91 Planning Abilities as a Dynamic Perceptual-motor Skill Chapter 6 Planning Abilities as a Dynamic Perceptual-motor Skill: an Actualist Study of Different Levels of Expertise Involved in Stone Knapping The evolution of lithic industries is supposedly bound to the evolution of this capacity to elaborate mental schemes. It is therefore argued that since lithic industries reflect our ancestors’ planning and decision-making abilities, they can be used to directly assess the latter’s mental capacities or ‘intelligence’. In a previous experiment with Indian stone-bead knappers, the question of the role of planning capaci- ties for stone knapping has been raised through the analysis of the course of action followed by craftsmen to obtain truncated ellipsoid beads (see Bril et al. this volume). Courses of action are the observable suc- cession of sub-goals performed in order to actualize knapping methods in particular contexts, that is on stones whose properties are not standard. Knapping methods are here defined as an orderly set of function- al operations aimed to transform a pebble into a bead. Valentine Roux & Eva David In order to get a better understanding of the role of planning abilities in stone knapping as well as on the dynamic of their emergence, an actualist study has been conducted in India where stone beads are still knapped according to a traditional technique. The course of action aimed at transforming pebbles into parallelepipedals is studied for subjects with different levels of expertise. Patterning of planning is investigated through the following points: the ordering of the operations, the variability at both the intra- and inter-subject levels and the temporal structure of the sequences. Results show that the knapping expertise results from a dynamic involving interaction between the elementary movements, perceptual information and planning. The elementary movements are tuned according to the goal of the knapper, here the quality of the beads. Perception of the stone characteristics and adjustment of the subgoals to the final goal depend on this regulation. The same way, data on apprentice- ship suggest that planning should be construed as a perceptual-motor skill emerging from action and perception. This result has direct implications for studying evolution of lithic industries. In particular, it appears that technical actions as expressed by lithic industries should be considered as complex phenomena whose actualization is not reducible to a sole prime mover alleged to be the development of planning abilities. Prehistoric stone tools are commonly looked upon as the evidence from which inferences about our ances- tors’ cognitive abilities can be drawn. According to a very broad evolutionary scheme, Oldowan technology supposedly reflects the mental capacities of extant apes, whereas the later Acheulean industries betoken the ability to elaborate mental schemes, the complexity of which increases with Middle Palaeolithic technologies (e.g. Ambrose 2001; Pelegrin 1993; Wynn 2002). Mental schemes are thought to be crucial to the execution of complex efficient knapping sequences. Not only are they supposed to exist prior to the manufacture of the tool, but also to guide the course of action. As stated by Keller (2002, 117): ‘Monitoring the progress of each piece requires constant comparison of mental images of the goal form, as well as appropriate intermediate shapes, with the actual state of the work piece’.