The impact of background speech varying in intelligibility: effects on cognitive performance and perceived disturbance

The effects of irrelevant speech on physiological stress, cognitive performance, and subjective experience - Focus on heart rate variability

Irrelevant speech impairs cognitive performance, especially in tasks requiring verbal short-term memory. Working on these tasks during irrelevant speech can also cause a physiological stress reaction. The aim of this study was to examine heart rate variability (HRV) as a non-invasive and easy-to-use stress measure in an irrelevant speech paradigm. Thirty participants performed cognitive tasks (n-back and serial recall) during two sound conditions: irrelevant speech (50 dB) and quiet (33 dB steady-state noise). The influence of conditions as well as presentation orders of conditions were examined on performance, subjective experience, and physiological stress. Working during irrelevant speech compared to working during quiet reduced performance, namely accuracy, in the serial recall task. It was more annoying, heightened the perceived workload, and lowered acoustic satisfaction. It was related to higher physiological stress by causing faster heart rate and changes in HRV frequency-domain analysis (LF, HF and LF/HF). The order of conditions showed some additional effects. When speech was the first condition, 3-back performance was less accurate, and serial recall response times were longer, heart rate was faster, and successive heart beats had less variability (lower RMSSD) during speech than during quiet. When quiet was the first condition, heart rate was faster and reaction times in 3-back were slower during quiet than during speech. The negative effect of irrelevant speech was clear in experience, performance, and physiological stress. The study shows that HRV can be used as a physiological stress measure in irrelevant speech studies.

Effects of Auditory Pre-Stimulation on Cognitive Task Performance in a Noisy Environment

The accident rate due to human errors in industrial fields has been consistently high over the past few decades, and noise has been emerging as one of the main causes of human errors. In recent years, auditory pre-stimulation has been considered as a means of preventing human errors by improving workers’ cognitive task performance. However, most previous studies demonstrated the effectiveness of the auditory pre-stimulation in a quiet environment. Accordingly, studies on the effects of pre-stimulation in a noisy environment are still lacking. Therefore, this study aimed to empirically investigate: (1) the effects of noisy environments on the performances of cognitive tasks related to different functions of working memory and (2) the effects of auditory pre-stimulation on the performances of cognitive tasks in a field-noise environment. To accomplish these research objectives, two major experiments were conducted. In the first experiment, a total of 24 participants performed each of three basic short-term/working memory (STM/WM) tasks under two different experimental conditions (quiet-noise environment and field-noise environment) depending on the presence or absence of field noise. In the second experiment, the participants performed each of the three basic STM/WM tasks in a field-noise environment after they were provided with one of four different auditory pre-stimulations (quiet noise, white noise, field noise, and mixed (white and field) noise). The three STM/WM tasks were the Corsi block-tapping, Digit span, and 3-back tasks, corresponding to the visuospatial sketchpad, the phonological loop, and the central executive of WM, respectively. The major findings were that: (1) the field-noise environment did not affect the scores of the Corsi block-tapping and 3-back tasks, significantly affecting only the Digit span task score (decreased by 15.2%, p < 0.01); and (2) the Digit span task performance in the field-noise environment was improved by 17.9% (p < 0.05) when mixed noise was provided as a type of auditory pre-stimulation. These findings may be useful for the work-space designs that prevent/minimize human errors and industrial accidents by improving the cognitive task performance of workers in field-noise environments.

Loud Auditory Distractors Are More Difficult to Ignore After All

Abstract. Working memory performance is markedly disrupted when task-irrelevant sound is played during item presentation or retention. In a preregistered replication study, we systematically examined the role of intensity in two types of auditory distraction. The first type of distraction is the changing-state effect (i.e., increased disruption by changing-state relative to steady-state sequences). The second type is the auditory deviant effect (i.e., increased disruption by auditory deviant relative to steady-state sequences). In previous experiments, the changing-state effect was independent of intensity. Whether a deviation in intensity leads to an increase in disruption has not yet been examined. We replicated the classic finding that the increased disruption by changing-state relative to steady-state sequences is independent of intensity. Contrary to previous studies, we found an unexpected main effect of intensity. Steady-state and changing-state sequences presented at 75 dB(A) were more disruptive than presented at 45 dB(A), suggesting that intensity plays a more important role than previously assumed in the disruption of working memory performance. Furthermore, we tested the prediction of the violation of expectancy account, according to which deviant distractors at a lower and higher intensity than the rest of the sequence should be equally disruptive. Our results were consistent with this prediction.

Does the Macro-Temporal Pattern of Road Traffic Noise Affect Noise Annoyance and Cognitive Performance?

Noise annoyance is usually estimated based on time-averaged noise metrics. However, such metrics ignore other potentially important acoustic characteristics, in particular the macro-temporal pattern of sounds as constituted by quiet periods (noise breaks). Little is known to date about its effect on noise annoyance and cognitive performance, e.g., during work. This study investigated how the macro-temporal pattern of road traffic noise affects short-term noise annoyance and cognitive performance in an attention-based task. In two laboratory experiments, participants worked on the Stroop task, in which performance relies predominantly on attentional functions, while being exposed to different road traffic noise scenarios. These were systematically varied in macro-temporal pattern regarding break duration and distribution (regular, irregular), and played back with moderate L_Aeq of 42–45 dB(A). Noise annoyance ratings were collected after each scenario. Annoyance was found to vary with the macro-temporal pattern: It decreased with increasing total duration of quiet periods. Further, shorter but more regular breaks were somewhat less annoying than longer but irregular breaks. Since Stroop task performance did not systematically vary with different noise scenarios, differences in annoyance are not moderated by experiencing worsened performance but can be attributed to differences in the macro-temporal pattern of road traffic noise.

The metacognition of auditory distraction: Judgments about the effects of deviating and changing auditory distractors on cognitive performance

The duplex-mechanism account of auditory distraction has been extended to predict that people should have metacognitive awareness of the disruptive effect of auditory deviants on cognitive performance but little to no such awareness of the disruptive effect of changing-state relative to steady-state auditory distractors. To test this prediction, we assessed different types of metacognitive judgments about the disruptive effects of auditory-deviant, changing-state, and steady-state distractor sequences on serial recall. In a questionnaire, participants read about an irrelevant-speech experiment and were asked to provide metacognitive beliefs about how serial-recall performance would be affected by the different types of distractors. Another sample of participants heard the auditory distractors before predicting how their own serial-recall performance would suffer or benefit from the distractors. After participants had experienced the disruptive effects of the distractor sequences first hand, they were asked to make episodic retrospective judgments about how they thought the distractor sequences had affected their performance. The results consistently show that people are, on average, well aware of the greater disruptive effect of deviant and changing-state relative to steady-state distractors. Irrespective of condition, prospective and retrospective judgments of distraction were poor predictors of the individual susceptibility to distraction. These findings suggest that phenomena of auditory distraction cannot be categorized in two separate classes based on metacognitive awareness.

The relation between the intelligibility of irrelevant speech and cognitive performance-A revised model based on laboratory studies

Irrelevant background speech causes dissatisfaction and impairs cognitive performance in open-plan offices. The model of Hongisto (2005, Indoor Air, 15, 458-468) predicts the relation between cognitive performance and the intelligibility of speech described with an objectively measured quantity, the Speech Transmission Index (STI). The model has impacted research in psychology and room acoustics as well as the acoustic design guidelines of offices. However, the model was based on scarce empirical data. The aim of this study was to revise the model based on a systematic literature review, focusing on laboratory experiments manipulating the STI of speech by wide-band steady-state noise. Fourteen studies reporting altogether 34 tests of the STI-performance relation were included. According to Model 1 that includes all tests, performance begins to decrease approximately above STI = 0.21 while the maximum decrease is reached at STI = 0.44. Verbal short-term memory tasks were most strongly and very consistently affected by the STI of speech. The model for these tasks showed a deterioration in performance between STI 0.12 and 0.51. Some evidence of an STI-performance relation was found in verbal working memory tasks and limited evidence in complex verbal tasks. Further research is warranted, particularly concerning task-specific effects.

Open plan office space? If you're going to do it, do it right: A fourteen-month longitudinal case study

There are compelling findings that open-plan office environments are associated with declines in employee wellbeing. In spite of this, the move towards shared office environments continues; yet there is a lack of research describing open-plan offices that have positive outcomes for workers. We describe a "best practice" open-plan fit-out of a law firm and provide data from occupants relating to their performance, well-being, and collegial relationships. Six months after moving to an open-plan office, staff were anonymously surveyed, and 24 were interviewed. Fourteen months later, occupants responded to a follow-up survey. Positive outcomes relating to aesthetics, collegiality, and communication were achieved through good technical design and thoughtful ergonomic assessment of the needs of employees and the requirements of their tasks. A gender difference emerged whereby female, but not male, workers in this environment reported feeling observed. This has implications for the relatively different impact these environments may have on workers. Thus, by following ergonomic principles to create open-plan offices that are 'safe by design' organizations can ameliorate many of the negative consequences associated with these environments.

The role of ambient sound levels, signal-to-noise ratio, and stimulus pulse rate on behavioural disturbance of seabass in a net pen

Anthropogenic sources increasingly contribute to the underwater soundscape and this may negatively impact aquatic life, including fish. Anthropogenic sound may mask relevant sound, alter behaviour, physiology, and may lead to physical injury. Behavioural effect studies are often seen as critical to evaluate individual and population-level impact. However, behavioural responsiveness likely depends on context and characteristics of sound stimuli. We pose that ambient sound levels, signal-to-noise ratio (SNR), and pulse rate interval (PRI), could affect the behavioural response of fish. To study this, we experimentally exposed groups of tagged European seabass (Dicentrarchus labrax) to different impulsive sound treatments that varied in pulse level, elevated background level, SNR, and PRI. Upon sound exposure, the seabass increased their swimming depth. The variation in the increase in swimming depth could not be attributed to pulse level, background level, SNR or PRI. It may be that the current range of sound levels or PRIs was too narrow to find such effects.

Audio-video virtual reality environments in building acoustics: An exemplary study reproducing performance results and subjective ratings of a laboratory listening experiment

The present study adopted a human-centred approach to explore the potential of audio-video Virtual Reality (VR) to evaluate indoor noise protection by building characteristics. Different background speech conditions, convolved with sound insulation filters of adjacent office rooms, were presented in a VR office environment and the effects on cognitive performances and subjective ratings were measured. The found effect patterns were the same as those obtained in a real laboratory setting reported by Schlittmeier, Hellbrück, Thaden, and Vorländer. [(2008). Ergonomics 51, 719-736]. This exemplary study promises various options for research on noise effects by the use of virtual built environments which are of high plausibility and unlimited variability.

Noise disturbance in open-plan study environments: a field study on noise sources, student tasks and room acoustic parameters

The aim of this study is to gain more insight in the assessment of noise in open-plan study environments and to reveal correlations between noise disturbance experienced by students and the noise sources they perceive, the tasks they perform and the acoustic parameters of the open-plan study environment they work in. Data were collected in five open-plan study environments at universities in the Netherlands. A questionnaire was used to investigate student tasks, perceived sound sources and their perceived disturbance, and sound measurements were performed to determine the room acoustic parameters. This study shows that 38% of the surveyed students are disturbed by background noise in an open-plan study environment. Students are mostly disturbed by speech when performing complex cognitive tasks like studying for an exam, reading and writing. Significant but weak correlations were found between the room acoustic parameters and noise disturbance of students. Practitioner Summary: A field study was conducted to gain more insight in the assessment of noise in open-plan study environments at universities in the Netherlands. More than one third of the students was disturbed by noise. An interaction effect was found for task type, source type and room acoustic parameters.

Perception of Water-Based Masking Sounds-Long-Term Experiment in an Open-Plan Office

A certain level of masking sound is necessary to control the disturbance caused by speech sounds in open-plan offices. The sound is usually provided with evenly distributed loudspeakers. Pseudo-random noise is often used as a source of artificial sound masking (PRMS). A recent laboratory experiment suggested that water-based masking sound (WBMS) could be more favorable than PRMS. The purpose of our study was to determine how the employees perceived different WBMSs compared to PRMS. The experiment was conducted in an open-plan office of 77 employees who had been accustomed to work under PRMS (44 dB L_Aeq). The experiment consisted of five masking conditions: the original PRMS, four different WBMSs and return to the original PRMS. The exposure time of each condition was 3 weeks. The noise level was nearly equal between the conditions (43–45 dB L_Aeq) but the spectra and the nature of the sounds were very different. A questionnaire was completed at the end of each condition. Acoustic satisfaction was worse during the WBMSs than during the PRMS. The disturbance caused by three out of four WBMSs was larger than that of PRMS. Several attributes describing the sound quality itself were in favor of PRMS. Colleagues' speech sounds disturbed more during WBMSs. None of the WBMSs produced better subjective ratings than PRMS. Although the first WBMS was equal with the PRMS for several variables, the overall results cannot be seen to support the use of WBMSs in office workplaces. Because the experiment suffered from some methodological weaknesses, conclusions about the adequacy of WBMSs cannot yet be drawn.

Office noise: Can headphones and masking sound attenuate distraction by background speech?

BACKGROUND

Background speech is one of the most disturbing noise sources at shared workplaces in terms of both annoyance and performance-related disruption. Therefore, it is important to identify techniques that can efficiently protect performance against distraction. It is also important that the techniques are perceived as satisfactory and are subjectively evaluated as effective in their capacity to reduce distraction.

OBJECTIVE

The aim of the current study was to compare three methods of attenuating distraction from background speech: masking a background voice with nature sound through headphones, masking a background voice with other voices through headphones and merely wearing headphones (without masking) as a way to attenuate the background sound. Quiet was deployed as a baseline condition.

METHODS

Thirty students participated in an experiment employing a repeated measures design.

RESULTS

Performance (serial short-term memory) was impaired by background speech (1 voice), but this impairment was attenuated when the speech was masked - and in particular when it was masked by nature sound. Furthermore, perceived workload was lowest in the quiet condition and significantly higher in all other sound conditions. Notably, the headphones tested as a sound-attenuating device (i.e. without masking) did not protect against the effects of background speech on performance and subjective work load.

CONCLUSIONS

Nature sound was the only masking condition that worked as a protector of performance, at least in the context of the serial recall task. However, despite the attenuation of distraction by nature sound, perceived workload was still high - suggesting that it is difficult to find a masker that is both effective and perceived as satisfactory.

Distraction distance and perceived disturbance by noise-An analysis of 21 open-plan offices

Previous research suggests that, in open-plan offices, noise complaints may be related to the high intelligibility of speech. Distraction distance, which is based on the Speech Transmission Index, can be used to objectively describe the acoustic quality of open-plan offices. However, the relation between distraction distance and perceived noise disturbance has not been established in field studies. The aim of this study was to synthesize evidence from separate studies covering 21 workplaces (N = 883 respondents) and a wide range of room acoustic conditions. The data included both questionnaire surveys and room acoustic measurements [ISO 3382-3 (2012) (International Organization for Standardization, Geneva, Switzerland]. Distraction distance, the spatial decay rate of speech, speech level at 4 m from the speaker, and the average background noise level were examined as possible predictors of perceived noise disturbance. The data were analyzed with individual participant data meta-analysis. The results show that distracting background speech largely explains the overall perception of noise. An increase in distraction distance predicts an increase in disturbance by noise, whereas the other quantities may not alone be associated with noise disturbance. The results support the role of room acoustic design, i.e., the simultaneous use of absorption, blocking, and masking in the attainment of good working conditions in open-plan offices.

Unmasking the effects of masking on performance: The potential of multiple-voice masking in the office environment

Broadband noise is often used as a masking sound to combat the negative consequences of background speech on performance in open-plan offices. As office workers generally dislike broadband noise, it is important to find alternatives that are more appreciated while being at least not less effective. The purpose of experiment 1 was to compare broadband noise with two alternatives-multiple voices and water waves-in the context of a serial short-term memory task. A single voice impaired memory in comparison with silence, but when the single voice was masked with multiple voices, performance was on level with silence. Experiment 2 explored the benefits of multiple-voice masking in more detail (by comparing one voice, three voices, five voices, and seven voices) in the context of word processed writing (arguably a more office-relevant task). Performance (i.e., writing fluency) increased linearly from worst performance in the one-voice condition to best performance in the seven-voice condition. Psychological mechanisms underpinning these effects are discussed.

The impact of road traffic noise on cognitive performance in attention-based tasks depends on noise level even within moderate-level ranges

Little empirical evidence is available regarding the effects of road traffic noise on cognitive performance in adults, although traffic noise can be heard at many offices and home office workplaces. Our study tested the impact of road traffic noise at different levels (50 dB(A), 60 dB(A), 70 dB(A)) on performance in three tasks that differed with respect to their dependency on attentional and storage functions, as follows: The Stroop task, in which performance relied predominantly on attentional functions (e.g., inhibition of automated responses; Experiment 1: n = 24); a non-automated multistage mental arithmetic task calling for both attentional and storage functions (Exp. 2: n = 18); and verbal serial recall, which placed a burden predominantly on storage functions (Experiment 3: n = 18). Better performance was observed during moderate road traffic noise at 50 dB(A) compared to loud traffic noise at 70 dB(A) in attention-based tasks (Experiments 1-2). This contrasted with the effects of irrelevant speech (60 dB(A)), which was included in the experiments as a well-explored and common noise source in office settings. A disturbance impact of background speech was only given in the two tasks that called for storage functions (Experiments 2-3). In addition to the performance data, subjective annoyance ratings were collected. Consistent with the level effect of road traffic noise found in the performance data, a moderate road traffic noise at 50 dB(A) was perceived as significantly less annoying than a loud road traffic noise at 70 dB(A), which was found, however, independently of the task at hand. Furthermore, the background sound condition with the highest detrimental performance effect in a task was also rated as most annoying in this task, i.e., traffic noise at 70 dB(A) in the Stroop task, and background speech in the mental arithmetic and serial recall tasks.

The effects of intelligible irrelevant background speech in offices – cognitive disturbance, annoyance, and solutions

Purpose

– This paper aims to give an overview on four empirical studies which explored the impact of background speech on cognitive performance and subjectively perceived disturbance. Background speech is the most serious noise problem in shared-room and open-plan offices for employees who are supposed to do silent, concentrated work. Different measures of acoustic office optimization, as well as the outstanding role of the intelligibility of background speech for its disturbance impact, are empirically evaluated.

Design/methodology/approach

– The article provides a synopsis describing the core empirical results of four of our empirical studies. A survey study among office employees (n = 659) explored the subjective importance of office acoustics. Three experimental studies (n1 = 20; n2 = 30; n3 = 24) evaluated the effects of reduced background speech level, play-back of partial maskers and reduced speech intelligibility on cognitive performance and subjective ratings.

Findings

– Background speech is subjectively perceived as a severe problem, and the different noise abatement measures affect objective performance and subjective ratings differently. Speech intelligibility is – besides level – a key determinant for the acoustic optimization regarding these two dimensions.

Research limitations/implications

– Practitioners are encouraged to apply the findings and described measures when planning and/or evaluating open-plan offices.

Practical implications

– It is concluded that different acoustically efficient measures need to be combined to minimize the negative effects of background speech on cognitive performance and subjectively perceived disturbance. The aspired set value for open-office concepts is the lowest possible sound level with a bad intelligibility of the background speech at the same time.

Originality/value

– The synopsis of several empirical studies allows deriving comprehensive and well-founded information for practitioners involved in the evaluation and/or design of offices environments.

Relating traffic, construction, and ventilation noise to cognitive performances and subjective perceptions

The present study investigates the cognitive performance and subjective perceptions in the context of road traffic noise alone and multiple noises, including construction and ventilation noises. A total of 20 university students were exposed to seven noise conditions. Laboratory experiments employed semantic and episodic memory tasks. Self-reports of perception were collected from the participants. It was found that multiple noise sources impaired the free recall of words, and free recall scores were affected by noise type. Significant differences in free recall scores were found when the noise level difference between the individual noise and multiple noise sources was more than 5 dB. In contrast, word comprehension did not mediate the effects of noise on semantic memory. Annoyance caused by multiple noise sources correlated highly with the results of the free recall and word comprehension tasks. Moreover, loudness and roughness were found to account for the annoyance ratings of combinations of road traffic noise with construction or ventilation noises.

Irrelevant speech effect under stationary and adaptive masking conditions

The irrelevant speech effect was investigated in this study where the serial-recall task was performed under six different conditions: Silence, speech-only, noise-only, speech masked by a stationary noise at two different signal-to-noise ratios (SNRs), and speech masked by an adaptive noise. Measured in five test blocks distributed throughout the four test days, the error rate of the serial-recall task under the silence condition sharply decreased in the first few test blocks, halved after completing about seven blocks. When the adaptive masking scheme was used, the error rate of the serial-recall test was reduced compared to the speech-only condition (by 9%) and to the lower-SNR stationary noise (by 4.4%). However, the serial-recall performance was not significantly different between the stationary and the adaptive maskers when the average sound level was carefully matched. Speech Transmission Index (STI) and the correlation coefficient of power spectra were used as the estimators of the temporal and spectral distinctiveness between sound tokens, respectively. The comparison to the test results implied that the frequency-domain estimator may be a better predictor of the relative ISE especially for a non-stationary masker, although it was also suggested that such estimators may have to be combined possibly with an appropriate weighting.

Algorithmic modeling of the irrelevant sound effect (ISE) by the hearing sensation fluctuation strength

Background sounds, such as narration, music with prominent staccato passages, and office noise impair verbal short-term memory even when these sounds are irrelevant. This irrelevant sound effect (ISE) is evoked by so-called changing-state sounds that are characterized by a distinct temporal structure with varying successive auditory-perceptive tokens. However, because of the absence of an appropriate psychoacoustically based instrumental measure, the disturbing impact of a given speech or nonspeech sound could not be predicted until now, but necessitated behavioral testing. Our database for parametric modeling of the ISE included approximately 40 background sounds (e.g., speech, music, tone sequences, office noise, traffic noise) and corresponding performance data that was collected from 70 behavioral measurements of verbal short-term memory. The hearing sensation fluctuation strength was chosen to model the ISE and describes the percept of fluctuations when listening to slowly modulated sounds (f(mod) < 20 Hz). On the basis of the fluctuation strength of background sounds, the algorithm estimated behavioral performance data in 63 of 70 cases within the interquartile ranges. In particular, all real-world sounds were modeled adequately, whereas the algorithm overestimated the (non-)disturbance impact of synthetic steady-state sounds that were constituted by a repeated vowel or tone. Implications of the algorithm's strengths and prediction errors are discussed.

Combined effects of acoustic and visual distraction on cognitive performance and well-being

Information work is usually performed in offices and influenced by the combined effects of acoustics, room climate, lighting and air quality. However, the principal part of literature solely focuses on the individual effects of physical parameters. This study (n = 32) investigates the combined effects of acoustic and visual distraction with regard to cognitive performance and well-being. Therefore low level background speech (40 dB(A)) of good or poor intelligibility was combined with either static or dynamic lighting. Experimental testing lasted for approx. 7 h for each participant and was conducted in mock-up offices. No interaction effects of background speech and lighting conditions with regard to cognitive performance were found. However, the results prove that even low level background speech of high intelligibility significantly impairs short-term memory, reasoning ability and well-being. But no effect of background speech on text comprehension and sustained attention was found. Visual distraction due to dynamic lighting caused significant complaints but did not impair performance. An interaction effect of background speech and lighting conditions was found with regard to perceived performance during task processing. Test persons only felt to perform better, if background speech of low intelligibility was combined with static lighting. It is shown that the effects on cognitive performance and well-being must be considered separately since these effects are rarely consistent.

Spoken word recognition in adolescent cochlear implant users during quiet and multispeaker babble conditions

OBJECTIVE

To assess overall speech intelligibility in adolescent cochlear implant speakers during quiet and multispeaker babble conditions.

STUDY DESIGN

A cross-sectional assessment of intelligibility incorporating group (auditory-oral versus total communication speakers), sentence context (high versus low contexts), and background conditions (quiet versus multispeaker babble).

SETTING

A camp designed to assess adolescents over a concentrated period.

PARTICIPANTS

Fifty-seven adolescents who participated in an earlier study when they were 8 to 9 years old examining functional outcomes of speech perception, speech production, and language were asked to participate in follow-up study.

METHODS

Speech intelligibility was assessed by asking the adolescents to repeat sentences. Sentences were digitally edited and played to normal hearing listeners who either provided broad transcriptions of sound accuracy or wrote down the words they understood when the sentences were presented in quiet and in multispeaker babble.

MAIN OUTCOME VARIABLE

The dependent variables were percent correct consonants, vowels, and total words identified.

RESULTS

Very few substitutions or omissions occurred, resulting in high levels of accuracy for consonants and vowels. Speech intelligibility in quiet was significantly greater than in the multispeaker babble condition. Multispeaker babble decreased performance uniformly across sentence context for the 2 groups.

CONCLUSION

Accurate consonant production based on measures of substitutions and omissions fails to account for distortions and allophonic variations. Reductions in speech intelligibility relative to the phoneme correct productions suggest that the allophonic variations related to distortions may influence naive listener's ability to understand the speech of profoundly deaf individuals.

Effects of white noise on Callsign Acquisition Test and Modified Rhyme Test scores

The Callsign Acquisition Test (CAT) is a speech intelligibility test developed by the US Army Research Laboratory. The test has been used to evaluate speech transmission through various communication systems but has not been yet sufficiently standardised and validated. The aim of this study was to compare CAT and Modified Rhyme Test (MRT) performance in the presence of white noise across a range of signal-to-noise ratios (SNRs). A group of 16 normal-hearing listeners participated in the study. The speech items were presented at 65 dB(A) in the background of white noise at SNRs of -18, -15, -12, -9 and -6 dB. The results showed a strong positive association (75.14%) between the two tests, but significant differences between the CAT and MRT absolute scores in the range of investigated SNRs. Based on the data, a function to predict CAT scores based on existing MRT scores and vice versa was formulated. STATEMENT OF RELEVANCE: This work compares performance data of a common speech intelligibility test (MRT) with a new test (CAT) in the presence of white noise. The results here can be used as a part of the standardisation procedures and provide insights to the predictive capabilities of the CAT to quantify speech intelligibility communication in high-noise military environments.

Mental strain and annoyance during cognitive performance in different traffic noise conditions

In built-up areas, an increasing number of persons are affected by road traffic noise while performing mental work. This experimental study focused on annoyance and mental strain due to various noise scenarios. A total of 102 healthy, young persons (51 women, 51 men, aged 18-31 years) were randomly assigned to one of five experimental conditions determined by traffic flow (even, lumped) and traffic composition (20%, 40% heavy vehicles). While exposed to noise they performed a grammatical reasoning and a mathematical processing task. Performance and mental strain were not affected by any of the five noisy conditions. Individuals with high noise sensitivity were partially more annoyed and performed less than persons with low sensitivity. STATEMENT OF RELEVANCE: The present study provides information about mental strain due to tasks with different cognitive demands and the role of noise sensitivity in various traffic noise conditions. The results show that measures aiming at the reduction of the proportion of heavy vehicles should additionally consider particular traffic flow.

Performance effects and subjective disturbance of speech in acoustically different office types--a laboratory experiment

This study examined how the intelligibility of irrelevant speech, determined with the Speech Transmission Index (STI), affects demanding cognitive task performance. Experiment was carried out in a laboratory that resembled an open-plan office. Three speech conditions were tested corresponding to a private office (STI = 0.10), an acoustically excellent open office (STI = 0.35) and an acoustically poor open office (STI = 0.65). All conditions were presented at equal level, 48 dBA. The STI was adjusted by the relative levels of speech and masking sound. Thirty-seven students participated in the experiment that lasted for 4 h. All participants performed five tasks in each of the three speech conditions. Questionnaires were used to assess subjective perceptions of the speech conditions. Performance in the operation span task, the serial recall and the activation of prior knowledge from long-term memory were deteriorated in the speech condition with the highest speech intelligibility (STI = 0.65) in comparison with the other two conditions (STI = 0.10 and STI = 0.35). Unlike performance measures, questionnaire results showed consistent differences among all three speech conditions, i.e. subjective disturbance increased with ascending speech intelligibility. Thus, subjective comfort was disturbed more easily than performance. The results support the use of STI as an essential room acoustic design measure in open-plan offices.

PRACTICAL IMPLICATIONS

Reduction of speech intelligibility in office environments by proper acoustic design would be beneficial in terms of both work performance and subjective comfort. Proper acoustic design requires both the use of high acoustic absorption and an appropriate masking sound.