Cues to intention: The role of movement information
Introduction
Perception of others’ action is not simply a post-hoc reconstruction of the visual input, but an intrinsically predictive activity. When we observe the movements of other people, we cannot help but anticipate their future course. At the most basic level, from seeing the start of a movement, we can predict how it will end (Frith & Frith, 2006). For instance, by observing a person throwing a dart on a target board, we can predict the landing position of the dart on the board (Knoblich & Flach, 2001). Similarly, we can anticipate the depth of a volleyball or a tennis serve (Abernethy and Zawi, 2007, Abernethy et al., 2008), predict the success of free shots at a basket (Aglioti, Cesari, Romani, & Urgesi, 2008), or determine whether a player is about to throw the ball or mimic a throw (Sebanz & Shiffrar, 2009). In more complex situations, predictive coding allows us to understand others’ intentions and to predict what they will do next (Frith & Frith, 2006). For example, from seeing someone approaching her hand at a cup of coffee, we can anticipate not only the closing of her fingers on the handle, but the intention to drink.
A current controversy concerns the possibility to understand the intention of others by simply observing their movements (Jacob, 2008, Jacob and Jeannerod, 2005, Kilner et al., 2007). It has been proposed that inferences regarding the intentions associated with a movement are made at the start of the movement and tested by predicting how the movement will continue (Wolpert, Doya, & Kawato, 2003). But is information from movement sufficient to make an inference regarding the intention associated with an action? Someone grasping a cup may grasp it to drink, to hand it to another person or to examine the cup itself. Is it possible to understand her intention by simply observing the start of her movement?
In the present research, we investigate how well people can distinguish between social and non-social intentions based on movement information. Specifically, we asked whether by observing the initial phase of a two-stage action, observers would be able to understand whether the movement was associated with a cooperative, competitive, or individual intent. Both cooperation and competition necessitate the ability to anticipate the action of the interacting partner. In cooperative situations, understanding the partner’s intention might be important to optimally adapt to her action in service of a common goal (Sebanz, Bekkering, & Knoblich, 2006). In competitive situations, intention understanding might be equally important to prevent the other person’s move in service of a conflicting goal (Ruys & Aarts, 2010).
We conducted two psychophysical experiments to determine how well observers can discriminate between cooperatively, competitively, and individually motivated actions under temporal and spatial occlusion conditions (Abernethy & Zawi, 2007). In Experiment 1, we used a temporal occlusion procedure to determine whether advance information picked up during the initial phase of the movement allowed observers to infer the model’s intention. In Experiment 2, we examined what kind of cues observers relied upon for the detection of social intentions. This was done by masking selected spatial areas of the video clips representing the model’s movement.
Section snippets
Experiment 1
In most daily life situations, grasping is the initial component of a broader action sequence in which the grasped object is used to achieve a desired goal. For instance, a cup might be grasped with the intention to drink or to clean up the table. It has been demonstrated that although the to-be-grasped object remains the same, movements performed with different end goals are characterized by different profiles of movement (Ansuini et al., 2008, Ansuini et al., 2006, Becchio et al., 2008a)
Experiment 2
Results from Experiment 1 suggest that observers have the ability to pick up and use advance information as to judge the intent associated with a specific movement. However, it remains unclear to which specific source of information observers rely upon as to discriminate between movements associated with different intentions. To explore this issue here we used a spatial occlusion procedure. Visibility to selected spatial areas of the model’s movement was masked so that either the models’
General discussion
A fundamental prerequisite for successful social interaction is the ability to understand the intentions of others. The better we can understand another person’s intention, the more successful our interactions with that person will be (Frith, 2007). In real-life social interactions, multiple cues to intentions are often available: observers can rely – among other cues – on information gathered from the context, as well as on pre-existing contextual information, including information derived
Acknowledgments
This work was supported by a grant from the (MIUR). CB was supported by the Regione Piemonte, bando Scienze Umane e Sociali 2008, L.R. n. 4/2006. We thank Dr. Marco Del Giudice for his advise regarding data analysis.
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