Latency of auditory evoked field deflection N100m ruled by pitch or spectrum?

The auditory evoked field (AEF) in response to pure tones of 250 and 1000 Hz and a complex tone with a periodicity of 4 ms (composed of the frequencies 1000, 1250, 1500, 1750, and 2000 Hz), corresponding to a pitch of 250 Hz, was recorded with a 37-channel neuromagnetometer system. The intensity was 60 dB sensation level (SL). Two different stimulus durations were examined in 12 subjects: 500 ms (long tones) and 100 ms (short tones). The stimulus onset asynchrony (SOA) was uniformly distributed between 3 and 4 s for the long tones and between 0.8 and 1.2 s for the short tones. Each subject was investigated four times, to assess the intraindividual variability. The mean latency of the AEF deflection N100m turned out to be similar for the long and the short tones: about 98 and 87 ms for the pure tones of 250 Hz and 1000 Hz, respectively, and 95 ms for the complex tone with a pitch of 250 Hz. However, a great interindividual variability was observed, exhibiting no consistent relationship between the N100m latencies for the three different tones, except that the response to the pure tone of 1000 Hz generally occurred earlier. In conclusion, this study does not support the proposal that the N100m latency represents a code for pitch, although a low pitch appears to be a factor favoring a longer N100m latency.