Listener Fatigue – Some speculations James D. (jj) Johnston Chief Scientist Neural Audio, Kirkland, Wa

A Reminder – Loudness vs. Intensity Intensity: – Sound pressure level – Measured excitation in the atmosphere Loudness – PERCIEVED “sound level” – Proportional to inner hair cell firing on the basilar membrane How do they relate to fatigue???

Is there one kind of fatigue? Mechanical cochlear fatigue Neural/physiological cochlear fatigue CNS fatigue Reflexive fatigue????

Mechanical fatigue due to high intensity – Outer hair cell damage, at least, seems to correlate to intensity, but outer hair cells also depolarize due to high loudness – This raises the issue of both biochemical and mechanical fatigue, perhaps due to differing

Neural fatigue due to high loudness – Inner hair cell firing rate is pretty much proportional to loudness (not intensity), and there must be some biochemical fatigue there.

CNS fatigue due to missing, false, or contradictory cues – Does having to extract “what was that” from missing information create some kind of CNS Fatigue What about balance/hearing interaction? – Do balance and hearing interact? – What do conflicts in the two cause? Especially at “rock and roll” levels

How does one measure Listener Fatigue? There are no units There is no external manifestation that can be singled out as listener fatigue – Annoyance Fatigue? Material? Genre? Lyrics? – “upset” sensations Motion sickness Normal fatigue Time spent listening willingly, under controlled circumstances – How in the world will we avoid other factors like Boredom Lack of time Dislike of test setup

Some very speculative ideas But first level: – Too loud (either intensity or loudness) is bad in many ways. Conflicting cues – Hearing very close to balance organs. At least anecdotal examples of induced motion sickness have been reported. – Unnatural effects (cognative effort?).

Basic research is necessary