The blue-eyed black lemur (Elemur flavirons) may be a close genetic cousin of ours, but these small, lanky tree-dwellers, with their long bushy tails and opposable toes, are sufficiently different that you wouldn’t expect a baby to recognise them as part of the family.
But scientists searching for the boundary line between which animal voices help babies learn – and which don’t – have found that non-human primate calls, like that of the lemur, stimulate human babies’ cognition just as much as human voices do, while birdsong has no notable effect.
The new study, published in PLOS ONE, explored whether birdsong from the zebra finch (Taeniopygia guttata) enhanced three-to-four-month-old babies’ object categorisation abilities (their ability to identify commonalities among objects). The researchers previously found that the lemur calls support this function as effectively as human voices.
The researchers chose to investigate birdsong because songbirds are phylogenetically distinct from humans, but their vocalisations have striking similarities to human voices, including rhythm, changes in duration and intonations.
The study’s finding – that birdsong has no effect on human infant object categorisation abilities – raises future questions about whether the call-cognition connection is limited to primates, or extends further into the animal kingdom, perhaps encompassing all mammals.
The results suggest that the link between language and cognition emerges early, and perhaps reaches back into our evolutionary lineage, linking us with our long-lost primate cousins.
“This new evidence brings us closer to identifying which vocalizations initially support infant cognition,” says senior author Sandra Waxman, a cognitive psychology professor at Northwestern University, US.
“This will shed light on the ontogenetic and phylogenetic antecedents to human language acquisition and its quintessential link to cognition.”
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