Planning and on-line control of catching as a function of perceptual-motor constraints

Two experiments were conducted in order to investigate the adaptability and associated strategies of the human perceptuo-motor system to deal with changing constraints. In a catching task, perceptual-motor constraints were internally controlled by coupling movement onset of the catch and the illumination circuit in the lab: upon the first movement of the catcher, all lights went out within 3 ms. The authors studied (a) how much movement time catchers prefer if no visual information is available after movement onset, and (b) how movement execution changes under such temporal constraints. It was hypothesised that, in order to accomplish successful catching behaviour, (1) movement initiation would be postponed in order to allow sufficient information uptake before the lights went out, and (2) an alternative control strategy would have to be mobilised, since on-line control becomes inappropriate when catching in the dark. In the first experiment, the adaptation process to the light-dark paradigm was investigated. In the second experiment, the conclusions from experiment 1 were challenged under varying ball speeds. In order to maintain catching performance, subjects initiated the catch approximately 280 ms before ball-hand contact. Next to changes in temporal structure of the catch and subtle kinematic adaptations, evidence for a change in the control mode emerged: while an on-line control strategy was adopted under normal illumination, catching movements seemed to be executed as planned in advance when catching in the dark. Additionally, perceptual constraints seem to determine the time of movement initiation, rather than motor constraints. These results emphasize the capability of the human perceptuo-motor system to adjust promptly to new task constraints.     

Non-linear gaining in precision aiming: making Fitts' task a bit easier

The role of information in the processes underlying kinematic trajectory-formation was examined by manipulating the relation between effector space (movement of a hand-held stylus on a graphics tablet) and task space (movement of a cursor on a screen where targets were presented) in a precision aiming task with five different levels of task difficulty. Movement patterns were found to evolve as a function of the flow of information in task space, with participants (N = 13) producing more rapid and more fluent movements when the mapping between spaces included the softening-spring characteristics typical of behavioural patterns at higher levels of task difficulty. We conclude that the kinematic changes (movement time and pattern) observed when task difficulty increases result from informational influences. Information affects behavioural dynamics at the level of the parameters without affecting the underlying dynamical structure.     

Attentional strategies and the visual control of discrete movements

The relationship between the availability of visual information and attention demands during the production of a discrete motor act was examined. Subjects were required to move a linear slide a distance of 15 cm in both 150 and 600 msec conditions under three light manipulations, viz., light always on; light always terminated as movement began; or, subject was unsure as to whether light would stay on or terminate. A simple key press by the index finger of the opposite hand to a tone was used as a secondary task and a measure of attention demands. The light manipulation influenced attention demands on the rapid 150 msec movement such that more attention was demanded when the subject knew the light would terminate. No such attentional strategy differences were found with the slow 600 msec movement. These findings suggest that task constraints in the form of kinematic criteria, together with the perceived availability of visual information, contribute to determining attentional strategy in movement production.     

任务信息通达对视觉表象眼动的影响

通过两个实验探讨了视觉表象任务信息的通达对表象加工眼动的影响。结果表明, 在低通达条件下, 表象任务的眼动复制了知觉任务的眼动; 随着表象任务信息通达水平的提高, 眼动的注视点平均持续时间、平均眼跳距离和平均眼跳时间会发生规律性变化; 眼动控制与任务信息通达水平对表象眼动的影响存在不同的机制。实验结果佐证了眼动在视觉表象中起机能性作用的观点。     

Parkinson's disease differentially affects adaptation to gradual as compared to sudden visuomotor distortions

Patients with Parkinson’s disease (PD) have difficulties in movement adaptation to optimize performance in novel environmental contexts such as altered screen cursor-hand relationships. Prior studies have shown that the time course of the distortion differentially affects visuomotor adaptation to screen cursor rotations, suggesting separate mechanisms for gradual and sudden adaptation. Moreover, studies in human and non-human primates suggest that adaptation to sudden kinematic distortions may engage the basal ganglia, whereas adaptation to gradual kinematic distortions involves cerebellar structures. In the present studies, participants were patients with PD, who performed center-out pointing movements, using either a digitizer tablet and pen or a computer trackball, under normal or rotated screen cursor feedback conditions. The initial study tested patients with PD using a cross-over experimental design for adaptation to gradual as compared with sudden rotated hand-screen cursor relationships and revealed significant after-effects for the gradual adaptation task only. Consistent with these results, findings from a follow-up experiment using a trackball that required only small finger movements showed that patients with PD adapt better to gradual as against sudden perturbations, when compared to age-matched healthy controls. We conclude that Parkinson’s disease affects adaptation to sudden visuomotor distortions but spares adaptation to gradual distortions.     

Kinematic information feedback and task constraints

The experiments were designed to examine the effect of task constraints on the influence of kinematic information feedback to facilitate the acquisition of discrete arm movements. The findings of Experiments 1 and 3 revealed that when the criterion kinematic trajectory was an increasing acceleration function, the most effective control space representation for kinematic feedback (i.e. position-time; velocity-position) was the one that matched the error criterion to be minimized. Furthermore, in Experiment 1 the velocity-position feedback condition led to greater performance error than the discrete knowledge of results of movement time or integrated position-time error. Experiment 2 showed that kinematic information feedback of the movement trajectory (position-time; velocity-position) did not facilitate acquisition of a constant velocity criterion, in contrast to knowledge of results of movement time or integrated velocity-position error. Collectively the findings suggest that the interaction of task and organismic constraints dictates the nature of the information feedback required to facilitate the acquisition of skill. The augmented information available must match the degrees of freedom requiring constraint in the movement sequence.     

Difference in sensorimotor adaptation to horizontal and vertical mirror distortions during ballistic arm movements

When learning a novel motor task, the sensorimotor system must develop new strategies to efficiently control the limb(s) involved, and this adaptation appears to be developed through the construction of a behavioral map known as an 'internal model'. A common method to uncover the mechanisms of adaptation and reorganization processes is to expose the system to new environmental conditions, typically by introducing visual or mechanical distortions. The present study investigated the adaptation mechanisms of the human sensorimotor system to horizontal and vertical mirror distortions (HMD and VMD) during the execution of fast goal-directed arm movements. Mirror distortions (MDs) were created by means of virtual visual feedback on a computer screen while the movement was executed on a graphics tablet. Twenty healthy adult participants were recruited and assigned to one of two groups of 10 people each. Tests were divided in two subsequent blocks of five trials. The first block consisted of trials with no mirror distortion (NMD), while the second block was recorded when exposing one group to HMD and the other to VMD. Both MDs resulted in kinematic changes: during the tests with the MDs the participants did not reach the performance level found at the NMD test. Motor performance during HMD appeared to be globally better than during VMD and the adaptation process to VMD appeared to be slower than to HMD, but data interpretation was hampered by large within-participant and between-participant variability. In-depth analyses of the data revealed that most of the motor performance information was contained in the direction of movement. The data supported the idea that the internal model for HMD was already partially built.     

Expertise and attunement to kinematic constraints

Three experiments were undertaken to ascertain the extent to which expertise in natural anticipatory tasks is characterised by superior attunement to the biomechanical (kinematic) constraints of the movement pattern being observed. Twelve world-class and twelve non-expert badminton players were required to predict the depth of an opponent's stroke from either video displays or point-light displays of the opposing player's hitting action. The information available within the displays was manipulated through temporal and/or spatial occlusion. Consistent with predictions that can be derived from the constraint-attunement hypothesis (Vicente and Wang, 1998 Psychological Review 105 33-57), experts showed: (i) an unchanged pattern of information pick-up when the display was reduced from video to point-light and only kinematic information was available; (ii) superior information pick-up from kinematic features that non-experts could use; and (iii) attunement to early kinematic information from the lower body to which non-experts were not sensitive. Consistent with predictions that can be derived from a common-coding perspective (Prinz, 1997 European Journal of Cognitive Psychology 9 129-154), the anticipation of stroke depth was facilitated more for experts than non-experts when the perceptual display provided linked segment information reminiscent of the cross-segmental torque transfers that occur during expert movement production.     

Specificity of task constraints and effects of visual demonstrations and verbal instructions in directing learners' search during skill acquisition

In the present study, the efficacy of visual demonstrations and verbal instructions as instructional constraints on the acquisition of movement coordination was investigated. Fifteen participants performed an aiming task on 100 acquisition and 20 retention trials, under 1 of 3 conditions: a modeling group (MG), a verbally directed group (VDG), and a control group (CG). The MG observed a model intermittently throughout acquisition, whereas the VDG was verbally instructed to use the model's movement pattern. Participants in the CG received neither form of instruction. Kinematic analysis revealed that compared with verbal instructions or no instructions, visual demonstrations significantly improved participants' approximation of the model's coordination pattern. No differences were found in movement outcomes. Coordination data supported the visual perception perspective on observational learning, whereas outcome data suggested that the modeling effect is mainly a function of task constraints, that is, the novelty of a movement pattern.     

Task requirements influence sensory integration during grasping in humans

The sensorimotor transformations necessary for generating appropriate motor commands depend on both current and previously acquired sensory information. To investigate the relative impact (or weighting) of visual and haptic information about object size during grasping movements, we let normal subjects perform a task in which, unbeknownst to the subjects, the object seen (visual object) and the object grasped (haptic object) were never the same physically. When the haptic object abruptly became larger or smaller than the visual object, subjects in the following trials automatically adapted their maximum grip aperture when reaching for the object. This adaptation was not dependent on conscious processes. We analyzed how visual and haptic information were weighted during the course of sensorimotor adaptation. The adaptation process was quicker and relied more on haptic information when the haptic objects increased in size than when they decreased in size. As such, sensory weighting seemed to be molded to avoid prehension error. We conclude from these results that the impact of a specific source of sensory information on the sensorimotor transformation is regulated to satisfy task requirements.     

Specificity of Task Constraints and Effects of Visual Demonstrations and Verbal Instructions in Directing Learners' Search During Skill Acquisition

In the present study, the efficacy of visual demonstrations and verbal instructions as instructional constraints on the acquisition of movement coordination was investigated. Fifteen participants performed an aiming task on 100 acquisition and 20 retention trials, under 1 of 3 conditions: a modeling group (MG), a verbally directed group (VDG), and a control group (CG). The MG observed a model intermittently throughout acquisition, whereas the VDG was verbally instructed to use the model's movement pattern. Participants in the CG received neither form of instruction. Kinematic analysis revealed that compared with verbal instructions or no instructions, visual demonstrations significantly improved participants' approximation of the model's coordination pattern. No differences were found in movement outcomes. Coordination data supported the visual perception perspective on observational learning, whereas outcome data suggested that the modeling effect is mainly a function of task constraints, that is, the novelty of a movement pattern.     

Hand, eye, and head coordination while pointing to perturbed targets

Normal human subjects were required to manually point to small visual targets that suddenly changed location upon finger movement initiation. They pointed either as fast or as accurately as possible. Movements of the eyes were measured by electrooculography, and the movements of the unrestrained limb and head were monitored by an optoelectric system (WATSMART), which allowed for the analysis of kinematic parameters in three-dimensional space. The temporal and kinematic reorganization of each body part in response to the target perturbations were variable, which indicated independent control for each part of the system. That is, the timing and nature of the reorganization varied for each body part. In addition, the pattern of reorganization depended upon the speed and accuracy demands of the movement task. As well, the movement termination patterns (eyes finished first, the finger reached the target, then the head stopped moving) were extremely consistent, indicating that movement termination may be a controlled variable. Finally, no evidence was found to suggest that visual information was used to amend arm movements early (before peak velocity) in the trajectory.     

Run-up strategies in competitive long jumping: How an ecological dynamics rationale can support coaches to design individualised practice tasks

Understanding how individuals navigate challenging accuracy demands required to register a legal jump is important in furthering knowledge of competitive long jumping. Identification of co-ordination tendencies unique to each individual emphasises the need to examine the presence of unique movement solutions and presents important information for individualisation of training environments. In this study, key measures of gait were recorded during the long jump run-ups of 8 athletes at 8 national level competitions in the 2015 and 2016 Australian track and field seasons. These gait measures were examined to identify whether different visual regulation strategies emerged for legal and foul jumps for each competitor. Emergence of different footfall variability data curves, illustrating how step adjustments were distributed across the run-up for each athlete, suggests that athletes interacted differently with features of the competition environment. This observation highlights the importance of movement adaptability as constraints change and emerge across each performance trial. Results provided further support in conceptualising the run-up as a continuous interceptive action task consisting of a series of interconnected events (i.e., individual step lengths) influencing the regulation of gait towards the take-off board. This information can be used by coaches and practitioners in designing training environments that promote athlete adaptation of more functional movement solutions closely matched to the dynamics of competition environments. Results suggest that training designs that help athletes to search, explore and exploit key sources of information from the competition environment will enhance the fit between the individual and the environment and the development of rich, adaptable movement solutions for competitive performance.     

Intrinsic and extrinsic contributions to heavy tails in visual foraging

Eyes move over visual scenes to gather visual information. Studies have found heavy-tailed distributions in measures of eye movements during visual search, which raises questions about whether these distributions are pervasive to eye movements, and whether they arise from intrinsic or extrinsic factors. Three different measures of eye movement trajectories were examined during visual foraging of complex images, and all three were found to exhibit heavy tails: Spatial clustering of eye movements followed a power law distribution, saccade length distributions were lognormally distributed, and the speeds of slow, small amplitude movements occurring during fixations followed a 1/f spectral power law relation. Images were varied to test whether the spatial clustering of visual scene information is responsible for heavy tails in eye movements. Spatial clustering of eye movements and saccade length distributions were found to vary with image type and task demands, but no such effects were found for eye movement speeds during fixations. Results showed that heavy-tailed distributions are general and intrinsic to visual foraging, but some of them become aligned with visual stimuli when required by task demands. The potentially adaptive value of heavy-tailed distributions in visual foraging is discussed.     

Effects of visual and auditory guidance on bimanual coordination complexity

Perceptual guidance of movement with simple visual or temporal information can facilitate performance of difficult coordination patterns. Guidance may override coordination constraints that usually limit stability of bimanual coordination to only in-phase and anti-phase. Movement dynamics, however, might not have the same characteristics with and without perceptual guidance. Do visual and auditory guidance produce qualitatively different dynamical organization of movement? An anti-phase wrist flexion and extension coordination task was performed under no specific perceptual guidance, under temporal guidance with a metronome, and under visual guidance with a Lissajous plot. For the time series of amplitudes, periods and relative phases, temporal correlations were measured with Detrended Fluctuation Analysis and complexity levels were measured with multiscale entropy. Temporal correlations of amplitudes and relative phases deviated from the typical 1/f variation towards more random variation under visual guidance. The same was observed for the series of periods under temporal guidance. Complexity levels for all time series were lower in visual guidance, but higher for periods under temporal guidance. Perceptual simplification of the task’s goal may produce enhancement of performance, but it is accompanied by changes in the details of movement organization that may be relevant to explain dependence and poor retention after practice under guidance.     

视觉表象眼动的变化：知识还是技能表征的差异？

以表象看到一个运动员完成三级跳远项目为实验任务,对表象任务的信息通达水平、眼动注视点的活动位置和被试对三级跳远项目的知识水平和技能水平进行系统的操纵,通过2个实验探讨了视觉表象眼动的变化是基于知识学习表征差异还是技能训练表征差异的问题。实验1以没有三级跳远运动专业技能知识且对该运动的认知水平也较低的大学生为被试,结果表明,在完成高信息通达水平的表象任务时,注视点需要较短的持续时间,但眼跳距离会增大,眼跳频率会变低;实验2对表象任务的知识学习表征水平和技能训练表征水平进行操纵,分别以对实验任务进行过知识学习和专业技能训练的人为被试,结果表明,随着被试知识习得水平和技能水平表征能力的提高,不同表象任务信息通达水平间的眼动差异将消失,但知识学习和技能表征的差异在平均眼跳时间上有差异,技能训练型的被试其平均眼跳时间要短于知识学习型被试,达到临界水平显著,注视点平均持续时间和平均眼跳距离等均没有差异。     

Experiencing the Cross-Sensory Error Signal During Movement Leads to Proprioceptive Recalibration

Abstract

Reaching to targets in a virtual reality environment with misaligned visual feedback of the hand results in changes in movements (visuomotor adaptation) and sense of felt hand position (proprioceptive recalibration). We asked if proprioceptive recalibration arises even when the misalignment between visual and proprioceptive estimates of hand position is only experienced during movement. Participants performed a “shooting task” through the targets with a cursor that was rotated 30° clockwise relative to hand motion. Results revealed that, following training on the shooting task, participants adapted their reaches to all targets by approximately 16° and recalibrated their sense of felt hand position by 8°. Thus, experiencing a sensory misalignment between visual and proprioceptive estimates of hand position during movement leads to proprioceptive recalibration.     

Selective weighting of action-related feature dimensions in visual working memory

Planning an action primes feature dimensions that are relevant for that particular action, increasing the impact of these dimensions on perceptual processing. Here, we investigated whether action planning also affects the short-term maintenance of visual information. In a combined memory and movement task, participants were to memorize items defined by size or color while preparing either a grasping or a pointing movement. Whereas size is a relevant feature dimension for grasping, color can be used to localize the goal object and guide a pointing movement. The results showed that memory for items defined by size was better during the preparation of a grasping movement than during the preparation of a pointing movement. Conversely, memory for color tended to be better when a pointing movement rather than a grasping movement was being planned. This pattern was not only observed when the memory task was embedded within the preparation period of the movement, but also when the movement to be performed was only indicated during the retention interval of the memory task. These findings reveal that a weighting of information in visual working memory according to action relevance can even be implemented at the representational level during maintenance, demonstrating that our actions continue to influence visual processing beyond the perceptual stage.     

Vision Using Routines: A Functional Account of Vision

This paper presents the case for a functional account of vision. A variety of studies have consistently revealed “change blindness” or insensitivity to changes in the visual scene during an eye movement. These studies indicate that only a small part of the information in the scene is represented in the brain from moment to moment. It is still unclear, however, exactly what is included in visual representations. This paper reviews experiments using an extended visuo-motor task, showing that display changes affect performance differently depending on the observer's place in the task. These effects are revealed by increases in fixation duration following a change. Different task-dependent increases suggest that the visual system represents only the information that is necessary for the immediate visual task. This allows a principled exploration of the stimulus properties that are included in the internal visual representation. The task specificity also has a more general implication that vision should be conceptualized as an active process executing special purpose “routines” that compute only the currently necessary information. Evidence for this view and its implications for visual representations are discussed. Comparison of the change blindness phenomenon and fixation durations shows that conscious report does not reveal the extent of the representations computed by the routines.