<p>Sustained attention, the ability to direct and maintain attentional focus on tasks and stimuli, emerges during infancy and undergoes rapid development throughout early childhood. Abnormal patterns of sustained attention are implicated in several childhood psychological disorders. Improving our measurement of infant sustained attention may clarify how child psychopathology develops and inform targeted prevention and early intervention efforts. While several behavioral and psychophysiological measures index infant sustained attention, previous studies have employed these measures in isolation, focused on analyses at short timescales of milliseconds to a few seconds, and examined synchronous associations among these measures. Therefore, the associations and temporal relationships across multiple, concurrent behavioral and psychophysiological measures of infant sustained attention remain unclear, particularly at long timescales. The present study assessed sustained attention in 12-month-old infants using behavioral (looking), cardiac (heart rate), and neural (theta and alpha oscillations) measures to investigate two temporal aspects of infant sustained attention. First, we examined whether associations among infant sustained attention measures were similar or different across short (1-second) and long (10-second) timescales. Covariation analyses indicated largely similar association patterns among these measures across the two timescales. Second, we evaluated whether specific infant sustained attention measures temporally preceded other measures. Cross-correlation analyses broadly revealed that short-timescale measures exhibited asynchronous temporal relationships, such that looking behaviors preceded neural oscillations that in turn preceded cardiac responses. Our findings highlight the value of considering the temporal dimension when studying and measuring infant sustained attention. Additional multimodal research may yield greater insights into dynamic biobehavioral processes that underlie infant sustained attention and enhance clinical interventions aimed at promoting optimal outcomes for young children with abnormalities in sustained attention.</p>