How to tell a target from a spiral: The two probe problem

Targets and spirals are ubiquitous wave patterns found in excitable media. Here, we show how to distinguish a target from a spiral using only two probes to measure activity and deliver stimuli. The different spatiotemporal symmetry properties of targets and spirals are revealed applying stimuli interchangeably at both probes. Our technique has diagnostic implications for cardiology since targets and spirals are associated with different mechanisms of cardiac arrhythmia.