Gesture,thoughtandspatiallanguage * Gesture 1:1 (2001), 35–50. issn 1568–1475 © 2001 John Benjamins Publishing Company Karen Emmorey and Shannon Casey The Salk Institute for Biological Studies / University of California, San Diego This study explores the conceptual and communicative roles of gesture by examining the consequences of gesture prevention for the type of spatial language used to solve a spatial problem. English speakers were asked to describe where to place a group of blocks so that the blocks completely filled a puzzle grid. Half the subjects were allowed to gesture and half were pre- vented from gesturing. In addition, half the subjects could see their address- ee and half could not. Addressee visibility affected how reliant subjects were on specifying puzzle grid co-ordinates, regardless of gesture condition. When describing block locations, subjects who were allowed to gesture were more likely to describe block orientation and rotation, but only when they could see the addressee. Further, gesture and speech complemented each other such that subjects were less likely to lexically specify rotation direction when this information was expressed by gesture; however, this was not a deliberate communicative choice because subjects who were not visible to their addressee also tended to leave rotation direction unspecified when they gestured. Finally, speakers produced deictic anaphoric constructions (e.g., “turn it this way”) which referred to their own gestures only when they could see the addressee. Together, these findings support the hypothesis that gesture is both an act of communication and an act of thought, and the results fail to support the hypothesis that gesture functions primarily to facilitate lexical retrieval. Keywords: spatial language, effects of gesture prevention, sign language Spontaneous gestures, particularly representational (iconic) gestures,have been found to be more prevalent when speakers use language with spatial content (e.g., accompanying spatial prepositional phrases) compared to when they do not (Rauscher, Krauss & Chen, 1996). Furthermore, Rauscher et al. (1996) found that when people were prevented from gesturing, their speech was less