Interpersonal synchrony increases prosocial behavior in infants

Source: L. K. Cirelli, K.M. Einarson, L.J. Trainor 

Developmental Science 17:6 (2014), pp 1003-1011

http://onlinelibrary.wiley.com/doi/10.1111/desc.12193/abstract

Summary:

The current article reports a new study on the effect of interpersonal motor synchrony in prosocial behaviors in infancy, within a context of musical engagement. The work was conducted by Prof. Laurel Trainor and her team at the Auditory Development Lab at McMaster University. Previous studies by other researchers suggested that adults who engaged in synchronized tasks such as walking, singing or finger tapping showed increased cooperative behaviors. Nevertheless, no studies in infants had been developed to date revealing whether infants would behave similarly to adults.

In this study, 48 infants of 14 months old were tested through two different experiments. The first experiment consisted of 2 phases: the “Interpersonal Movement Phase” followed by the “Prosocial Test Phase”. In the first phase, infants were divided in four bounce conditions, as the authors intended to control the confounding effect of predictability of the musical movement. The conditions included synchronous bouncing/evenly spaced beats, synchronous bouncing/unevenly spaced beats, asynchronous bouncing/evenly spaced beats and asynchronous bouncing/unevenly spaced beats. 

All infants listened to 145s of a Musical Instrument Digital Interface (MIDI) version of “Twist and Shout” (by the Beatles) played over loudspeakers, either the original version of the track (beats per minute=129) or the modified version, in which the inter-beats intervals changed after each successive beat. During listening to music, infants were being held and bounced by the help of an assistant, while facing and watching the experimenter. The experimenter would also bounce either in synchrony or out of synchrony with the way the infant was being bounced. Both the assistant and experimenter listened to wood block beats on “bounce instruction tracks” via headphones.  In the “Prosocial Test Phase”, the objective was to measure the prosocial behavior of the infant, by dropping a target object and expecting its collection by the infant within 30 s.

In the second experiment, the procedure was mostly identical with the first experiment having the same synchronous/evenly spaced condition of Experiment 1, but with alternating (anti-phase) bounces between the assistant and the experimenter.

Results in the first experiment demonstrated that experiencing interpersonal motor synchrony with an unfamiliar adult promotes spontaneous prosocial behavior in 14-month-old infants, with more significant results on spontaneous helping (within 0-10s). The obtained results from the second experiment also indicated an increased prosocial behavior in anti-phase synchronous bouncing. The main effect of beat predictability and the interaction between synchrony and beat predictability were not significant.

Reflections:

I initially became interested in this topic when I first heard about it during the second lecture of Prof. Bartel. I found it quite impressive how interpersonal synchrony movements during 145 s can develop prosocial behaviors in early child development. It was of great surprise that these empathic behaviors were observed in synchrony in both evenly (predictable beats) and unevenly spaced conditions. The latter finding can be encouraging news for those parents lacking rhythm skills, as being synchronous with infants while bouncing is more important than keeping a steady beat.

To me, this study has been very well designed. Usually carrying out research using infants and young children is very challenging, as the development of the effective paradigms to test research questions is not easy. I believe this model could be further developed to be utilized as a clinical assessment tool to investigate prosocial behaviors in child development field.

I would be very curious to see how young children with early signs of autism spectrum disorders (ASD) would behave in this experiment. Children with ASD not only manifest social- emotional deficits, but also demonstrate some degree of motor abnormality and difficulties in self-synchrony (1). Studies suggest that ASD is associated with developmental abnormalities in the brain stem systems and cerebellum in early fetal stage, which can lead to abnormal timing and sensory perception (2).

In addition, in the present study, Trainor et al. did not discuss how the prosocial effects of synchronized interpersonal activity are being mediated by the human brain, information that could be given to deepen our understanding of brain connectivity.  As mentioned by Prof. Bartel in his lecture, Steven Brown (3) found evidence of cerebellar activity during entrainment (synchronizing timing and movement with musical rhythm). In one recent study conducted by Kokal et al., they addressed specifically which neural structures could possibly link synchronized activity and prosocial behavior. Findings showed a preliminary neural evidence that the caudate nucleus (a region of the basal ganglia known to play a role in synchronization or pulse-keeping) relates synchronized activity to basic reward processing in the brain, and that a history of reward with a particular person influences future decisions to help that person (4).

More research is required on these two subcortical structures (basal ganglia and cerebellum) to reveal their individually role in motor timing processing and their connections to social-emotional networks.

References:

1 – M.W  Hardy, A.B Lagasse, “Rhythm, movement and autism: using rhythmic rehabilitation research as a model for autism” , Frontiers in Integrative Neuroscience (2013) Mar 28; 7 (19).

2 - C.Trevarthen, J. Delafield-Butt, “Autism as a developmental disorder in intentional movement and affective engagement”, Frontiers in Integrative Neuroscience (2013) July 17; 7 (49).

3- S. Brown, M.J Martinez, L.M Parsons, “The neural basis of human dance”, Cerebral Cortex (2006); 16:1157-1167

4- I. Kokal, A. Engel, S. Kirschner, C. Keysers, “Synchronized Drumming enhances activity in the caudate and facilitates prosocial commitment- if the rhythm comes easily”, PLoS ONE (2011) 6: (11)