time range in response to differences in tone frequency. Whereas, changes in tone loudness produced changes in oscillations in the 7.5-40 Hz frequencies in the 350-800 msec range. No significant changes in EROs were found to differences in tone probability. In previous investigations changes in frequency and loudness of auditory stimuli were found to modify N1 ERP components that occurred in the 10-50 msec (N1a) and 50-150 msec (N1b) ranges, whereas P3 components in the 200-400 msec range were found to be sensitive to probability, but not to tone frequency or loudness (Ehlers & Somes, 2002). For instance, while shifts upward in tone frequency produced decreases in N1a amplitude, it had no effect on the amplitude of the N1b component. Moreover, increasing the loudness of the tone produced an increase in the amplitudes of both N1a and N1b components. In contrast, mouse N1 components were not sensitive to changes in stimulus probability (Ehlers & Somes, 2002). Previous studies also found that P3 amplitudes were larger following the less probable or infrequently occurring tone, compared to the frequent tone, but were not affected by changes in tone frequency and loudness (Ehlers & Somes, 2002). These findings suggest that mouse EROs may
