Assessing the Role of Place and Timing Cues in Coding Frequency and Amplitude Modulation as a Function of Age
Natural sounds can be characterized by their fluctuations in amplitude and frequency. Ageing may affect sensitivity to some forms of fluctuations more than others. The present study used individual differences across a wide age range (20–79 years) to test the hypothesis that slow-rate, low-carrier frequency modulation (FM) is coded by phase-locked auditory-nerve responses to temporal fine structure (TFS), whereas fast-rate FM is coded via rate-place (tonotopic) cues, based on amplitude modulation (AM) of the temporal envelope after cochlear filtering. Using a low (500 Hz) carrier frequency, diotic FM and AM detection thresholds were measured at slow (1 Hz) and fast (20 Hz) rates in 85 listeners. Frequency selectivity and TFS coding were assessed using forward masking patterns and interaural phase disparity tasks (slow dichotic FM), respectively. Comparable interaural level disparity tasks (slow and fast dichotic AM and fast dichotic FM) were measured to control for effects of binaural processing not specifically related to TFS coding. Thresholds in FM and AM tasks were correlated, even across tasks thought to use separate peripheral codes. Age was correlated with slow and fast FM thresholds in both diotic and dichotic conditions. The relationship between age and AM thresholds was generally not significant. Once accounting for AM sensitivity, only diotic slow-rate FM thresholds remained significantly correlated with age. Overall, results indicate stronger effects of age on FM than AM. However, because of similar effects for both slow and fast FM when not accounting for AM sensitivity, the effects cannot be unambiguously ascribed to TFS coding.
Keywordsfrequency modulation amplitude modulation temporal fine structure age
This work was supported by a grant from the National Institutes of Health (R01 DC005216).
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
- Hartmann WM, Hnath GM (1982) Detection of mixed modulation. Acustica 50:297–312Google Scholar
- Maiwald D (1967a) Die Berechnung von Modulationsschwellen mit Hilfe eines Funktionsschemas. Acustica 18:193–207Google Scholar
- Maiwald D (1967b) Ein Funktionsschema des Gehörs zur Beschreibung der Erkennbarkeit kleiner Frequenz-und Amplitudenänderungen. Acustica 18:81–92Google Scholar
- Zwicker E (1956) Die elementaren Grundlagen zur Bestimmung der Informationskapazität des Gehörs. Acustica 6:365–381Google Scholar
- Zwicker E (1970) Masking and psychological excitation as consequences of the ear’s frequency analysis. In: Plomp R, Smoorenburg GF (eds) Frequency analysis and periodicity detection in hearing. Sijthoff, Leiden, pp 376–394Google Scholar