Perceived urgency of and response time to multi-tone and frequency-modulated warning signals in broadband noise

Neurocognitive processing efficiency for discriminating human non-alarm rather than alarm scream calls

Across many species, scream calls signal the affective significance of events to other agents. Scream calls were often thought to be of generic alarming and fearful nature, to signal potential threats, with instantaneous, involuntary, and accurate recognition by perceivers. However, scream calls are more diverse in their affective signaling nature than being limited to fearfully alarming a threat, and thus the broader sociobiological relevance of various scream types is unclear. Here we used 4 different psychoacoustic, perceptual decision-making, and neuroimaging experiments in humans to demonstrate the existence of at least 6 psychoacoustically distinctive types of scream calls of both alarming and non-alarming nature, rather than there being only screams caused by fear or aggression. Second, based on perceptual and processing sensitivity measures for decision-making during scream recognition, we found that alarm screams (with some exceptions) were overall discriminated the worst, were responded to the slowest, and were associated with a lower perceptual sensitivity for their recognition compared with non-alarm screams. Third, the neural processing of alarm compared with non-alarm screams during an implicit processing task elicited only minimal neural signal and connectivity in perceivers, contrary to the frequent assumption of a threat processing bias of the primate neural system. These findings show that scream calls are more diverse in their signaling and communicative nature in humans than previously assumed, and, in contrast to a commonly observed threat processing bias in perceptual discriminations and neural processes, we found that especially non-alarm screams, and positive screams in particular, seem to have higher efficiency in speeded discriminations and the implicit neural processing of various scream types in humans.

Ergonomic Auditory Alarm Signals for the Oil and Chemical Processing Industry

OCCUPATIONAL APPLICATIONSAuditory alarm signals are a safety measure that would benefit from improvement across many industries. There is a considerable research base that can be applied to the development and testing of audible alarms, though this is rarely done in practice. We describe a process that can be adopted in any area where audible alarm signals are widespread. A comprehensive approach to updating and improving auditory alarms requires consideration not only of individual alarm sounds but also of how the alarm signals will work together. We show the development and design of alarm signal sets following best practices from acoustic, psychoacoustic, and psychological knowledge to ensure that the resultant alarms are localizable, audible, easy to learn, appropriately urgency-mapped, and differentiable. We also describe benchmarking tests, and a protocol for thinking about how auditory alarm signals might be implemented in control rooms of different sizes.

Using timbre to improve performance of larger auditory alarm sets

Identifiability and perceived urgency were compared for two sets of alarms in a healthcare inpatient setting. One contained currently used alarms where possible, with new sounds added as needed. The other was designed together, was more heterogenous, used timbre to encode intended similarities and explicitly encoded intended urgency across the set. Twenty nurses reported the identity and perceived urgency of the sounds in each set. Participants correctly identified the sound (0.89 vs. 0.77) and alarm category (0.93 vs. 0.82) more often in the new set than in the baseline set. In addition, multiple sounds in the new set were more identifiable. The new sounds also had a larger range of perceived urgency and better urgency match. The results indicate that timbre is well-suited to encode alarm groupings in larger alarm sets and that this, along with increased heterogeneity and explicit urgency mapping, improves alarm set performance. Practitioner summary: Clinical alarms are frequently misidentified. We found that making alarms more acoustically rich, using timbre to convey alarm groups, and explicitly encoding intended urgency improved identifiability and urgency match. These findings can be used to improve alarm performance across all safety-critical industries.

Effect of Providing the Uncertainty Information About a Tornado Occurrence on the Weather Recipients' Cognition and Protective Action: Probabilistic Hazard Information Versus Deterministic Warnings

Currently, a binary alarm system is used in the United States to issue deterministic warning polygons in case of tornado events. To enhance the effectiveness of the weather information, a likelihood alarm system, which uses a tool called probabilistic hazard information (PHI), is being developed at National Severe Storms Laboratory to issue probabilistic information about the threat. This study aims to investigate the effects of providing the uncertainty information about a tornado occurrence through the PHI's graphical swath on laypeople's concern, fear, and protective action, as compared with providing the warning information with the deterministic polygon. The displays of color-coded swaths and deterministic polygons were shown to subjects. Some displays had a blue background denoting the probability of any tornado formation in the general area. Participants were asked to report their levels of concern, fear, and protective action at randomly chosen locations within each of seven designated levels on each display. Analysis of a three-stage nested design showed that providing the uncertainty information via the PHI would appropriately increase recipients' levels of concern, fear, and protective action in highly dangerous scenarios, with a more than 60% chance of being affected by the threat, as compared with deterministic polygons. The blue background and the color-coding type did not have a significant effect on the people's cognition of the threat and reaction to it. This study shows that using a likelihood alarm system leads to more conscious decision making by the weather information recipients and enhances the system safety.

Musical Intensity Applied in the Sports and Exercise Domain: An Effective Strategy to Boost Performance?

In the sports and exercise domain, it has been suggested that musical intensity might boost performance. Previous research revealed that pumping up the volume of music might increase running speed, grip strength, and choice reaction time while simultaneously decreasing time to exhaustion and level of perceived exhaustion. However, evidence is still scarce, experimental designs and tested groups vary significantly, and contradicting evidence exists as well. Yet, listening to high-intensity music could be a risky business and exercisers employing such a strategy to improve performance are vulnerable to developing noise-induced hearing problems. Therefore, future research should inquire more profoundly into the inherent boosting qualities of musical intensity and juxtapose experimental results and auditory repercussions in order to uncover possible strategies to combine both in such a way that the exerciser’s health can be safeguarded at all times.

The Recognizability and Localizability of Auditory Alarms: Setting Global Medical Device Standards

Objective Four sets of eight audible alarms matching the functions specified in IEC 60601-1-8 were designed using known principles from auditory cognition with the intention that they would be more recognizable and localizable than those currently specified in the standard. Background The audible alarms associated with IEC 60601-1-8, a global medical device standard, are known to be difficult to learn and retain, and there have been many calls to update them. There are known principles of design and cognition that might form the basis of more readily recognizable alarms. There is also scope for improvement in the localizability of the existing alarms. Method Four alternative sets of alarms matched to the functions specified in IEC 60601-1-8 were tested for recognizability and localizability and compared with the alarms currently specified in the standard. Results With a single exception, all prototype sets of alarms outperformed the current IEC set on both recognizability and localizability. Within the prototype sets, auditory icons were the most easily recognized, but the other sets, using word rhythms and simple acoustic metaphors, were also more easily recognized than the current alarms. With the exception of one set, all prototype sets were also easier to localize. Conclusion Known auditory cognition and perception principles were successfully applied to an existing audible alarm problem. Application This work constitutes the first (benchmarking) phase of replacing the alarms currently specified in the standard. The design principles used for each set demonstrate the relative ease with which different alarm types can be recognized and localized.

Concurrent audio-visual feedback for supporting drivers at intersections: A study using two linked driving simulators

A large portion of road traffic crashes occur at intersections for the reason that drivers lack necessary visual information. This research examined the effects of an audio-visual display that provides real-time sonification and visualization of the speed and direction of another car approaching the crossroads on an intersecting road. The location of red blinking lights (left vs. right on the speedometer) and the lateral input direction of beeps (left vs. right ear in headphones) corresponded to the direction from where the other car approached, and the blink and beep rates were a function of the approaching car's speed. Two driving simulators were linked so that the participant and the experimenter drove in the same virtual world. Participants (N = 25) completed four sessions (two with the audio-visual display on, two with the audio-visual display off), each session consisting of 22 intersections at which the experimenter approached from the left or right and either maintained speed or slowed down. Compared to driving with the display off, the audio-visual display resulted in enhanced traffic efficiency (i.e., greater mean speed, less coasting) while not compromising safety (i.e., the time gap between the two vehicles was equivalent). A post-experiment questionnaire showed that the beeps were regarded as more useful than the lights. It is argued that the audio-visual display is a promising means of supporting drivers until fully automated driving is technically feasible.

The Effect of Sonification Pulse Rate on Perceived Urgency and Response Behaviors

Emergency signal researchers have devoted considerable energy to understanding the perceived urgency and performance effects of reliable and marginally reliable discrete auditory signals. Relatively little attention has been paid to aspects of continuous auditory displays. The purpose of the current study was to demonstrate and document the effects of sonification presentation rate on perceived urgency and response behaviors during a simulated patient monitoring task. As expected, participants rated shorter interpulse intervals as being significantly more urgent than longer pulse intervals. Participants also responded faster to patient problems when interacting with a sonification system that used shorter pulse intervals.

The Relationship between Task Performance, Reaction Time, and Perceived Urgency in Nonverbal Auditory Warnings

Two experiments are described in which participants were required to respond to auditory warnings known to vary in their perceived urgency. In the first, they simply responded to a warning of high, medium or low urgency whilst performing a simultaneous tracking task. Responses to the high urgency warning were faster than to the others. In the second experiment participants carried out an addition task on hearing the warning, and the warnings were either matched or mismatched to the difficulty of the task. Results show that responses to the most urgent warnings were again faster, and also that the degree of mismatching between warning and task degraded performance in some conditions.

Measuring Perceived Urgency to Create Safe Auditory Warnings

Various pulse parameters, which were believed to affect the perceived urgency of multitone auditory warning signals, were investigated in a factorial experiment. The three independent variables included pulse fundamental frequency (200, 500, and 800 Hz), pulse sound pressure level above ambient (5, 25, and 40 dB sound pressure level [SPL]), and inter-pulse interval (0,250, and 500 ms). The psychophysical method of free-modulus magnitude estimation was used to measure subjective perceived urgency. Multivariate statistical analysis indicated that all independent variables and most variable interactions were significant. Perceived urgency increased as pulse level increased and inter-pulse interval decreased. Multidimensional scaling analysis indicated that signal level and inter-pulse interval were important in subject perception of signal similarity in terms of perceived urgency. Signals with high sound pressure levels and short inter-pulse intervals were perceived by subjects to have similar perceived urgency, as were signals with low sound pressure levels and long inter-pulse intervals.

Connoted Hazard of Voiced Warning Signal Words: An Examination of Auditory Components

Signal words, such as DANGER and WARNING have been used in print (visual) warnings with the intention of evoking different levels of perceived hazard. However, there is limited research on whether auditory presentation of these words connote different levels of perceived hazard. In the present study, five voiced signal words were used to produce sound clips each composed of the words spoken three times and were manipulated according to the following factors: speaker gender, word unit duration (fast, slow), inter-word interval, (short, long), with the sound level held constant. Results indicate that the sound clips with short word unit duration were given higher carefulness ratings than long word unit duration ( ps < .01). The results showed a similar pattern of ratings for the signal words as shown in research using print presentations. Implications for the design of voiced warnings are described.

A human factors perspective on medical device alarms: problems with operating alarming devices and responding to device alarms

Medical devices emit alarms when a problem with the device or with the patient needs to be addressed by healthcare personnel. At present, problems with device alarms are frequently discussed in the literature, the main message being that patient safety is compromised because device alarms are not as effective and safe as they should - and could - be. There is a general consensus that alarm-related hazards result, to a considerable degree, from the interactions of human users with the device. The present paper addresses key aspects of human perception and cognition that may relate to both operating alarming devices and responding to device alarms. Recent publications suggested solutions to alarm-related hazards associated with usage errors based on assumptions on the causal relations between, for example, alarm management and human perception, cognition, and responding. However, although there is face validity in many of these assumptions, future research should provide objective empirical evidence in order to deepen our understanding of the actual causal relationships, and hence improve and expand the possibilities for taking appropriate action.

The effects of spectral and temporal parameters on perceived confirmation of an auditory non-speech signal

In human-machine interactions, the confirmation of an action or input is a very important information for users. A paired comparison experiment explored the effects of four acoustic parameters on the perceived confirmation of auditory non-speech signals. Reducing the frequency-ratio and the pulse-to-pulse time between two successive pulses increased perceived confirmation. The effects of the parameters frequency and number of pulses were not clear-cut. The results provide information for designing auditory confirmation signals. It is shown that findings about the effects of certain parameters on the perceived urgency of warning signals cannot be easily inverted to perceived confirmation.

Effects of inter-stimulus interval and intensity on the perceived urgency of tactile patterns

This research examines the feasibility of coding urgency into tactile patterns. Four tactile patterns were presented at either, 12 or 23.5 dB above mean threshold, with an ISI of either 0 (no interval) or 500 msec. Measures included pattern identification and urgency rating on a scale of 1 (least urgent) to 10 (most urgent). Two studies were conducted, a laboratory study and a field study. In the laboratory study, participants received the tactile patterns while seated in front of a computer. For the field study, participants performed dismounted Soldier maneuvers while receiving the tactile patterns. Higher identification rates were found for the 23.5 dB intensity. Patterns presented at the 23.5 dB intensity and no ISI were rated most urgent. No differences in urgency ratings were found for 12 dB based on ISI. Findings support the notion of coding urgency into tactile patterns as a way of augmenting tactile communication.

Learning medical alarms whilst performing other tasks

Two studies are reported which first observe, and then attempt to replicate, the cognitive demands of intensive care unit (ICU) activity whilst concurrently learning audible alarms. The first study, an observational study in an ICU ward, showed that the alarms are very frequent and co-occur with some activities more than others. The three most frequently observed activities observed in the ICU were drugs (calculation, preparation and administration), patient observation and talking. The cognitive demands of these activities were simulated in a second, laboratory-based experiment in which alarms were learned. The results showed that performance in the alarm task generally improved as participants were exposed to more repetitions of those alarms, but that performance decrements were observed in the secondary tasks, particularly when there were two or three of them. Some confusions between the alarms persisted to the end of the study despite prolonged exposure to the alarms, confusions which were likely caused by both acoustic and verbal labelling similarities.

PRACTITIONER SUMMARY

The cognitive demands of working in an ICU were observed and simulated whilst alarms were learned. Alarms should generally avoid sharing similar rhythmic (and other) characteristics. The simulation task described here could be used for testing alarm learning without requiring a clinical environment.

Medical audible alarms: a review

OBJECTIVES

This paper summarizes much of the research that is applicable to the design of auditory alarms in a medical context. It also summarizes research that demonstrates that false alarm rates are unacceptably high, meaning that the proper application of auditory alarm design principles are compromised.

TARGET AUDIENCE

Designers, users, and manufacturers of medical information and monitoring systems that indicate when medical or other parameters are exceeded and that are indicated by an auditory signal or signals.

SCOPE

The emergence of alarms as a 'hot topic'; an outline of the issues and design principles, including IEC 60601-1-8; the high incidence of false alarms and its impact on alarm design and alarm fatigue; approaches to reducing alarm fatigue; alarm philosophy explained; urgency in audible alarms; different classes of sound as alarms; heterogeneity in alarm set design; problems with IEC 60601-1-8 and ways of approaching this design problem.

The impact of intonation and valence on objective and subjective attention capture by auditory alarms

OBJECTIVE

The objective was to study the involuntary capture of attention by spoken words varying in intonation and valence.

BACKGROUND

In studies of verbal alarms, the propensity of alarms to capture attention has been primarily assessed with the use of subjective ratings of their perceived urgency. Past studies suggest that such ratings vary with the alarms' spoken urgency and content.

METHOD

We measured attention capture by spoken words varying in valence (negative vs. neutral) and intonation (urgently vs. nonurgently spoken) through subjective ratings and behavioral measures. The key behavioral measure was the response latency to visual stimuli in the presence of spoken words breaking away from the periodical repetition of a tone.

RESULTS

The results showed that all words captured attention relative to a baseline standard tone but that this effect was partly counteracted by a relative speeding of responses for urgently compared with nonurgently spoken words. Word valence did not affect behavioral performance. Rating data showed that both intonation and valence increased significantly perceived urgency and attention grabbing without any interaction.

CONCLUSION

The data suggest a congruency between subjective ratings and behavioral performance with respect to spoken intonation but not valence.

APPLICATION

This study demonstrates the usefulness and feasibility of objective measures of attention capture to help design efficient alarm systems.

Perceived Urgency and Annoyance of Auditory Alerts in a Driving Context

Complex in-vehicle technology and safety systems are finding their way into many cars on the road today. These systems require alerts and warnings that appropriately convey multiple levels of urgency, but if these are deemed excessively annoying, then their implementation may be of little consequence. In this study we used a well-documented psychophysical approach to identify the relationship between specific auditory parameters, perceived urgency and perceived annoyance. In agreement with existing literature, increases in all parameters led to increases in both urgency and annoyance - although differentially. Of the parameters investigated, only pulse rate exhibited a stronger psychophysical relationship with urgency than annoyance. The tradeoff between urgency and annoyance is of practical concern and results from this study provide a potential guideline to determine the viability of future in vehicle alerts based on this relationship.

Perceptual and emotional categorization of sound

This paper investigates how different types of data from psychoacoustical experiments may be combined to render further knowledge about the mechanisms underlying sound perception. Two studies were conducted with auditory alerts of short duration. First, an experiment where participants rated the dissimilarity among the auditory alerts was performed. This resulted in a two-dimensional multi-dimensional scaling solution. Second, an experiment where participants evaluated the stimuli with semantic descriptors and rated their emotional reactions to the sounds was performed. The output of this experiment was a reduced set of underlying perceptual and emotional dimensions. The results of the two experiments were then integrated by the use of multi-dimensional perceptual unfolding and a set mediation analyses. The integrative analyses showed that part of the cognitive categorization of the semantic descriptors was mediated by the emotional reactions to the sounds. The results are discussed in relation to theories of auditory perception and emotional response categorization.

Effects of talker sex and voice style of verbal cockpit warnings on performance

OBJECTIVE

The effects of talker sex and voice style of verbal cockpit warnings on performance were investigated to help make warning messages distinct from speech on the flight deck.

BACKGROUND

Auditory warnings are used in aircraft to alert the crew to hazards and their associated levels of danger. Failing to comply with a warning has led to aviation incidents and accidents.

METHODS

Participants were required to monitor the auditory channel and identify the verbal warning while simultaneously performing a visual pursuit tracking task. A male and a female actor annunciated the warning words in three styles: monotone, urgent, and whisper. In Experiment 1, warning words were presented in quiet, and in Experiment 2, they were presented in a background of speech babble that simulated cockpit radio communication.

RESULTS

Experiment 1 showed that the monotone and urgent styles resulted in the fastest identification response time (RT) regardless of the talker and listener's sex. Experiment 2 showed that the male talker annunciating in either the monotone or the urgent style resulted in the largest proportion correct and fastest identification RT regardless of the listener's sex. Both experiments showed effects of word semantics on performance.

CONCLUSION

Effective use of speech parameters and word semantics can increase the saliency of verbal cockpit warnings.

APPLICATION

Potential applications of this research include improving the attention-getting capability of an alerting system, which could lead to increased warning compliance, potentially resulting in fewer incidents and accidents.

The effect of sonification display pulse rate and reliability on operator trust and perceived workload during a simulated patient monitoring task

The present study investigated the effects of sonification pulse rate and sensor reliability on operator trust and mental workload. Processing resources and operator trust were sensitive to both pulse rate and sensor reliability. These findings suggest that setting pulse rates to 60 pulses per min may have considerable benefits in critical task environments.

The influence of 70 and 120 kHz tonal signals on the behavior of harbor porpoises (Phocoena phocoena) in a floating pen

Two harbor porpoises in a floating pen were subjected to five pure tone underwater signals of 70 or 120 kHz with different signal durations, amplitudes and duty cycles (% of time sound is produced). Some signals were continuous, others were intermittent (duty cycles varied between 8% and 100%). The effect of each signal was judged by comparing the animals' surfacing locations and number of surfacings (i.e. number of respirations) during test periods with those during baseline periods. In all cases, both porpoises moved away from the sound source, but the effect of the signals on respiration rates was negligible. Pulsed 70 kHz signals with a source level (SL) of 137 dB had a similar effect as a continuous 70 kHz signal with an SL of 148 dB (re 1 microPa, rms). Also, a pulsed 70 kHz signal with an SL of 147 dB had a much stronger deterring effect than a continuous 70 kHz signal with a similar SL. For pulsed 70 kHz signals (2 s pulse duration, 4s pulse interval, SL 147 dB re 1 microPa, rms), the avoidance threshold sound pressure level (SPL), in the context of the present study, was estimated to be around 130 dB (re 1 microPa, rms) for porpoise 064 and around 124 dB (re 1 microPa, rms) for porpoise 047. This study shows that ultrasonic pingers (70 kHz) can deter harbor porpoises. Such ultrasonic pingers have the advantage that they do not have a "dinner bell" effect on pinnipeds, and probably have no, or less, effect on other marine fauna, which are often sensitive to low frequency sounds.

Alerts for in-vehicle information systems: annoyance, urgency, and appropriateness

OBJECTIVE

This study assesses the influence of the auditory characteristics of alerts on perceived urgency and annoyance and whether these perceptions depend on the context in which the alert is received.

BACKGROUND

Alert parameters systematically affect perceived urgency, and mapping the urgency of a situation to the perceived urgency of an alert is a useful design consideration. Annoyance associated with environmental noise has been thoroughly studied, but little research has addressed whether alert parameters differentially affect annoyance and urgency.

METHOD

Three 2(3) x 3 mixed within/between factorial experiments, with a total of 72 participants, investigated nine alert parameters in three driving contexts. These parameters were formant (similar to harmonic series), pulse duration, interpulse interval, alert onset and offset, burst duty cycle, alert duty cycle, interburst period, and sound type. Imagined collision warning, navigation alert, and E-mail notification scenarios defined the driving context.

RESULTS

All parameters influenced both perceived urgency and annoyance (p < .05), with pulse duration, interpulse interval, alert duty cycle, and sound type influencing urgency substantially more than annoyance. There was strong relationship between perceived urgency and rated appropriateness for high-urgency driving scenarios and a strong relationship between annoyance and rated appropriateness for low-urgency driving scenarios.

CONCLUSION

Sound parameters differentially affect annoyance and urgency. Also, urgency and annoyance differentially affect perceived appropriateness of warnings.

APPLICATION

Annoyance may merit as much attention as urgency in the design of auditory warnings, particularly in systems that alert drivers to relatively low-urgency situations.

The effects of music tempo and loudness level on treadmill exercise

This study examined the effects of loudness and tempo of background music on exercise performance. A total of 30 volunteers performed five 10-min exercise sessions on a treadmill. The music listened to whilst exercising was either fast/loud, fast/quiet, slow/loud, slow/quiet or absent. Measures of running speed, heart rate, perceived exertion and affect were taken. Significant effects and interactions were found for running speed and heart rate across the different music tempo and loudness levels. More positive affect was observed during the music condition in comparison to the 'no music' condition. No significant differences for perceived exertion were found across conditions. These results confirm that fast, loud music might be played to enhance optimal exercising, and show how loudness and tempo interact.

Alarms and human behaviour: implications for medical alarms

Alarms are used in many clinical applications, but they are often less than optimal because the design and implementation of alarms has not always taken the cognitive capacity and processing mechanisms of the user into account. As a result alarms are frequently too loud, irritating, confusing, badly designed, and too numerous, resulting in them often being turned off and hindering, rather than enhancing, task performance. This paper reviews some of the main areas where it is essential to take account of the cognitive system of the user and behavioural processes more generally. Five central areas of concern are discussed: the number of alarms and ways that this might be reduced; false alarm rates and their impact on human responses; the design of alarms and the application of research into auditory cognition on design; intelligent alarm systems; and the proposals for alarm design set out in a recent worldwide medical alarms standard. In each area some background is given and the implications for alarm design and implementation outlined. The conclusion is that there are some indications that alarm design and implementation takes account of relevant research data, but that there is still some way to go before these findings are fully integrated and the situation is improved upon further.

Judging the urgency of non-verbal auditory alarms: a case study

When designed correctly, non-verbal auditory alarms can convey different levels of urgency to the aircrew, and thereby permit the operator to establish the appropriate level of priority to address the alarmed condition. The conveyed level of urgency of five non-verbal auditory alarms presently used in the Canadian Forces CH-146 Griffon helicopter was investigated. Pilots of the CH-146 Griffon helicopter and non-pilots rated the perceived urgency of the signals using a rating scale. The pilots also ranked the urgency of the alarms in a post-experiment questionnaire to reflect their assessment of the actual situation that triggers the alarms. The results of this investigation revealed that participants' ratings of perceived urgency appear to be based on the acoustic properties of the alarms which are known to affect the listener's perceived level of urgency. Although for 28% of the pilots the mapping of perceived urgency to the urgency of their perception of the triggering situation was statistically significant for three of the five alarms, the overall data suggest that the triggering situations are not adequately conveyed by the acoustic parameters inherent in the alarms. The pilots' judgement of the triggering situation was intended as a means of evaluating the reliability of the alerting system. These data will subsequently be discussed with respect to proposed enhancements in alerting systems as it relates to addressing the problem of phase of flight. These results call for more serious consideration of incorporating situational awareness in the design and assignment of auditory alarms in aircraft.

Localizable auditory warning pulses

Three important forms of information available to the listener may be identified in any auditory warning: what (semantic), where (location) and when (perceived urgency). Each form is addressed in the present design study of auditory warning pulses. Recordings were made via a dummy head, and were presented dichotically to listeners in a left/right localization task. The first experiment identified a suitable notched noise component for providing location information in the pulse stimulus. The second experiment required participants to simultaneously identify a distinct tonal signature and the location of the sound when they were presented with one of three tonal types, or one of three compound (tone plus noise) stimuli. Response accuracy and response latency for this identification and localization task were significantly better with the compound than with tone alone stimuli. Perceived urgency of compound complex tone plus noise stimuli was investigated in the third experiment. While there may be a trade-off between localization acuity and perceived urgency, the addition of noise components to the auditory warning pulse was shown to enhance the location information available to the listener. It is suggested that some auditory warning designs will benefit from the simultaneous provision of what and where forms of information in the sounds.

Alarm mistrust in automobiles: how collision alarm reliability affects driving

As roadways become more congested, there is greater potential for automobile accidents and incidents. To improve roadway safety, automobile manufacturers are now designing and incorporating collision avoidance warning systems; yet, there has been little investigation of how the reliability of alarm signals might impact driver performance. We measured driving and alarm reaction performances following alarms of various reliability levels. In Experiment One, 70 participants operated a driving simulator while being presented console emitted collision alarms that were 50%, 75%, or 100% reliable. In Experiment Two, the same participants were presented spatially generated collision alarms of the same reliability levels. The results were similar in both experiments: alarm and automobile swerving reactions were significantly better when alarms were more reliable; however, drivers still failed to avoid collisions following reliable alarms. These results emphasize that alarm designers should maximize alarm reliability while minimizing alarm invasiveness.

Using auditory streaming to reduce disruption to serial memory by extraneous auditory warnings

Three experiments were conducted to examine the effects of extraneous speech warnings (i.e., low-priority warnings initiated during high-priority tasks) on cognitive performance and whether organizing the auditory warnings into streams can attenuate any disruption. Experiment 1 demonstrated that a variety of speech warnings can be separated into perceptually distinct streams by allocating them to discrete spatial locations. Experiment 2 showed that increasing the rate of presentation of the warnings to promote streaming decreased clarity ratings but increased perceived urgency ratings. Experiment 3 demonstrated that the disruption to serial memory for navigational information by extraneous speech warnings could be attenuated by streaming. Results are interpreted in light of previous research, and practical implications for auditory warning design are discussed.

Research-based guidelines for warning design and evaluation

During the past two decades, the body of empirical research on warning design and evaluation has grown. Consequently, there are now basic principles and guidelines addressing warning design (e.g., signal words, color, symbols, and text/content), placement (e.g., location within product instructions), and how to enhance the usability of designs by considering factors internal to the user (e.g., beliefs, perceptions of risk, stress). Similarly, evaluation methods have been developed that can be used to measure the effectiveness of warnings such as the degree to which warnings are communicated to recipients and the degree to which they encourage or influence behavioral compliance. An overview of the empirical literature on warning guidelines and evaluation approaches is provided. Researchers, practitioners, and manufacturers can use these guidelines in various contexts to reduce the likelihood that injury and product damage from exposure to a hazard will occur.

Impact of speech presentation level on cognitive task performance: implications for auditory display design

Speech displays and verbal response technologies are increasingly being used in complex, high workload environments that require the simultaneous performance of visual and manual tasks. Examples of such environments include the flight decks of modern aircraft, advanced transport telematics systems providing invehicle route guidance and navigational information and mobile communication equipment in emergency and public safety vehicles. Previous research has established an optimum range for speech intelligibility. However, the potential for variations in presentation levels within this range to affect attentional resources and cognitive processing of speech material has not been examined previously. Results of the current experimental investigation demonstrate that as presentation level increases within this 'optimum' range, participants in high workload situations make fewer sentence-processing errors and generally respond faster. Processing errors were more sensitive to changes in presentation level than were measures of reaction time. Implications of these findings are discussed in terms of their application for the design of speech communications displays in complex multi-task environments.

The perceived urgency of speech warnings: semantics versus acoustics

The relationship between the semantics of words and the acoustics of the way they are spoken is explored. Actors spoke warning signal words in an urgent, nonurgent and monotone style, and participants rated the urgency of the words. Results showed effects for signal word and style of presentation. Acoustic analysis showed that the urgent words were spoken at higher frequency with a broader pitch range and were louder than the nonurgent or monotone words. These acoustic differences were used to synthesize artificial versions of signal words in urgent and nonurgent formats. The urgent words were rated as more urgent than the nonurgent words, a finding attributable to their differing acoustics. Within each speaking style the words were acoustically the same, yet effects for signal word were found, suggesting that semantics is also important in urgency perception. This research has implications for the design and implementation of speech warning systems, particularly those in which urgency mapping is required.

A new class of auditory warning signals for complex systems: auditory icons

This simulator-based study examined conventional auditory warnings (tonal, nonverbal sounds) and auditory icons (representational, nonverbal sounds), alone and in combination with a dash-mounted visual display, to present information about impending collision situations to commercial motor vehicle operators. Brake response times were measured for impending front-to-rear collision scenarios under 6 display configurations, 2 vehicle speeds, and 2 levels of headway. Accident occurrence was measured for impending side collision scenarios under 2 vehicle speeds, 2 levels of visual workload, 2 auditory displays, absence/presence of mirrors, and absence/presence of a dash-mounted iconic visual display. For both front-to-rear and side collision scenarios, auditory icons elicited significantly improved driver performance over conventional auditory warnings. Driver performance improved when collision warning information was presented through multiple modalities. Brake response times were significantly faster for impending front-to-rear collision scenarios using the longer headway condition. The presence of mirrors significantly reduced the number of accidents for impending side collision scenarios. Subjective preference data indicated that participants preferred multimodal displays over single-modality displays. Actual or potential applications for this research include auditory displays and warnings, information presentation, and the development of alternative user interfaces.

Use of auditory icons as emergency warnings: evaluation within a vehicle collision avoidance application

In the context of emergency warnings, auditory icons, which convey information about system events by analogy with everyday events, have the potential to be understood more quickly and easily than abstract sounds. To test this proposal, an experiment was carried out to evaluate the use of auditory icons for an in-vehicle collision avoidance application. Two icons, the sounds of a car horn and of skidding tyres, were compared with two conventional warnings, a simple tone and a voice saying 'ahead'. Participants sat in an experimental vehicle with a road scene projected ahead, and they were required to brake in response to on-screen collision situations and their accompanying warning sounds. The auditory icons produced significantly faster reaction times than the conventional warnings, but suffered from more inappropriate responses, where drivers reacted with a brake press to a non-collision situation. The findings are explained relative to the perceived urgency and inherent meaning of each sound. It is argued that optimal warnings could be achieved by adjusting certain sound attributes of auditory icons, as part of a structured, user-centred design and evaluation procedure.

A user-centred approach to the design and evaluation of auditory warning signals: 1. Methodology

This paper presents a method for the design and evaluation of auditory warning signals modelled on an existing internationally standardized method for evaluating public information systems (ISO/DIS 7001: 1979). The procedure is essentially user-centred, capitalizing upon users' associations between sounds and their meanings. The procedure is presented in a step-by-step manner, from the initial identification of referents for which warnings might be required, through the generation of ideas for warning sounds, an appropriateness ranking test, a learning and confusion test, an urgency mapping test, a recognition test and an operational test. Practical issues are discussed with respect to each of the stages, and suggestions are made as to courses of action that might be taken if problems are encountered. Theory behind the relationship between sound and meaning is discussed with reference to the practical issues addressed.