Exploring MEMR and natural sounds with a connection with hyperacusis

The Middle Ear Muscle Reflex (MEMR) is an involuntary response of the stapedius muscle to loud sounds. Activation of the muscle stiffens the tympanic membrane and thereby reduces the amount of energy transmitted into the ear protecting the auditory pathway from potential damage. MEMR is usually assessed in laboratory environments and clinics using artificial sounds like tones (500 Hz, 1 kHz or 2 kHz) or noise (wide band, WB or narrow band, NB) from 70 to 100 dB SPL as stimuli. These sounds have only very low ecological validity and can be perceived as uncomfortable. As a hearing screening tool, the MEMR provides an indication about the health status of the auditory system using a simple presence/absence criterion. The MEMR characteristics can, however, vary substantially from subject to subject, even in case of similar hearing profiles.
Hyperacusis is defined as an increased sensitivity to everyday sounds, and often intended as an umbrella term that also includes noise sensitivity and misophonia. But hyperacusis is specifically related to the level of the sound, that can cause perception of discomfort and sometimes pain at levels that are generally not characterized as uncomfortable by the average listener. Saxena et al. (2020) explored the relationship between MEMR and hyperacusis. The results showed that MEMR thresholds were higher in the group of participants with hyperacusis with respect to the controls. Hence, the activity of the middle ear muscle and the perception of sound intensity in terms of loudness and pleasantness could be interconnected.
In a preliminary experiment done on two participants with 16 sounds, 5 of which artificial (4 tones: 0.5, 1, 4, 8 kHz and WB noise) and 11 natural (’fork scratch on a plate’, ’fingernails on chalkboard’, ’female scream’, ’cymbal crash’, ’breaking glass’, ’car horn’, ’clapping’, ’distorted guitar’, ’bell’, ’guitar chord’, ’harp’), it was found that the MEMR strength differed for the different sounds, despite being presented at the same intensity.
In this study, we explore the characteristics of the MEMR with natural sounds and compare them with the results obtained with artificial sounds. In addition to the MEMR, we collected a subjective evaluation of the sound perceived in loudness and unpleasantness and the answers to the Hyperacusis Questionnaire (HQ; Khalfa English, 2002). We also performed the Core Discriminant Sounds (CDS) test (Enzler et al. 2021) to determine the level of hyperacusis. With these measures we wanted to get information about the personal predisposition towards the sounds, since the presence or not of hyperacusis and noise sensitivity could play a role in the reflex response (Saxena, 2020).
We hypothesize that the MEMR growth function will be shallower for participants showing trends towards increased hearing sensitivity and hyperacusis in the questionnaires and/or the CDS score. Moreover, we hypothesize that, at the same physical intensity, natural sounds are able to elicit a stronger or comparable MEMR response compared to artificial sounds, potentially with lower annoyance and lower perceived loudness.