Gilles Dietrich

The role of expertise in tool use: skill differences in functional action adaptations to task constraints.

Tool use can be considered a particularly useful model to understand the nature of functional actions. In 3 experiments, tool-use actions typified by stone knapping were investigated. Participants had to detach stone flakes from a flint core through a conchoidal fracture. Successful flake detachment requires controlling various functional parameters simultaneously. Accordingly, our goals were twofold: (a) to examine the regulation of kinetic energy by varying the properties of the hammers and the goal, and (b) to characterize the difference in action regulation across skill levels. All groups were able to modify their actions according to changes in task goals, but only experts displayed fine-tuning to functional parameters (i.e., regulate actions according to changes in hammer weight in a manner that left kinetic energy unchanged). Expertise is considered to depend on the identification of the interactions between functional parameters.

Functional mastery of percussive technology in nut-cracking and stone-flaking actions: experimental comparison and implications for the evolution of the human brain.

Various authors have suggested behavioural similarities between tool use in early hominins and chimpanzee nut cracking, where nut cracking might be interpreted as a precursor of more complex stone flaking. In this paper, we bring together and review two separate strands of research on chimpanzee and human tool use and cognitive abilities. Firstly, and in the greatest detail, we review our recent experimental work on behavioural organization and skill acquisition in nut-cracking and stone-knapping tasks, highlighting similarities and differences between the two tasks that may be informative for the interpretation of stone tools in the early archaeological record. Secondly, and more briefly, we outline a model of the comparative neuropsychology of primate tool use and discuss recent descriptive anatomical and statistical analyses of anthropoid primate brain evolution, focusing on cortico-cerebellar systems. By juxtaposing these two strands of research, we are able to identify unsolved problems that can usefully be addressed by future research in each of these two research areas.

Tool use as a way to assess cognition: how do captive chimpanzees handle the weight of the hammer when cracking a nut?

Tool use in apes has been considered a landmark in cognition. However, while most studies concentrate on mental operations, there are very few studies of apes’ cognition as expressed in manual skills. This paper proposes theoretical and methodological considerations on movement analysis as a way of assessing primate cognition. We argue that a privileged way of appraising the characteristics of the cognitive abilities involved in tool use lies at the functional level. This implies that we focus on how the action proceeds, and more precisely, on how the functional characteristics of the task are generated. To support our view, we present the results of an experiment with five captive chimpanzees investigating the way how chimpanzees adapt to hammers of various weights while cracking nuts. The movement performed in the hammering task is analyzed in terms of energy production. Results show that chimpanzees mobilise passive as well as active forces to perform the compliant movement, that is, they modulate the dynamics of the arm/tool system. A comparison between chimpanzees suggests that experience contributes to this skill. The results suggest that in tool use, movements are not key per se, but only in as much as they express underlying cognitive processes.

Practice of Contemporary Dance Promotes Stochastic Postural Control in Aging

As society ages and the frequency of falls increases, counteracting gait and posture decline is a challenging issue for countries of the developed world. Previous studies have shown that exercise and hazard management help to improve balance and/or decrease the risks for falling in normal aging. Motor activity based on motor-skill learning, particularly dance, can also benefit balance and decreases falls with age. Recent studies have suggested that older dancers have better balance, posture, or gait than non-dancers. Additionally, clinical or laboratory measures have shown improvements in some aspects of balance after dance interventions in elderly trainees. This study examined the impact of contemporary dance (CD) and of fall prevention (FP) programs on postural control of older adults. Posturography of quiet upright stance was performed in 41 participants aged 59–86 years before and after 4.4-month training in either CD or FP once a week. Though classical statistic scores failed to show any effect, dynamic analyses of the center-of-pressure displacements revealed significant changes after training. Specifically, practice of CD enhanced the critical time interval in diffusion analysis, and reduced recurrence and mathematical stability in recurrence quantification analysis, whereas practice of FP induced or tended to induce the reverse patterns. Such effects were obtained only in the eyes open condition. We suggest that CD training based on motor improvisation favored stochastic posture inducing plasticity in motor control, while FP training based on more stereotyped behaviors did not.

How similar are nut-cracking and stone-flaking? A functional approach to percussive technology.

Various authors have suggested similarities between tool use in early hominins and chimpanzees. This has been particularly evident in studies of nut-cracking which is considered to be the most complex skill exhibited by wild apes, and has also been interpreted as a precursor of more complex stone-flaking abilities. It has been argued that there is no major qualitative difference between what the chimpanzee does when he cracks a nut and what early hominins did when they detached a flake from a core. In this paper, similarities and differences between skills involved in stone-flaking and nut-cracking are explored through an experimental protocol with human subjects performing both tasks. We suggest that a ‘functional’ approach to percussive action, based on the distinction between functional parameters that characterize each task and parameters that characterize the agents actions and movements, is a fruitful method for understanding those constraints which need to be mastered to perform each task successfully, and subsequently, the nature of skill involved in both tasks.

The role of head stabilization in locomotion in children with cerebral palsy

OBJECTIVE The objective of the present study was to highlight the role of head stabilization and to analyze multisegment head-trunk coordination during gait in children with cerebral palsy (CP). MATERIAL AND METHOD Postural control was measured and compared in a group of 16 CP subjects and a control group of 16 healthy subjects. The subjects had to walk along an out-and-back course at their freely chosen gait speed. For each gait cycle, motion analysis techniques were used to calculate the amplitude of the head angle (relative to the trunk) in the sagittal and frontal planes. RESULTS Kinematic analysis revealed a number of significant intergroup differences, with a more pronounced variation in the head angle (relative to the trunk) in the CP group than in the control group. There were no significant intergroup differences in terms of the angular amplitude of the head in the sagittal plane. CONCLUSION The greater variability of the head angle in the frontal plane in the CP subjects might reflect the presence of greater head roll as a compensatory strategy. These finding suggest that the clinical evaluation of posture during gait in children with CP should be reconsidered.

Tool use ability depends on understanding of functional dynamics and not specific joint contribution profiles

Researchers in cognitive neuroscience have become increasingly interested in how different aspects of tool use are integrated and represented by the brain. Comparatively less attention has been directed toward tool use actions themselves and how effective tool use behaviors are coordinated. In response, we take this opportunity to consider the mechanical principles of tool use actions and their relationship to motor learning. Using kinematic analysis, we examine both functional dynamics and joint contribution profiles of subjects with different levels of experience in a primordial percussive task. Our results show that the ability to successfully produce stone flakes using the Oldowan method did not correspond with any particular joint contribution profile. Rather, expertise in this tool use action was principally associated with the subjects ability to regulate the functional parameters that define the task itself.

One month of contemporary dance modulates fractal posture in aging

Understanding the human aging of postural control and how physical or motor activity improves balance and gait is challenging for both clinicians and researchers. Previous studies have evidenced that physical and sporting activity focusing on cardiovascular and strength conditioning help older adults develop their balance and gait and/or decrease their frequency of falls. Motor activity based on motor-skill learning has also been put forward as an alternative to develop balance and/or prevent falls in aging. Specifically dance has been advocated as a promising program to boost motor control. In this study, we examined the effects of contemporary dance (CD) on postural control of older adults. Upright stance posturography was performed in 38 participants aged 54–89 years before and after the intervention period, during which one half of the randomly assigned participants was trained to CD and the other half was not trained at all (no dance, ND). CD training lasted 4 weeks, 3 times a week. We performed classical statistic scores of postural signal and dynamic analyses, namely signal diffusion analysis (SDA), recurrence quantification analysis (RQA), and detrended fluctuation analysis (DFA). CD modulated postural control in older trainees, as revealed in the eyes closed condition by a decrease in fractal dimension and an increase in DFA alpha component in the mediolateral plane. The ND group showed an increase in length and mean velocity of postural signal, and the eyes open a decrease in RQA maximal diagonal line in the anteroposterior plane and an increase in DFA alpha component in the mediolateral plane. No change was found in SDA in either group. We suggest that such a massed practice of CD reduced the quantity of exchange between the subject and the environment by increasing their postural confidence. Since CD has low-physical but high-motor impact, we conclude that it may be recommended as a useful program to rehabilitate posture in aging.

Cognitive Style in Attainment of an Upside-Down Posture in Water with and without Vision:

It is well known that adopting a posture required by the central nervous system takes into account a frame of reference. This frame of reference is built on sensory information and, more particularly, on vision, which is often considered to be the main input. The contribution of vision varies by participant and defines their cognitive style. This study investigates the contribution of visual information and cognitive style to postural strategy and, more precisely, to the construction of an upside-down posture in an underwater condition. Eight synchronized swimmers performed the Rod-and-Frame Test (RFT) to assess their cognitive style and practiced upside-down posture in water to measure their body inclination. The Rod-and-Frame Test scores did not distinguish the participants, as the results of the test showed that most of them were visual-field independent. However, in a closed-eyes condition, participants achieved a more precise vertical position than when using translucent goggles.

A Gibsonian Motor Analysis of the Nut-Cracking Technique

Nut-cracking may be described as the action of choosing a stone with one hand, positioning the nut on an anvil with the other hand, and hitting the nut with a ballistic movement. A functional description of the nut-cracking action will consider the mechanical properties that must be satisfied to succeed in the task at hand, that is, the mechanical energy produced through the movement. In the wild, chimpanzees have been observed to select the appropriate tools, that is, size, shape, and material of hammer and anvil, suggesting that chimpanzees do control the functional properties of the nut-cracking task. However, these studies do not analyze how the action is processed. In this chapter, we propose to focus on the chimpanzees’ capacity to perceive the functionality of the tools and on how the functional characteristics of the task are generated. Taking a Gibsonian perspective, we discuss some dimensions of the functional coupling between the animal and its environment as can be seen in a controlled nut-cracking experiment. The behavior of the animal is analyzed at two levels of action: the choice of the best tool that fit the goal, and the capacity of the chimpanzee to adapt his or her behavior to the properties of the tool and of the nut.