Extended mind and visuo-spatial integration: three hands for the Neandertal lineage.

Visuo-spatial integration is indeed one of the cognitive domains in which humans have clearly undergone evolutionary development (Wynn, 1989, 2010). Our ability to conceive of and organize our actions in space is arguably unmatched among primates. And as Bruner & Lozano explicate, this spatial cognition relies on our ability to generate an " inner virtual space " using neural resources of the IPS and precune-ous, resources that initially evolved for coordination of hands and eyes. The archaeological record suggests that much of this evolutionary development occurred early in hominin evolution, and that the modern ability to generate an inner virtual space was in place by half a million years ago, arguably prior to the split of the Neandertal and human lineages. The earliest evidence for hominin-specific abilities in visuo-spatial integration manifests itself in the first Acheulean bifaces ca. 1.8 million years ago (Lepre et al., 2011; Wynn, 2002). Hominins who knapped bifaces imposed a two-dimensional shape – bilateral symmetry – onto tools. This seemingly simple task required the knapper to coordinate two quite separate streams of visual information – the ventral shape recognition stream, which engages occipital and inferior temporal (fusiform gyrus) resources, and the dorsal spatial location and orientation stream of the parietal lobes. This ability to coordinate shape and space was arguably the initial step in the evolutionary sequence of modern visuo-spatial integration. It seems probable that this development was one consequence of one million years of brain/artifact co-evolution. The earliest confidently dated stone tools are the 2.6 million year old artifacts (Semaw et al., 2003, 2009), and there is indirect evidence (cut-marked bone) from Dikika that dates to 3.4 million (McPherron et al., 2010). The knap-pers at Gona had already developed the classic two-handed knapping gesture in which a dominant hand delivered a well-aimed blow onto a core held in the other hand (Toth et al., 2006). Aimed striking for over one million years acted as a procedural scaffold for the co-evolution of spatial location (core, and later flake, edges) and shape recognition in the form of the finished products. Initially an embodied system of hand-eye coordination, the lithic products acted as visual placeholders of shape information. These physical placeholders were eventually internal-ized into a neural network coordinating space and shape, and one result was early bifaces in which the much older symmetry recognition system was integrated into artifact production. Exactly how this played out in terms …