Infant's emotional variability associated to interactive stressful situation: a novel analysis approach with Sample Entropy and Lempel-Ziv Complexity

The purpose of the study was to examine to which extent a lack of mother’s communicative input is associated to variability of infant’s behavioral and emotional states at microtemporal level. Two non-linear signal-processing statistical metrics were used as regularity indexes during both normal and stressful interactive situations (Face-to-Face Still-Face paradigm). The first one, Sample Entropy estimates the presence of similar states epochs in data-series, according with a moment-to-moment analysis. The second, Lempel-Ziv Complexity, evaluates the occurrence and recurrence of analogous states patterns along the data sequence. Fourteen mothers and their healthy full-term 7-months-old infants were videotaped. Infants’ socio-emotional behaviors were coded off-line micro-analytically using. a .20 s time sampling method. During maternal still-face episode, when infants confronted with the perturbation of their unresponsive caregiver, both regularity indexes were lower than in normal interactions. Findings provide evidence that, during a stressful interactive situation, non-linear techniques allow to detect inherent variability in infant’s states better than linear methods traditional approach (i.e., time- and frequency-domain analyses).