Phase Discrimination Ability in Mongolian Gerbils Provides Evidence for Possible Processing Mechanism of Mistuning Detection

Abstract

Compared to humans, Mongolian gerbils (Meriones unguiculatus) are much more sensitive at detecting mistuning of frequency components of a harmonic complex (Klinge and Klump. J Acoust Soc Am 128:280-290, 2010). One processing mechanism suggested to result in the high sensitivity involves evaluating the phase shift that gradually develops between the mistuned and the remaining components in the same or separate auditory filters. To investigate if this processing mechanism may explain the observed sensitivity, we determined the gerbils' thresholds to detect a constant phase shift in a component of a harmonic complex that is introduced without a frequency shift. The gerbils' detection thresholds for constant phase shifts were considerably lower for a high-frequency component (6,400 Hz) than for a low-frequency component (400 Hz) of a 200-Hz harmonic complex and increased with decreasing stimulus duration. Compared to the phase shifts calculated from the mistuning detection thresholds, the detection thresholds for constant phase shifts were similar to those for gradual phase shifts for the low-frequency harmonic but considerably lower for the high-frequency harmonic. A simulation of the processing of harmonic complexes by the gerbil's peripheral auditory filters when components are phase shifted shows waveform changes comparable to those assessed for mistuning detection Klinge and Klump (J Acoust Soc Am 128:280-290, 2010) and provides evidence that detection of the gradual phase shifts may underlie mistuning detection.

Processing of interaural phase differences in components of harmonic and mistuned complexes in the inferior colliculus of the Mongolian gerbil

“…For the frequency range applied in the current study, the behavioural threshold for mistuning detection in the gerbil was between 1% and 2% (Klinge & Klump, ). The mistuning of a frequency component in a harmonic complex resulting in a gradual phase shift between the mistuned component and the components of the harmonic complex is detectable by humans and gerbils (Moore & Glasberg, ; Klinge‐Strahl et al ., ). Klinge‐Strahl et al .…”

“…23° for harmonic components with base frequencies below 1700 Hz) appears to be better than the behavioural sensitivity for monaural phase detection (e.g. 65° for the second harmonic of a harmonic tone complex with a fundamental of 200 Hz, Klinge‐Strahl et al ., ).…”

“…In case of the processing of the base‐frequency component with that of the mistuned complex, the interaction in the processing is weaker as indicated by the smaller effect of varying the IPD. This difference can be explained as follows: a mistuned component in a complex will provide for an increasing phase shift over time that will make it more difficult to evaluate a constant phase shift due to the interaural time disparity (Klinge‐Strahl et al ., ). In case of a harmonically related component, such an increasing phase shift does not occur that may disrupt the evaluation of the constant IPD.…”

“…Klinge‐Strahl et al . () suggested that gradual phase shifts between the mistuned component and the rest of the harmonic tone complex provide the cue for detecting the mistuning of a component as its phase shift at the mistuning detection threshold was similar to the threshold for detecting a constant phase shift of a tuned component of a harmonic complex. Although the detection of gradual phase shifts discussed so far relates to monaural processing mechanisms, similar patterns might emerge due to phase shifts between the two ears and result in neural response changes on a level of the auditory pathway, for example in the IC, where the interaction between both inputs is represented.…”