Auditory Motion
The auditory stimulus consisted of an amplitude modulated (F c =
20 Hz) broadband white noise sampled at 48 kHz that was created at the
beginning of each trial. This noise was divided into 11 segments, one
for each of the 11 speakers along the soundbar. Smooth apparent motion
was created by playing each speaker in sequence using a crossfade and by
applying a sine window to the onset and offset of each noise segment. To
eliminate loudness variations between individual speakers, the sound
pressure level of each speaker was tested and calibrated to ensure equal
loudness of (~75 dBA), as measured at a distance of 1 m
with a sound pressure meter. To prevent subjects from using distance and
location cues as a basis for velocity judgements, the start- and
end-points of the sounds were randomly jittered by ±15° (3 speaker
intervals, see Freeman et al, 2014). All stimuli were generated on a
MacPro (Apple Inc.) running MATLAB (R2016b, The MathWorks, Inc., Natick,
Massachusetts, United States) and Psychophysics Toolbox
extensions35,36.