Christoph Schütz

Active tactile exploration for adaptive locomotion in the stick insect

Insects carry a pair of actively movable feelers that supply the animal with a range of multimodal information. The antennae of the stick insect Carausius morosus are straight and of nearly the same length as the legs, making them ideal probes for near-range exploration. Indeed, stick insects, like many other insects, use antennal contact information for the adaptive control of locomotion, for example, in climbing. Moreover, the active exploratory movement pattern of the antennae is context-dependent. The first objective of the present study is to reveal the significance of antennal contact information for the efficient initiation of climbing. This is done by means of kinematic analysis of freely walking animals as they undergo a tactually elicited transition from walking to climbing. The main findings are that fast, tactually elicited re-targeting movements may occur during an ongoing swing movement, and that the height of the last antennal contact prior to leg contact largely predicts the height of the first leg contact. The second objective is to understand the context-dependent adaptation of the antennal movement pattern in response to tactile contact. We show that the cycle frequency of both antennal joints increases after obstacle contact. Furthermore, inter-joint coupling switches distinctly upon tactile contact, revealing a simple mechanism for context-dependent adaptation.

Influence of mechanical load on sequential effects.

Almost two decades ago, sequential effects of human grasping behaviour were described for the first time: In a sequential task, participants persisted in using the previous grasp type. According to the plan-modification hypothesis, such sequential effects reduce the movement planning costs and occur within a limited range of indifference. In the current study, we asked whether the anticipated mechanical costs of a movement would compete with the movement planning costs and, thus, reduce the magnitude of the sequential effect. To this end, participants were tested in a sequential, perceptual-motor task (opening a column of drawers), which offered a continuous range of posture solutions for each trial. In a pre-/post-test design, the magnitude of the sequential effect was measured before and after a manipulation phase with increased mechanical costs. Participants displayed a sequential effect for the majority of drawers in the pre-test, which was significantly reduced in the post-test. This finding indicates that each executed movement is a weighted function of both its cognitive and mechanical costs. The result also implies that sequential effects do not result solely from dynamical properties of the motor system, but instead reflect computational features of the movement selection process.

Habitual vs non-habitual manual actions: an ERP study on overt movement execution.

This study explored the neurophysiological mechanisms underlying the planning and execution of an overt goal-related handle rotation task. More specifically, we studied the neural basis of motor actions concerning the influence of the grasp choice. The aim of the present study was to differentiate cerebral activity between grips executed in a habitual and a non-habitual mode, and between specified and free grip choices. To our knowledge, this is the first study to differentiate cerebral activity underlying overt goal-related actions executed with a focus on the habitual mode. In a handle rotation task, participants had to use thumb-toward (habitual) or thumb-away (non-habitual) grips to rotate a handle to a given target position. Reaction and reach times were shorter for the habitual compared to the non-habitual mode indicating that the habitual mode requires less cognitive processing effort than the non-habitual mode. Neural processes for action execution (measured by event-related potentials (ERPs)) differed between habitual and non-habitual conditions. We found differential activity between habitual and non-habitual conditions in left and right frontal areas from −600 to 200 ms time-locked to reaching the target position. No differential neural activity could be traced for the specification of the grip. The results suggested that the frontal negativity reflected increased difficulty in movement precision control in the non-habitual mode compared to the habitual mode during the homing in phase of grasp and rotation actions.

Prospective and retrospective effects in a virtual pointing task.

Over two decades ago prospective and retrospective effects of posture selection in a sequential task were described for the first time. Since then, both effects have been reproduced in a number of reaching studies. We asked (1) whether retrospective effects would also be found in a sequential pointing task and (2) whether pro/retrospective effects of posture selection would transfer to the end-effector position in the absence of haptic feedback. To this end, we created a sequential, perceptual-motor task in a virtual environment. Participants had to point to a row of targets in the frontal plane in sequential order. In a control experiment, physical targets were placed at the same locations. Results showed that kinematic parameters were similar in the virtual and real environment. Retrospective effects of posture/position were found in neither environment, indicating that pointing movements require lower cognitive planning costs than reaching movements. Prospective effects of posture were found both in the virtual and real environment. Prospective effects of position, on the other hand, were present in the virtual but not in the real environment, indicating that the absence of haptic feedback may result in unconscious shifts of the end-effector position.

Motor hysteresis in a sequential grasping and pointing task is absent in task-critical joints

In a prior study (Schütz et al. in Exp Brain Res 2016. doi:10.1007/s00221-016-4608-6), we demonstrated that the cognitive cost of motor planning did not differ in a vertical pointing and grasping task. It was unclear whether the similar cost implied that both tasks required the same number of independent degrees of freedom (IDOFs) or that the number of IDOFs did not affect motor planning. To differentiate between both cases, a reanalysis of the prior data was conducted. The number of IDOFs in the pointing and grasping tasks was computed by factor analysis. In both tasks, two IDOFs were used, which was the minimum number required for position control. This indicates that hand alignment in the grasping task did not require an additional IDOF. No conclusions regarding the link between the cognitive cost of motor planning and the number of IDOFs could be drawn. A subset of task-critical joint angles was not affected by motor hysteresis. This indicates that a joint’s susceptibility to motor hysteresis depends on its relevance to the task goal. In task-critical joints, planning cost minimization by motor plan reuse is suppressed in favor of the task goal.

Cognitive costs of motor planning do not differ between pointing and grasping in a sequential task

Neurophysiologic studies have shown differences in brain activation between pointing and grasping movements. We asked whether these two movement types would differ in their cognitive costs of motor planning. To this end, we designed a sequential, continuous posture selection task, suitable to investigate pointing and grasping movements to identical target locations. Participants had to open a column of drawers or point to a column of targets in ascending and descending progression. The global hand pro/supination at the moment of drawer/target contact was measured. The size of the motor hysteresis effect, i.e., the persistence to a former posture, was used as a proxy for the cognitive cost of motor planning. A larger hysteresis effect equals higher cognitive cost. Both motor tasks had similar costs of motor planning, but a larger range of motion was found for the grasping movements.

Representation and Anticipation in Motor Action

This paper introduces a cognitive architecture model of human action, showing how it is organized over several levels and how it is built up to connect the anticipation of future states and related action execution. Basic Action Concepts (BACs) are identified as major building blocks on a representation level. These BACs are considered cognitive tools for mastering the functional demands of movement tasks. Different lines of research, ranging from complex action to manual action, are presented that provide evidence for a systematic relation between the cognitive representation structures and the actual motor performance. It is concluded that such motor representations provide the basis for action anticipation and motor execution by linking higher-level action goals with the lower-level perceptual effects in the form of cognitive reference structures.

Cognitive Representation of a Complex Motor Action Executed by Different Motor Systems

Abstract The present study evaluates the cognitive representation of a kicking movement performed by a human and a humanoid robot, and how they are represented in experts and novices of soccer and robotics, respectively. To learn about the expertise-dependent development of memory structures, we compared the representation structures of soccer experts and robot experts concerning a human and humanoid robot kicking movement. We found different cognitive representation structures for both expertise groups under two different motor performance conditions (human vs. humanoid robot). In general, the expertise relies on the perceptual-motor knowledge of the human motor system. Thus, the soccer experts’ cognitive representation of the humanoid robot movement is dominated by their representation of the corresponding human movement. Additionally, our results suggest that robot experts, in contrast to soccer experts, access functional features of the technical system of the humanoid robot in addition to their perceptual-motor knowledge about the human motor system. Thus, their perceptual-motor and neuro-functional machine representation are integrated into a cognitive representation of the humanoid robot movement.

Movement plans for posture selection do not transfer across hands.

In a sequential task, the grasp postures people select depend on their movement history. This motor hysteresis effect results from the reuse of former movement plans and reduces the cognitive cost of movement planning. Movement plans for hand trajectories not only transfer across successive trials, but also across hands. We therefore asked whether such a transfer would also be found in movement plans for hand postures. To this end, we designed a sequential, continuous posture selection task. Participants had to open a column of drawers with cylindrical knobs in ascending and descending sequences. A hand switch was required in each sequence. Hand pro/supination was analyzed directly before and after the hand switch. Results showed that hysteresis effects were present directly before, but absent directly after the hand switch. This indicates that, in the current study, movement plans for hand postures only transfer across trials, but not across hands.

Modeling of Biomechanical Parameters Based on LTM Structures

Previous studies concerned with the interaction of cognition and biomechanics demonstrated correlations between ‘global’ parameters of a movement (e. g. duration) and the cognitive representation structure in long term memory. We asked if more ‘local’ biomechanical parameters (i. e. postures) are integrated into such a representation structure as well. To this end, the movement kinematics and representation structures of table tennis experts were measured for the forehand backspin serve and combined in a multilinear regression model. Results show that a few selected parameters of the ball’s flight can be predicted with good accuracy, while task-relevant posture parameters cannot. Thus, the measurement of cognitive representation structures cannot be used for the joint angle modeling of movement kinematics.