Exploring the role of feedback-based auditory reflexes in forward masking by schroeder-phase complexes

Area of Science:

• Auditory Neuroscience
• Psychoacoustics
• Otoacoustic Emissions

Background:

• Previous research suggests efferent pathways in the auditory system modulate cochlear responses, impacting auditory perception.
• These efferent-induced changes, particularly the medial olivocochlear reflex (MOCR), have been hypothesized to influence psychoacoustic measures like forward-masked thresholds.
• However, direct experimental evidence testing these hypotheses, especially concerning stimulus phase curvature, has been limited.

Purpose of the Study:

• To investigate the influence of stimulus phase curvature and temporal envelope modulation on the medial olivocochlear reflex (MOCR) and middle-ear muscle reflex (MEMR).
• To test whether efferent effects, specifically MOCR, account for the psychoacoustic dependence of forward-masked thresholds on masker phase curvature.
• To measure cochlear responses under varying conditions to elucidate the role of efferent auditory pathways.

Main Methods:

• Measured ear-canal pressure changes at 6 kHz with and without specific auditory stimuli (band-limited harmonic complex tones).
• Varied the phase curvature of stimuli, presenting them either on-frequency or off-frequency relative to the probe tone.
• Assessed middle-ear muscle reflex (MEMR) influences by measuring phase-gradient functions and ear-canal pressure changes with a continuous suppressor tone.

Main Results:

• Both on-frequency and off-frequency complex tone stimuli significantly altered ear-canal sound pressure, indicating efferent pathway activation.
• The observed pattern of results did not support the hypothesis that efferent effects directly explain the psychoacoustic relationship between forward-masked thresholds and masker phase curvature.
• Unexpectedly long time constants were observed for some efferent effects, suggesting complex underlying mechanisms.

Conclusions:

• While efferent activity (MOCR) influences cochlear responses, it does not fully account for the psychoacoustic effects of masker phase curvature on forward-masked thresholds.
• The findings challenge previous assumptions about the direct role of MOCR in specific psychoacoustic phenomena.
• The origin of the observed long time constants in efferent effects requires further investigation.