Failure to Apply Signal Detection Theory to the Montreal Battery of Evaluation of Amusia May Misdiagnose Amusia

This article considers a signal detection theory (SDT) approach to evaluation of performance on the Montreal Battery of Evaluation of Amusia (MBEA). One hundred fifty-five individuals completed the original binary response version of the MBEA (n = 62) or a confidence rating version (MBEA-C; n = 93). Confidence ratings afforded construction of empirical receiver operator characteristic (ROC) curves and derivation of bias-free performance measures against which we compared the standard performance metric, proportion correct (PC), and an alternative signal detection metric, d ′. Across the board, PC was tainted by response bias and underestimated performance as indexed by A_z, a nonparametric ROC-based performance measure. Signal detection analyses further revealed that some individuals performing worse than the standard PC-based cutoff for amusia diagnosis showed large response biases. Given that PC is contaminated by response bias, this suggests the possibility that categorizing individuals as having amusia or not, using a PC-based cutoff, may inadvertently misclassify some individuals with normal perceptual sensitivity as amusic simply because they have large response biases. In line with this possibility, a comparison of amusia classification using d ′- and PC-based cutoffs showed potential misclassification of 33% of the examined cases.