Understanding the Point of Chimpanzee Pointing: Epigenesis and Ecological Validity

Abstract— Pointing has long been considered to be a uniquely human, universal, and biologically based gesture. However, pointing emerges spontaneously, without explicit training, in captive chimpanzees. Because pointing is commonplace in captive chimpanzees and virtually absent in wild chimpanzees, and because both captive and wild chimpanzees are sampled from the same gene pool, pointing by captive apes is attributable to environmental influences on communicative development. If pointing by captive chimpanzees is so variably expressed in different rearing environments, this suggests that pointing by humans may also be attributable to situational factors that make pointing effective in certain developmental contexts.     

Role of proprioceptive information in movement programming and control in 5 to 11-year old children

The role of proprioceptive inputs in the control of goal-directed movements was examined, by means of the tendon vibration technique, in 5 to 11-year old children performing a serial pointing task. Children pointed, with movements of various amplitudes and at various positions, by alternating wrist flexions and extensions. Tendon vibration was applied to both agonist and antagonist muscles to perturb relevant muscular proprioceptive inputs during the static or dynamic phase of the task, i.e., during stops on targets or during movement execution. Constant and variable amplitude errors as well as constant position error were evaluated. Vibratory perturbation applied during movement execution resulted in a similar reduction in movement amplitude, yielding an increased constant error in all age groups and a systematic position error in the direction of the movement starting point. Perturbing proprioception during static phases preceding movement resulted in an age-related increase in the variable amplitude error, which was maximal in 5-year old children performing extension movements. The results were interpreted in terms of the use of proprioceptive information in the feedforward and feedback based components of movement control in children. In particular, the results indicated (1) developmental changes in the relative weighting of each component, (2) an increased capacity to move from one strategy to the other, depending on the availability of information, and (3) developmental changes from an alternated to an integrated control of amplitude and position in serial pointing.     

Maternal gestures with 20-month-old infants in two contexts

Speech directed towards young children ("motherese") is subject to consistent systematic modifications. Recent research suggests that gesture directed towards young children is similarly modified (gesturese). It has been suggested that gesturese supports speech, therefore scaffolding communicative development (the facilitative interactional theory). Alternatively, maternal gestural modification may be a consequence of the semantic simplicity of interaction with infants (the interactional artefact theory). The gesture patterns of 12 English mothers were observed with their 20-month-old infants while engaged in two tasks, free play and a counting task, designed to differentially tap into scaffolding. Gestures accounted for 29% of total maternal communicative behaviour. English mothers employed mainly concrete deictic gestures (e.g. pointing) that supported speech by disambiguating and emphasizing the verbal utterance. Maternal gesture rate and informational gesture-speech relationship were consistent across tasks, supporting the interactional artefact theory. This distinctive pattern of gesture use for the English mothers was similar to that reported for American and Italian mothers, providing support for universality. Child-directed gestures are not redundant in relation to child-directed speech but rather both are used by mothers to support their communicative acts with infants.     

Age-related differences in the visual processes implied in perception and action: distance and location parameters

The aim of the two present experiments was to examine the ontogenetic development of the dissociation between perception and action in children using the Duncker illusion. In this illusion, a moving background alters the perceived direction of target motion. Targets were held stationary while appearing to move in an induced displacement. In Experiment 1, 30 children aged 7, 9, and 12 years and 10 adults made a perceptual judgment or pointed as accurately as possible, with their index finger, to the last position of the target. The 7-year-old children were more perceptually deceived than the others by the Duncker illusion but there were no differences for the goal-directed pointing movements. In Experiment 2, 50 children aged 7, 8, 9, 10, and 11 years made a perceptual judgment or reproduced as accurately as possible, with a handle, the distance traveled by the target. Participants were perceptually deceived by the illusion, judging the target as moving although it was stationary. When reproducing the distance covered by the target, children were unaffected by the Duncker illusion. Our results suggest that the separation of the allocentric visual perception pathway from the egocentric action pathway occurs before 7 years of age.     

Age-related differences in the integration of sensory information during the execution of a bimanual coordination task

Young (n = 7) and elderly (n = 7) subjects performed bimanual coordination patterns in the transverse plane according to the in-phase or antiphase mode. Sensory information was manipulated through visual (with or without vision of the limbs) and proprioceptive input (with or without vibratory stimuli on one limb). Movement patterns with vibrations showed higher deviations from the intended relative phase than did those without vibrations. This finding suggests that the proprioceptive information induced by the vibrations and the movement interfered, leading to a disruption of the coordination patterns. In addition, as compared with the elderly, the young subjects performed more stable movements under normal circumstances but were more strongly affected by vibratory stimuli during the performance of in-phase movements. During antiphase movements, both age groups experienced a decrease of pattern stability. Furthermore, the absence or presence of visual feedback influenced the performance of the young subjects more than that of the elderly. The presence of vision led to stable in-phase movements, whereas a decrease of pattern stability was observed for antiphase movements. In general, these results demonstrate that manipulation of feedback sources affects young subjects more than elderly ones, and this can be related to a reduced sensory sensitivity as a function of aging.     

Development of self-recognition in chimpanzees (Pan troglodytes).

Chimpanzees (Pan troglodytes) demonstrate the ability to recognize themselves in mirrors, yet investigations of the development of self-recognition in chimpanzees are sparse. Twelve young chimpanzees, grouped by age, were given mirror exposure and tested for self-recognition and contingent movement. All 6 juveniles, 4 and 5 years old, exhibited mirror-guided, mark-directed behavior and clear evidence of self-recognition. In contrast, among the infants, only the oldest group of 2 1/2-year-olds exhibited clear evidence of self-recognition. All chimpanzees exhibited both self-directed behaviors and contingent movements. These results suggest that self-recognition occurs at a slightly older age in chimpanzees than in human infants. In humans, self-recognition is linked with other cognitive abilities. The results conform to the general pattern that great apes exhibit many cognitive skills comparable to those of 2-year-old humans.     

Control of Rapid Arm Movements When Target Position Is Altered During Saccadic Suppression

This experiment examined whether rapid arm movements can be corrected in response to a change in target position that occurs just prior to movement onset, during saccadic suppression of displacement. Because the threshold of retinal input reaches its highest magnitude at that time, displacement of the visual target of a saccade is not perceived. Subjects (N = 6) were instructed to perform very rapid arm movements toward visual targets located 16, 20, and 24 degrees from midline (on average, movement time was 208 ms). On some trials the 20 degrees target was displaced 4 degrees either to the right or to the left during saccadic suppression. For double-step trials, arm movements did not deviate from their original trajectory. Movement endpoints and movement structure (i.e., velocity-and acceleration-time profiles) were similar whether or not target displacements occurred, showing the failure of proprioceptive signals or internal feedback loops to correct the arm trajectory. Following this movement, terminal spatially oriented movements corrected the direction of the initial movement (as compared with the single-step control trials) when the target eccentricity decreased by 4 degrees. Subjects were unaware of these spatial corrections. Therefore, spatial corrections of hand position were driven by the goal level of the task, which was updated by oculomotor corrective responses when a target shift occurred.     

Resolving power of the perceptual- and sensorimotor systems in 6- to 10-year-old children

Children aged 6 to 10 were tested on their ability to move accurately and to perceptually evaluate their motor response. Subjects performed a directional and an amplitude visuo-manual aiming task without vision of their moving limb. They were asked to correct their error, after completion of their movements, only if they felt they were not accurate. Terminal aiming errors and correction responses (adjustments) were analyzed, and threshold detection was determined relative to terminal aiming error. Action accuracy and evaluation of action accuracy are two abilities that do not develop synchronously. Moreover, the relationship between these abilities depends on whether accuracy and direction or amplitude are required. Amplitude undergoes more corrections than direction, suggesting that the spatial system of reference involved depends more upon the coding of the final position than on direction. Two spatial comparators, operating on the basis of two types of evaluation, seem to have a variably distinct contribution to movement and perception accuracy, according to age.     

Eyetracking for two-person tasks with manipulation of a virtual world

Eyetracking facilities are typically restricted to monitoring a single person viewing static images or prerecorded video. In the present article, we describe a system that makes it possible to study visual attention in coordination with other activity during joint action. The software links two eyetracking systems in parallel and provides an on-screen task. By locating eye movements against dynamic screen regions, it permits automatic tracking of moving on-screen objects. Using existing SR technology, the system can also cross-project each participant’s eyetrack and mouse location onto the other’s on-screen work space. Keeping a complete record of eyetrack and on-screen events in the same format as subsequent human coding, the system permits the analysis of multiple modalities. The software offers new approaches to spontaneous multimodal communication: joint action and joint attention. These capacities are demonstrated using an experimental paradigm for cooperative on-screen assembly of a two-dimensional model. The software is available under an open source license.