Vectorial synchrony: A method for quantifying directional alignment of audience movements using three-axis...

Collective audience movements at live performances are difficult to quantify unobtrusively and on a large scale. We propose vectorial synchrony, a method that reduces three-axis acceleration data from multiple participants to a scalar measure of directional alignment at each time point. The method uses smartphone accelerometers and a measurement application to collect audience movements without using dedicated sensing devices. Its computational complexity scales linearly with the number of valid participants, supporting the processing of large groups. We evaluated the method in two field settings: a men's cheerleading performance and a public viewing of a music video. Audience arm movements were recorded, and vectorial synchrony was calculated in both settings. In the validation test, surrogate-data testing identified significant temporal increases and decreases in synchrony corresponding to changes in the performance. These results demonstrate that smartphone accelerometers can be used to measure collective movement over time and that vectorial synchrony provides a scalar signal for performance analysis and interactive control.•Smartphone accelerometers enable the measurement of audience movement without requiring dedicated sensing devices.•Vectorial synchrony summarizes directional alignment as a scalar time series.•Field experiments demonstrate the method under live performance conditions.