Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science




Grahn, Jessica


Spontaneous intrapersonal synchronization is the spontaneous synchronization of periodic behaviors within an individual. It is less investigated than spontaneous interpersonal synchronization, the synchronization of periodic behaviors that occurs spontaneously between individuals integrated into a single system through coupling, caused by the exchange of sensory feedback between them. It was therefore hypothesized that periodic behaviors produced by an individual, a single system by default, would spontaneously be more synchronous through exchange of sensory feedback, coupling and integration within the individual, when the behaviors are produced simultaneously, compared to separately. Based on a postulate that explains spontaneous interpersonal synchronization as a strategy by the brain to conserve resources, and predicts individuals under high cognitive load to spontaneously synchronize their behaviors with others to conserve resources, it was hypothesized that spontaneous intrapersonal synchronization would increase under additional cognitive load. We tested our hypotheses through two experiments, each with a different pair of periodic tasks, and a different cognitive load task. In each experiment, we compared the phase coherence of two periodic tasks, tapping-walking or tapping-ticking, when produced by an individual simultaneously versus separately; we also compared the same when produced simultaneously with additional cognitive load versus without load. Here, ticking was a periodic task where the word “tick” was uttered repetitively. Counting backwards and visual pattern-matching were used as cognitive load tasks. Results showed that spontaneous intrapersonal synchronization between periodic tasks was higher when produced simultaneously, compared to separately, and the same was lower with additional cognitive load, compared to without load.

Summary for Lay Audience

People walking side by side synchronize their footsteps spontaneously with each other; This phenomenon is called spontaneous interpersonal synchronization; it occurs due to exchange of sensory feedback between individuals, causing their movements to get coupled. Based on that, we hypothesized1 that coupling of simultaneous periodic movements, such as walking and clapping, would occur within an individual as well, triggering spontaneous synchronization between periodic movements produced by the individual, called spontaneous intrapersonal synchronization. Furthermore, spontaneous interpersonal synchronization has been postulated as a strategy by the brain to conserve resources, as tracking one periodic movement at a time is more economical, compared to tracking multiple; it is predicted that a high cognitive load in addition to, say, walking or clapping together, will cause individuals to synchronize more, to conserve resources. Given how, musicians, when asked to track two beats simultaneously, show a tendency to combine the two beats rather than track them independently, we argued that this could be to conserve resources as well, and predicted this tendency to extend beyond perception into production. We therefore hypothesized2 that spontaneous intrapersonal synchronization would increase with additional cognitive load. We tested the hypotheses by comparing the synchronicity between finger-tapping and walking in Experiment 1, and between finger-tapping and ticking (uttering the word “tick” repetitively) in Experiment 2. We tested hypothesis1 by comparing the synchronicity between the periodic task pairs when they were performed simultaneously, versus when they were performed separately. We tested hypothesis2 by comparing the synchronicity between the periodic task pairs when they were performed simultaneously with additional cognitive load, versus without additional load. We induced additional cognitive load by using the counting backwards task (in 3’s & 7’s) in Experiment 1, and a visual pattern-matching task (4 to 9-block patterns) in Experiment 2. In both experiments, results supported Hypothesis 1: Spontaneous intrapersonal synchronization between the periodic tasks was higher when performed simultaneously, compared to separately. In both experiments, results failed to support Hypothesis 2: Spontaneous intrapersonal synchronization decreased with additional cognitive load.