Visual control of movement patterns and the grammar of action

In this experiment adult subjects copied three types of material (letters, reversed letters and geometric shapes) with and without sight of the hand and the writing trace. Without vision the number of movement segments decreased and the sequence and direction of movements were altered. This means that subjects did not use a fixed stored representation to produce items nor did they obey the rules of Goodnow and Levine's (1973) grammar of action. When spatial location is made more difficult by the removal of vision, movement production is simplified to reduce the number of relocations required. The use of consistent directions of movement depends on the ability to use visual control of spatial location.     

Kinematic Analyses of Manual Asymmetries in Visual Aiming Movements

The right hand advantage has been thought to arise from the greater efficiency of the right hand/left hemisphere system in processing visual feedback information. This hypothesis was examined using kinematic analyses of aiming performance, focusing particularly on time after peak velocity which has been shown to be sensitive to visual feedback processing demands. Eight right-handed subjects pointed at two targets with their left and right hands with or without vision available and either as accurately or as fast as possible. Pointing errors and movement time were found to be smaller with the right hand. Analyses of the temporal componenets of movement time revealed that the hands differed only in time after peak velocity (in deceleration), with the right hand spending significantly less time. This advantage for the right hand, however, was apparent whether or not vision was available and only when accuracy was emphasized in performance. These findings suggest that the right hand system may be more efficient at processing feedback information whether this be visual or nonvisual (e.g., proprioceptive).     

Online versus offline processing of visual feedback in the control of movement amplitude

Researchers have suggested that visual feedback not only plays a role in the correction of errors during movement execution but that visual feedback from a completed movement is processed offline to improve programming on upcoming trials. In the present study, we examined the potential contribution of online and offline processing of visual feedback by analysing spatial variability at various kinematic landmarks in the limb trajectory (peak acceleration, peak velocity, peak negative acceleration and movement end). Participants performed a single degree of freedom video aiming task with and without vision of the cursor under four criterion movement times (225, 300, 375 and 450 ms). For movement times of 225 and 300 ms, the full vision condition was less variable than the no vision condition. However, the form of the variability profiles did not differ between visual conditions suggesting that the contribution of visual feedback was due to offline processes. In the 375 and 450 ms conditions, there was evidence for both online and offline control as the form of the variability profiles differed significantly between visual conditions.     

Sequential vs simultaneous encoding of spatial information: a comparison between the blind and the sighted

The aim of this research is to assess whether the crucial factor in determining the characteristics of blind people's spatial mental images is concerned with the visual impairment per se or the processing style that the dominant perceptual modalities used to acquire spatial information impose, i.e. simultaneous (vision) vs sequential (kinaesthesis). Participants were asked to learn six positions in a large parking area via movement alone (congenitally blind, adventitiously blind, blindfolded sighted) or with vision plus movement (simultaneous sighted, sequential sighted), and then to mentally scan between positions in the path. The crucial manipulation concerned the sequential sighted group. Their visual exploration was made sequential by putting visual obstacles within the pathway in such a way that they could not see simultaneously the positions along the pathway. The results revealed a significant time/distance linear relation in all tested groups. However, the linear component was lower in sequential sighted and blind participants, especially congenital. Sequential sighted and congenitally blind participants showed an almost overlapping performance. Differences between groups became evident when mentally scanning farther distances (more than 5m). This threshold effect could be revealing of processing limitations due to the need of integrating and updating spatial information. Overall, the results suggest that the characteristics of the processing style rather than the visual impairment per se affect blind people's spatial mental images.     

Visual scanning with or without spatial uncertainty and divided and selective attention.

An experiment was conducted to address the relation between theories of selective attention and theories of divided attention by examining the pattern of task interference between visual scanning as a sequential and selective attention process and other concurrent spatial or verbal processing tasks. A distinction is proposed between visual scanning with or without spatial uncertainty regarding their possible differential effects on interference with other concurrent processes. The experiment required the subjects to perform a primary tracking task, which was concurrently performed with a secondary spatial or verbal decision task. The relevant information that was needed to perform the decision tasks was displayed with or without spatial uncertainty. The results provide evidence that visual scanning as a spatial exploratory activity produces greater task interference with concurrent spatial tasks than with verbal tasks. Furthermore, spatial uncertainty in scanning is identified to be the crucial factor in producing this differential effect.     

Bimanual circling in deafferented patients: Evidence for a role of visual forward models

The present study investigated the role of ideation and visual feedback, and their interaction in movement control in the absence of somatosensory feedback, with the hypothesis that visual imagery and internal visual models may play a crucial role in performance even without feedback. Two chronically deafferented participants, GL and IW, circled bimanually two occluded cranks first without vision and then with hand‐congruent and hand‐incongruent visual feedback provided by visible flags. Without vision, GL was unable to circle the cranks. In contrast, IW performed spontaneously a symmetric pattern. Again without feedback, IW performed an instructed symmetric crank pattern well, but was unable to perform anti‐phase cranking. With hand‐congruent visual feedback, GL and IW were able to perform both symmetric and anti‐phase movements, with symmetry being more accurate. Visual feedback during preceding trials made possible trials without visual feedback in GL and improved anti‐phase trials in IW. Frequency‐transformed incongruent visual feedback resulted in poor performance in part due to unsuitable hand‐related strategies. However, IW improved in the latter task after detailed explanations of the condition. In conclusion, we suggest that both participants use visual imagery and visual forward models to control their hand movements. Visual updating of the forward model also improves performance with no vision. In addition, IW seemed to have been able to move from a focus on hand position to one on the transformed visual feedback to improve movement control in the incongruent feedback/movement condition.     

Visual regulation of manual aiming: A comparison of methods

Visual regulation of upper limb movements occurs throughout the trajectory and is not confined to discrete control in the target area. Early control is based on the dynamic relationship between the limb, the target, and the environment. Despite robust outcome differences between protocols involving visual manipulations, it remains difficult to identify the kinematic events that characterize these differences. In this study, participants performed manual aiming movements with and without vision. We compared several traditional approaches to movement analysis with two new methods of quantifying online limb regulation. As expected, participants undershot the target and their movement endpoints were more variable when vision was not available. Although traditional measures such as reaction time, time after peak velocity, and the presence of discontinuities in acceleration were sensitive to the visual manipulation, measures quantifying the trial-to-trial spatial variability throughout the trajectory were the most effective in isolating the time course of online regulation.     

Determining the Temporal Limits of a Visual Sample for Visual Regulation

The author examined the minimum amount of time needed for vision to increase aiming accuracy and decrease movement duration. Participants selected when they would receive a visual sample during aiming movements by pressing a switch held with the left hand. The sample was one of the following durations: 40 ms, 30 ms, 20 ms, 10 ms, or 0 ms (no vision). Decreased accuracy in the no-vision condition compared to the vision conditions was observed when the duration of the impending sample was unknown (Experiment 1). Samples 40 ms in duration were sufficient to decrease endpoint variability when the duration of the sample was known before the movement (Experiment 2). These results indicate that short visual samples can be used to decrease movement time and increase accuracy and that knowledge of the impending visual context can impact the individual's subsequent behavior.     

Optimal control strategies under different feedback schedules: kinematic evidence

Two experiments were conducted in which participants (N = 12, Experiment 1; N = 12, Experiment 2) performed rapid aiming movements with and without visual feedback under blocked, random, and alternating feedback schedules. Prior knowledge of whether vision would be available had a significant impact on the strategies that participants adopted. When they knew that vision would be available, less time was spent preparing movements before movement initiation. Participants also reached peak deceleration sooner but spent more time after peak deceleration adjusting limb trajectories. Consistent with those findings, analysis of spatial variability at different points in the trajectory indicated that variability increased up to peak deceleration but then decreased from peak deceleration to the end of the movement.     

Specificity of practice: interaction between concurrent sensory information and terminal feedback

In 2 experiments, the authors investigated a potential interaction involving the processing of concurrent feedback using design features from the specificity of practice literature and the processing of terminal feedback using a manipulation from the guidance hypothesis literature. In Experiment 1, participants produced (198 trials) flexion-extension movements to reproduce a specific pattern of displacement over time with or without vision of the limb position and with 100% or 33% knowledge of results (KR) frequency. The transfer test was performed without vision and KR. In Experiment 2, the authors assessed whether sensory information processing was modulated by the amount of practice. Participants performed 54 or 396 trials under a 100% or a 33% KR frequency with vision before being transferred to a no-vision condition without KR. Results of both experiments indicated that the Vision-33% condition suffered a larger detrimental effect of withdrawing visual information than the Vision-100% condition. Experiment 2 indicated that this detrimental effect increased with practice. These results indicated the reduction in terminal feedback prompted participants to more deeply process the concurrent visual information thus reinforcing their dependency on the visual information.     

Partial visual feedback and spatial end-point accuracy of discrete aiming movements

Five experiments are reported in which the effect of partial visual feedback on the accuracy of discrete target aiming was investigated. Visual feedback was manipulated through a spectacle-mounted liquid-crystal tachistoscope. The length of the visual feedback interval was varied as a percentage of the instructed movement time. In Experiment 1, the length of the vision interval was manipulated symmetrically at the beginning- and end-phase of the movement, whereas in the remaining experiments, the vision time was varied with respect to the end-phase only. The variations at the end were examined for different distances (Experiment 2), different movement speeds at the same distance (Experiment 3), and in small interstep intervals (Experiment 4). A vision time of more than 150 ms at the end-phase of the movement enhanced aiming performance in all experiments. Longer vision times monotonously improved aiming accuracy; the fifth experiment showed that a vision time of about 275 ms was sufficient for near-perfect aiming. Furthermore, the significance of vision during the first phase of a movement was demonstrated again. The results of the five experiments pointed to shorter visuomotor processing times. To explain the beneficial effects of short vision times for aiming accuracy, we propose a model of visuomotor processing that is based on the stochastic optimized submovement model of Meyer, Abrams, Kornblum, Wright, and Smith (1988).     

Visual guidance for hand advance but not hand withdrawal in a reach-to-eat task in adult humans: reaching is a composite movement

Many animal species use reaching for food to place in the mouth (reach-to-eat) with a hand, and it may be a primitive movement. Although researchers (I. Q. Whishaw, 2005; A. N. Iwaniuk & I. Q. Whishaw, 2000; M. Gentiluci, I. Toni, S. Chieffi, & G. Pavesi, 1994) have described visual guidance of reaching in both normal and brain-injured human and nonhuman primates, researchers have not described the contribution of vision during advance of the limb to grasp food and during withdrawal of the limb with food to the mouth. To evaluate visual contributions, the authors monitored eye movements in young adults as they reached for food with and without vision. Participants visually engaged the target prior to the 1st hand movement and disengaged it as the food was grasped. Visual occlusion slowed limb advance and altered digit shaping but did not affect withdrawal. The dependence on visual control of advance but not withdrawal suggests that the reach-to-eat movement is a composite of 2 basic movements under visual and tactile/proprioceptive guidance, respectively.     

Visual feedback,movement learning and the representation of movement

Two experiments on movement learning are reported where the orientation of a visual curve on a graphics terminal, defining a relatively complex arm movement, was either orthogonal to or compatible with the direction of the required movement. In addition, individual differences in spatial orientation and visualization abilities were correlated with motor performance. Results in both experiments showed that equivalent amounts of learning occurred in the two visual conditions. However, during transfer trials to the opposite condition, virtually no transfer occurred for the compatible group when they performed in the orthogonal condition whereas there was tranfer when the orthogonal group performed in the compatible condition. The results supported the idea that very early in learning the orthogonal orientation of visual curve promoted the development of an orientation processing stage which facilitated transrer performance of the orthogonal group. Integrating these results with the past literature on movement learning led to the notion that the orientation information processing stage can be considered a cognitive system that interacts with the image of the act. Finally, contrary to expectations, spatial orientation ability failed to account for any performance while spatial visualization ability moderately correlated with performance.     

The utilization of visual information in the control of reciprocal aiming movements

Two experiments examined on-line processing during the execution of reciprocal aiming movements. In Experiment 1, participants used a stylus to make movements between two targets of equal size. Three vision conditions were used: full vision, vision during flight and vision only on contact with the target. Participants had significantly longer movement times and spent more time in contact with the targets when vision was available only on contact with the target. Additionally, the proportion of time to peak velocity revealed that movement trajectories became more symmetric when vision was not available during flight. The data indicate that participants used vision not only to 'home-in' on the current target, but also to prepare subsequent movements. In Experiment 2, liquid crystal goggles provided a single visual sample every 40 ms of a 500 ms duty cycle. Of interest was how participants timed their reciprocal aiming to take advantage of these brief visual samples. Although across participants no particular portion of the movement trajectory was favored, individual performers did time their movements consistently with the onset and offset of vision. Once again, performance and kinematic data indicated that movement segments were not independent of each other.     

Influence of visual guidance on braille recognition: Low lighting also helps touch

This study was an attempt to clarify the mechanisms responsible for the benefits of visual guidance in tactual braille recognition. Subjects touched +90° tilted braille under normal room lighting, or with low lighting, with or without visual guidance. Both visual information about finger angle and spatial reference information were manipulated with stained glass and light-emitting diodes. The provision of visual information about finger angle alone was no help to braille recognition, and performance was low. Adding visual spatial reference information to vision of finger angle raised performance. However, recognition accuracy was also substantially improved by low lighting. The benefits of darkness for haptics did not generalize to the reading of upright, two-letter braille words. It was proposed that extraneous visual information may distract sighted subjects in haptic tasks that require mental rotation of visual images.     

Coding processes in preselected and constrained movements: effect of vision

Three experiments were conducted in which visual information was manipulated either at the endpoint or during preselected, subject defined and constrained, experimenter-defined movements. In Experiments 1 and 2 the subject's task was to reproduce the movement in the absence of vision. Augmenting the terminal location of the criterion movement with vision had no differential effect on reproduction in Experiment 1, although preselected movement accuracy was significantly superior to constrained. Providing vision throughout the criterion movement in Experiment 2 not only failed to improve the accuracy of constrained movements but decreased reproduction performance in preselected movements. In Experiment 3 procedures were adopted to control the allocation of the subjects' attention during the criterion movement. The subjects reproduced by vision alone, movement alone, or with both visual and movement information available. When subjects were informed of the modality of reproduction prior to criterion presentation, they were able to ignore concurrent input from vision and attend to movement information. In the absence of precues visual information was spontaneously attended. The data were interpreted as contrary to closed-loop assumptions that additional information necessarily enhances the strength of a motor memory representation. Rather, they can be accommodated in terms of Posner, Nissen and Klein's (1976) theoretical account of visual dominance and serve to illustrate the importance of selective attention effects in movement coding.     

Constructing and representing visual objects

The objects we see are not given in the images at the eyes, but must be constructed by the human visual system. Indeed, damage to specific brain regions often leads to specific impairments of visual abilities (for example, the perception of shape, color or motion). Human vision constructs the various properties of visual objects, not independently of each other, but in a highly coordinated fashion. The construction of one visual property strongly influences the constructions of other properties. Visual shape is an important construction for successfully recognizing objects. There is growing consensus that human vision represents shapes in terms of component parts and their spatial relationships. These parts and their spatial relationships provide a powerful first index into one's visual memory of shapes.     

The contribution of peripheral and central vision in the control of movement amplitude

Past research has revealed that central vision is more important than peripheral vision in controlling the amplitude of target-directed aiming movements. However, the extent to which central vision contributes to movement planning versus online control is unclear. Since participants usually fixate the target very early in the limb trajectory, the limb enters the central visual field during the late stages of movement. Hence, there may be insufficient time for central vision to be processed online to correct errors during movement execution. Instead, information from central vision may be processed offline and utilised as a form of knowledge of results, enhancing the programming of subsequent trials. In the present research, variability in limb trajectories was analysed to determine the extent to which peripheral and central vision is used to detect and correct errors during movement execution. Participants performed manual aiming movements of 450 ms under four different visual conditions: full vision, peripheral vision, central vision, no vision. The results revealed that participants utilised visual information from both the central and peripheral visual fields to adjust limb trajectories during movement execution. However, visual information from the central visual field was used more effectively to correct errors online compared to visual information from the peripheral visual field.     

Motor coordination uses external spatial coordinates independent of developmental vision

The constraints that guide bimanual movement coordination are informative about the processing principles underlying movement planning in humans. For example, symmetry relative to the body midline benefits finger and hand movements independent of hand posture. This symmetry constraint has been interpreted to indicate that movement coordination is guided by a perceptual code. Although it has been assumed implicitly that the perceptual system at the heart of this constraint is vision, this relationship has not been tested. Here, congenitally blind and sighted participants made symmetrical and non-symmetrical (that is, parallel) bimanual tapping and finger oscillation movements. For both groups, symmetrical movements were executed more correctly than parallel movements, independent of anatomical constraints like finger homology and hand posture. For the blind, the reliance on external spatial factors in movement coordination stands in stark contrast to their use of an anatomical reference frame in perceptual processing. Thus, the externally coded symmetry constraint evident in bimanual coordination can develop in the absence of the visual system, suggesting that the visual system is not critical for the establishment of an external-spatial reference frame in movement coordination.     

Adults with probable developmental coordination disorder selectively process early visual,but not tactile information during action preparation. An electrophysiological study

Developmental coordination disorder (DCD) is a neurodevelopmental condition affecting motor coordination in children and adults. Here, EEG signals elicited by visual and tactile stimuli were recorded while adult participants with and without probable DCD (pDCD) performed a motor task. The task cued reaching movements towards a location in visible peripersonal space as well as an area of unseen personal space. Event-related potentials elicited by visual and tactile stimuli revealed that visual processing was strongly affected by movement preparation in the pDCD group, even more than in controls. However, in contrast to the controls, tactile processing in unseen space was unaffected by movement preparation in the pDCD group. The selective use of sensory information from vision and proprioception is fundamental for the adaptive control of movements, and these findings suggest that this is impaired in DCD. Additionally, the pDCD group showed attenuated motor rhythms (beta: 13–30 Hz) over sensorimotor regions following cues to prepare movements towards unseen personal space. The results reveal that individuals with pDCD exhibit differences in the neural mechanisms of spatial selection and action preparation compared to controls, which may underpin the sustained difficulties they experience. These findings provide new insights into the neural mechanisms potentially disrupted in this highly prevalent disorder.