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|Year : 2013
: 15 | Issue : 66 | Page
|Using the effect of alcohol as a comparison to illustrate the detrimental effects of noise on performance
Brett R.C Molesworth1, Marion Burgess2, Belinda Gunnell1
1 School of Aviation, University of New South Wales, Sydney, New South Wales 2052, Australia
2 Acoustics and Vibration Unit, University of New South Wales, Canberra, Australian Capital Territory 2600, Australia
Click here for correspondence address
|Date of Web Publication||17-Aug-2013|
The aim of the present research is to provide a user-friendly index of the relative impairment associated with noise in the aircraft cabin. As such, the relative effect of noise, at a level typical of an aircraft cabin was compared with varying levels of alcohol intoxication in the same subjects. Since the detrimental effect of noise is more pronounced on non-native speakers, both native English and non-native English speakers featured in the study. Noise cancelling headphones were also tested as a simple countermeasure to mitigate the effect of noise on performance. A total of 32 participants, half of which were non-native English speakers, completed a cued recall task in two alcohol conditions (blood alcohol concentration 0.05 and 0.10) and two audio conditions (audio played through the speaker and noise cancelling headphones). The results revealed that aircraft noise at 65 dB (A) negatively affected performance to a level comparable to alcohol intoxication of 0.10. The results also supported previous research that reflects positively on the benefits of noise cancelling headphones in reducing the effects of noise on performance especially for non-native English speakers. These findings provide for personnel involved in the aviation industry, a user-friendly index of the relative impairment associated with noise in the aircraft cabin as compared with the effects of alcohol. They also highlight the benefits of a simple countermeasure such as noise cancelling headphones in mitigating some of the detrimental effects of noise on performance.
Keywords: Alcohol, aviation, english as a second language, noise cancelling headphone, speech intelligibility
|How to cite this article:|
Molesworth BR, Burgess M, Gunnell B. Using the effect of alcohol as a comparison to illustrate the detrimental effects of noise on performance. Noise Health 2013;15:367-73
|How to cite this URL:|
Molesworth BR, Burgess M, Gunnell B. Using the effect of alcohol as a comparison to illustrate the detrimental effects of noise on performance. Noise Health [serial online] 2013 [cited 2020 Jan 22];15:367-73. Available from: http://www.noiseandhealth.org/text.asp?2013/15/66/367/116565
| Introduction|| |
The effect of alcohol on performance has been used as a comparison to highlight the detrimental effect of fatigue on performance. , This research has shown that a moderate level of fatigue impairs performance to an extent equivalent to the legal intoxication level for safe driving in many countries including Australia, namely a blood alcohol concentration (BAC) level of 0.05. The main aim of the present research is to provide a similar comparison. Specifically, the present research sought to use alcohol as a user-friendly index to highlight the relative impairment associated with noise in the aircraft cabin. The context for the study is commercial aviation aircraft cabins where many passengers try to undertake useful work in a noise environment that is below the occupational noise exposure limits, but clearly above the acceptable level for a working environment as recommended in guidelines for noise levels in areas of occupancy (such as Australian Standard-2107, 2000). 
Aircraft cabin noise, which is largely generated from the engines, can range from 65 decibels (dB) (A) to over 100 dB (A) depending on the phase of flight and type of aircraft. ,, Exposure to aircraft noise, both within and outside the cabin has repeatedly been demonstrated to degrade performance. ,,, For passengers of commercial airlines and in particular for commuters wishing to use this time to complete work, the effect of aircraft noise on performance is an important concern. For modern aircraft, there have been reductions in the cabin noise and this is used as a marketing advantage. Aircraft manufacturers now make statements featuring low noise such as "Airbus cabins are quietest in the sky,"  "… cleaner, quieter and more fuel efficient."  However, it will be many decades before the aircraft with quieter cabins replace all the existing passenger aircraft fleet.
Road and aviation authorities around the world have long known about the effect of alcohol on motorist and pilot performance. Laboratory studies reveal that alcohol impairs cognitive performance such as information processing,  attention,  memory,  hand-eye coordination (i.e. psychomotor performance)  as well vision.  Alcohol can also induce fatigue as it reduces the quality of sleep.  This has resulted in many countries setting limits for alcohol levels for driving (see Chamberlain and Solomon  for summary) and in the case of aviation, a virtual blanket ban on alcohol for air crew (BAC below 0.02). 
The effect of alcohol on performance is also widely accepted within the community and the majority of countries have established a legal limit for operating a motor vehicle. For example in Australia, the legal BAC limit is 0.05 for a fully licensed motorist. The actual quantified value for BAC is promoted by the regulatory authorities with regular advertising over all forms of media. So not only does the community know there is an effect of alcohol on performance, they also know there is a limit above which society considers their performance is degraded to such an extent that they are considered not capable of controlling a motor vehicle.
Thus, the effect of alcohol on performance can provide a benchmark for comparison of other effects on performance. Hence and against an aviation backdrop of high noise levels within the cabin of commercial aircraft, the main aim of the present research is to provide a user-friendly index of the relative impairment associated with noise in the aircraft cabin. A secondary aim of the present research is to build upon previous studies highlighting the benefits on performance from the use of noise cancelling headphones in the noise environment of an airline cabin , and compare this also with the effects of alcohol on performance. This investigation stemmed from an applied situation where a commercial airline passenger was threatened with refusal of carriage if he continued to use his noise cancelling headphones during the taxi phase of flight. The passenger claimed that the headphones reduced the engine noise, thereby allowing him to hear the pre-flight safety announcement clearer. This airline, like the vast majority around the world has restricted the use of noise cancelling headphones since they fall within the category of a personal electronic device (PED), albeit non-transmitting (Molesworth and Burgess,  for a discussion on PEDs).
In a similar manner to previous studies, , the current study also assessed the change in performance for a cognitive task that is typically encountered in an aircraft cabin, namely recall of the safety briefing. Hence, a simple cued recall task was used where participants were exposed to a series of audio briefs, each lasting approximately 90 s, under varying conditions (i.e. noise, alcohol and noise cancelling headphones). They were then tested on their recall of the information. Since, it is well-established that the effect of noise on such cognitive tasks is greater for speakers for whom the language used in the task is not their native language, but a second language (i.e. non-native English speakers), , both native English speakers as well as non-native English speakers were in the study sample.
In summary, the present research is designed to answer the following question; using alcohol as a comparison, to what extend does simulated aircraft noise at 65 dB (A) impair performance on a cued recall task? It is also hypothesized that performance on a cued recall task will be superior using noise cancelling headphones than without and that there will be a difference in findings between native and non-native English speakers.
| Methods|| |
A total of 32 participants (originally 34; 28 male), 16 native English speakers and 16 non-native English speakers (English as a second language [ESL]) were recruited for the study. The mean age of participants was 20 (SD = 5.20; native English = 20 years, ESL = 21 years). Six ESL speakers reported their native language to be Portuguese, five reported their native language as Cantonese, three reported their native language as Chinese, one reported Norwegian as their native language and one reported Dutch as their native language. All participants had reached the level of competency in written and spoken English as required for acceptance to a program of study at an English speaking University. On average, the ESL speakers had been speaking English for 10 years (range 1-18 years). Eight ESL speakers reported they could speak in two languages, six reported they could speak in three languages while two reported they could speak in four languages. All participants underwent an auditory screening procedure and none were found to have a hearing deficit (i.e. any loss in either ear at any frequency considerably <20 dB[A]).
As noted above, two participants were replaced in the study. The first participant (#11) was replaced when it became clear that the participant failed to understand the instructions relating to both the hearing test and the experimental exercise. The second participant (#24), unbeknown to the participant at the time of the research, had a medical condition that reduced his ability to metabolise alcohol effectively. The research, including all stimuli was approved in advance by the University of New South Wales Ethics Committee.
The study comprised a 2 × (2 × 2) mixed repeated measures design. Native language (English or ESL) was the between-groups independent variable and alcohol (BAC at 0.05 vs. BAC at 0.10) and audio condition (speaker-no headphones vs. active noise cancelling headphones) were the two repeated measures independent variables. Since the origin of this research stemmed from an applied situation involving a passenger using his noise cancelling headphones without external audio, this condition was employed as the baseline condition and so formed the basis of all analyses. The four repeated measures conditions included [Table 1]:
- No headphones, audio brief played through the external speaker and external wideband noise (baseline),
- Noise cancelling headphones active, audio brief played through headphones and external wideband noise,
- No headphones, audio brief played through the speaker, no external wideband noise, BAC of 0.05 and
- No headphones, audio brief played through the speaker, no external wideband noise and BAC of 0.10.
To reduce potential order effects, the stimuli were presented similar to a crossover design method as well as in a counterbalanced order. Moreover, since both independent variables (i.e., audio condition and alcohol condition) had two levels, half of the participants completed the audio conditions (1 and 2) prior to the consumption of alcohol while the second half completed these in the days directly following the consumption of alcohol. Similarly, half of the participants were presented condition 1 followed by condition 2 while the remainder were presented condition 2 followed by condition 1. Those participants who consumed alcohol first, were tested in the audio condition, on average 2 days later. This was to reduce the potential of any carryover effects from the alcohol on the test day. For the two alcohol conditions (3 and 4), half of the participants were tested at BAC of 0.05 on the way up to a BAC of 0.10 while the second half were tested at this level on the way down from a BAC of 0.10. Hence, the careful design of the project meant that participants were required in multiples of four, excluding the between-groups factor (e.g. 4 × 4 = 16 for native English speakers).
Finally, since the dependent variable featured four different audio briefs, these briefs were systematically varied to also ensure equal pairing among all conditions. The four audio conditions employed replicated those previously used by Molesworth et al. (e.g. Molesworth and Burgess,  Molesworth et al.  ). None of the participants in this study had participated in previous studies using this audio material. Each audio brief included information, both factual and non-factual about various aircraft: (a) Bombardier Dash 8, (b) Airbus A330, (c) Boeing 767 and (d) Saab 340. The maximum score, which could be obtained on any of the four multiple-answer cued recall audio tests, was 12 (dependent variable).
| Materials|| |
The laboratory equipment comprised: Sennheiser® noise cancelling headphones PXC450, two personal computers (one with internet access), Sennheiser® HD265 linear headphones (used for the audiometric screening procedure), one audiometric screening procedure (Digital Audiometer-Screen v6.2), a Casella sound level meter (model CEL-240; calibrated prior to every use), Alcolizer LE breathalyser (calibrated prior to the research), sound power source-type 4205 as well as a Logitech 5.1 surround speaker system (stereo mode).
The experimental documentation included: an information sheet, consent form, demographics questionnaire (i.e. age, gender and native language background), four audio briefs and their respective multiple-answer written tests. The audio briefs and written tests were a replication of each other except in the form presented (e.g. audio vs. written). Specifically, each audio brief contained information about a particular aircraft (Bombardier Dash 8, Airbus A330, Boeing 767, or Saab 340). Importantly, each of the audio briefs was designed as a combination of both factual and non-factual information to reflect as opposed to replicate the pre-flight safety briefs provided by commercial airlines. Non-factual information was included in case any of the participants had detailed knowledge about the aircraft. The time for each audio brief was planned to correspond to the typical time for a pre-flight safety brief (e.g. 90 s). The information contained within each audio brief was also manipulated to ensure that each contained equal pieces of numerical information, namely 22 pieces. Hence, each multiple-answer written test examined three pieces of numerical information and nine pieces of non-numerical information.
An example (non-numerical) extracted from the Bombardier Dash 8 audio file stated:
"The airframe structure is made aluminium while the airframe itself is made from composite plastics."
The same sentence appeared in the written test except with three options for one word as shown below:
"The airframe structure is made aluminium while the airframe itself is made from composite/hardened/uncertain plastics."
In the written test, participants were tasked to choose one of the options and were given the specific instruction "if you do not know the word, circle uncertain."
In terms of alcohol, participants were asked their preference in type of alcohol, including spirits, wine and beer. Every endeavour was made to provide their drink of choice along with mixer drinks and constant supply of water. In addition, a selection of food such as biscuits, bread, hors d'oeuvre, olives, salty snacks, cold meats and cheese was provided for the participants.
Participants were recruited via flyers placed around campus at the University of New South Wales as well as during classes held on campus. Participants initially read the information sheet, completed the consent form, followed by demographics questionnaire (age, gender and language background) and a computer controlled audiometric screening procedure.
Importantly, participants were reminded that the audio briefs were derived from both factual and non-factual information. When presented the written tests, no conflicting audio was presented, nor were the active noise cancelling headphones worn. The typical noise level inside the research laboratory without any participants or experimental generated noises (only computers operating) was found to be, in terms of L eq, 1 min , between 38 and 40 dB (A).
Recall the experimental conditions were presented in a counterbalanced order while the audio briefs were systematically varied to ensure equal pairing within each experimental condition. In the experimental condition 1 and 2, continuous wideband noise was produced from the sound power source placed out of view of the participant. No wideband noise was produced in the experimental condition 3 and 4. Consistent with previous research,  the sound level of the wideband noise measured in the vicinity of the participant's head was 65 dB (A), (A weighted L eq, 1 min ,). This level as determined by Ozcan and Nemlioglu,  is reflective of that during the taxi phase of flight for a commercial aircraft.
The sound level of the audio brief produced through the external speaker in experimental conditions 1, 3 and 4 was measured in the vicinity of the participant's head to be 70 dB (A) (A weighted L eq, 1 min ). This level is consistent with Molesworth and Burgess  as originally determined by a subject matter expert (i.e. flight attendant with 16 years of experience on task). In the experimental condition 2, the audio brief was played through the active noise cancelling headphones at a level determined by the participant. Specifically, participants were instructed prior to the commencement of the experiment to set the auditory volume at a level that facilitates extracting the most information from the audio file, in the presence of the wideband background noise. This was performed with a test audio file (a short segment from the audio file not used in the present study) for no more than 5 s in the presence of the wideband noise. Importantly, this condition is reflective of the applied environment where passengers on commercial airlines are free to select their desired audio volume level (i.e. real life situation under investigation) and is hence the basis of this research. Following each audio file, participants were asked to complete the paper based audio test, which required the recall of the information.
Alcohol was administered approximately every 30 min and participants' BAC was tested 15 min after each dosage. Dosages were adjusted for participants' age, sex and weight. The study concluded once participants' BAC was below 0.05, at which time they were thanked and transported to their respective place of residence (within a 5 km radius of the university). The total time taken to complete the testing ranged from 5 to 9 h.
| Results|| |
Since the main aim of the present study was to compare the effects of noise on performance with the effects of alcohol on performance, a series of planned comparisons, opposed to a mixed repeated measures analysis of variance (ANOVA) were employed. This method, according to Tabachnick and Fidell  maximizes power since it restricts analyses to only those of theoretical interest. For all analyses, the statistical package "PSY" developed by Bird et al.,  was employed.
As previous research has identified the beneficial effect of employing active noise cancelling headphones in the presence of noise (wideband), the first analysis sought to determine if this effect was present in the current experiment. With alpha set at 0.017 (alpha adjusted accordingly to control for family-wise error-Bonferroni adjusted α = 0.05/3) and assumptions of normality met, the results of a planned comparison between experimental condition 1 (brief through the speaker) and condition 2 (brief through active noise cancelling headphones) revealed a statistically significant difference, F(1, 31) = 18.02, P < 0.000, ηp 2 = 0.80 [Table 2].
|Table 2: Mean number of correct responses and standard deviation on the experimental conditions distributed across native language background |
Click here to view
While this result supports the previous research , and reflects favourably on the use of active noise cancelling headphones to reduce the detrimental effects of noise on performance, it is important to determine if the benefits of such technology extends equally across native language backgrounds. Therefore, two subsequent planned comparisons were performed, the first comparing condition 1 (i.e. baseline condition) and condition 2 with only native English speakers; the second comparing the same conditions; however, with only ESL speakers. With alpha set at 0.017 and assumptions of normality met, the results of the first planned comparison failed to reveal a statistically significant difference, F(1, 15) = 4.22, P = 0.058, ηp 2 = 0.76 while a statistically significant difference was identified with the second analysis, F(1, 15) = 19.92, P < 0.000, ηp 2 = 0.57. As can be seen in [Table 2], the effect of noise on performance is most profound for non-native speakers where compared to their native English speaking counterparts.
Having established the negative effects of noise on performance is more profound for non-native English speakers and consequently the beneficial effects of active noise cancelling headphones on performance, the next series of analyses sought to determine the extent noise degrades performance and compare with the effect of alcohol on performance. Following the same analysis sequence as above, the first planned comparison examined differences between condition 1 (brief through the speaker and wideband noise) and the condition where participants had a BAC of 0.05 (condition 3). With alpha set at 0.017 (Bonferroni adjusted α = 0.05/3) and assumptions of normality met, the results of the planned comparison revealed a statistically significant difference, F(1, 31) = 9.44, P = 0.004, ηp 2 = 0.79 [Table 3]. On average, participants were able to recall 25% more when intoxicated to a BAC of 0.05 (mean score = 7.13) compared with when exposed to noise (mean score = 5.72).
|Table 3: Correlation among experimental conditions and years of spoken English |
Click here to view
In order to determine if the effect of alcohol on performance impacted equally across groups, two further planned comparisons were performed, one for each between-group condition (i.e. native English speaker and ESL). With alpha set at 0.017, the results of the first planned comparison between condition 1 and condition 3 for native English speakers failed to reveal a statistically significant difference, F(1, 15) = 3.201, P = 0.094, ηp 2 = 0.18. In other words, performance in the noisy condition with the audio played through the speaker (condition 1; mean score 6.25) was similar to performance in the quiet condition with a BAC of 0.05 (condition 3; mean score 7.63). In contrast, the results of the second planned comparison between the same experimental conditions for the ESL speakers revealed a statistically significant difference, F(1, 15) = 7.521, P = 0.015, ηp = 0.33. On average, ESL speakers were able to recall accurately 5 items correct in the condition with the audio played through the speaker and wideband noise (condition 1) while in the quiet condition with a BAC of 0.05, they were able to recall 28% more (condition 3; mean score 6.63).
Planned comparisons, consistent with the two previous analysis sequences were used to determine if a BAC of 0.10 (i.e. double the legal limit for driving in Australia) impairs performance to a level similar to that of wideband noise at 65 dB (A). With alpha set at 0.017 (Bonferroni adjusted α = 0.05/3) and assumptions of normality met, the results failed to reveal a statistically significant difference, F(1, 31) = 1.529, P = 0.226, ηp 2 = 0.76 [Table 2]. This result suggests that performance on the cue recall task with wideband noise and the audio brief played through the speaker (condition 1; mean score 5.72) was similar to performance in a quiet condition with a BAC of 0.10 (condition 4; mean score 6.34). As this data was inclusive of all participants, what remained unknown is whether performance varied as a result of native language background and so two further planned comparisons were performed. The results of the first analyses between condition 1 and condition 4 (quiet condition with BAC of 0.10) for native English speakers failed to reveal a statistically significant difference, F(1, 15) = 1.095, P0 = 0.312, ηp 2 = 0.07. A similar result was evident between the same two conditions with ESL speakers, F(1, 15) = 0.403, P = 0.535, ηp 2 = 0.03. Combined these results suggest that noise impairs performance to a level similar to a BAC of 0.10 and this effect is consistent across native language background.
Since the experimental design involved testing half of the participants on the way up to BAC of 0.10 and the remaining half on the way down from 0.10, it was important to determine if this procedure impacted the results. Hence, a series of planned comparisons were performed, comparing performance at both 0.05 and 0.10 for native English speakers as well as ESL speakers across group (ascending or descending). The results of four different planned comparisons failed to reveal a statistically significant difference, largest F, F(1, 14) = 0.937, P = 0.349, ηp 2 = 0.06. This result suggests the order in which participants completed the experimental tasks (i.e. ascending or descending from 0.10) had no impact on the results.
The final series of analyses were undertaken to determine if a relationship existed between years of spoken English and performance for the ESL speakers. Hence, a series of Pearson product-moment correlations were performed. As can be seen in [Table 3], apart from condition 4 (r (15) = 0.39, P = 0.149), a moderate to very strong positive relationship was evident between years of spoken English and the three remaining experimental conditions, smallest r, r (15) = 0.57, P = 0.028. This relationship was at its strongest when the participants were using active noise cancelling headphones in the presence of wideband noise (condition 2), r (15) = 0.84, P < 0.000.
| Discussion|| |
Auditory noise has been repeatedly shown to degrade performance. ,, For pilots and the travelling public alike, there are limited options available to reduce the effect of aircraft noise on performance. The most obvious is using noise attenuating devices, such as active noise cancelling headphones. As illustrated in the present research, active noise cancelling headphones reduce the effect of noise on performance, but only notably for non-native English speakers. However, due to the restrictions placed on PEDs, active noise cancelling headphones are not permitted during certain phrases of flight such as during taxi, take-off and landing. Conversely, it is the taxi phase of flight where airlines provide important safety related information for passengers, in the form of a pre-flight safety brief, in case of an emergency.
The results from the present research indicate that exposure to noise levels akin to those present during the taxi phase of flight (wideband noise at 65 dB(A)) impairs performance to a level equivalent to that produced by alcohol intoxication of approximately 0.10. Moreover, these results show that passengers on commercial airlines are exposed to conditions that impair their performance to a level judged to be twice as much as the legal limit for driving safely in Australia.
For one particular commuter, namely the commuter who insisted active noise cancelling headphones improves his ability to hear the pre-fight safety announcement, these results may not be surprising. For airlines and governing bodies, these results may provide some insight into why some passengers are inattentive when the pre-flight safety announcement occurs.  Most importantly for everyone involved in aviation, including the travelling public, these results provide a user-friendly index of the relative impairment associated with noise in this environment.
Limitations and future research
While the results of the present study highlight the negative effect of noise on performance, the study is not without its limitations. The most obvious involving the sample of participants, which were drawn from a university and is hence reflected in their average age. While there is little evidence to suggest that a negative relationship exists between age and the effects of alcohol on performance in terms of physical skill,  there is considerable evidence about the effect of excessive drinking on cognitive performance. , Hence, whether having older and/or possibly cognitive impaired individuals owing to previous alcohol consumption over a period of time would alter the results remains unknown; an area for future research.
It must also be noted that the present study employed no exclusion criteria regarding alcohol abuse or habitual alcohol usage. While there is limited evidence to suggest that a greater quantity and frequency of alcohol consumption impairs cognitive functions such as memory and recall, there is evidence that it does reduce alcohol induced motor skill impairment.  Therefore, it would be prudent for future research to consider employing such an exclusion criterion.
Recall the aim of the present research is to provide a user-friendly index for the relative impairment associated with noise in the aircraft cabin. This index is based on a widely used and accepted substance - alcohol, where its effect on cognition and human performance is widely documented. ,,,,, However, the effect of alcohol on performance is not always in a dose dependent relationship. For example, Moskowitz and Depry  found that while alcohol degraded performance in a divided attention task, it failed to negatively impact performance on a vigilance task. It is possible that the variation in results is due to experimental methodologies; however, it is also possible that alcohol affects various cognitive functions differently. While the present research focused on the effects of alcohol on a memory and recall task, how alcohol precisely impacted the various functions  required to acquire and store information such as stimulus detection, perception or encoding remains unknown and is hence an area for future research.
Future research should also investigate the effects of noise at increased volumes on performance. Moreover, the noise level tested in the present study was reflective of a commercial passenger aircraft during taxi. According to Ozcan and Nemlioglu,  noise levels during the cruise phase of flight are approximately 15-20 dB louder. For commuters wishing to work during flights, the impacts of this noise level on performance remain unknown. However, it would seem reasonable to conclude that a direct relationship would exist between the noise levels and the cognitive impairment.
| Conclusion|| |
It is well-established that noise in the aircraft cabin impairs performance in terms of memory and recall. However, there is no simple user-friendly metric to highlight the extent to which this occurs, until now. The results of the present research show that the effect of simulated aircraft noise (wideband noise at 65 dB(A)) on performance is equivalent to that produced by alcohol intoxication at a BAC of 0.10. For aviation authorities and airlines alike, the results imply that the conditions in which they communicate important information such as the pre-flight safety brief is less than ideal. The results also highlight that using countermeasures such as noise cancelling headphones is an easy and simple method to reduce the detrimental effect of noise on performance. Most importantly, the results provide for all who are involved in the aviation industry, a user-friendly index of the relative impairment associated with noise in the aircraft cabin.
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Brett R.C Molesworth
School of Aviation, Room 205, University of New South Wales, Sydney, New South Wales 2052
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2], [Table 3]
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|[Pubmed] | [DOI]|