[Eeglablist] Auditory ERP asymmetry

[Piers Dawes]

Dear list

We have obtained an odd asymmetric auditory ERP. Does anyone have an explanation? Any suggestions would be welcome.

We recorded ERPs to pure tone beeps of 500 and 3000 Hz at 3 intensity levels. Tones were randomised and played separately to left and right ears, with responses recorded at Cz with a nose tip reference using a Neuroscan system. Insert headphones were calibrated before testing and re-checked after; left and right headphones provide identical levels of output. Participants were 58 older people (mean age 70 years) with age-related hearing loss (Mean HL of 45 dB at 2kHz). Selection criteria included symmetrical hearing (not greater than 15dB difference at any frequency), and overall mean HL is symmetrical.

Grand mean ERPs are higher in amplitude for tones played to left ear compared to right ear (by about ~1uV for N1 and ~.5uV for P2), and this is a consistent pattern among participants. Latencies are similar. I would have thought amplitudes should also be very similar between left and right ear. What is happening here?

Thanks for your help
Piers Dawes PhD
Audiology and Deafness Research Group
School of Psychological Sciences
Ellen Wilkinson Building
University of Manchester
Manchester M13 9PL
Tel: +44 (0)161 30 61758

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