Eartone 3a

The experiment was performed in a soundproof room with each participant seated upright in a comfortable chair facing a monitor where the experimental stimuli were presented. A recording microphone was placed 3–5 cm in front of the participant’s mouth and binaural insert earphones (EARTONE 3A^®, 3M Company, Indianapolis, IN, USA) were used for sound stimuli delivery. Two separate computers were installed outside of the participant testing room for EEG recording and stimuli presentation, respectively. The stimulus presentation computer was connected to the microphone to record the participant’s utterances (during the Talk condition), which were later delivered to the participants using the insert earphones. In addition, the stimulus presentation computer was linked to the EEG recording computer to enable the insertion of stimulus-locked triggers in the EEG data.

Pure tone audiometry, assessed at ARIC visit 6 (2016-2017), was completed in a soundproof booth using insert earphones (EARTone 3a; 3M) and an Interacoustics AD629 or Equinox audiometer (Interacoustics A/S). Measurement of air conduction was completed at standard octaves from 500 to 8000 Hz. For each frequency, the hearing threshold was recorded in decibels hearing level (dB HL). We calculated a 4-frequency (0.5, 1, 2, and 4 kHz) pure tone average for each ear and modeled a continuous measure of hearing (better-hearing ear pure tone average [BPTA]) scaled to 10 dB HL, with higher BPTA indicating worse hearing function. Hearing was also categorized according to World Health Organization standards as normal hearing (BPTA≤25 dB HL), mild hearing impairment (BPTA of 26-40 dB HL), moderate hearing impairment (BPTA of 41-60 dB HL), or severe hearing impairment (BPTA>60 dB HL).¹⁹