Figure 1.

(A) The schematics of global analysis. Spatiotemporally processed signals recorded from multiple points on a line, showing staggered action potentials upstrokes consistent with wavefront propagation. (B) Same signals as A shifted to align the upstrokes. (C) The first principle component ( $W_1$) displays alternans. (D) Spectrogram of C, showing a 1:2 peak of alternans. The second principle component ( $W_2$) displays more pronounced alternans larger than C (E). Spectrogram of E, shows a prominent 1:2 peak of alternans (F). The bar in A depicts 200 ms.