Background: The middle latency response (MLR) can be a powerful tool for assessing integrity
of cortical and subcortical auditory structures. Most research on the MLR, however,
is constrained to relatively slow repetition rates by the time window necessary for
response acquisition. Maximum length sequence (MLS) paradigms enable the recording
of the MLR at high repetition rates, which could reduce test time and provide information
about the behavior of auditory structures at rapid rates of stimulation.
Purposes: To examine potential timing advantages and differences in waveforms between an MLS-MLR
paradigm compared to a conventional MLR paradigm (Experiment 1), and to examine effects
of rate on MLR morphology within the MLS paradigm (Experiment 2).
Research Design: A repeated measures study. All subjects within each experiment underwent every condition
for that experiment.
Study Sample: Ten young adult female subjects participated in each experiment of this study. All
subjects had normal hearing and negative neurological history.
Data Collection and Analysis: Latency and amplitude values as well as the presence/absence of Na, Pa, Nb, and Pb
components of the MLR were measured. Comparisons were made between the MLS-MLR and
conventional MLR paradigms, as well as between repetition rates within the MLS-MLR
paradigm.
Results: Significant latency and amplitude differences were found between MLS and conventional
MLR paradigms. The late components of the MLR (Nb, Pb) were present significantly
more often when the MLS paradigm was used. No timing advantage was found with the
MLS-MLR paradigm. Within the MLS paradigm, as repetition rate increases, latency becomes
significantly shorter and amplitude significantly lower.
Conclusions: Middle latency responses evoked by the MLS-MLR paradigm show significant differences
from those evoked by a conventional MLR paradigm. The MLS-MLR paradigm can reliably
evoke the late components (Nb, Pb) of the MLR and may be an important clinical tool
for future investigation of these elements.
Key Words
Auditory evoked potentials - central auditory processing - repetition rate
