Emotional modulation of temporal density in natural grasping: a vision-based kinematic study

While emotions affect perception, their influence on physical interaction remains underexplored. This study investigated how the emotional valence of everyday objects manifests in hand kinematics during natural grasping.

Hand movements were recorded from 40 participants using an overhead smartphone camera (1080p; 30 fps), combined with MediaPipe and OpenCV. Participants were randomly assigned to either a Visual Modality (n = 20) or a Non-Visual Modality (n = 20) and were instructed to grasp five objects designed to evoke distinct emotional responses (fear, disgust, neutrality, and happiness). Kinematic measures, including grasping frame rate (frames/s) and hand velocity (px/frame), were extracted alongside self-reported emotional ratings.

Results revealed that motor behavior is not merely functional but emotionally reactive: threat-based objects (e.g., a spider) elicited significantly higher grasping frame rates, indicating more sustained interaction with these stimuli, potentially reflecting heightened monitoring or cautious engagement. A linear mixed-effects model identified a significant Modality × Object interaction, indicating that visual access influenced object-related effects selectively rather than uniformly. Notably, these affect-related changes were captured in grasping frame rate (a temporal-density measure) rather than in hand velocity.

The emotional properties of objects systematically modulate motor behavior during grasping. These findings help bridge the gap between affect and physical action. They also show that consumer-grade smartphone technology can detect subtle variations in natural hand interaction, opening the door for affect-aware interfaces and scalable studies of motor-affective behavior in naturalistic environments.