AXS and SOM: A new statistical approach for treating within-subject, time-varying, multivariate data collected using the AXS Test Battery
Judith L. Lauter, Chris Ninness · The Journal of the Acoustical Society of America · 2003
The Auditory Cross-Section (AXS) Test Battery [J. L. Lauter, Behav. Res. Methods Instrum. Comput. 32, 180–190 (2000)], described in presentations to ASA in 2002 and 2003, is designed to document dynamic relations linking the cortex, brainstem, and body periphery (whether physics, physiology, or behavior) on an individually-specific basis. Data collections using the battery typically employ a within-subject, time-varying, multivariate design, yet conventional group statistics do not provide satisfactory means of treating such data. We have recently developed an approach based on Kohonens (2001) Self-Organizing Maps (SOM) algorithm, which categorizes time-varying profiles across variables, either within- or between-subjects. The treatment entails three steps: (1) z-score transformation of all raw data; (2) employing the SOM to sort the time-varying profiles into groups; and (3) deriving an estimate of the bounds for the Bayes error rate. Our three-step procedure will be briefly described and illustrated with data from a recent study combining otoacoustic emissions, auditory brainstem responses, and cortical qEEG.