Alternative Technologies _ ASSR


 Introduction to ASSR

by Terry Pincton Ph.D.

 Just as the speech signal can be viewed as either a change in amplitude over time or a spectrum of frequencies, so can the auditory evoked potentials be considered in either the time domain or the frequency domain. Steady-state responses are evoked potentials that maintain a stable frequency-content over time. Steady-state evoked potentials are usually evoked by stimuli that occur at rapid rates. The response then shows a spectrum with energy only at the rate of stimulation and its harmonics.

          Amplitude-modulated and frequency-modulated tones evoke clear steady-state responses. Amplitude-modulated tones have excellent frequency-specificity since they contain energy only at the frequency of the carrier tone and at two sidebands, separated from the carrier by the frequency of modulation. The most widely recorded auditory steady state response is the 40 Hz potential. This can be used to measure audiometric thresholds in waking adults and older children. However, the response is difficult to measure in infants and young children. Furthermore, the 40-Hz response is very susceptible to changes in the level of arousal, showing small amplitudes during sleep and even smaller amplitudes during anesthesia. Recently, it has been shown that the auditory steady-state responses can be recorded at stimulus rates between 75and 110 Hz.

          These responses can be readily recorded in infants and are unaffected by sleep. The responses to several amplitude-modulated stimuli presented simultaneously can be independently assessed if each stimulus is modulated at a different rate. The recorded activity, when viewed in the frequency-domain, shows a response to each carrier-frequency at its signature modulation-frequency. Since amplitude-modulated tones are not significantly distorted by free-field speakers or hearing aids, they can be used to test how well a hearing-aid is working. Responses evoked by frequency-modulated stimuli may become helpful in assessing supra-threshold auditory processes, such as those necessary for speech perception.


Additional Resources 

      •  Although the technology behind the ASSR was not intended (at least initially) as a new application for neonatal and infant screening / monitoring, the progresses in the field are important and in the near future ASSR protocol might assist EHDI programs. . The following  lectures are presented as pdf files. If you don't have the Pdf  Adobe Acrobat reader you can download it from here  (approximatelly 6 M).

      • A powerpoint presentation on the use of ASSR technology in NHS programs (pdf format) . By Dr. Barbara Cone-Wesson (ISA round Table, Phoenix Arizona, September 25-29 2004).

      • Lecture by Dr. James Hall on the topic "The Role of Auditory Steady State Response (ASSR)in Audiology Today". NOTE The lecture is offered as a pdf file (5 MB) of relative large dimensions. If you have problems downloading it please  This email address is being protected from spambots. You need JavaScript enabled to view it.  us.
      • Lecture by Dr. James Hall on the topic "Application of Auditory Steady State Response (ASSR) in Diagnosis of Infant Hearing Loss in the Era of Universal Newborn Hearing Screening". NOTE The lecture is offered as a pdf file (1.8 MB). If you have problems downloading it please  This email address is being protected from spambots. You need JavaScript enabled to view it.  us.