hemispheres were recorded in 40 individuals with MDD and 40 healthy participants during a pre-cued mental arithmetic task. The task required addition of one-digit numbers, which were presented 5 s after an acoustic warning signal. Response time on the task was longer in individuals with MDD than in healthy controls. Moreover, individuals with MDD exhibited smaller bilateral blood flow increases between the cuing tone and task presentation. In contrast, no group difference arose for blood flow modulations associated with arithmetic processing. The prolonged response time accords with previous reports of attentional impairments in MDD. As a measure of brain metabolism, cerebral blood flow modulations are indirectly associated with neural activity. Therefore, reduced cerebral blood flow increase during the preparatory period may reflect diminished neural processing related to proactive control in MDD. In contrast, processes associated with the actual execution of the arithmetic task seemed to be unaffected.

Differential effects of intensity and response preparation components of acoustic warning signals

Abstract It is known that the increase of intensity on a warning signal (WS) usually decreases reaction times to targets and occasionally is accompanied by a startle reflex reaction that influences the speediness of response execution. In a simple detection task (Experiment 1), a detection task with catch trials (Experiment 2) and a Go-NoGo discrimination task (Experiment 3), we studied the relationship between response preparation and alerting mechanisms operating upon the presentation of warning signals. A WS was presented either synchronously with the target (simultaneous condition) or 1400 ms before it (delayed condition). In all three experiments, the intensity of the WS and the simultaneity between WS and target were orthogonally manipulated. Results confirmed shorter reaction times by increasing the WS intensity. In Experiment 1, all conditions presented a clear acoustic intensity effect. In Experiment 2 we observed shorter reaction times in higher intensity conditions but only when the WS and the target were presented simultaneously. In Experiment 3, the intensity effect was observed only when the WS preceded the target. In all experiments, trials where the WS triggered a startle reflex showed a systematic increase in reaction time, which was independent of response preparation and task demands. In general, our findings suggest that response preparation modulates the alerting mechanisms, as a function of task set, but not the startle reflex. The dissociation between intensity, response preparation and startle supports the interdependence between these mechanisms elicited by the presentation of warning signals.

Cerebral blood flow modulations during cognitive control in major depressive disorder

BackgroundThis study investigated cerebral blood flow modulations during proactive and reactive cognitive control in major depressive disorder (MDD). Proactive control refers to preparatory processes during anticipation of a behaviorally relevant event; reactive control is activated after such an event to ensure goal attainment. MethodsUsing functional transcranial Doppler sonography, blood flow velocities in the middle cerebral arteries of both hemispheres were recorded in 40 MDD patients and 40 healthy controls during a precued Stroop task. The font color of color words, which appeared 5 s after an acoustic warning signal, had to be indicated while ignoring word meaning. ResultsPatients, as compared to controls, exhibited smaller bilateral blood flow increases during task preparation and larger increases after color word presentation. Response time was longer in patients irrespective of the match or mismatch between font color and word meaning. The blood flow increase after word presentation correlated positively with response time. LimitationsPotential effects of psychotropic medication on cognition and cerebral blood flow could not be controlled. ConclusionsThe study revealed evidence of reduced cortical activity during proactive and elevated activity that occurs during reactive control in MDD. Deficient implementation of proactive control in MDD may lead to increased reliance on reactive control. The association between the blood flow increase after color word presentation and poorer performance indicates that deficient response preparation cannot be compensated for by reactive strategies. The findings are clinically relevant, as they may contribute to our understanding of the mechanisms relevant to cognitive impairments in MDD.

Detection of traffic sound for driving safety: Effects of car body sound insulation

Hearing is an important physiological function that humans rely on to sense the surrounding situations. It is well understood that acoustic cues are critical for pedestrians, bicycle and motorcycle riders to identify traffic, thus to avoid potential risks in a timely manner. Similarly, efficient and accurate perception of external acoustic warning signals (e.g., car horn and siren sounds) in the traffic environment are also important for driving safety. As modern vehicles are made more and more sound proofing, mainly for the sake of riding comfort, it is increasingly difficult for drivers to hear external sounds, which can impair the driver's hearing perception and detection of potential danger posed by nearby traffic through natural hearing. Currently, there is a lack of research in the literature regarding the relationship between the sound perception capability by drivers and driving safety. Therefore, this study focuses on investigating how well the acoustic warning signals in the surrounding traffic environment can be perceived by the driver under various conditions and its potential influences on driving safety. To correlate the effectiveness of drivers detecting the external traffic sound to the sound isolation level of the car body, the sound insulation performance of two selected passenger car models and the subjective sound localization accuracy through vehicle structures are measured. It is found that the existence of the car body, more specifically the car body sound insulation effect, noticeably degrades the sound localization accuracy of drivers. In addition, the perceived sound source direction is found to shift toward the side of the car body with lower sound insulation performance.

Objectification of Acoustic Warning Signals in the Vehicle

Objectification of Acoustic Warning Signals in the Vehicle

Reduction of Radiation Exposure for the Examiner in Angiography using a Direct Dosimeter

To evaluate whether a reduction in radiation exposure can be achieved using a direct dosimeter with an acoustic warning signal (model EDD-30, Unfors Instruments, Billdal, Sweden). A total of 183 diagnostic and interventional angiographies of the pelvis and lower limbs using a direct dosimeter were analyzed. The vascular interventions were performed either by an experienced examiner (> 5000 interventions), an intermediate examiner (> 1000 interventions) or by a beginner (< 200 interventions). The measuring sensor of the direct dosimeter was attached to the back of the left hand, below the sterile glove, and was worn throughout the examination. If the limit values set on the dosimeter were exceeded, an acoustic signal sounded. At the end of the examination, the mean dose and the mean dose rate could be read off directly. Exposure is clearly dependent on the experience of the examiner. The highest mean dose rate was found for the beginner, followed by the intermediate examiner. The lowest dose rate was shown by the experienced examiner, even though he mostly performed complex interventions. Over the course of 3 months, an improvement in the average dose rate can be shown in the third month for the intermediate examiner. The use of a direct dosimeter with an acoustic warning signal is a practicable tool for sensitizing interventional radiologists to unavoidable radiation exposure, with the aim of reducing the dose. "Real-time" dosimetry represents a sensible extension of indirect protection of the radiation-exposed examiner in angiography.

Gaze strategies for avoiding obstacles: Differences between young and elderly subjects

Visual input is highly relevant for safely stepping over obstacles. In this study, gaze-behaviour was investigated in elderly, middle-aged and young subjects as they walked on a treadmill repeatedly stepping over obstacles, which approached either on the right or left side. In between obstacle-steps, subjects visually fixated a target N or F located two or four steps ahead on the floor, respectively. An acoustic warning signal announced the obstacles, after which subjects were free to look wherever they wanted. Gaze-movements were measured by video-oculography. Four conditions with 20 obstacles were conducted (two with target N, two with target F). In two conditions, high-precision stepping was investigated by asking subjects to step with minimal foot-clearance over the obstacles, while receiving acoustic feedback about their performance. In the high-precision conditions, more subjects (target N: 70%, F: 81%) turned their gaze on the obstacles and for a longer time than in unrestricted conditions. When fixating on the near target N and unrestricted stepping over the obstacles, significantly more elderly subjects (85%) turned their gaze on the obstacle compared to middle-aged (17%) and young subjects (29%). The elderly turned their gaze earlier and longer on the obstacle than middle-aged or young subjects. Our results reveal a different gaze-behaviour strategy of elderly subjects suggesting a greater dependency on visual inputs.

Independent Component Analysis Applied to Pharmacological Magnetic Resonance Imaging (phMRI): New Insights Into the Functional Networks Underlying Panic Attacks as Induced by CCK-4

Pharmacological magnetic resonance imaging (phMRI) is a method to study effects of psychopharmacological agents on neural activation. Changes of the blood oxygen level dependent (BOLD), the basis of functional MRI (fMRI), are typically obtained at relatively high sampling frequencies. This has more recently been exploited in the field of fMRI by applying independent component analysis (ICA), an explorative data analysis method decomposing activation into distinct neural networks. While already successfully used to investigate resting network and task-induced activity, its use in phMRI is new. Further extension of this method to tensorial probabilistic ICA (tensor PICA) allows to group similar brain activation across the anatomical, temporal, subject or session domain. This approach is useful for pharmacological experiments when no pharmacokinetic model exists. We exemplify this method using data from a placebo-controlled cholecystokinine-4 (CCK-4) injection experiment performed on 16 neuropsychiatrically and medically healthy males (age 25.6 +/- 4.2 years). Tensor PICA identified strong increases in activity in 12 networks. Comparison with results gained from the standard approach (voxelwise regression analysis) revealed good reproduction of areas previously associated with CCK-4 action, such as the anterior cingulate, orbitofrontal cortex, cerebellum, temporolateral, left parietal and insular areas, striatum, and precuneus. Several other components such as the dorsal anterior cingulate and medial prefrontal cortex were identified, suggesting higher sensitivity of the method. Exploration of the time courses of each activated network revealed differences, that might be lost when a fixed time course is modeled, e. g. neuronal responses to an acoustic warning signal prior to injection. Comparison of placebo and CCK-4 runs further showed that a proportion of networks are newly elicited by CCK-4 whereas other components are significantly active in the placebo conditions but further enhanced by CCK-4. In conclusion, group ICA is a promising tool for phMRI studies that allows quantifying and visualizing the modulation of neural networks by pharmacological interventions.

Multimodal warning signals for a multiple predator world

Aposematism is an anti-predator defence, dependent on a predator's ability to associate unprofitable prey with a prey-borne signal. Multimodal signals should vary in efficacy according to the sensory systems of different predators; however, until now, the impact of multiple predator classes on the evolution of these signals had not been investigated. Here, using a community-level molecular phylogeny to generate phylogenetically independent contrasts, we show that warning signals of tiger moths vary according to the seasonal and daily activity patterns of birds and bats-predators with divergent sensory capacities. Many tiger moths advertise chemical defence using conspicuous colouration and/or ultrasonic clicks. During spring, when birds are active and bats less so, we found that tiger moths did not produce ultrasonic clicks. Throughout both spring and summer, tiger moths most active during the day were visually conspicuous. Those species emerging later in the season produced ultrasonic clicks; those that were most nocturnal were visually cryptic. Our results indicate that selective pressures from multiple predator classes have distinct roles in the evolution of multimodal warning displays now effective against a single predator class. We also suggest that the evolution of acoustic warning signals may lack the theoretical difficulties associated with the origination of conspicuous colouration.

Time-locked association between rapid cerebral blood flow modulation and attentional performance

Objective The study investigated relationships between rapid cerebral hemodynamic modulation and attentional performance. Based on former results on complex cognitive functioning, a specific association between the first seconds of the hemodynamic response and performance was hypothesized. Methods Using transcranial Doppler sonography, blood flow velocities in the middle cerebral arteries of both hemispheres were recorded in 48 healthy subjects. The applied task comprised motor reactions on a visual stimulus which was preceded by an acoustic warning signal (interstimulus interval 5 s). Task-induced hemodynamic changes were assessed second-by-second, and related to reaction time using analysis of variance and linear regression. Results A right dominant blood flow response was observed. Flow velocity increase in the middle fraction of the interstimulus interval, i.e. seconds 2 and 3 after the cuing signal, significantly correlated with reaction time. This was not the case for the very early and late components of the response. Conclusions The results suggest a time-locked association between cerebral blood flow increase and attentional performance. This is in accordance with neurophysiological studies that revealed the closest relationship between brain perfusion and cortical activity during a similar time window. Significance The study supports the assumption of a specific, relatively early time interval in which relationships between cerebral blood flow and behavior become apparent.

Facilitation of spinal reflexes assists performing but not learning an obstacle‐avoidance locomotor task

The aim of this study was to investigate spinal reflex (SR) modulation during the performance and learning of a precision locomotor task. Healthy subjects had to minimize foot clearance when repeatedly stepping on a treadmill over a randomly approaching obstacle. The subjects walked with reduced vision and were informed about the approaching obstacle and task performance by acoustic warning and feedback signals, respectively. SRs were randomly evoked by tibial nerve stimulation (with non-nociceptive and nociceptive stimulus intensity) during the mid-stance phase in both normal and pre-obstacle stepping. Foot clearance and electromyographic activity of the tibialis anterior and biceps femoris muscles of the right leg were analysed. Only if a delay was introduced between warning signal and nerve stimulation, was the SR amplitude in both muscles enhanced prior to obstacle steps compared with normal steps for both stimulus intensities. Thus, the reflex enhancement depended on the subject's awareness of the approaching obstacle. Improved performance was reflected in a decreased foot clearance, but did not correlate with the course of SR amplitude. It is concluded that obstacle stepping is associated with a facilitation of SR pathways, probably by supraspinal drive. This facilitation might provide assistance in safe obstacle stepping, e.g. to compensate quickly if resistance is encountered.

A Psychoacoustical Model for Specifying the Level and Spectrum of Acoustic Warning Signals in the Workplace

A psychoacoustic model is presented to facilitate the installation of acoustic warning devices in noisy settings, reflecting a major upgrade of a former tool, Detectsound. The model can be used to estimate the optimal level and spectrum of acoustic warning signals based on the noise field in the workplace, the hearing status of workers, and the attenuation provided by hearing protectors. The new version can be applied to a wider range of situations. Analyses can now be conducted to meet the functional requirements for a specific worker or to suit the needs for a group of co-workers sharing a work area. Computation of optimal warning signals can also be made from estimated hearing parameters based on the worker age, gender, and level and duration of noise exposure. The results of a laboratory validation study showed that the mean error in estimating detection thresholds for normal hearing individuals is typically within ±1 dB with a standard deviation of less than 2.5 dB in white noise or continuous noise fields. The model tends to yield slightly overestimated warning signal detection thresholds in fluctuating noises. Proper application of the tool also requires consideration of the variability in estimating noise levels, hearing status, and hearing protector attenuation under field conditions to ensure that acoustic warning signals are sufficiently loud and well adjusted in practice.

Learning a high‐precision locomotor task in patients with Parkinson's disease

We evaluated the acquisition and performance of a high-precision locomotor task in patients with Parkinson's disease (PD) and healthy subjects. All subjects walked on a treadmill and had to step repetitively as low as possible over an obstacle without touching it. During blocks 1 and 2, the subjects had full vision and received additional acoustic warning and feedback signals. During block 3, vision became restricted. Changes in foot clearance and the number of obstacle hits were evaluated. Initially, PD patients performed poorer and improved foot clearance slower. After task repetition, the groups performed similarly. Restricting vision deteriorated performance in both groups. The similar performance of PD patients after task repetition might indicate that adequate training could improve adaptive locomotor behavior in PD patients.

Patient alert in implantable cardioverter defibrillators: toy or tool?

ObjectivesThe purpose of this study was to analyze the utility of patient-alert features in implantable cardioverter defibrillators (ICDs). BackgroundVarious alert features producing acoustic warning signals have been implemented in newer generation ICDs, but their role in early detection of system-related complications has not been systematically evaluated. MethodsIn 240 patients implanted with Medtronic ICD devices, the following alert features were routinely activated: pacing lead impedance <200 or >2,000 Ω, high-voltage lead impedance <10 or >200 Ω, low battery voltage (elective replacement indicator), long charge time (>18 s), >3 shocks delivered per episode, and all therapies in a zone delivered. Alert events occurring during follow-up were assessed in relation to actual findings (hospital charts, chest X-rays, ICD printouts including sensing/pacing/defibrillation threshold tests, episode data) to determine incidence, sensitivity, and specificity of the alert function. ResultsDuring 12.2 ± 8.9 months, 24 alert events occurred in the 240 patients (pacing lead impedance, n = 4; high-voltage lead impedance, n = 7; low battery voltage, n = 1; >3 shocks, n = 6; all therapies, n = 6). A total of 22 serious complications (necessitating reprogramming or device/lead replacement) were observed, 14 of which were primarily identified through a patient alert (lead fracture, n = 11; connector defect, n = 1; T-wave oversensing, n = 1; battery depletion, n = 1). This reflects a sensitivity of 64% and a specificity of 96% of the alert function for serious complications. With 14 of 24 patient alerts being caused by serious complications, the positive predictive value reached 58%. ConclusionsPatient-alert features are a useful additional tool facilitating early detection of serious ICD complications, but they do not substitute for regular ICD follow-up, because of their low sensitivity.

The influence of age on learning a locomotor task

Objective: Knowledge about locomotor task performance and learning in the elderly is important in optimizing rehabilitation strategies. The aim of this study was to evaluate differences between young and elderly subjects in the acquisition and performance of a precision locomotor task, with full and restricted vision. Methods: The subjects walked on a treadmill and had to step as low as possible over an obstacle, without touching it. They received acoustic warning and feedback signals, indicating obstacle appearance and foot clearance, respectively. Full vision was provided during the first two runs and became restricted during the third run. The number of obstacle hits and adaptations in foot clearance, leg muscle activity, range of motion of leg joints and swing phase duration were assessed. Results: With vision, the performance improved in both groups. Restricted vision reduced the task accuracy in both the young and the elderly. However, only the young subjects regained optimal foot clearance with practice. Conclusions: Elderly subjects rely more on visual control when acquiring and performing a precision locomotor task. We suggest that this is due to an impaired function of proprioceptive feedback mechanisms, which can replace visual information in young subjects. Significance: In the elderly, therapeutical attention should be directed towards optimizing the use of the remaining proprioceptive inputs.

The influence of age on learning a locomotor task

Objective: Knowledge about locomotor task performance and learning in the elderly is important in optimizing rehabilitation strategies. The aim of this study was to evaluate differences between young and elderly subjects in the acquisition and performance of a precision locomotor task, with full and restricted vision. Methods: The subjects walked on a treadmill and had to step as low as possible over an obstacle, without touching it. They received acoustic warning and feedback signals, indicating obstacle appearance and foot clearance, respectively. Full vision was provided during the first two runs and became restricted during the third run. The number of obstacle hits and adaptations in foot clearance, leg muscle activity, range of motion of leg joints and swing phase duration were assessed. Results: With vision, the performance improved in both groups. Restricted vision reduced the task accuracy in both the young and the elderly. However, only the young subjects regained optimal foot clearance with practice. Conclusions: Elderly subjects rely more on visual control when acquiring and performing a precision locomotor task. We suggest that this is due to an impaired function of proprioceptive feedback mechanisms, which can replace visual information in young subjects. Significance: In the elderly, therapeutical attention should be directed towards optimizing the use of the remaining proprioceptive inputs.

Being prepared on time: on the importance of the previous foreperiod to current preparation, as reflected in speed, force and preparation-related brain potentials

How do participants adapt to temporal variation of preparatory foreperiods? For reaction times, specific sequential effects have been observed. Responses become slower when the foreperiod is shorter on the current than on the previous trial. If this effect is due to changes in motor activation, it should also be visible in force of responses and in EEG measures of motor preparation, the contingent negative variation (CNV) and the lateralized readiness potential (LRP). These hypotheses were tested in a two-choice reaction task, with targets occurring 500, 1500, or 2500 ms after an acoustic warning signal. The reaction time results showed the expected pattern and were accompanied by similar effects on a fronto-central CNV and the LRP. In contrast, the increase of response force with brief current foreperiods did not depend on previous foreperiods. Thus, EEG measures confirm that sequential effects on RT are at least partially due to changes in motor activation originating from previous trials. Effects found on response force may be related to general response readiness rather than activation of motor-hand areas, which may explain the absence of a sequential effect on force in the current experiment.

Obstacle avoidance during human walking: H-reflex modulation during motor learning.

The goal of this study was to investigate changes of H-reflex amplitudes during a motor learning task. Subjects with reduced vision were instructed to step over an obstacle on a treadmill as low as possible, while the soleus H-reflex was elicited. Acoustic warning and feedback signals about performance were provided. Performance improvement was associated with a decrease of muscle activity, needed to step over the obstacle (rectus femoris, biceps femoris, tibialis anterior and gastrocnemius medialis muscles), and of foot clearance, while joint angle trajectories from knee and ankle became more stable. The experiment consisted of five runs, three with normal treadmill walking and two with randomly stepping over the obstacle (100 times). H-reflexes were elicited at early and late stance phase before stepping over the obstacle. H/M ratio, latency and duration were determined. The values of these measures were calculated for the onset and end of a run and their course over time was evaluated using a correlation coefficient. The largest adaptations with a significant increase of reflex amplitude occurred during the first obstacle run. This increase lasted only briefly and the reflex amplitudes decreased to their previous values. During the later obstacle run, no H-reflex modulation occurred. It is concluded that a motor learning task causes adaptational effects not only on performance, but also on H-reflex responses. The results indicate that most of the modulation of H-reflexes is probably due to supraspinal influences on reflex transmission. The observations made are probably less specific for this motor task (stepping over the obstacle), but rather associated with the increased attention required by the motor learning task during the first obstacle run.

Specifying a General Criterion for Hearing Protectors with the Aim of Ensuring Good Acoustic Perception

The development of occupational hearing impairment in German industry reveals that noise is still a serious problem. Industrial practitioners observe employees who refuse to wear hearing protectors sometimes (or all the time) while exposed to noise of levels higher than 85 dB(A) or even 90 dB(A). These employees frequently maintain that the hearing protectors used are not comfortable enough or they impede communication with colleagues or perception of acoustic warning signals or informative operating sound.