Emotional consistency as a signal for word learning in early development.

Emotions are critical social signals that guide early learning. However, research has predominantly focused on momentary emotional valence, leaving the influence of dynamic emotional properties, such as consistency over time, largely underexplored. The present study investigated whether informants' emotional consistency shapes toddlers' novel word learning. Toddlers (18-36 months; N = 43) were introduced to two unfamiliar informants: one displaying consistent emotional responses toward objects and another exhibiting variable, inconsistent reactions. Following this exposure, both informants labeled novel objects. Word learning was assessed using the "looking-while-listening" paradigm, and caregivers reported on family emotional expressiveness. Results indicated that toddlers demonstrated reliable learning from the emotionally inconsistent informant, but did not show-above chance learning from the emotionally consistent informant, despite comparable visual attention to both informants during learning. Time-course analyses further revealed that emotional inconsistency prompted a steadier, more robust trajectory of word recognition. Furthermore, individual differences in everyday emotional environments predicted learning outcomes: toddlers from more emotionally expressive families exhibited better learning from the inconsistent informant. These findings challenge the assumption that informant predictability uniformly facilitates social learning. Instead, emotional variability may function as an informative social cue that increases informational salience and promotes deeper cognitive processing. Ultimately, everyday experiences may calibrate toddlers' sensitivity to these dynamic emotional cues.