Reliability of P50 auditory event-related potential indices of sensory gating.

We examined the reliability of three traditional P50 auditory event-related potential indices under paired-click conditions: (a) the conditioning response (C), (b) the testing response (T), and (c) the testing to conditioning suppression ratio (T/C). Three alternative indices, (a) the (C - T) difference, (b) the (C - T)/(C + T) adjusted difference, and (c) the (T - T') residualized difference, where T' is the regression of T on C, were also studied. The N100 wave was used as a generalizability check. Although C and T amplitudes were reliably measured by traditional means, the T/C suppression ratio was not. For psychometric reasons that are described, the reliability of the suppression ratio is undermined principally by the correlation between C and T. The C - T difference score is a promising alternative to the unreliable T/C suppression ratio. Theoretical consequences of changed metrics are discussed.