Analysis of Cortical Auditory Responses With the Probability Pulse

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Abstract
A short sound pulse, having the modulation envelope of a normal distribution curve was used to analyze distribution of potential in the MES auditory cortex of the dog. Potential due to the sound pulse (called the probability or p pulse) was found to localize in the area in accordance with its spectrum. Responses for high frequencies were found in the anterior part of the area, responses for low frequencies in the posterior part. Logarithm of mid-frequency was identified as a function of linear distance along the cortex. Size of cortical segment excited was proportional to the bandwidth of the pulse. Three db down the pulse produced a response in 1 mm of cortex, and at 40 db down, the segment was 2 mm wide. Difference in representation of left and right ears was shown for the MES area. The latencies of cortical responses were related to the mid-frequencies of the p pulses. Above 0.36 kc latencies were independent of the mid-frequency, and measured about 10 msec. Below 0.36 kc latencies at threshold were related to duration of the signal. At higher intensity levels, latencies decreased to the limiting value of 10 to 15 msec. With low frequency p pulses, several cortical potentials were observed which were attributable to individual cycles of the p pulse.