Recruitment in conduction deafness. Observations using a midline loudness balance test

Area of Science:

• Audiology
• Otolaryngology
• Hearing Science

Background:

• Conductive hearing loss involves the outer or middle ear, affecting sound transmission.
• Understanding loudness perception in conductive hearing loss is crucial for diagnosis and management.
• The Alternate Binaural Loudness Balance (ABLB) test, or Fowler's test, is a clinical tool to assess loudness perception.

Purpose of the Study:

• To investigate the efficacy of the midline loudness balance test in differentiating normal hearing from conductive hearing loss.
• To explore the relationship between middle ear mechanics and loudness perception in conductive hearing loss.
• To evaluate the midline balance method's sensitivity to alterations in bone-conducted sound and labyrinthine window mechanics.

Main Methods:

• Conducted a midline loudness balance test on 10 normal ears and 104 ears with conductive hearing loss (loss ≤ 45 dB).
• Tones at 500 Hz and 2000 Hz were presented simultaneously at 10, 60, and 80 dB sensation levels.
• Compared results from normal ears to those with varying degrees of conductive hearing loss.

Main Results:

• Normal ears showed no reduction in threshold differences using the midline balance method.
• Significant reductions in threshold differences were observed across all groups with conductive hearing loss.
• The findings suggest true partial recruitment in conductive deafness, linked to altered middle ear mechanics.

Conclusions:

• The midline loudness balance test effectively identifies alterations in loudness perception associated with conductive hearing loss.
• Altered middle ear mechanics in conductive deafness lead to differential stimulation of the inner ear by loud versus threshold tones.
• The midline balance method's dependency on bone-conducted sound highlights its utility in assessing labyrinthine window function.