Artificial intelligence. Autonomous mental development by robots and animals.
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Animals↗
Biomedical subjects
E Thelen
Publications and source records attributed to E Thelen.
The role of target distinctiveness in infant perseverative reaching.
From a dynamic systems perspective, perseverative errors in infancy arise from the interaction of the perceptual cues with the memory of previous actions. To evaluate this account, we tested 9-month-old infants in a task in which they reached for two targets. Experimenters repeatedly cued the first target, which always matched the background (A), and then cued the second target, which varied in its distinctiveness (B). We predicted that a sufficiently distinctive B target would lessen perseverative responding. Results showed that infants perseverated when reaching for two identical targets, but that they made nonperseverative responses when reaching in the presence of a highly distinctive B target. Reach direction on each trial was jointly determined by the distinctiveness of the target, the immediately preceding perceptual events, and the history of reaches in the task.
Child Development↗
The dynamics of embodiment: a field theory of infant perseverative reaching.
The overall goal of this target article is to demonstrate a mechanism for an embodied cognition. The particular vehicle is a much-studied, but still widely debated phenomenon seen in 7-12 month-old-infants. In Piaget's classic "A-not-B error," infants who have successfully uncovered a toy at location "A" continue to reach to that location even after they watch the toy hidden in a nearby location "B." Here, we question the traditional explanations of the error as an indicator of infants' concepts of objects or other static mental structures. Instead, we demonstrate that the A-not-B error and its previously puzzling contextual variations can be understood by the coupled dynamics of the ordinary processes of goal-directed actions: looking, planning, reaching, and remembering. We offer a formal dynamic theory and model based on cognitive embodiment that both simulates the known A-not-B effects and offers novel predictions that match new experimental results. The demonstration supports an embodied view by casting the mental events involved in perception, planning, deciding, and remembering in the same analogic dynamic language as that used to describe bodily movement, so that they may be continuously meshed. We maintain that this mesh is a pre-eminently cognitive act of "knowing" not only in infancy but also in everyday activities throughout the life span.
Child Development↗
A multimuscle state analysis of adult motor learning.
We introduce a new EMG state analysis to test two competing hypotheses about the role of muscle coactivity in learning a complex, multijoint reaching movement. Following Bernstein, one hypothesis is that as a task is learned, coactivity should decrease as degrees of freedom are released and limb stiffness is reduced. An alternative hypothesis is that as movement speed increases with learning, muscle coactivity should increase, possibly to stabilize joints against high inertial forces. Three participants performed a vertical reaching movement identical to that used by Schneider et al. We monitored the activity of four arm and shoulder muscles as participants completed 100 practice trials. Each frame of EMG activity was assigned to one of 16 possible combinations of the four monitored muscles based on an on-off activation threshold. This analysis yielded a time-based summary of muscle coactivity during the movement and across practice trials. Results of the state analysis supported the second hypothesis. As participants decreased their movement times over practice, coactivity increased - participants used more three- and four-muscle coactivity states. Changes were especially dramatic during the braking phase of the Up and Down portion of the vertical movement. When participants performed deliberately slow movements after speeded practice, three- and four-muscle coactivity was suppressed. We suggest that increased use of muscle coactivity may serve to counteract unwanted rotational forces generated during fast movements.
Adult↗
Knowing in the context of acting: the task dynamics of the A-not-B error.
The A-not-B error is one of the most robust and highly studied phenomena in developmental psychology. The traditional Piagetian interpretation is that the error reflects the immaturity of infants' understanding of objects as permanent entities. More recently, the error has been interpreted in terms of changes in representation, in memory, in spatial knowledge, and in inhibitory processes. Each account may be partially right but none offers a unified account of the many accumulated facts about this error. This article presents and tests a new unified explanation. The authors propose that the perseverative reach back to A is the product of the processes that take a hand to a location in visual space: the body-centered nature of the spatial code, memories for previous reaching activity, and the close coupling of looking and reaching. The results from 6 experiments support this explanation. The results are used to challenge the idea of knowledge independent of and distinct from behavior.
Analysis of Variance↗
An unlearned principle for controlling natural movements.
Recently, Gottlieb and colleagues discovered a linear relation between elbow and shoulder dynamic torque in natural pointing movements in the sagittal plane. The present study investigates if the process of learning to reach involves discovering this linearity principle. We inspected torque data from four infants who were learning to reach and grab a toy in front of them. In a longitudinal study, we collected data both in the period before and after they performed their first successful reaches. Torque profiles at the shoulder and elbow were typically multipeaked and became more and more biphasic toward the end of the first year of life. Torques at the shoulder and elbow were correlated tightly for movements in the prereaching period as well as for reaches later in the year. Furthermore, slopes of a regression of shoulder dynamic torque on elbow dynamic torque were remarkably constant at a value approximately 2.5-3.0. If linear synergy is used by the nervous system to reduce the controlled degrees of freedom, it will act as a strong constraint on the complex of possible coordination patterns for arm movement early in life. Natural reaching movements can capitalize on this constraint because it simplifies the process of learning to reach.
Aging↗
Lateral biases and fluctuations in infants' spontaneous arm movements and reaching.
The development of hand preference in infant reaching is marked by several lateral fluctuations. This study investigated whether similar lateral fluctuations were present in infants' spontaneous, nonreaching, and freely performed movements. We collected reaching and nonreaching movements kinematics in 4 infants that we followed longitudinally during their 1st year. In their 4th year, we assessed the direction of their hand preference. We found that lateral biases in spontaneous, nonreaching movements in the 1st year showed several shifts that were similar to those observed in reaching. Despite these shifts, all 4 infants traversed a short period of right-handedness. This right-handedness matched the direction of their hand preference at 3 years of age. We propose that shifts in the development of hand preference in the 1st year are linked to successive reorganizations of the motor system. These reorganizations take place as infants learn to sit, crawl, and walk.
Arm↗
Postural control during reaching in young infants: a dynamic systems approach.
We conceptualize the coordinated development of posture and reaching within Schöner's (Ecological Psychology, 7:291-314, 1995) dynamic model of coupled levels of control: load, timing, and goal. In particular, the goal of postural stability must be maintained during a reach. Using longitudinal data from four infants followed from 3 weeks to 1 year, we show that coordination of the head with upper and lower arm activity is critical for successful reaching. First, infants acquire stable head control several weeks before reaching onset. Furthermore, reaching onset is characterized by a reorganization of muscle patterns to include more trapezius and deltoid activity, serving to stabilize the head and shoulder and provide a stable base from which to reach. We argue that initially, the system is working on postural stability and reaching as goals. Infants secondarily select appropriate muscle patterns to achieve those goals depending, in part, on their individual body sizes, body proportions and energy levels. Motor development proceeds as a continual dialogue between the nervous system, body, and environment.
Humans↗
Training infant treadmill stepping: the role of individual pattern stability.
In this study, we investigated the responsiveness of a developing neuromotor system to training: When is training effective and when are the effects specific to the training condition? Eight infants, six 3-month-olds and two 7-month-olds, received month-long daily training on either a fast-running treadmill, a slow-running treadmill, or a stationary treadmill. Two additional 3-month-old infants served as controls and received no training. Results showed that training led to an increased number of steps. This improvement was inversely related to initial performance: Training had more effect on infants that initially performed unstable stepping patterns. Furthermore, training facilitated the transition from multiple stepping patterns to more alternate stepping. Again, initial pattern preferences influenced these effects of training and often remained visible throughout training. Infant's responses to training at specific speeds were less clear-cut, but some indications were found that this also depended on their initial performances as well as on the characteristics of training. In general, when initial performances corresponded to the training condition, they were strengthened. When they were different from the training condition, training effects generalized to other speeds. These results suggest that the developing neuromotor system is amenable to training whenever performance is unstable, and that training effects interact with the individual's initially preferred patterns. These results are consistent with a dynamic systems view of motor development.
Analysis of Variance↗
The developmental origins of bimanual coordination: a dynamic perspective.
Patterns of interlimb coordination associated with infant reaching fluctuate frequently over developmental time. This study investigated whether these fluctuations are related to coordination tendencies. Interlimb patterns were studied in reaching and nonreaching movements in 4 infants, which were followed through their 1st year. Each week, reaching and nonreaching endpoint kinematics were recorded in both arms during multiple 14-s trials. It was found that patterns of interlimb coordination in reaching matched coordination tendencies in nonreaching. Reaching fluctuated between uni- and bimanual periods. During the bimanual periods, nonreaching interlimb activity tended to be synchronous. During the unimanual periods, nonreaching activity revealed no predominant form of interlimb coordination. It is argued that changing coordination tendencies may influence the organization of specific goal-oriented behaviors from early in life.
Female↗
Development of reaching during the first year: role of movement speed.
When infants first learn to reach at about 4 months, their hand paths are jerky and tortuous, but their reaches become smoother and straighter over the first year. Here the authors consider the role of the underlying limb dynamics, which scale with movement speed, on the development of trajectory control. The authors observed 4 infants weekly and then biweekly from reach onset to 1 year. Improvements in trajectories were not linear, but showed plateaus and regressions in straightness and smoothness. When infants' nonreaching movements were fast, their reaches were also fast, and faster reaches were also less straight. This is consistent with an equilibrium trajectory form of control, where development involves the increasing ability to stabilize the trajectory against self-generated movement perturbations.
Female↗
[Preparation for colonoscopy: a reliable and easily implemented regimen].
Three different colonoscopy preparation methods were tested in 150 out-patients who received colonoscopies, 50 in each group, a randomized prospective simple blind study. The original Golytely-recepture with three litres of liquid was tested against Clean Prep which has to be dissolved in four litres of liquid. Both receptures had the same isotonic salt solutions. The third group was a method with a laxans (X-Prep) including eating restriction lasting three days. The judgment criteria were the cleanliness of the bowel, the formation of foam and the subjective sensitivity of the patient during the preparation phase. The preparation with the three bags containing three litres of Golytely solution according to the original recepture proved to be the least troublesome for the patients and was the most efficient method when it came to cleanliness and the formation of foam. The costs of this preparation methods were lower than those of the other methods.
Administration, Oral↗
Motor development. A new synthesis.
The study of the acquisition of motor skills, long moribund in developmental psychology, has seen a renaissance in the last decade. Inspired by contemporary work in movement science, perceptual psychology, neuroscience, and dynamic systems theory, multidisciplinary approaches are affording new insights into the processes by which infants and children learn to control their bodies. In particular, the new synthesis emphasizes the multicausal, fluid, contextual, and self-organizing nature of developmental change, the unity of perception, action, and cognition, and the role of exploration and selection in the emergence of new behavior. Studies are concerned less with how children perform and more with how the components cooperate to produce stability or engender change. Such process approaches make moot the traditional nature-nurture debates.
Aptitude↗
Treadmill stepping in infants born prematurely.
Premature infants stepped on a treadmill as early as 1-month corrected age and they performed more coordinated alternate steps than their full-term peers. Twelve low-risk premature infants were observed at 1-, 6- and 9-months corrected-age. The infants were supported on a treadmill for five 20-s trials at three speeds. The following data were analysed from the video records: (1) Leg postures in treadmill-moving and non-moving trials, (2) various parameters of limb position and movement during each step cycle, and (3) multiple anthropometric measures. Premature infants at all ages performed coordinated alternating steps which responded to changes in speed. The premature infants had more extended leg postures during non-stepping analysis than they did once the swing was initiated. Low-risk premature birth did not interfere with the neuromotor pathway. Experience out-of-utero may have facilitated stepping.
Anthropometry↗
Proximal control of fetal rat behavior.
We examined the influence of the amniotic sac on spontaneous movement in late gestation fetal rats. Using techniques for in vivo observation of fetal behavior, Day 21 rat fetuses were exteriorized from the uterus, with umbilical connections to the dam intact, and videotaped for 15 min either: (a) through the intact amniotic membranes, or (b) following removal of the membranes. Analysis of fetal behavior categories replicated the findings of previous investigators: Movements of the head, forelimbs, and rearlimbs were significantly increased by sac removal, as was the total frequency of behavior categories and the simultaneous occurrence of different behavior categories. Frame-by-frame analysis of videotaped behavior revealed that amniotic sac removal increased the frequency of movement bouts without altering the overall amount of time that fetuses spent moving. Movement bout durations ranged from 50 msec to 70 s. The average duration of movement bouts was significantly reduced for fetuses lacking the amniotic sac as compared to fetuses within the sac, as was the overall distribution of movement bout durations. Frequency distributions of movement bout durations and interbout interval (IBIs) revealed that sac removal significantly increased the occurrence of short (1-2 s) movement bouts and reduced the frequency of protracted movement bouts and interbout intervals (> 10-s duration). Taken together, these findings indicate that the quantitative dimensions of fetal rat movements are influenced by proximal features of the uterine environment. During prenatal life, the amniotic sac appears to sustain movement, possibly by providing proprioceptive feedback or physical support to the fetus, or by regulating the chemical milieu.
Animals↗
Exploration and selection in the early acquisition of skill.
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Aging↗
The transition to reaching: mapping intention and intrinsic dynamics.
The onset of directed reaching demarks the emergence of a qualitatively new skill. In this study we asked how intentional reaching arises from infants' ongoing, intrinsic movement dynamics, and how first reaches become successively adapted to the task. We observed 4 infants weekly in a standard reaching task and identified the week of first arm-extended reach, and the 2 weeks before and after onset. The infants first reached at ages ranging from 12 to 22 weeks, and they used different strategies to get the toy. 2 infants, whose spontaneous movements were large and vigorous, damped down their fast, forceful movements. The 2 quieter infants generated faster and more energetic movements to lift their arms. The infants modulated reaches in task-appropriate ways in the weeks following onset. Reaching emerges when infants can intentionally adjust the force and compliance of the arm, often using muscle coactivation. These results suggest that the infant central nervous system does not contain programs that detail hand trajectory, joint coordination, and muscle activation patterns. Rather, these patterns are the consequences of the natural dynamics of the system and the active exploration of the match between those dynamics and the task.
Arm↗
Developmental biodynamics: brain, body, behavior connections.
This special section, Developmental Biodynamics: Brain, Body, Behavior Connections, celebrates a renewed and revitalized interest in the study of motor development. The renewed interest has been sparked by advances in the neurosciences, biomechanics, and behavioral sciences and, importantly, in the attempts to integrate theories and findings across these disciplines. In this introduction to the special section, we consider the contributions that have led to a reinvigorated field of motor development and to its new interdisciplinary look. We highlight the papers in the special section by discussing how they illustrate related advances across research in the neurosciences, biomechanics, and behavioral sciences and how progress across these domains has come to define and characterize the emerging field of developmental biodynamics.
Biomechanical Phenomena↗