Perceiving tools: visual attention during Lower Paleolithic stone tool exploration

Abstract

Humans evolved specializations to integrate tools into their cultural, perceptive and cognitive systems. Tools extend cognitive functions beyond the brain and directly improve the range of our cognitive skills. A characteristic of human beings is their hand-eye coordination, associated with a specialized visuospatial system. In fact, parietal lobes, larger and more complex in modern humans, are involved in the management of the relationships between brain, body and environment. Tools activate brain motor regions even during passive viewing. When a tool is touched, it is integrated into the body scheme, expanding the peripersonal space. Recently, different disciplines have adopted an embodied cognition perspective arguing that physical tools should be considered as a functional part of the cognitive network. Vision is the dominant source of sensory information in primates, channelling action and body-environment relationships. We applied eye-tracking technology to investigate visual perception during human interaction with Lower Paleolithic stone tools. We quantified visual attention during a free exploration of stone tools in peripersonal space and during tool physical manipulation. Our results suggest that choppers are usually more explored at the upper region and cortex, while handaxes receive more attention at the base and edges. We can consider whether choppers, displaying a simpler morphology, may require less attention associated with the grasping strategy, while handaxes, with a more complex profile and more grasping and use possibilities, may need a finer exploration of its base. That differences during visual exploration are the same whether or not the tools are physically manipulated, suggesting haptic exploration simply serves visual perception, without influencing the visual exploration scheme. The analysis of visual behaviour associated with these affordances can supply information on the early steps of this brain-body-tool interaction, evidencing common factors as well as type-specific perceptual differences.