HIS Study Guide 2026

The ossicular chain consists of three tiny bones located in the middle ear: the malleus (hammer), incus (anvil), and stapes (stirrup). These bones work together as a lever system to transmit and amplify sound vibrations from the tympanic membrane to the oval window of the inner ear. They are crucial for efficient sound conduction and hearing.

The modified Hughson-Westlake procedure is a standardized threshold-seeking method using a 10 dB down, 5 dB up bracketing approach, where threshold is defined as the lowest level with 50% correct responses in ascending trials.

The microphone is a fundamental component of a hearing aid, acting as the input transducer. Its primary function is to capture ambient sound waves from the environment. It then converts these acoustic signals into electrical signals, which are subsequently processed and amplified by other components within the hearing aid.

The pinna collects sound and directs it into the ear canal; its complex asymmetric folds create frequency-dependent reflections (head-related transfer functions/HRTFs) that encode sound elevation (vertical localization) cues.

WRS (also called speech discrimination score) is the percentage of phonetically balanced monosyllabic words correctly repeated when presented at a suprathreshold comfortable level, reflecting speech clarity independent of loudness.

Psychological and physiological stress activates the limbic system and autonomic nervous system, which have bidirectional connections with the auditory system; this can amplify the perceived annoyance and loudness of tinnitus and create a reinforcing distress cycle.