2.2 Setup and stimuli
All
tests were conducted in a double-walled soundproof
laboratory.
Participants sat in a chair placed 1 m in front of seven
loudspeakers.
Sound field hearing thresholds were obtained by warble tones for octave
frequencies across 0.25–4 kHz in
dB
hearing level (HL).
Speech
perception under quiet was measured by the word recognition score (WRS
[%]) of the
Mandarin
speech test materials (MSTMs) 12 at 65 dB speech
presentation level
(SPL).
Speech perception in noise was measured by the speech reception
threshold (SRT) of the MSTMs.
The
spectrum-shaped noise (SSN) was set at 65 dB
SPL,
and the speech signal started at 0 dB speech-to-noise ratio (SNR), with
the following disyllables changing adaptively in 2 dB SPL steps as the
participants responded.
The
SRT was defined as the speech signal level presented when a participant
identified 50% of the words correctly. The SNR was calculated as the
difference between the SRT and
SSN.
The sound localisation test
(Supplementary
Fig. 1a) consisted of seven audiometric loudspeakers placed at 30°
intervals in a semicircle within a horizontal plane (± 90°, azimuth).
Broadband noise (0.5–20 kHz) was randomly played at three different
sound levels (65-, 70-, and 75-dB SPL). Each time the loudspeakers
finished a presentation, participants indicated which loudspeaker they
believed to be the source of the burst.