How humans optimize their interaction with the environment: The impact of action context on human perception Agnieszka Wykowska 1 , Alexis Maldonado 2 , Michael Beetz 2 , and Anna Schub¨ o 1 1 Department of Experimental Psychology, Ludwig Maximilians Universit¨at, M¨ unchen, Germany 2 Computer Science Department, Chair IX, Technische Universit¨at, M¨ unchen, Germany Abstract. Humans have developed various mechanisms to optimize interaction with the envi- ronment. Optimization of action planning requires efficient selection of action-relevant features. Selection might also depend on the environmental context in which an action takes place. The present study investigated how action context influences perceptual processing in action planning. The experimental paradigm comprised two independent tasks: (1) a perceptual visual search task and (2) a grasping or a pointing movement. Reaction times in the visual search task were measured as a function of the movement type (grasping vs. pointing) and context complexity (context varying along one dimension vs. context varying along two dimensions). Results showed that action context influenced reaction times, which suggests a close bidirectional link between action and perception as well as an impact of environmental action context on perceptual selection in the course of action planning. Such findings are discussed in the context of application for robotics. Key words: Action Context, Action Planning, Human Perception 1 Introduction When humans perform a particular action such as, for example, reaching for a cup in a cupboard, they need not only to specify movement parameters (e.g., the correct width of the grip aperture) but also to select movement-related information from the per- ceptual environment (e.g., the size and orientation of the cups handle - but not its color - are rele- vant for grasping). Moreover, the context in which the grasping action is performed may also have an impact on both the action performance and the pre- vailing selection processes of the agent. If the cup is placed among other cups of different sizes and han- dle orientations, selection might be more difficult as compared to when the cup would be placed among plates. In the first case, the context varies along at least two dimensions that are relevant for grasping a cup (size and orientation of handles). In the sec- ond case, the cup is embedded in a homogeneous context also consisting of dimensions irrelevant for grasping a cup (breadth of plates). Therefore, the two environmental contexts might result in different processing speed of the environmental characteris- tics. Several authors have investigated the influence of intended actions on perceptual processes. For ex- ample, Craighero and colleagues [2] showed that when agents were asked to grasp a tilted bar, on- set latencies of their movement depended on the characteristics of a visually presented stimulus that signaled when the movement should begin (a so- called ”go signal” ). If the ”go signal” shared action- related features with the to-be grasped object (e.g., was of the same orientation), the onset of the move- ment occurred faster as compared to the condition when the ”go signal” differed from the to-be grasped object. These results support a close link between perception and action. Similar results were reported by Tucker and El- lis [11]. The authors conducted a study in which participants were presented with natural objects (e.g., grape, cucumber) or manufactured objects (e.g., screw, hammer). The objects could be smaller (grape, screw) or larger (cucumber, hammer) im- plying either precision grip (small objects) or power grip (larger objects). The task was to categorize the objects as natural or manufactured. Half of the par- ticipants had to respond with a power grip to natu- ral objects and precision grip to manufactured ob- jects; the other half had opposite instructions. The results showed that although size of the objects was completely orthogonal to the categorization task, it influenced performance: Precision grips were faster to small objects relative to large objects and power grips were faster to large objects compared to small objects. This suggests that size was implicitly pro- cessed as an action-related feature of an object and, as such, had an impact on behavior. More recent studies demonstrated that visual detection processes are highly dependent on in- tended action types [1] and that the percep- tual system can bias action-relevant dimensions if they are congruent with the performed action [3].