Slowness is a well-recognized feature of movements in aging. One of the possible reasons for slowness suggested by previous research is production of corrective submovements that compensate for shortened primary submovement to the target. Here, we re-examine this traditional interpretation and argue that the majority of submovements in older adults may be a consequence rather than the cause of slowness.
Pointing movements in young and older adults were recorded. Conditions for submovement emergence were manipulated by using small and large targets and three movement modes: discrete (required stopping on the target), reciprocal (required reversal on the target), and passing (required crossing the target and stopping after that). Movements were parsed into a primary and secondary submovement based on zero-crossings of velocity (type 1 submovements), acceleration (type 2 submovements), and jerk (type 3 submovements). In the passing mode, secondary submovements were analyzed only after crossing the target to exclude that they were accuracy adjustments.
Consistent with previous research, the primary submovement was shortened and total secondary submovement incidence was increased in older adults. However, comparisons across conditions suggested that many submovements were non-corrective in both groups. Type 1 submovements were non-corrective because they were more frequent for large than small targets. They predominantly emerged due to arm stabilization and energy dissipation during motion termination in the discrete and passing mode. Although type 2 and 3 submovements were more frequent for small than large targets, this trend was also observed in the passing mode, suggesting that many of these submovements were non-corrective. Rather, they could have been velocity fluctuations associated predominantly with low speed of movements to small targets.
The results question the traditional interpretation of frequent submovements in older adults as corrective adjustments. Rather, the increased incidence of submovements in older adults is directly related to low movement speed observed in aging, whereas the relationship between submovement incidence and target size is a result of speed-accuracy trade-off. Aging-related declines in muscular control that may contribute to the disproportional increases in submovement incidence during slow movements of older adults are discussed.
Natural movements are corrected in part by the generation of submovements, occuring early in a movement such that they amend an ongoing action. Submovements are associated with activity of the basal ganglia, implying a role for the structures in error correction. In parallel, the basal ganglia are linked to the generation and control of force amplitude, change and duration. Here we tested if activity in human basal ganglia is associated with submovements generally, or was specific to a condition where the submovements only occurred in the face of unexpected proprioceptive error. Submovements were induced by introducing unexpected and variable viscous loads (augmenting the need for trial specific grip forces) or by reducing target size (augmenting the need for visually guided on-line control) in a 1-D target capture task. In both cases, subjects compensated for the increased task difficulty by generating corrective submovements, which were closely matched in frequency and type. Activity in the internal segment of the globus pallidus and subthalamic nucleus correlated strongly with the number of submovements during the viscous challenge but not with the target challenge. The effects could not be explained by kinematic differences, i.e. movement amplitude or average number of submovements. The results support a specific role for the basal ganglia in error correction under conditions of variable load where there is a need for the dynamic control of force within an ongoing movement.
Motor control; on-line correction; error; adaptation; basal ganglia; human
Limb movement is smooth and corrections of movement trajectory and amplitude are barely noticeable midflight. This suggests that skeletomuscular motor commands are smooth in transition, such that the rate of change of acceleration (or jerk) is minimized. Here we applied the methodology of minimum-jerk submovement decomposition to a member of the skeletomuscular family, the head movement. We examined the submovement composition of three types of horizontal head movements generated by nonhuman primates: head-alone tracking, head-gaze pursuit, and eye-head combined gaze shifts. The first two types of head movements tracked a moving target, whereas the last type oriented the head with rapid gaze shifts toward a target fixed in space. During head tracking, the head movement was composed of a series of episodes, each consisting of a distinct, bell-shaped velocity profile (submovement) that rarely overlapped with each other. There was no specific magnitude order in the peak velocities of these submovements. In contrast, during eye-head combined gaze shifts, the head movement was often comprised of overlapping submovements, in which the peak velocity of the primary submovement was always higher than that of the subsequent submovement, consistent with the two-component strategy observed in goal-directed limb movements. These results extend the previous submovement composition studies from limb to head movements, suggesting that submovement composition provides a biologically plausible approach to characterizing the head motor recruitment that can vary depending on task demand.
Elderly adults often exhibit performance deficits during goal-directed movements of the dominant arm compared with young adults. Recent studies involving hemispheric lateralization have provided evidence that the dominant and non-dominant hemisphere-arm systems are specialized for controlling different movement parameters and that hemispheric specialization may be reduced during normal aging. The purpose was to examine age-related differences in the movement structure for the dominant (right) and non-dominant (left) during goal-directed movements. Young and elderly adults performed 72 aiming movements as fast and as accurately as possible to visual targets with both arms. The findings suggest that previous research utilizing the dominant arm can be generalized to the non-dominant arm because performance was similar for the two arms. However, as expected, the elderly adults showed shorter relative primary submovement lengths and longer relative primary submovement durations, reaction times, movement durations, and normalized jerk scores compared to the young adults.
Aging; Feedback; Hand; Laterality; Submovement
We present in outline a theory of sensorimotor control based on dynamic primitives, which we define as attractors. To account for the broad class of human interactive behaviors—especially tool use—we propose three distinct primitives: submovements, oscillations and mechanical impedances, the latter necessary for interaction with objects. Due to fundamental features of the neuromuscular system, most notably its slow response, we argue that encoding in terms of parameterized primitives may be an essential simplification required for learning, performance, and retention of complex skills. Primitives may simultaneously and sequentially be combined to produce observable forces and motions. This may be achieved by defining a virtual trajectory composed of submovements and/or oscillations interacting with impedances. Identifying primitives requires care: in principle, overlapping submovements would be sufficient to compose all observed movements but biological evidence shows that oscillations are a distinct primitive. Conversely, we suggest that kinematic synergies, frequently discussed as primitives of complex actions, may be an emergent consequence of neuromuscular impedance. To illustrate how these dynamic primitives may account for complex actions, we briefly review three types of interactive behaviors: constrained motion, impact tasks, and manipulation of dynamic objects.
Discrete; submovement; rhythmic; oscillation; impedance; primitive
Rapid center of pressure (COP) movements are often required to avoid falls. Little is known about the effect of age on rapid and accurate volitional COP movements. We hypothesized that COP movements to a target would be slower and exhibit more submovements in older versus younger adults, particularly in posterior versus anterior movements. Healthy older (N = 12, mean age = 76 years) and young women (N = 13, mean age = 23 years) performed anterior and posterior lean movements while standing on a force plate, and were instructed to move their COP ‘as fast and as accurately as possible’ using visual feedback. The results show that rapid posterior COP movements were slower and had an increased number of submovements and ratio of peak-to-average velocity, in comparison to anterior movements (p < .005). Moreover, older compared to younger adults were 27% slower and utilized nearly twice as many compensatory submovements (p < .005), particularly when moving posteriorly (p < .05). Older women also had higher ratios of peak-to-average COP velocity than young (p < .05). Thus, despite moving more slowly, older women needed to take more frequent submovements to maintain COP accuracy, particularly posteriorly, thereby providing evidence of a compensatory strategy that may be used for preventing backward falls.
Balance; Center of pressure; Speed-accuracy trade-offs; Gerontology
Humans achieve locomotor dexterity that far exceeds the capability of modern robots, yet this is achieved despite slower actuators, imprecise sensors, and vastly slower communication. We propose that this spectacular performance arises from encoding motor commands in terms of dynamic primitives. We propose three primitives as a foundation for a comprehensive theoretical framework that can embrace a wide range of upper- and lower-limb behaviors. Building on previous work that suggested discrete and rhythmic movements as elementary dynamic behaviors, we define submovements and oscillations: as discrete movements cannot be combined with sufficient flexibility, we argue that suitably-defined submovements are primitives. As the term “rhythmic” may be ambiguous, we define oscillations as the corresponding class of primitives. We further propose mechanical impedances as a third class of dynamic primitives, necessary for interaction with the physical environment. Combination of these three classes of primitive requires care. One approach is through a generalized equivalent network: a virtual trajectory composed of simultaneous and/or sequential submovements and/or oscillations that interacts with mechanical impedances to produce observable forces and motions. Reliable experimental identification of these dynamic primitives presents challenges: identification of mechanical impedances is exquisitely sensitive to assumptions about their dynamic structure; identification of submovements and oscillations is sensitive to their assumed form and to details of the algorithm used to extract them. Some methods to address these challenges are presented. Some implications of this theoretical framework for locomotor rehabilitation are considered.
discrete; submovement; rhythmic; oscillation; impedance; primitive; locomotion; rehabilitation
Subcortical loops through the basal ganglia and the cerebellum form computationally powerful distributed processing modules (DPMs). This paper relates the computational features of a DPM's loop through the basal ganglia to experimental results for two kinds of natural action selection. First, functional imaging during a serial order recall task was used to study human brain activity during the selection of sequential actions from working memory. Second, microelectrode recordings from monkeys trained in a step-tracking task were used to study the natural selection of corrective submovements. Our DPM-based model assisted in the interpretation of puzzling data from both of these experiments. We come to posit that the many loops through the basal ganglia each regulate the embodiment of pattern formation in a given area of cerebral cortex. This operation serves to instantiate different kinds of action (or thought) mediated by different areas of cerebral cortex. We then use our findings to formulate a model of the aetiology of schizophrenia.
modularity; serial order; pattern classification; error correction; schizophrenia; presynaptic inhibition
A Fitts’ task was used to investigate how tools are incorporated into the internal representations that underlie pointing movements, and whether such knowledge can be generalized across tasks. We measured the speed-accuracy trade-offs that occurred as target width was varied for both real and imagined movements. The dynamics of the pointing tool used in the task were manipulated—regular pen, top-heavy tool, and bottom-heavy tool—to test the fidelity of internal representations of movements involving the use of novel tools. To test if such representations can be generalized, the orientation of the pointing task was also manipulated (horizontal vs. vertical). In all conditions, both real and imagined performances conformed to the speed-accuracy relationship described by Fitts’ law. We found significant differences in imagined MTs for the two weighted tools compared to the regular pen, but not between the weighted tools. By contrast, real movement durations differed between all tools. These results indicate that even relatively brief experience using novel tools is sufficient to influence the internal representation of the dynamics of the tool-limb system. However, in the absence of feedback, these representations do not make explicit differences in performances resulting from the unique dynamics of these weighted tools.
Tool use; Imagery; Visually guided movement; Sensorimotor control; Fitts’ law; Motor learning
It is generally believed that accuracy and confidence in one’s memory are related, but there are many instances when they diverge. Accordingly, it is important to disentangle the factors which contribute to memory accuracy and confidence, especially those factors that contribute to confidence, but not accuracy. We used eye movements to separately measure fluent cue processing, the target recognition experience, and relative evidence assessment on recognition confidence and accuracy. Eye movements were monitored during a face-scene associative recognition task, in which participants first saw a scene cue, followed by a forced-choice recognition test for the associated face, with confidence ratings. Eye movement indices of the target recognition experience were largely indicative of accuracy, and showed a relationship to confidence for accurate decisions. In contrast, eye movements during the scene cue raised the possibility that more fluent cue processing was related to higher confidence for both accurate and inaccurate recognition decisions. In a second experiment, we manipulated cue familiarity, and therefore cue fluency. Participants showed higher confidence for cue-target associations for when the cue was more familiar, especially for incorrect responses. These results suggest that over-reliance on cue familiarity and under-reliance on the target recognition experience may lead to erroneous confidence.
The main objective of this study was to analyze the motor variability in the performance of the tennis serve and its relationship to performance outcome. Seventeen male tennis players took part in the research, and they performed 20 serves. Linear and non-linear variability during the hand movement was measured by 3D Motion Tracking. Ball speed was recorded with a sports radar gun and the ball bounces were video recorded to calculate accuracy. The results showed a relationship between the amount of variability and its non-linear structure found in performance of movement and the outcome of the serve. The study also found that movement predictability correlates with performance. An increase in the amount of movement variability could affect the tennis serve performance in a negative way by reducing speed and accuracy of the ball.
variability; tennis serve; performance
Rapid discrete goal-directed movements are characterized by a well known coordination pattern between the gaze and the hand displacements. The gaze always starts prior to the hand movement and reaches the target before hand velocity peak. Surprisingly, the effect of the target size on the temporal gaze-hand coordination has not been directly investigated. Moreover, goal-directed movements are often produced in a reciprocal rather than in a discrete manner. The objectives of this work were to assess the effect of the target size on temporal gaze-hand coordination during fast 1) discrete and 2) reciprocal pointings.
Subjects performed fast discrete (experiment 1) and reciprocal (experiment 2) pointings with an amplitude of 50 cm and four target diameters (7.6, 3.8, 1.9 and 0.95 cm) leading to indexes of difficulty (ID = log2[2A/D]) of 3.7, 4.7, 5.7 and 6.7 bits. Gaze and hand displacements were synchronously recorded. Temporal gaze-hand coordination parameters were compared between experiments (discrete and reciprocal pointings) and IDs using analyses of variance (ANOVAs).
Data showed that the magnitude of the gaze-hand lead pattern was much higher for discrete than for reciprocal pointings. Moreover, while it was constant for discrete pointings, it decreased systematically with an increasing ID for reciprocal pointings because of the longer duration of gaze anchoring on target.
Overall, the temporal gaze-hand coordination analysis revealed that even for high IDs, fast reciprocal pointings could not be considered as a concatenation of discrete units. Moreover, our data clearly illustrate the smooth adaptation of temporal gaze-hand coordination to terminal accuracy requirements during fast reciprocal pointings. It will be interesting for further researches to investigate if the methodology used in the experiment 2 allows assessing the effect of sensori-motor deficits on gaze-hand coordination.
Cadaveric models of the shoulder evaluate discrete motion segments
using the glenohumeral joint in isolation over a defined trajectory.
The aim of this study was to design, manufacture and validate a
robotic system to accurately create three-dimensional movement of
the upper body and capture it using high-speed motion cameras.
In particular, we intended to use the robotic system to simulate
the normal throwing motion in an intact cadaver. The robotic system
consists of a lower frame (to move the torso) and an upper frame
(to move an arm) using seven actuators. The actuators accurately
reproduced planned trajectories. The marker setup used for motion
capture was able to determine the six degrees of freedom of all
involved joints during the planned motion of the end effector.
The testing system demonstrated high precision and accuracy based
on the expected versus observed displacements of individual axes.
The maximum coefficient of variation for displacement of unloaded
axes was less than 0.5% for all axes. The expected and observed
actual displacements had a high level of correlation with coefficients
of determination of 1.0 for all axes.
Given that this system can accurately simulate and track simple
and complex motion, there is a new opportunity to study kinematics
of the shoulder under normal and pathological conditions in a cadaveric
Shoulder biomechanics; Pitching; Shoulder; Range of motion; Motion analysis; Shoulder kinematics
This study investigated pointing movements in 3D asking two questions: (1) Is goal-directed reaching accompanied by self-motion, a component of the joint velocity vector that leaves the hand’s movement unaffected? (2) Are differences in the terminal joint configurations among different speeds of reaching motor equivalent (i.e., terminal joint configurations differ more in directions of joint space that do not produce different pointer-tip positions than in directions that do) or non-motor equivalent (i.e., terminal joint configurations differ equally or more in directions of joint space that lead to different pointer-tip positions than in directions that do not affect the pointer-tip position). Subjects reached from an identical starting joint configuration and pointer-tip location to targets at slow, moderate, and fast speeds. Ten degrees of freedom of joint motion of the arm were recorded. The relationship between changes in the joint configuration and the three-dimensional pointer-tip position was expressed by a standard kinematic model, and the range- and null subspaces were computed from the associated Jacobian matrix. (1) The joint velocity vector and (2) the difference vector between terminal joint configurations from pairs of speed conditions were projected into the two subspaces. The relative length of the two components was used to quantify the amount of self-motion and the presence of motor equivalence, respectively. Results revealed that reaches were accompanied by a significant amount of self-motion at all reaching speeds. Self-motion scaled with movement speed. In addition, the difference in the terminal joint configuration between pairs of different reaching speeds revealed motor equivalence. The results are consistent with a control system that takes advantage of motor redundancy, allowing for flexibility in the face of perturbations, here induced by different movement speeds.
Reaching; Motor Control; Motor equivalence; Movement velocity
We tested whether changing accuracy demands for simple pointing movements leads humans to adjust the feedback control laws that map sensory signals from the moving hand to motor commands. Subjects made repeated pointing movements in a virtual environment to touch a button whose shape varied randomly from trial-to-trial – between squares, rectangles oriented perpendicular to the movement path and rectangles oriented parallel to the movement path. Subjects performed the task on a horizontal table, but saw the target configuration and a virtual rendering of their pointing finger through a mirror mounted between a monitor and the table. On a one-third of trials, the position of the virtual finger was perturbed by ±1 cm either in the movement direction or perpendicular to the movement direction when the finger passed behind an occluder. Subjects corrected quickly for the perturbations despite not consciously noticing them; however, they corrected almost twice as much for perturbations aligned with the narrow dimension of a target than for perturbations aligned with the long dimension. These changes in apparent feedback gain appeared in the kinematic trajectories soon after the time of the perturbations, indicating that they reflect differences in the feedback control law used throughout the duration of movements. The results indicate that the brain adjusts its feedback control law for individual movements “on-demand” to fit task demands. Simulations of optimal control laws for a two-joint arm show that accuracy demands alone, coupled with signal dependent noise lead to qualitatively the same behavior.
Feedback; optimal control; motor control; pointing; online control
Magnetic resonance imaging (MRI) is a widely used method for non-invasive study of the structure and function of the human brain. Increasing magnetic field strengths enable higher resolution imaging; however, long scan times and high motion sensitivity mean that image quality is often limited by the involuntary motion of the subject. Prospective motion correction is a technique that addresses this problem by tracking head motion and continuously updating the imaging pulse sequence, locking the imaging volume position and orientation relative to the moving brain. The accuracy and precision of current MR-compatible tracking systems and navigator methods allows the quantification and correction of large-scale motion, but not the correction of very small involuntary movements in six degrees of freedom. In this work, we present an MR-compatible tracking system comprising a single camera and a single 15 mm marker that provides tracking precision in the order of 10 m and 0.01 degrees. We show preliminary results, which indicate that when used for prospective motion correction, the system enables improvement in image quality at both 3 T and 7 T, even in experienced and cooperative subjects trained to remain motionless during imaging. We also report direct observation and quantification of the mechanical ballistocardiogram (BCG) during simultaneous MR imaging. This is particularly apparent in the head-feet direction, with a peak-to-peak displacement of 140 m.
High speed Optical Coherence Tomography (OCT) has made it possible to rapidly capture densely sampled 3D volume data. One key application is the acquisition of high quality in vivo volumetric data sets of the human retina. Since the volume is acquired in a few seconds, eye movement during the scan process leads to distortion, which limits the accuracy of quantitative measurements using 3D OCT data. In this paper, we present a novel software based method to correct motion artifacts in OCT raster scans. Motion compensation is performed retrospectively using image registration algorithms on the OCT data sets themselves. Multiple, successively acquired volume scans with orthogonal fast scan directions are registered retrospectively in order to estimate and correct eye motion. Registration is performed by optimizing a large scale numerical problem as given by a global objective function using one dense displacement field for each input volume and special regularization based on the time structure of the acquisition process. After optimization, each volume is undistorted and a single merged volume is constructed that has superior signal quality compared to the input volumes. Experiments were performed using 3D OCT data from the macula and optic nerve head acquired with a high-speed ultra-high resolution 850 nm spectral OCT as well as wide field data acquired with a 1050 nm swept source OCT instrument. Evaluation of registration performance and result stability as well as visual inspection shows that the algorithm can correct for motion in all three dimensions and on a per A-scan basis. Corrected volumes do not show visible motion artifacts. In addition, merging multiple motion corrected and registered volumes leads to improved signal quality. These results demonstrate that motion correction and merging improves image quality and should also improve morphometric measurement accuracy from volumetric OCT data.
(170.4500) Optical coherence tomography; (170.4470) Ophthalmology; (100.2980) Image enhancement; (100.5010) Pattern recognition
One of the main characteristics of Autism Spectrum Disorder (ASD) are problems with social interaction and communication. Here, we explored ASD-related alterations in ‘reading’ body language of other humans. Accuracy and reaction times were assessed from two observational tasks involving the recognition of ‘biological motion’ and ‘emotions’ from point-light displays (PLDs). Eye movements were recorded during the completion of the tests. Results indicated that typically developed-participants were more accurate than ASD-subjects in recognizing biological motion or emotions from PLDs. No accuracy differences were revealed on two control-tasks (involving the indication of color-changes in the moving point-lights). Group differences in reaction times existed on all tasks, but effect sizes were higher for the biological and emotion recognition tasks. Biological motion recognition abilities were related to a person’s ability to recognize emotions from PLDs. However, ASD-related atypicalities in emotion recognition could not entirely be attributed to more basic deficits in biological motion recognition, suggesting an additional ASD-specific deficit in recognizing the emotional dimension of the point light displays. Eye movements were assessed during the completion of tasks and results indicated that ASD-participants generally produced more saccades and shorter fixation-durations compared to the control-group. However, especially for emotion recognition, these altered eye movements were associated with reductions in task-performance.
It is virtually impossible to camouflage a moving target against a non-uniform background, but strategies have been proposed to reduce detection and targeting of movement. Best known is the idea that high contrast markings produce ‘motion dazzle’, which impairs judgement of speed and trajectory. The ability of the cuttlefish Sepia officinalis to change its visual appearance allows us to compare the animal's choice of patterns during movement to the predictions of models of motion camouflage. We compare cuttlefish body patterns used during movement with those expressed when static on two background types; one of which promotes low-contrast mottle patterns and the other promotes high-contrast disruptive patterns. We find that the body pattern used during motion is context-specific and that high-contrast body pattern components are significantly reduced during movement. Thus, in our experimental conditions, cuttlefish do not use high contrast motion dazzle. It may be that, in addition to being inherently conspicuous during movement, moving high-contrast patterns will attract attention because moving particles in coastal waters tend to be of small size and of low relative contrast.
motion; camouflage; dazzle; cuttlefish; vision
Suppose that the variability in our movements1–9 is caused not by noise in the motor system itself, nor by fluctuations in our intentions or plans, but rather by errors in our sensory estimates of the external parameters that define the appropriate action. For tasks in which precision is at a premium, performance would be optimal if no noise were added in movement planning and execution: motor output would be as accurate as possible given the quality of sensory inputs. Here we use visually guided smooth-pursuit eye movements in primates10 as a testing ground for this notion of optimality. In response to repeated presentations of identical target motions, nearly 92% of the variance in eye trajectory can be accounted for as a consequence of errors in sensory estimates of the speed, direction and timing of target motion, plus a small background noise that is observed both during eye movements and during fixations. The magnitudes of the inferred sensory errors agree with the observed thresholds for sensory discrimination by perceptual systems, suggesting that the very different neural processes of perception and action are limited by the same sources of noise.
Recently, it has been reported that grasping with the left hand is more vulnerable to visual size illusions than grasping with the right hand. The present study investigated whether this increased sensitivity of the left hand for visual context extends to reaching. Left- and right-handed participants reached for targets embedded in two different visual contexts with either left or right hands. Visual context was manipulated by presenting targets either in a blank field or within an array of placeholders marking possible target locations. Regardless of handedness, the presence of placeholders affected left hand, but not right hand, reaching by improving end-point accuracy and reducing movement speed. Furthermore, left hand reaching was more accurate for far than near targets, whereas right hand reaching showed the opposite pattern. We discuss two possible hemispheric lateralization accounts of these findings.
Laterality; Handedness; Dominance; Reaching; Motor control
Coupling of spine and hip joints during full body reaching tasks was investigated in sixteen participants (8 male & 8 female) who performed reaching tasks at comfortable and fast-paced movement speeds to three targets located in a para-sagittal plane. The participants paused at target contact for 500 ms and then returned to an upright posture. Three dimensional joint motions of the spine and hip were recorded using an electromagnetic tracking device. We found an effect of movement phase (i.e. reach and return) on the onset timing of the spine and hip joints. For most target locations and movement speeds, spine motion onset preceded hip motion onset during the reaching phase of the movement task. In the reach phase, when averaged across all movement conditions, spine joint motion preceded hip joint motion by an average of 48.9 ms. In contrast, in the return phase, hip joint motion preceded spine joint motion by an average of 63.0 ms. Additionally, when subjects were instructed to use either a knee flexion or knee extension strategy to perform the reaching tasks there was no effect of movement strategy on timing of the spine and hip. There was also no effect of target height on the spine hip ratio, but as movement speed increased, the spine/hip ratio decreased for all target locations due primarily to an increase in hip joint excursion. The findings indicate clear differences in onset timing of the spine and hip joints during reaching tasks that necessitate some forward bending of the trunk and that onset timing is reversed for the return to an upright posture.
Kinematics Spine Hip Timing Coordination
When goal-directed movements are inaccurate, two responses are generated by the brain: a fast motor correction toward the target and an adaptive motor recalibration developing progressively across subsequent trials. For the saccadic system, there is a clear dissociation between the fast motor correction (corrective saccade production) and the adaptive motor recalibration (primary saccade modification). Error signals used to trigger corrective saccades and to induce adaptation are based on post-saccadic visual feedback. The goal of this study was to determine if similar or different error signals are involved in saccadic adaptation and in corrective saccade generation. Saccadic accuracy was experimentally altered by systematically displacing the visual target during motor execution. Post-saccadic error signals were studied by manipulating visual information in two ways. First, the duration of the displaced target after primary saccade termination was set at 15, 50, 100 or 800 ms in different adaptation sessions. Second, in some sessions, the displaced target was followed by a visual mask that interfered with visual processing. Because they rely on different mechanisms, the adaptation of reactive saccades and the adaptation of voluntary saccades were both evaluated. We found that saccadic adaptation and corrective saccade production were both affected by the manipulations of post-saccadic visual information, but in different ways. This first finding suggests that different types of error signal processing are involved in the induction of these two motor corrections. Interestingly, voluntary saccades required a longer duration of post-saccadic target presentation to reach the same amount of adaptation as reactive saccades. Finally, the visual mask interfered with the production of corrective saccades only during the voluntary saccades adaptation task. These last observations suggest that post-saccadic perception depends on the previously performed action and that the differences between saccade categories of motor correction and adaptation occur at an early level of visual processing.
The aim of this study was to investigate the perception of possibilities for action (i.e., affordances) that depend on one’s movement capabilities, and more specifically, the passability of a shrinking gap between converging obstacles. We introduce a new optical invariant that specifies in intrinsic units the minimum locomotor speed needed to safely pass through a shrinking gap. Detecting this information during self-motion requires recovering a component of the obstacles’ local optical expansion due to obstacle motion, independent of self-motion. In principle, recovering the obstacle motion component could involve either visual or non-visual self-motion information. We investigated the visual and non-visual contributions in two experiments in which subjects walked through a virtual environment and made judgments about whether it was possible to pass through a shrinking gap. On a small percentage of trials, visual and non-visual self-motion information were independently manipulated by varying the speed with which subjects moved through the virtual environment. Comparisons of judgments on such catch trials with judgments on normal trials revealed both visual and non-visual contributions to the detection of information about minimum walking speed.
Relations between a modifiable psychosocial factor, self-efficacy (SE), and behavioral and neural indices of self-regulation, including post-error behavior, the error-related negativity (ERN), and error positivity (Pe) were examined in young adults during a flanker task emphasizing either accuracy or speed. SE was predicted to be associated with larger ERN and Pe amplitudes, as well as greater post-error behavioral performance during task conditions emphasizing accuracy, but not speed. Results showed that higher SE was associated with greater post-error response accuracy during the accuracy condition, but not the speed condition, and higher SE was related with greater ERN amplitudes across instruction conditions. Further, ERN amplitude mediated the relationship between SE and post-error response accuracy in the accuracy condition. These findings emphasize the role of motivation and incentive on the self-regulatory system and suggest that SE is beneficially related to self-regulatory processes and outcomes.
Self-efficacy (SE); Self-regulation; Error-Related Negativity (ERN); Event-Related Brain Potentials (ERPs)