Communicative interactions improve visual detection of biological motion

Abstract

Background: In the context of interacting activities requiring close-body contact such as fighting or dancing, the actions of one agent can be used to predict the actions of the second agent. In the present study, we investigated whether interpersonal predictive coding extends to interactive activities--such as communicative interactions--in which no physical contingency is implied between the movements of the interacting individuals.

Methodology/principal findings: Participants observed point-light displays of two agents (A and B) performing separate actions. In the communicative condition, the action performed by agent B responded to a communicative gesture performed by agent A. In the individual condition, agent A's communicative action was substituted with a non-communicative action. Using a simultaneous masking detection task, we demonstrate that observing the communicative gesture performed by agent A enhanced visual discrimination of agent B.

Conclusions/significance: Our finding complements and extends previous evidence for interpersonal predictive coding, suggesting that the communicative gestures of one agent can serve as a predictor for the expected actions of the respondent, even if no physical contact between agents is implied.

Figure 1. Example of a communicative signal trial.

Agent A points to an object to be picked up; agent B bends down and picks it up. B was presented using limited-lifetime technique (6 signal dots) and masked with temporally scrambled noise dots. The noise level displayed is the minimum allowed in the experiment (5 noise dots). To provide a static depiction of the animated sequence, dots extracted from 3 different frames are superimposed and simultaneously represented; the silhouette depicting the human form was not visible in the stimulus display.

Figure 2. Sensitivity (d') in the two experimental conditions.

Error bars represents 95% confidence intervals.

Figure 3. Scatter plot showing the correlation between communicative action identification and d'.

Identification scores are plotted on the ordinate, and represent the percentage of participants who correctly identified A's communicative actions (normative data [12]). The difference between communicative condition and individual condition is plotted on the abscissa (d'). The black line represents the linear regression line fitted to the data.