Single point motion kinematics convey emotional signals in children and adults

Abstract

This study investigates whether humans recognize different emotions conveyed only by the kinematics of a single moving geometrical shape and how this competence unfolds during development, from childhood to adulthood. To this aim, animations in which a shape moved according to happy, fearful, or neutral cartoons were shown, in a forced-choice paradigm, to 7- and 10-year-old children and adults. Accuracy and response times were recorded, and the movement of the mouse while the participants selected a response was tracked. Results showed that 10-year-old children and adults recognize happiness and fear when conveyed solely by different kinematics, with an advantage for fearful stimuli. Fearful stimuli were also accurately identified at 7-year-olds, together with neutral stimuli, while, at this age, the accuracy for happiness was not significantly different than chance. Overall, results demonstrates that emotions can be identified by a single point motion alone during both childhood and adulthood. Moreover, motion contributes in various measures to the comprehension of emotions, with fear recognized earlier in development and more readily even later on, when all emotions are accurately labeled.

Fig 1

Trajectories for the fearful (a), happy (b), and neutral (c) stimuli. (a) After a Translational entrance, the shape jumps, shakes, and goes back down following a Parabolic course; (b) the shape jumps following a Wavelike motion; (c) a neutral Translational series of movements.

Fig 2. Boxplot for speed and acceleration patterns.

The speed distributions are shown on the left, and the acceleration distributions on the right for neutral (1), fearful (2), and happy (3) videos.

Fig 3

(a) Displayed key responses for the fearful (1), happy (2), and neutral (3) conditions. All the response buttons had the same dimension (1.43 x 1.29 cm) and were aligned to the top left and right corners of the screen. (b) Visual display of the experimental procedure, presented with Mouse Tracker. Participants pressed the "Start" button, and the videos appeared at the center of the screen. They were instructed to press the response button that better represented the emotional category of the stimuli by clicking a mouse button. After the response was given, another "Start" button appeared to begin the subsequent trial. No feedback on the accuracy was given to the participants.

Fig 4. RTs observed for the different emotions across age groups.

In the fearful condition, RTs were lower than in both the happy and the neutral conditions, while the happy and the neutral condition did not differ from each other (***p < 0.001). Error bars represent the standard errors of the means (dark grey: fear; light grey: happiness; diagonal lines: neutral).

Fig 5. Results of the ANOVAs performed separately for the three age groups.

In the adult and 10-year-olds groups, faster RTs in the fearful condition compared with the happy and the neutral condition. In the 7-year-olds, lower RTs were observed only for fear compared with happiness (***p < 0.001; **p < 0.01; *p < 0.05). Error bars represent the standard errors of the means (dark grey: fear; light grey: happiness; diagonal lines: neutral).

Fig 6. AUC and MD, Mouse Tracker indexes of the strength of attraction towards the alternative response for the 10-year-old children (the upper line represents responses to the neutral condition; the lower line represents responses to the fear condition).