Sources of Information in Human Action

Sources of Information in Human Action Jeff Loucks (jloucks@uoregon.edu) Department of Psychology, 1227 University of Oregon, Eugene, OR, 97403 USA Dare Baldwin (baldwin@uoregon.edu) Department of Psychology, 1227 University of Oregon, Eugene, OR, 97403 USA for discriminating between everyday, dynamic human actions. What kind of information do people key on, for example, in discriminating a slap from a caress? Although one could analyze the physical motion differences between these two actions, the number of possible points of comparison is immense. Given this computational complexity, it is not at all self-evident which among these physical differences observers actually track and register in the context of actual action processing. With little previous research to guide us, we looked to another domain of research that has explored similar questions regarding sources of information utilized in identification and discrimination – the domain of face processing. Abstract Despite the importance of action identification and discrimination in social cognition, little research has explored how these tasks are accomplished. We investigated whether adults capitalize on local and global sources of information when discriminating human actions. The results of two experiments indicate adults are sensitive to both sources of information in action but selectively attend to local over global information. The findings also parallel what is known about face processing: processing of global information in action is disrupted by inversion, whereas processing of local information is especially reliant on high spatial frequencies. Keywords: Human action; intentions; selective attention; face processing; discrimination; information processing. Faces and Action Research suggests people are sensitive to two main sources of information in faces: salient, local information, and more global, relational information (Maurer, Le Grand, & Mondloch, 2002). Local information is characterized as information about highly defined, local elements of the face, such as the eyes, nose and mouth (sometimes called “features”). In contrast, global information is characterized as information about the spatial relations among these local elements. Faces and action have much in common: processing of both seems to require minimal effort on our part, and efficient processing of both has important consequences for social cognition. Given these similarities, we questioned whether faces and action might also share similar processing characteristics. In particular, we were interested in whether people use local and global sources of information to process human action similar to those used to process faces. Some have argued that this dual processing approach may not be specific to faces, and may develop whenever stimuli are processed with expertise (Diamond & Carey, 1986; Gauthier & Tarr, 1997). In the face processing literature, there is evidence that local and global sources of information are relatively distinct from one another in that they are affected in predictably different ways by different visual manipulations. One such line of evidence is the “face-inversion effect” – the finding that faces are difficult to recognize when turned upside down (Yin, 1969). Research indicates that inversion specifically disrupts the processing of global information while having little to no impact on the processing of local information (Freire, Lee, & Symons, 2000). Presumably the standard global face template people make use of during upright processing is less accessible in the inverted Every day we are witness to the exceptionally complex stimulus that is other people’s behavior. In the face of such complexity, it is striking how readily we make sense of others’ actions, not only registering the surface form of such action, but also gleaning underlying intent. Processing action in this way is essential for everyday functioning and social interaction. Given the centrality of action processing to everyday cognitive and social functioning, it is surprising that there has been little research on the fundamental task of identifying and discriminating human actions. Discrimination is a basic component of action categorization. Although every instance of human action is a unique event, it is likely actions are treated as category members in our processing of the behavior stream. Rapidly discriminating actions on the category level is a skill employed countless times per day in everyday life. Moreover, imitation – a hallmark of human social cognition – requires a finely-tuned analysis of the behavior stream to discriminate between different functional actions. Research on people’s discrimination of point-light action displays has demonstrated that low-level visual information can be used to discriminate some basic actions (Johansson, 1973). However, we still know little about people’s everyday action processing skills. Processing everyday action may differ from processing point-light action, as such events are more complex, unfold over longer periods, and contain additional information about objects and settings. Given the rich information present in everyday action, it would be beneficial to assess what information people are sensitive to in the context of such action. Our goal with the current research was to explore basic kinds of information people extract from the motion stream