Spatial release from masking deficits often reduce to an audibility problem

Evidence

In many situations, listeners with sensorineural hearing impairment (HI) demonstrate reduced SRM compared to listeners with normal hearing (NH). This observation commonly leads to the conclusion that spatial processing is disrupted by hearing loss. However, convergent evidence from other kinds of spatial tasks is somewhat lacking. For example, studies that have measured fine discrimination of binaural cues have noted that individual variability is high, and some HI listeners perform as well as NH listeners (e.g. Colburn 1982 ; Spencer 2013 ). Free-field localization is not strongly affected by hearing loss unless it is highly asymmetric or very severe at low frequencies (e.g. Noble et al. 1994 ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 1722

Thresholds for the colocated conditions (Fig. 2 left panel) were basically independent of amplification level, and for the NH subjects were about 2.5 dB lower than for the HI subjects. Thresholds for the spatially separated condition (middle panel) clearly improved with increasing amplification for both the NH and HI subjects and were maximal for “normal” audibility. However, thresholds for the NH subjects were on average 4.8 dB lower than for the HI subjects. The corresponding SRM, i.e., the difference in threshold between the colocated and separated conditions (right panel), increased with increasing gain similarly to the spatially separated thresholds, but the overall difference between NH and HI subjects was reduced to about 2.5 dB. It appears that under these conditions, a large proportion of the SRM deficit in the HI (and simulated HI) group could be attributed to reduced audibility. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1721

Thresholds for the colocated conditions (Fig. 2 left panel) were basically independent of amplification level, and for the NH subjects were about 2.5 dB lower than for the HI subjects. Thresholds for the spatially separated condition (middle panel) clearly improved with increasing amplification for both the NH and HI subjects and were maximal for “normal” audibility. However, thresholds for the NH subjects were on average 4.8 dB lower than for the HI subjects. The corresponding SRM, i.e., the difference in threshold between the colocated and separated conditions (right panel), increased with increasing gain similarly to the spatially separated thresholds, but the overall difference between NH and HI subjects was reduced to about 2.5 dB. It appears that under these conditions, a large proportion of the SRM deficit in the HI (and simulated HI) group could be attributed to reduced audibility. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1740

Categorization

• QUESTION: Worth chasing: why would reduced SRM coexist with spared binaural discrimination and localization? The chapter’s core puzzle.
• XREF: Directly relevant to the reader’s overall book purpose on normal hearing physiology; the residual ~2.5 dB SRM gap that audibility cannot explain points to suprathreshold/binaural processing deficits beyond audiogram shape.
• SHARE: For someone working in audiology or hearing-aid fitting: the finding that colocated thresholds were amplification-independent but spatially-separated thresholds improved with gain is a striking dissociation worth sharing.
• corroborated: 7 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 1722; Dijk, Pim van, Physiology, Psychoacoustics and…, 1721; Dijk, Pim van, Physiology, Psychoacoustics and…, 1740