Linking language and categorization in infancy.
Brock Ferguson, Sandra Waxman
PMID 27830633WHAT IT FOUND
Across infancy, infants formed object categories while hearing human language, but not while hearing tones or backward speech.
Early on the effect was broad, including lemur calls, then narrowed to speech and specific word types.
Key findings
01Infants who heard novel words formed object categories, while those who heard tones or no-word phrases did not.
02Lemur vocalizations supported object categorization at 3 and 4 months but not at 6 months.
03Exposing 7-month-olds to lemur vocalizations in the lab let them form categories with lemur calls, and showing 6-month-olds a communicative exchange using tones let them form categories with tones.
STILL TO COME
How it was doneWhat they found
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What it does not show
This is a narrative review, not a systematic review or meta-analysis, so it does not report a search strategy, study quality appraisal, or combined results. It reviews infant laboratory studies, not clinical trials, so it does not show what to do with patients. The outcomes measured were object categorization in a lab task, not speech, language, cognition, or therapy outcomes. The article does not provide enough detail about sample sizes, randomisation, blinding, or dropouts for the reviewed studies to judge how solid each study is. Much of the work summarized comes from the authors' own research program, so the review may reflect that line of work.
The easy way to misread this
Do not read this as evidence that exposing infants to speech improves clinical language outcomes. The reviewed studies measured object categorization in laboratory tasks, not speech, language, or therapy results.