Frequency Specificity of ABR Evaluated by Tuning Curves in Rats

A tone on tone simultaneous masking paradigm was used to determine tuning curves of ABR in rats. Probe stimuli were 0.5, 0.8, 1.0, 2.0, 4.0-kHz short tone bursts. ABR tuning curves were constructed to define masker intensity that resulted in a 50% reduction in probe-elicited wave-V amplitude. The frequency specificity of each probe stimulus was evaluated by Q10 and the maximum masker frequency (MMF) calculated for the tuning curves. Q10's were gradually increased with the increase in rise time. However, a prolongation of the rise time beyond 2 cycles of probe frequency yielded little improvement in Q10. Maximum masker frequencies (MMF) of the tuning curves were not necessarily equal to the frequency of probe without the 2.0-kHz. For the 0.5, 0.8, 1.0-kHz probe, the MMF of the tuning curves showed higher values than the frequency of probe. For the 4.0-kHz probe, the MMF of the tuning curves showed lower values than the frequency of probe. These rusults indicate that the short tone burst stimuli may enable to assess certain auditory function at different frequencies, and they have wider frequencies' spread of the cochlear area around stimulus frequencies.