Emotions in motion: How fear and anger differently influence forward single-step initiation.

The perception of emotional faces plays a critical role in shaping human motor responses. However, the relationship between perceived facial expressions, particularly fear, and approach-related movement remains unclear as prior research often employed ambiguous approach behaviour and tasks requiring emotion identification before action planning, potentially introducing biases from differences in recognition accuracy across emotions. To address these limitations, we examined the effect of emotional (fearful, angry, happy) faces on unambiguous approach-related movement, i.e., forward single-step initiation by using a go/no-go paradigm, in two conditions: a neutral-versus-emotional condition (motor responses depended on whether the face was emotional or neutral), or a face-gender condition. Results showed that the perception of emotional faces impacted forward single-step initiation in the neutral-versus-emotional condition only. More precisely, the motor response was stronger (higher anticipatory postural adjustments amplitude) in front of fearful and happy faces than angry faces, and faster (shorter time to reach the forward velocity peak of the centre of body mass) to fearful than to angry faces. This modulation of approach-related motor response, with facilitation of motor output for fearful relative to angry faces, may reflect a more effective preparation of forward stepping when the emotional information is compatible with the movement. Furthermore, the fact that emotional effects were observed only in the neutral-versus-emotional condition can be interpreted in terms of whether the emotional information was task-relevant or incidental.