by Stephanie Kulke, Northwestern University

Study design. In each study, infants were first introduced to sine-wave tone sequences during an Exposure vignette. This vignette varied across studies. In Study 1, the vignette consisted of a dialogue between two agents, with one agent producing tone sequences and one producing English sentences. In Study 2, the English sentences were replaced with other, higher-pitched tone sequences. Study 3's vignette featured a single agent moving in synchrony to the tone sequences (as if producing them), and Study 4 featured the same agent moving out of synchrony with the tone sequences. After the exposure vignette, infants participated in an object categorization task, where they were first familiarized with a series of exemplars paired with a novel tone sequence, and then presented with a novelty preference test. Credit: Scientific Reports (2024). DOI: 10.1038/s41598-024-78801-9

A new study by developmental scientists at Northwestern University provides new insight into a hallmark of human communication: our flexibility to use nonlinguistic signals to serve our communication needs.

Just as humans can use the taps of Morse Code or the patterns of smoke signals to communicate precise messages, infants show a remarkable flexibility to interpret nonlinguistic signals to aid their learning.

But what conditions are required for babies to elevate new nonlinguistic signals in this way? And how early can they do so?

Sandra Waxman, the study's senior author, and her colleagues discovered that infants as young as six months old were able to harness nonlinguistic signals for learning, a surprising finding because at this age, babies are just beginning to acquire their own language.

The evidence revealed the conditions under which babies conferred communicative status to the novel tone signals and then recruited them to successfully complete a learning task. Infants' success did not depend on whether the signals were produced by humans, or in a give-and-take interchange between individuals. Instead, what mattered was cross-modal temporal synchrony, in other words, if the method of signal delivery included synchronized sound and movement.

The findings were published in Scientific Reports.

Waxman is the Louis W. Menk professor of psychology and the director of the Infant and Child Development Center at Northwestern. Co-authors are Brock Ferguson, who completed a Ph.D. at Northwestern and worked on the study; and Alexander LaTourrette, who completed a Ph.D. at Northwestern and is now assistant professor of psychology at the University of Southern California.

"The study is significant because it helps us to understand what capacities the human mind is furnished with from the start and how infants use those capacities to identify important sources and signals for learning," Waxman said.

Sine-wave tone signals were chosen as a control in the studies because prior research has shown tones on their own are neutral and can't help babies in categorization or other tasks. They also knew from their previous research, that it is possible to confer communication status to tones.

Surprising findings

In this study, six-month-old babies were first introduced to novel tone sequences presented in a short animated video featuring two non-human agents—a triangle and a circle. Next, infants participated in a learning task. If the cues provided in the videos were sufficient to permit infants to infuse the tones with communicative status, then they should recruit tone signals later, using them to advance their performance in the subsequent learning task.

In part one of the study, the video showed a conversation between two agents, one agent producing tone sequences, and the other speaking English sentences. In part two, the English sentences were replaced with tone sequences. In part three, only one of the two agents moved, and did so in perfect temporal synchrony with the tone sequences, as if producing them. In part four, the same agent moved out, but the synchrony between the agent's movement and the tone sequences was disrupted.

The researchers were surprised to find the babies were able to elevate the signals to communication status in all three conditions in which the signal was produced synchronously with the motion of the agent.

"Even in the third video where one agent sat like a bump on a log, and the other bounced and beeped, the exposure still helped assign meaning to the tone," Waxman said.

"This is an important finding: When we provided cross-modal synchrony between the tones and the agents' motions, infants spontaneously elevated tone signals to communicative status. We think that when we disrupted this synchrony between different senses, we were effectively 'telling' the baby that the sounds were not produced by the agent, a potential source of learning."

What are the implications?

This study showed, for the first time, that the remarkable human capacity to elevate signals other than language to communicative status does not develop late and does not require a fully developed linguistic system as a foundation. Instead, this flexibility is available to infants from the beginning of language acquisition.

The study specified with precision what makes nonlinguistic signals communicative. It also opens new avenues for research, including tracing how an infant's own experience with other candidate communicative signals, like pointing and eye-gaze, yield downstream advantages for learning.

"This work offers valuable insights into theories of language acquisition. But equally important, it holds promise for designing effective interventions for infants and young children facing developmental delays and impairments," Waxman said.

More information: Brock Ferguson et al, Six-month-old infants use cross-modal synchrony to identify novel communicative signals, Scientific Reports (2024). DOI: 10.1038/s41598-024-78801-9

Journal information: Scientific Reports 

Provided by Northwestern University