It is well established that the magnitude of the cortical response decreases as the interstimulus interval decreases. We would like to examine this separately for adults vs babies, separately for sounds near threshold vs sounds well above threshold. These findings may provide insight into which parts of the cortical response are arising from neural structures that are specific to particular stimuli versus those that signify any acoustic event. They may also provide insight into which parts of the cortical response have significant magnitude during rapidly changing stimuli, as opposed to the slowly repeated identical sounds that are used in clinical tests.

An eventual practical application is to use very short interstimulus intervals and to use deconvolution techniques to remove the overlap in responses that occurs when the interstimulus interval is shorter than the duration of each response. This deconvolution is not simple linear deconvolution, because of the effect of varying interstimulus intervals on the following response, hence the need to first understand this interaction better. While the project has been described in terms of cortical responses, the issue about whether the neural structures that cause the observed response are frequency-specific also apply to auditory brainstem response (ABR) measurements.

The objectives of the project are:

• knowledge about the relationship of cortical responses to the stimuli that produce them, and
• information that will guide the development of faster clinical tests for the assessment of audibility of speech sounds in aided infants.