Binaural loudness constancy operates independently of stimulus type

Evidence

The small effect of stimulus type observed in experiment 1, was reversed in experiment 2. Taking these small and inconsistent effects together, we found no evidence that binaural loudness constancy is greater for more ecologically valid stimuli such as connected speech. Indeed, for both speech and noise, occlusion of the ear led to little reduction in loudness (a small summation effect), suggesting that loudness constancy occurs independently of stimulus type. It should be noted, however, that quite prominent reverberation was present in our experiment, which reliably cued the existence of an external sound source. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1561

Since the Silence and Virtual-Finger conditions of experiment 2 produced significantly different summation effects, it seems that a portion of the loudness constancy effect observed in experiment 1 may have been mediated by the residual sound at the occluded ear. Both the Silence and the Virtual-Finger conditions produced a collapse in externalisation for the monaural case, so it seems unlikely that the difference in effect can be attributed to this cause. On the other hand, 2.5–3 dB of summation was still observed in the Virtual-Finger condition, whereas less that 1 dB was observed in the Loudspeaker condition of experiment 1. It appears, therefore, that the listeners’ awareness of meatal occlusion, which would only be present in the first case, may still play a role. A major caveat to these conclusions is that KEMAR was not designed to realistically simulate the effects of bone-conducted sound, which likely plays a major role in listening in a sound field with an occluded ear. While probe microphones in the ear canal might more accurately record the stimulation at the tympanic membrane, they would still not capture the stimulation occurring at the cochlea. … Taking these small and inconsistent effects together, we found no evidence that binaural loudness constancy is greater for more ecologically valid stimuli such as connected speech. Indeed, for both speech and noise, occlusion of the ear led to little reduction in loudness (a small summation effect), suggesting that loudness constancy occurs independently of stimulus type. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1558

Categorization

• QUESTION: The claim that awareness of ear occlusion may mediate loudness summation suggests a possible top-down cognitive confirmation-bias mechanism worth comparing with how occlusion is usually acoustically modeled.
• corroborated: 3 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 1561; Dijk, Pim van, Physiology, Psychoacoustics and…, 1558
• XREF: connects to: A finger in the ear enables rapid 2-interval monaural-binaural loudness comparison