Headphone-deactivated monaural presentation collapses the externalised sound image

Evidence

In order to match the headphone and loudspeaker conditions physically, virtual presentation was used in a reverberant room. This approach resulted in a compelling impression of sound source externalisation for the headphone condition, which may have been accentuated by the presence of a loudspeaker at the appropriate position. A post-experiment test showed that listeners perceived the virtual binaural stimuli as emanating from the loudspeaker rather than the headphones. A consequence of this procedure was that when the left headphone was deactivated for monaural presentation, the externalisation of the sound collapsed, so that listeners found themselves comparing one sound that appeared to be from the loudspeaker with another that, although still reverberant and from the same side, appeared to come from the headphones. It is unclear whether this effect may have caused the apparent enhancement of the loudness summation effect in the Virtual condition. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1546

Categorization

• QUESTION: Whether the collapse of externalisation, rather than true monaural listening, enhanced the measured summation effect is unresolved and could confound ecological-validity conclusions.