As AI has begun to reach out beyond its symbolic, objectivist roots into the embodied, experientialist realm, many projects are exploring different aspects of creating machines which interact with and respond to the world as humans do. Techniques for visual processing, object recognition, emotional response, gesture production and recognition, etc., are necessary components of a complete humanoid robot. However, most projects invariably concentrate on developing a few of these individual components, neglecting the issue of how all of these pieces would eventually fit together. The focus of the work in this dissertation is on creating a framework into which such specific competencies can be embedded, in a way that they can interact with each other and build layers of new functionality. To be of any practical value, such a framework must satisfy the real-world constraints of functioning in real-time with noisy sensors and actuators. The humanoid robot Cog provides an unapologetically adequate platform from which to take on such a challenge. This work makes three contributions to embodied AI. First, it offers a general-purpose architecture for developing behavior-based systems distributed over networks of PC's. Second, it provides a motor-control system that simulates several biological features which impact the development of motor behavior. Third, it develops a framework for a system which enables a robot to learn new behaviors via interacting with itself and the outside world. A few basic functional modules are built into this framework, enough to demonstrate the robot learning some very simple behaviors taught by a human trainer. A primary motivation for this project is the notion that it is practically impossible to build an "intelligent" machine unless it is designed partly to build itself. This work is a proof-of-concept of such an approach to integrating multiple perceptual and motor systems into a complete learning agent.

The objects with which the hand interacts with may significantly change the dynamics of the arm. How does the brain adapt control of arm movements to this new dynamic? We show that adaptation is via composition of a model of the task's dynamics. By exploring generalization capabilities of this adaptation we infer some of the properties of the computational elements with which the brain formed this model: the elements have broad receptive fields and encode the learned dynamics as a map structured in an intrinsic coordinate system closely related to the geometry of the skeletomusculature. The low--level nature of these elements suggests that they may represent asset of primitives with which a movement is represented in the CNS.

The current study revisits the causal link between finite cognitive capacity and infant perseveration originally put forth by Berger (2004) wherein perseverative errors resulted from a limited amount of cognitive resources. A dynamic systems perspective was used to test the interaction of a limited cognitive capacity and task difficulty by manipulating the contextual layout of Berger’s stair A-not-B paradigm (i.e. from 90-degrees to 180-degrees). Two groups of infants, differing in walking experience but not in biological age, were presented the task of descending A-side 5 consecutive times and to B-side on the 6th trial. Perseveration was not seen in either experience group; however, inexperienced walkers exhibited slower decision-making and stair descent on B-trial than their experienced counterparts. Results suggest that task difficulty alone is not enough to elicit perseveration but is a considerable factor when investigating the error.

Children with myelomeningocele (MMC) usually have problems with daily life activities, but the background to their problems is not altogether obvious. An understanding of the possible causes of activity problems is a prerequisite for the effectiveness of physical therapy. The overall aim of the present studies was to identify impairments above the cele level, which might influence mobility in children with MMC (study I) and to analyse sitting posture (study II) and the movement characteristics of reaching movements (study III and IV). In total, 41 children and young adults with MMC and without mental retardation were investigated. Study I comprised 32 children, 6-11 years. Mobility and the caregiver assistance required for mobility were quantified according to the Paediatric Evaluation of Disability Inventory (PEDI) and correlation between mobility and neurological impairment, hand function and cognitive function were calculated. The results showed that nine children achieved independent mobility and that there was a moderate and significant correlation between the need for physical assistance and high cele level, impaired hand function and impaired cognitive function. In those children who used a wheelchair, only poor hand strength was significantly correlated with the need for caregiver assistance. Study II comprised 11 children, 10-13 years, and a control group of 20 healthy children. Sitting posture was investigated by using a force plate and analysed from the frequency and the amplitude of the postural sway. The reaction forces before and during rapid arm lift were also analysed. The result showed that children with MMC had significantly lower sway frequency compared to the controls. In both groups, the ground reaction forces were registered before the children lifted their arms. Study III and IV comprised 31 children and young adults, 9-19 years and 31 matched controls. Reaching movements were investigated with a digitising tablet, linked to a computer. The ability to program and execute reaching movements was analysed and also the ability to adapt reaching to new visuomotor conditions. The results showed that the MMC group had poorer precision, less straight movements and shorter deceleration phases as compared to the controls. In both groups the movements were pre-programmed. In addition, adaptation of reaching to new visuomotor conditions was poor in the MMC group as compared to the controls. In conclusion we found that impairments above the cele level influenced mobility and the control of sitting posture in children with MMC. Reduced precision and co-ordination of reaching, and also difficulties with motor adaptation, could partly explain thier problems with hand activities. These findings need to be considered in therapy programs for children and young adults with MMC.

This thesis presents two studies that investigate how vision is used to control rapid, compensatory reach-to-grasp reactions. Compensatory grasping reactions were evoked in healthy young adults via unpredictable translations of large platforms on which the subjects stood or walked. The first study tracked natural gaze behaviour during responses to unexpected balance perturbations. It provided evidence that, unlike with voluntary movements, the eyes do not lead the hand during balance recovery – subjects relied on ‘stored’ information from central vision, continuously-available peripheral vision, or a combination of these sources to guide the hand. The second study investigated the efficacy of reliance on peripheral vision to guide rapid reach-to-grasp balance-recovery reactions. Peripheral vision was found to guide reach-to-grasp responses with sufficient accuracy to achieve a functional grasp of a relatively small handhold; however, peripherally-guided movements were slower when the handhold was in the extreme periphery.

Head position signal is crucial for preparing reaching movements because it contributes to specifying the position of body and target in space and relative to each other. However, it is unclear whether sensory information pertaining head position is used to control the movement after movement onset. In this study, nineteen participants performed discrete reaches towards a virtual target while neck vibration was randomly applied before and/or during the movement or not at all. The main dependent variable was the directional bias of the reaching finger. Neck vibration induced early leftward or late rightward trajectory biases. It appears that participants interpreted the sensed head shift as a target or an eye-in-head motion, which can be explained by individual differences in the use of reference frames. Nevertheless, body-centered and head-centered frames of reference appear to be important for the early and late stages of a goal-directed movement, respectively.

Head position signal is crucial for preparing reaching movements because it contributes to specifying the position of body and target in space and relative to each other. However, it is unclear whether sensory information pertaining head position is used to control the movement after movement onset. In this study, nineteen participants performed discrete reaches towards a virtual target while neck vibration was randomly applied before and/or during the movement or not at all. The main dependent variable was the directional bias of the reaching finger. Neck vibration induced early leftward or late rightward trajectory biases. It appears that participants interpreted the sensed head shift as a target or an eye-in-head motion, which can be explained by individual differences in the use of reference frames. Nevertheless, body-centered and head-centered frames of reference appear to be important for the early and late stages of a goal-directed movement, respectively.

Two studies investigated the effects of various motor constraints of reaching on infants’ search performance on the A-not-B task. These studies were motivated by the idea that motor memories for reaching lead to A-not-B errors. The 2 motor constraints that were evaluated included barriers that blocked the path of the hand and hand-use preferences. Each of these motor constraints was examined separately. In Experiment 1, infants (N = 40, 20 8-month olds, 20 16-month olds) were given the A-not-B task twice. One condition was analogous to the traditional A-not-B task (i.e., using 2 hiding locations) and the other was modified such that a barrier (i.e., an opaque screen) blocked the infants’ reaching path of location A on A trials only. On A trials, all infants searched correctly less often when a barrier was present, and younger infants searched correctly less often than older infants. On B trials, younger infants made more errors in the no barrier condition, whereas older infants did not show any significant difference in B trial performance across conditions. In Experiment 2, infants (N = 51) completed an adapted handedness test (Michel, Ovrut, & Harkins, 1985) followed by a modified A-not-B task. The test assessed infants’ hand-use preferences for reaching, which was used to group infants into their respective preference group (i.e., consistent or inconsistent). Infants with a consistent preference were randomly assigned to a hiding side group (i.e., A on preferred side or A on non-preferred side). Infants searched correctly more often when hiding side was congruent with their preferred reaching hand, and older infants searched correctly more often than younger infants. On the B trial, neither age nor hiding side affected the production of the A-not-B error. Collectively, these studies present data that address the theory that motor memories for reaching are the cause for the production of A-not-B error. These studies provide novel evidence that motor memories for reaching are present in infants aged 8- and 16-months, and that motor memories can influence the production of such errors in certain A-not-B contexts. Implications and directions for future research are also discussed.

This thesis presents two studies that investigate how vision is used to control rapid, compensatory reach-to-grasp reactions. Compensatory grasping reactions were evoked in healthy young adults via unpredictable translations of large platforms on which the subjects stood or walked. The first study tracked natural gaze behaviour during responses to unexpected balance perturbations. It provided evidence that, unlike with voluntary movements, the eyes do not lead the hand during balance recovery – subjects relied on ‘stored’ information from central vision, continuously-available peripheral vision, or a combination of these sources to guide the hand. The second study investigated the efficacy of reliance on peripheral vision to guide rapid reach-to-grasp balance-recovery reactions. Peripheral vision was found to guide reach-to-grasp responses with sufficient accuracy to achieve a functional grasp of a relatively small handhold; however, peripherally-guided movements were slower when the handhold was in the extreme periphery.

Two studies investigated the effects of various motor constraints of reaching on infants’ search performance on the A-not-B task. These studies were motivated by the idea that motor memories for reaching lead to A-not-B errors. The 2 motor constraints that were evaluated included barriers that blocked the path of the hand and hand-use preferences. Each of these motor constraints was examined separately. In Experiment 1, infants (N = 40, 20 8-month olds, 20 16-month olds) were given the A-not-B task twice. One condition was analogous to the traditional A-not-B task (i.e., using 2 hiding locations) and the other was modified such that a barrier (i.e., an opaque screen) blocked the infants’ reaching path of location A on A trials only. On A trials, all infants searched correctly less often when a barrier was present, and younger infants searched correctly less often than older infants. On B trials, younger infants made more errors in the no barrier condition, whereas older infants did not show any significant difference in B trial performance across conditions. In Experiment 2, infants (N = 51) completed an adapted handedness test (Michel, Ovrut, & Harkins, 1985) followed by a modified A-not-B task. The test assessed infants’ hand-use preferences for reaching, which was used to group infants into their respective preference group (i.e., consistent or inconsistent). Infants with a consistent preference were randomly assigned to a hiding side group (i.e., A on preferred side or A on non-preferred side). Infants searched correctly more often when hiding side was congruent with their preferred reaching hand, and older infants searched correctly more often than younger infants. On the B trial, neither age nor hiding side affected the production of the A-not-B error. Collectively, these studies present data that address the theory that motor memories for reaching are the cause for the production of A-not-B error. These studies provide novel evidence that motor memories for reaching are present in infants aged 8- and 16-months, and that motor memories can influence the production of such errors in certain A-not-B contexts. Implications and directions for future research are also discussed.