Words influence cognition well before infants know their meanings. For example, three-month-olds are more likely to form visually based categories when exemplars are paired with spoken words than with sine-wave tones, a likely precursor to learning symbolic relations between words and their referents. However, it is unclear why words have these effects. In 3 experiments we tested the hypothesis that exaggerated "showing" gestures used when naming objects, and the resultant cross-modal synchrony between a name and object motion, can affect object categorization. Participants were 119 3-month-old infants (56 were female and 63 were male). According to caregiver report, the sample was composed of European American (N = 114) Black (N = 6), Hispanic (N = 2) and multiracial (N = 6) infants. Participants were growing up predominantly in homes with at least 1 parent who completed a college education or a higher degree (80%), and the remaining 20% completed high school. After replicating evidence that words and tones have different effects on categorization, we found that prefamiliarizing infants with tone-object synchrony leads tones to influence categorization as words do. Moreover, we found that concentrated experience with word-object synchrony enhances the effects that words themselves have on categorization. Thus, temporal structure within caregivers' communicative behaviors may lead words to facilitate categorization, and ultimately to aid in forming symbolic representations.