Contingency-based reinforcement of human vocalization: A review of empirical findings

Vocal development research has focused on auditory feedback-based and statistical learning mechanisms, with less attention on reinforcement principles. This review examines the effects of contingent feedback on human vocal development using reinforcement learning frameworks, based on an analysis of 70 empirical studies. A literature search using the terms "vocal learning," "vocal reinforcement," and "vocal contingency" identified three study categories: contingent imitation effects (12 studies), other contingent feedback effects (33 studies), and additional contingent feedback effects (21 studies). Analysis using the antecedent-behavior-consequence framework revealed that contingent responses increase vocal production rates and modify vocal quality, with contingent imitation being especially effective. Three effects accompany the increase in target behavior, including phonological change, collateral increase, and preparatory learning. Evidence also demonstrates other effects of contingent feedback, such as enhanced object recognition learning and longitudinal language development outcomes. In sum, empirical studies show that contingent feedbacks on human vocal behavior have reinforcement effects, a positive correlation with vocalization rate, and longitudinal effects on development. Thus, vocal learning is not merely imitative or developmental, but also shaped by structured environmental feedback.