The effective duration of the stimulus for the auditory brainstem and middle latency responses

ABR and MLR are considered “onset” responses, reflecting the auditory system's response to stimulus onset rather than its continuance. The studies in this dissertation were designed to determine the effective duration of the stimulus for ABR and MLR elicited by different stimuli and by stimulation of different regions of the cochlea using the “constant-slope” rise-time paradigm in which the slope of the rise (rather than intensity) for different rise times is kept constant.; ABRs and MLRs were recorded from 12 normal-hearing adults. In the first study, the acoustic stimuli consisted of 500- and 2000-Hz tones and broadband noiseburst stimuli with rise times ranging from 0.5 to 12 ms.; Results indicate that the effective duration for the ABR and MLR is stimulus dependent, with 500-Hz exhibiting the longest effective duration (∼12 ms), broadband noiseburst exhibiting the shortest effective duration (∼2 ms), and 2000-Hz falling in between (∼4 ms). No significant differences were seen between the effective duration of the ABR and MLR.; In the second study, ABR and MLR responses to brief broadband noisebursts were recorded using the high-pass masking noise (HP) subtraction technique. One-octave-wide narrowband derived responses were centered at 500-, 1000- and 2000-Hz.; Results indicate that the effective duration of the stimulus for the ABR and MLR is cochlear place dependent, with 500-Hz derived response exhibiting the longest effective duration (∼8 ms), 2000-Hz derived response exhibiting the shortest effective duration (∼2 ms), and 1000-Hz results falling in between (∼4 ms). No significant differences were seen between ABR and MLR effective durations.; Thus, the effective duration of the stimulus for ABR and MLR is cochlear place dependent with responses from the apical regions of the cochlea integrating longer portions of the stimuli. The lack of significant differences between the effective durations of the ABR and the MLR suggests that the time it takes to achieve maximum output is determined by peripheral processing, not by where the response is generated.