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.

Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part III. The validity of using subject-fit data.

The mandate of ASA Working Group S12/WG11 has been to develop "laboratory and/or field procedure(s) that yield useful estimates of field performance" of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested via an interlaboratory study, and incorporated into a draft standard that was approved in 1997 [J. D. Royster et at., "Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise," J. Acoust. Soc. Am. 99, 1506-1526 (1996); ANSI S12.6-1997, "American National Standard Methods for Measuring Real-Ear Attenuation of Hearing Protectors" (American National Standards Institute, New York, 1997)]. The real-world estimation procedure utilizes a subject-fit methodology with listeners who are audiometrically proficient, but inexperienced in the use of HPDs. A key factor in the decision to utilize the subject-fit method was an evaluation of the representativeness of the laboratory data vis-à-vis attenuation values achieved by workers in practice. Twenty-two field studies were reviewed to develop a data base for comparison purposes. Results indicated that laboratory subject-fit attenuation values were typically equivalent to or greater than the field attenuation values, and yielded a better estimate of those values than did experimenter-fit or experimenter-supervised fit types of results. Recent data which are discussed in the paper, but which were not available at the time of the original analyses, confirm the findings.

Technology advancements in hearing protection circa 1995: active noise reduction, frequency/amplitude-sensitivity, and uniform attenuation.

Conventional hearing protection devices represent a mature technology that has been widely used since the late 1950s. When worn consistently and correctly such devices can provide suitable hearing protection in many, if not most noise-hazardous or aurally annoying situations. However, such devices have often been implicated in compromised auditory perception, degraded signal detection, and reduced speech communication abilities. In some instances this can create hazards for the wearer, or at the very least, resistance to use by those in need of hearing protection. Recent technological developments have been used to augment hearing protectors in an attempt to alleviate these problems for the user while providing adequate attenuation. Operational characteristics, design alternatives, performance data, and applications for active noise reduction, active sound transmission, frequency selectively, adjustable attenuation, amplitude sensitivity, and uniform attenuation features in hearing protectors are discussed, and recommendations are provided.

Audibility of reverse alarms under hearing protectors for normal and hearing-impaired listeners.

The question of whether or not an individual suffering from a hearing loss is capable of hearing an auditory alarm or warning is an extremely important industrial safety issue. The ISO Standard that addresses auditory warnings for workplaces requires that any auditory alarm or warning be audible to all individuals in the workplace including those suffering from a hearing loss and/or wearing hearing protection devices (HPDs). Research was undertaken to determine how the ability to detect an alarm or warning signal changed for individuals with normal hearing and two levels of hearing loss as the levels of masking noise and alarm were manipulated. Pink noise was used as the masker and a heavy-equipment reverse alarm was used as the signal. The rating method paradigm of signal detection theory was used as the experimental procedure to separate the subjects' absolute sensitivities to the alarm from their individual criteria for deciding to respond in an affirmative manner. Results indicated that even at a fairly low signal-to-noise ratio (0 dB), subjects with a substantial hearing loss [a pure-tone average (PTA) hearing level of 45-50 dBHL in both ears] were capable of hearing the reverse alarm while wearing a high-attenuation earmuff in the pink noise used in the study.

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

Several pulse parameters that were believed to affect the perceived urgency and response time to auditory warning signals were investigated in a factorial experiment. The independent variables included pulse format (sequential, simultaneous, and frequency-modulated pulses), pulse level (65 and 79 dBC), and inter-pulse interval (0, 150 and 300 ms). The applications environments of interest were those having steady-state broadband noise. A probability monitoring task from the Criterion Task Set was used as an operator loading task to impose additional attentional demands during the signal detection and response task. The psychophysical methods of free-modulus magnitude estimation and paired comparison were used to measure subjective perceived urgency. An objective measure of response time to the signal was also obtained. Multivariate statistical analyses indicated that response time decreased significantly as perceived urgency increased. Perceived urgency of the signal increased and response time decreased as pulse level increased. Sequential signals took longer to detect and were rated as less urgent than the other two signal types. Shorter inter-pulse interval was associated with greater perceived signal urgency.

Speech intelligibility and protective effectiveness of selected active noise reduction and conventional communications headsets.

An experiment was conducted to compare both speech intelligibility and noise attenuation of a conventional passive headset (David Clark H10-76) and an electronic Active Noise Reduction (ANR) headset (Bose Aviation) operated with and without its ANR feature. Modified Rhyme Tests were conducted in pink and tank noise, and with and without bilateral phase reversal between earphones. The Bose ANR unit required a significantly higher speech-to-noise (S/N) ratio in both noise environments than the two passive headset systems to maintain equal intelligibility, in part because of its stronger noise reduction and higher required signal level. Articulation Index calculations corroborated the empirical result that the David Clark afforded comparable intelligibility to the Bose ANR device. Bilateral phase reversal proved to be of no benefit, and pink noise proved to be the harsher environment for speech intelligibility. On a speech intelligibility basis alone, the results do not justify the additional cost of the ANR headset; however, when severe noise exposure is at issue, a properly functioning ANR unit may afford more protection than a similar passive headset without electronics, especially in low-frequency noise spectra.

A controlled investigation of in-field attenuation performance of selected insert, earmuff, and canal cap hearing protectors.

A field study assessed the actual spectral noise attenuation achieved by 40 industrial workers wearing four different hearing protection devices (HPDs) while on the job. The effect of two different HPD fitting procedures (subject fit vs. trained fit) on attenuation performance over two three-week periods of protector use was determined. Subjects were retrieved from their workplaces without prior knowledge of when they were to be tested and were not permitted to readjust the fit of their HPDs. Attenuation data were then collected using psychophysical procedures testing real ear attenuation at threshold. Statistical analyses indicated that the earplugs' attenuation significantly improved when training for proper fitting was used, whereas the earmuff and the ear canal cap were relatively insensitive to the training effect. The training was most effective for a slow-recovery foam plug over the three-week period. Results confirmed that laboratory protocols designed to simulate workplace influences on attenuation may not be relied on to yield reasonable estimates of field protection performance of HPDs, particularly for earplugs; however, the laboratory results were much better predictors of field protection for the earmuff. This study also demonstrated that the labeled manufacturers' noise reduction ratings (NRRs) substantially overestimated the actual field attenuation performance.

Attenuation performance of four hearing protectors under dynamic movement and different user fitting conditions.

An experiment was conducted to determine the effects of movement activities and alternative fitting procedures on protection levels afforded by four hearing protection devices (HPDs). Psychophysical attenuation measurements at nine one-third-octave bands from 125 to 8000 Hz were obtained prior to, during, and following a 2-hr wearing stint that included periods of either highly kinematic but controlled work activity or vigorous temporomandibular movement. The 40 subjects, who were nonusers of HPDs, initially fit the protectors according to either the instructions on the package (i.e., subject fit) or after receiving interactive training on proper fit (i.e., trained fit). Thereafter no further protector adjustments were allowed during the wearing period. The subject-fit condition resulted in significantly lower protection levels, from 4 to 14 dB, at 1000 Hz and below for a premolded polymer earplug, a user-molded foam earplug, and a double protector consisting of a muff over the foam plug. The muff alone was significantly more resilient to fitting effects on attenuation than were the plugs. Movement activity caused up to a 6-dB significant reduction in frequency-specific attenuation over time for the premolded plug, muff, and muff-plug combination. The compliant foam earplug was largely resistant to either type of movement effect but did benefit more than the other devices from use of the trained-fit procedure. Implications of the results for hearing protector testing protocol, device selection, and user training are discussed.

An exploratory study of moderate physical activity and selected design attribute effects on earmuff attenuation.

Hearing protective devices are tested for their attenuation characteristics under controlled laboratory conditions. Unfortunately, these tests overestimate the typical attenuation performance of the devices in the field, posing the possibility of inadequate protection for the user. Many factors may affect achieved in-field attenuation. This research investigated the influence of the user's work-related movement and variations in headband compression force and earcup cushion material (liquid- or foam-filled) on the frequency-specific noise attenuation achieved with earmuffs. Real-ear attenuation at threshold (REAT) testing procedures were used to collect attenuation data on 24 subjects both prior to and following completion of a simulated work task. Statistical analyses indicated that moderate work-related movement significantly decreased low-frequency attenuation but by only a small amount (1.5 dB at 125 Hz). A high headband compression force was found to increase attenuation by approximately 1.5 to 4 dB at 125, 250, 500, and 8000 Hz. There was no significant difference at any frequency between cushion types. The results indicate a small effect of moderate physical work activity on hearing protector effectiveness and illustrate the importance of certain earmuff design parameters to achieved attenuation.

Seat belt usage: A potential target for applied behavior analysis.

Results of 1,579 observations of cars entering or exiting campus parking lots showed direct relationships between seat belt wearing and the intrusiveness of the engineering device designed to induce belt usage, and between device intrusiveness and system defeat. For example, all drivers with working interlocks or unlimited buzzer reminders were wearing a seat belt; but 62% of the systems with interlocks or unlimited buzzers had been defeated, and only 15.9% of the drivers in these cars were wearing a seat belt. The normative data indicated marked ineffectiveness of the negative reinforcement contingencies implied by current seat belt inducement systems; but suggested that unlimited buzzer systems would be the optimal system currently available if contingencies were developed to discourage the disconnection and circumvention of such systems. Positive reinforcement strategies are discussed that would be quite feasible for large-scale promotion of seat belt usage.