Pervasiveness of Early Middle Ear Muscle Contractions

Details

• Personal Author:
  Ahroon WA ; Deiters KK ; Flamme, Gregory A. ; Greene NT ; Jones HG ; Murphy, William J. ; Smith MV ; Tasko SM
• Description:
  Background: Middle ear muscle contractions (MEMCs) are expected to reduce the transmission of energy through the middle ear. Some damage-risk criteria (DRCs) for impulsive noise include MEMCs as a form of protection. Early MEMCs (eMEMCs) have been assumed in some DRCs to reach maximum effect prior to the arrival of the hazardous impulse. Despite decades of conjecture leading to the inclusion of eMEMCs in DRCs, no conclusive evidence exists of protective eMEMCs in the scientific literature. The inclusion in MIL-STD-14 74E of one model utilizing eMEMCs greatly elevates the need for conclusive evidence that eMEMCs are pervasive (i.e., present in 95% of the population with 95% confidence) in the military population. Purpose: The current study was designed to determine if eMEMCs are pervasive in the military population, either as conditioned responses (CRs) or the result of prior experiences. Methods: Participants were adults with excellent or very good hearing sensitivity, and no evidence of dysfunction affecting the ear or relevant cranial nerves. Changes in the levels of a click-based probe signal developed in the ear canal were used as the indicator of MEMCs. Participants were assigned to one of nine experimental tasks. Three tasks were designed to develop conditioned eMEMCs, with conditioning stimuli varying by sensory modality (visual or auditory) and the level of attention available to the conditioning stimulus. Six tasks, ranging from laboratory simulations through discharge of an M4 carbine on an outdoor target range, provided an opportunity to demonstrate eMEMCs among U.S. Anny Service Members and civilians with recent firearm experience. Pervasiveness was evaluated in terms of a tendency for a participant to exhibit an eMEMC and in terms of the proportions of individual impulses eliciting eMEMCs. Results: None of the nine experimental tasks produced proportions of eMEMC approaching the requirement for pervasiveness. The greatest likelihood of exhibiting eMEMCs was observed as a CR to an attended stimulus with a matching sensory modality (95% confidence of as low as 50% prevalence). However, the likelihood of a conditioned eMEMC declined precipitously when the sensory modality of the conditioning stimulus did not match the unconditioned stimulus and when attention to the conditioning stimulus was unavailable. Results showed a very low likelihood of observing an eMEMC for any of the tasks relying on prior experience. Fewer than 11% of participants showed a tendency toward eMEMCs when discharging live ammunition. Conclusion: This project found no evidence of pervasive eMEMCs and provides unambiguous evidence that eMEMCs are not a dependable form of protection against impulsive noise. Any DRC including eMEMCs will require modification and subsequent validation. [Description provided by NIOSH]
• Subjects:
  Ear Hearing Noise Noise, Occupational Occupational Health Safety Sense Organs
• Keywords:
  Ears Firearms Impulse Noise Military Personnel Muscle Contraction Noise Exposure
• Publisher:
  U.S. Army Aeromedical Research Laboratory (USAARL)
• Document Type:
  Text
• Funding:
  Contract
• Genre:
  Report
• Place as Subject:
  Alabama ; Ohio ; OSHA Region 4 ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  DFSE - Division of Field Studies and Engineering
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-83
• NIOSHTIC Number:
  nn:20062069
• Citation:
  Fort Rucker, AL: U.S. Army Aeromedical Research Laboratory (USAARL), Technical Report 2021-05, 2020 Dec; :1-83
• Federal Fiscal Year:
  2021
• Peer Reviewed:
  False
• Source Full Name:
  Pervasiveness of early middle ear muscle contractions
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:b202d6dc7e51c2bca9435568f557b164f16462058dab83d21cead7b36e713c70670d052dfb9780c16dcd4239f10c6f12aac1e6eba55803ba85f47efdde1eeb81
• Download URL:
  https://stacks.cdc.gov/view/cdc/225387/cdc_225387_DS1.pdf
• File Type:
  [PDF - 3.92 MB ]