Not a matter of shape: The influence of tool characteristics on electrodermal activity in response to haptic exploration of Lower Palaeolithic tools.

OBJECTIVES: Haptics involves somatosensory perception through the skin surface and dynamic touch based on the proprioceptive response of the whole body. Handling Palaeolithic stone tools influences the arousal and attentional engagement, which can be detected and measured through electrodermal activity. Although tool shape has generally been studied to consider tool functions or tool making, it is also a major factor in tool sensing and haptic perception. The purpose of this survey is to analyze whether the electrodermal reactions are influenced by stone tool morphology. METHODS: We first quantify the morphological variability of 72 stone tools through geometric morphometrics. Then, 12 stone tools from the previous sample were randomly selected to perform the electrodermal analysis in a sample of 46 right-handed adults. RESULTS: Elongation is the main factor involved in Lower Palaeolithic shape variation, followed by the position of the maximum thickness. Attention and manipulation time are mainly influenced by tool size, while arousal mostly correlates with tool weight. Electrodermal activity is apparently not influenced by the overall tool shape. Tool size, weight, and base morphology are the variables that mainly trigger an electrodermal reaction. CONCLUSIONS: Electrophysiological reaction is more sensitive to specific physical features of the tool than to its general outline. These features are not particularly different in worked pebbles and handaxes in terms of grasping, but underwent remarkable changes in other technological traditions. That changes associated with behavioral performances can be employed in cognitive archaeology to investigate the relationships between tool sensing and tool use.

Visual Attention and Cognitive Archaeology: An Eye-Tracking Study of Palaeolithic Stone Tools.

The study of lithic technology can provide information on human cultural evolution. This article aims to analyse visual behaviour associated with the exploration of ancient stone artefacts and how this relates to perceptual mechanisms in humans. In Experiment 1, we used eye tracking to record patterns of eye fixations while participants viewed images of stone tools, including examples of worked pebbles and handaxes. The results showed that the focus of gaze was directed more towards the upper regions of worked pebbles and on the basal areas for handaxes. Knapped surfaces also attracted more fixation than natural cortex for both tool types. Fixation distribution was different to that predicted by models that calculate visual salience. Experiment 2 was an online study using a mouse-click attention tracking technique and included images of unworked pebbles and 'mixed' images combining the handaxe's outline with the pebble's unworked texture. The pattern of clicks corresponded to that revealed using eye tracking and there were differences between tools and other images. Overall, the findings suggest that visual exploration is directed towards functional aspects of tools. Studies of visual attention and exploration can supply useful information to inform understanding of human cognitive evolution and tool use.

Hand morphometrics, electrodermal activity, and stone tools haptic perception.

OBJECTIVES: Tool use requires integration among sensorial, biomechanical, and cognitive factors. Taking into account the importance of tool use in human evolution, changes associated with the genus Homo are to be expected in all these three aspects. Haptics is based on both tactile and proprioceptive feedbacks, and it is associated with emotional reactions. Previous analyses have suggested a difference between males and females, and during haptic exploration of different typologies of stone tools. Here, we analyze the correlation between electrodermal reactions during stone tool handling and hand morphology to provide evidence of possible allometric factors shared by males and females. METHODS: Electrodermal analysis was used to investigate some specific parameters involved in these reactions, such as changes in the level of attention and arousal. We analyzed the responses of 46 right-handed adults to 20 distinct stone tools while blindfolded. RESULTS: Females have smaller hands and a wider range of electrodermal reactions. Within males and females, hand diameters and general hand size do not correlate with the degree of electrodermal level and response. CONCLUSIONS: Sex differences in electrodemal reaction during stone tool handling are apparently not due to the effect of hand size or proportions. Differences between males and females are better interpreted as real sex differences, either due to a biological or cultural influences. Hand size does not influence the degree of arousal or attention during tool exploration, suggesting that other factors trigger individual reactions. These results add to a general cognitive approach on hand-tool evolution and tool sensing.

Electrodermal activity during Lower Paleolithic stone tool handling.

OBJECTIVES: Hand coordination is a key feature in primate evolution at both behavioral and cognitive levels. Humans further improved their manual abilities, and their cognitive niche is deeply associated with hand-tool relationships and technological capacity. A main cognitive change is thought to be related to the transition from Oldowan to Acheulean stone tool technology around 1.7 million years ago. In this survey, we test whether distinct Lower Paleolithic tools induce different electrophysiological reactions during haptic exploration. METHODS: Electrodermal activity is a relatively quick way to measure emotional and attentional changes during specific tasks. We analyzed changes of the electrodermal response and electrodermal level during Oldowan and Acheulean stone tool handling in a sample of 46 right-handed adult subjects with no previous archeological knowledge. RESULTS: Electrodermal proxies for attention and emotion display a skewed distribution. Females present more variable reactions than males and more emotional engagement. Acheulean tools require longer manipulation time and exert less emotional response than Oldowan tools. Attention is influenced by tool length and weight, emotion is sensitive to tool thickness and weight, and manipulation time depends on tool length and width. CONCLUSIONS: This study suggests subtle but detectable perceptual differences when handling Oldowan and Acheulean stone tools. Such variations associated with hand-tool interaction can provide information on haptic and prosthetic capacities associated with our specialized technological resources. Perceptual changes in the archeological record can reveal evolutionary changes in the corresponding body-tool cognitive mechanisms.

Visuospatial Integration and Hand-Tool Interaction in Cognitive Archaeology.

Testing cognitive hypotheses in extinct species can be challenging, but it can be done through the integration of independent sources of information (e.g., anatomy, archaeology, neurobiology, psychology), and validated with quantitative and experimental approaches. The parietal cortex has undergone changes and specializations in humans, probably in regions involved in visuospatial integration. Visual imagery and hand-eye coordination are crucial for a species with a remarkable technological and symbolic capacity. Hand-tool relationships are not only a matter of spatial planning but involve deeper cognitive levels that concern body cognition, self-awareness, and the ability to integrate tools into body schemes, extending the body's functional and structural range. Therefore, a co-evolution between body and technology is to be expected not only in terms of anatomical correspondence but also in terms of cognitive integration. In prehistory, lithic tools are crucial in the interpretation of the cognitive abilities of extinct human species. The shape of tools and the grasping patterns associated with the corresponding haptic experience can supply some basic quantitative approaches to evaluate changes in the archaeological record. At the physiological level, electrodermal activity can be used as proxy to investigate the cognitive response during haptic experiences, revealing differences between tools and between subjects. These approaches can be also useful to evaluate whether and to what extent our complex cognitive resources are based on the capacity to export and delegate functions to external technological components.

Cognitive archeology, body cognition, and hand-tool interaction.

Body cognition and lateralization can be investigated in fossils by integrating anatomical and functional aspects. Paleoneurology cannot provide strong evidence in this sense, because hemispheric asymmetries are shared in all extinct human species, and motor cortical areas are difficult to delineate in endocranial casts. However, paleoneurological analyses also suggest that modern humans and Neanderthals underwent an expansion of parietal regions crucial for visuospatial integration and eye-hand-tool management. Because of our technological specialization, haptic cognition can be particularly targeted by evolutionary processes. Hand-tool relationships can be investigated through physical and physiological correlates. In terms of metrics, size is the main factor of hand morphological variation among adult humans, followed by the ratio between thumb length and palmar size. In modern humans, emotional changes during hand-tool contact can be measured by electrodermal activity. During tool manipulation, electrodermal response, which is a physiological correlate of emotional engagement, shows differences between males and females, and it is different for distinct Paleolithic technologies. Emotional engagement, hand management, and haptic cognition are part of a specialized prosthetic technological capacity of modern humans and can provide indirect evidence of cognitive discontinuities in the archeological record.