Global inhibition and midcourse corrections in speeded aiming

When some perceptual-motor relationships are reversed, participants might adopt a global inhibition strategy that replaces all normal movements with reversed movements. In two experiments, participants practiced moving a cursor from a start position to target locations. In a perceptual-motor reversal condition, in which horizontal but not vertical movements were reversed, participants were trained to move only to certain locations. Testing involved moving to all locations under the same reversal condition. Training on a subset of locations yielded partial transfer to untrained locations. These results support a global inhibition hypothesis modified to include both midcourse corrective movements and training specificity.     

Accessing the asymmetrical representations of causal relations and hierarchical relations in semantic memory

In a speeded aiming task, participants were trained to move a cursor with a mouse from a start position to target locations when the mouse–cursor relationships were either normal or reversed (vertically, horizontally, or both vertically and horizontally). Testing, which occurred after a 5-min delay, involved either the same or a different reversal condition. Response times improved across training, but no transfer occurred when reversal conditions were changed between training and testing. Specificity of training effects extended even to performance with the highly familiar normal mouse. Normal mouse use was slowed by a factor of two to three with training on a reversed mouse although the effect was transient in that case. To contend with a reversed mouse, participants apparently adopt a global inhibition strategy, suppressing all normal movements (and replacing them with sensorimotor remapped movements) but disinhibiting movements along any nonreversed dimension (selectively disengaging the sensorimotor remapping).     

Coordinated flexibility: how initial gaze position modulates eye-hand coordination and reaching

Reaching to targets in space requires the coordination of eye and hand movements. In two experiments, we recorded eye and hand kinematics to examine the role of gaze position at target onset on eye-hand coordination and reaching performance. Experiment 1 showed that with eyes and hand aligned on the same peripheral start location, time lags between eye and hand onsets were small and initiation times were substantially correlated, suggesting simultaneous control and tight eye-hand coupling. With eyes and hand departing from different start locations (gaze aligned with the center of the range of possible target positions), time lags between eye and hand onsets were large and initiation times were largely uncorrelated, suggesting independent control and decoupling of eye and hand movements. Furthermore, initial gaze position strongly mediated manual reaching performance indexed by increments in movement time as a function of target distance. Experiment 2 confirmed the impact of target foveation in modulating the effect of target distance on movement time. Our findings reveal the operation of an overarching, flexible neural control system that tunes the operation and cooperation of saccadic and manual control systems depending on where the eyes look at target onset.     

Repetitive pointing to remembered proprioceptive targets improves 3D hand positioning accuracy

Repetitive pointing movements to remembered proprioceptive targets were investigated to determine whether dynamic proprioception could be used to modify the initial sensorimotor conditions associated with an active definition of the target position. Twelve blindfolded subjects used proprioception to reproduce a self-selected target position as accurately as possible. Ten repetitions for each limb were completed using overhead and scapular plane pointing tasks. A 3D optical tracking system determined hand trajectory start and endpoint positions for each repetition. These positions quantified three-dimensional pointing errors relative to the target position and the initial and preceding movement repetitions, as well as changes in movement direction and extent. Target position and cumulative start position errors were significantly greater than the corresponding preceding movement (inter-repetition) errors, and increased as the trial progressed. In contrast, hand trajectory start and endpoint inter-repetition errors decreased significantly with repeated task performance, as did movement extent, although it was consistently underestimated for each repetition. Pointing direction remained constant, except for the angle of elevation for scapular plane pointing, which consistently decreased throughout the trial. The results suggest that the initial conditions prescribed by actively defining a proprioceptive target were subsequently modified by dynamic proprioception, such that movement reproduction capability improved with repeated task performance.     

The planning and execution of sequential eye movements: saccades do not show the one target advantage

The present experiment examined the one-target advantage (OTA) with regard to saccadic eye movements. The OTA, previously found with manual pointing responses, refers to the finding that movements are executed faster when the limb is allowed to stop on the target compared to the situation where it has to proceed and hit a second target. Using an adapted limb movement OTA task, saccades of 5 degrees and 15 degrees were made to (a) a single target (one-target), (b) one target and immediately to another target without a change in direction (two-target-extension), and (c) one target and immediately back to the start location (two-target-reversal). Unlike manual movements, the movement times for the initial saccade in the two-target-extension condition were not prolonged compared to either of the other two conditions. Moreover, this pattern of results was found for both the shorter and longer amplitude saccades. The results indicate that the OTA does not occur in the oculomotor system and therefore is not a general motor control phenomenon.     

Spatial accuracy demand in aiming movements: kinematic analysis of subtended angle and tolerance width

Subtended angle has been assumed to be an important factor in both response programming time and kinematic characteristics of aiming movements. Support for this assumption has come mainly from studies in which circular targets have been used. However, with circular targets, the subtended angle covaries with the size of the target in the principal direction of the movement (tolerance width). The purpose of this study was to examine the effects of tolerance width and subtended angle on aiming movement with multiple targets. Participants first hit a 5-cm-diameter circular target located 8 cm to the left of a starting position and then moved another 8 cm left to hit either a 5-cm diameter circular target or a 5- x 1-cm rectangular target oriented either horizontally or vertically, depending on the condition. Analysis showed that reaction times and movement times were longer for the vertical rectangular target, which had a smaller tolerance width than the other two targets. In addition, the vertical rectangular target also showed a greater percentage of secondary-submovement trials, lower movement velocity, and higher peak vertical displacement. Overall, the results indicate that the tolerance width of the target may impose more constraints on aiming movements than subtended angle.     

Ipsilesional arm reaching movements are not affected by the postural configuration adopted by individuals with stroke

Individuals with stroke present several impairments in the ipsilesional arm reaching movements that can limit the execution of daily living activities. These impairments depend on the side of the brain lesion. The present study aimed to compare the arm reaching movements performed in sitting and standing positions and to examine whether the effects of the adopted posture configuration depend on the side of the brain lesion. Twenty right-handed individuals with stroke (half with right hemiparesis and a half with left hemiparesis) and twenty healthy adults (half used the left arm) reached toward a target displayed on a monitor screen placed in one of three heights (i.e., upper, central, or lower targets). Participants performed the reaches in sitting and standing positions under conditions where the target location was either well-known in advance (certainty condition) or unknown until the movement onset (uncertainty condition). The values of movement onset time, movement time, and constant error were compared across conditions (posture configuration and uncertainty) and groups for each target height. Individuals with stroke were slower and spent more time to start to move than healthy participants, mainly when they reached the superior target in the upright position and under the uncertainty condition. Individuals who have suffered a right stroke were more affected by the task conditions and those who suffered a left stroke showed less accurate reaches. Overall, these results were observed regardless of the adopted posture. The current findings suggested that ipsilesional arm reaching movements are not affected by the postural configuration adopted by individuals with stroke. The central nervous system modulates the reaching movements according to the target position, adopted posture, and the uncertainty in the final target position to be reached.     

Cognitive constraints on motor imagery

Executed bimanual movements are prepared slower when moving to symbolically different than when moving to symbolically same targets and when targets are mapped to target locations in a left/right fashion than when they are mapped in an inner/outer fashion [Weigelt et al. (Psychol Res 71:238–447, 2007)]. We investigated whether these cognitive bimanual coordination constraints are observable in motor imagery. Participants performed fast bimanual reaching movements from start to target buttons. Symbolic target similarity and mapping were manipulated. Participants performed four action conditions: one execution and three imagination conditions. In the latter they indicated starting, ending, or starting and ending of the movement. We measured movement preparation (RT), movement execution (MT) and the combined duration of movement preparation and execution (RTMT). In all action conditions RTs and MTs were longer in movements towards different targets than in movements towards same targets. Further, RTMTs were longer when targets were mapped to target locations in a left/right fashion than when they were mapped in an inner/outer fashion, again in all action conditions. RTMTs in imagination and execution were similar, apart from the imagination condition in which participants indicated the start and the end of the movement. Here MTs, but not RTs, were longer than in the execution condition. In conclusion, cognitive coordination constraints are present in the motor imagery of fast (<1600 ms) bimanual movements. Further, alternations between inhibition and execution may prolong the duration of motor imagery.     

The role of goal representations in moving to temporal and spatial targets

Traditionally, movement kinematics are thought to reflect physical properties (e.g., position and time) of movement targets. However, targets may also evoke intentional goals like “to be in a certain position at a given time”. Therefore, kinematics may be viewed not as a reaction to stimuli, but rather as the means to attain intended goals. In the present study participants performed continuous reversal movements. It was first shown that kinematics towards temporal and spatial targets differ from kinematics away from those targets. Further, kinematics are different for movements to temporal (relatively short movement times, high and late peak velocity) and spatial (relatively long movement times, early peak velocity) targets (Experiments 1 and 2). In order to obtain evidence for the influence of goal representations on kinematics, combinations of temporal and spatial targets were investigated in Experiments 3 and 4. Specifically, the conditions were: spatial targets always present with varying temporal targets, temporal targets always present with varying spatial targets, and combined and separate spatial and temporal targets. Not only the physical features, but also how the targets were represented as movement goals, were important. Thus, movement kinematics do not simply reflect stimulus properties, but rather the representation of the intended goal.     

Influence of the movement parameter to be controlled on manual RT asymmetries in right-handers

In this experiment we test whether the effects of manual asymmetries on movement preparation depend on the parameter (amplitude or direction) to be programmed. In two experiments, only the amplitude, or the direction, of aiming movements was constrained. Reaction and movement times were measured. Results show that RTs are always shorter for left-hand than for right-hand movements. There is an effect of target extent in the amplitude condition, but not in the direction one. RTs for ipsilateral movements are shorter than RTs for contralateral movements. These results are discussed in the light of the processes involved in setting the amplitude or direction of the movement and with regard to the competency of the two hemispheres regarding these processes.     

Cinematographical Analysis of Movement Pathway Constraints in Rapid Target-Striking Tasks

Several features of the actual movement pathway in two rapid target-striking tasks were quantified by using high-speed cinematography, and whether the movement pathway is constrained as a function of the accuracy demands imposed by the size of the subtended angle was determined. Subjects (N = 16) first hit an 8-cm-diameter target located 10 cm to the left of a start position and then, depending on the condition, moved another 10 cm to hit either a 6-cm- or 1.5-cm-diameter target. Subtended angles were 17.1 and 4.3 degrees for the large and small second-target conditions, respectively. Fifty trials per condition were performed, the last 3 of which were filmed at 120 Hz. The vertical dimension of movement (peak height along the z-axis) was captured directly from the camera view, whereas the horizontal (y-axis) dimension, that is, the dimension orthogonal to the principal direction of motion, was captured through a mirror positioned above the target board. Reaction times and movement times were significantly longer in the small second-target condition, thus replicating the well-known response complexity effect. Kinematic analyses revealed that when the subtended angle was smaller, there was significantly less horizontal pathway deviation as well as significantly higher peak vertical displacement in the movement. Therefore, the accuracy demands imposed by a smaller subtended angle do constrain the actual movement pathway.     

On the Role of Visual Afferent Information for the Control of Aiming Movements Toward Targets of Different Sizes

The authors investigated (a) whether the specificity of practice hypothesis is mediated by the importance of visual afferent information for the control of manual aiming movements and (b) how movement planning and online correction processes to the movement initial impulse are affected by the withdrawal of visual information in transfer. In acquisition, participants (N = 40) aimed at targets of different sizes in a full-vision or in a target-only condition before being transferred to a target-only condition without knowledge of results. The results supported the hypothesis that learning is specific to the source or sources of afferent information that are more likely to ensure optimal performance. The results also suggested that individuals will not always use visual afferent information more extensively when aiming at a small rather than at a large target. Instead, in a temporally constrained task, the relative efficiency of visually based corrections appears to mediate how exclusively an individual will rely on online visual afferent information for movement control. Finally, the detailed kinematic analysis performed in the present study clearly indicated that online modifications to the movement primary impulse are possible, arguing for a continuous or pseudo-continuous control of relatively slow aiming movements on the basis of visual afferent input.     

Effects of directional uncertainty on visually-guided joystick pointing

Reaction times generally follow the predictions of Hick's law as stimulus-response uncertainty increases, although notable exceptions include the oculomotor system. Saccadic and smooth pursuit eye movement reaction times are independent of stimulus-response uncertainty. Previous research showed that joystick pointing to targets, a motor analog of saccadic eye movements, is only modestly affected by increased stimulus-response uncertainty; however, a no-uncertainty condition (simple reaction time to 1 possible target) was not included. Here, we re-evaluate manual joystick pointing including a no-uncertainty condition. Analysis indicated simple joystick pointing reaction times were significantly faster than choice reaction times. Choice reaction times (2, 4, or 8 possible target locations) only slightly increased as the number of possible targets increased. These data suggest that, as with joystick tracking (a motor analog of smooth pursuit eye movements), joystick pointing is more closely approximated by a simple/choice step function than the log function predicted by Hick's law.     

Extended practice of reciprocal wrist and arm movements of varying difficulties

An experiment was designed to determine the degree to which reciprocal aiming movements of the wrist and arm with various accuracy requirements (Fitts' tasks) are enhanced by extended practice. The vast majority of research on motor learning shows performance improvement over practice. However, literature examining the effect of practice on Fitts' task performance is limited and inconclusive. Participants were asked to flex/extend their limb/lever in the horizontal plane at the wrist (arm stabilized) or elbow joint (wrist stabilized) in an attempt to move back and forth between two targets as quickly and accurately as possible. The targets and current position of the limb were projected on the screen in front of the participant. Target width was manipulated with amplitude constant (16°) in order to create indexes of difficulty (ID) of 1.5, 3, 4.5, and 6. Contrary to the earlier reports, after 20 days of practice, we found minimal changes in movement time or the movement time-ID relationships for the arm and wrist over practice. However, the variability in the movement endpoints decreased over practice and wrist movements at ID=6 were characterized by shorter movement times and longer dwell times relative to arm movements with dwell time for the wrist increasing over practice. These data are consistent with the notion that Fitts' tasks provide a stable measure of perceptual-motor capabilities.     

The role of goal representations in moving to temporal and spatial targets

Traditionally, movement kinematics are thought to reflect physical properties (e.g., position and time) of movement targets. However, targets may also evoke intentional goals like “to be in a certain position at a given time”. Therefore, kinematics may be viewed not as a reaction to stimuli, but rather as the means to attain intended goals. In the present study participants performed continuous reversal movements. It was first shown that kinematics towards temporal and spatial targets differ from kinematics away from those targets. Further, kinematics are different for movements to temporal (relatively short movement times, high and late peak velocity) and spatial (relatively long movement times, early peak velocity) targets (Experiments 1 and 2). In order to obtain evidence for the influence of goal representations on kinematics, combinations of temporal and spatial targets were investigated in Experiments 3 and 4. Specifically, the conditions were: spatial targets always present with varying temporal targets, temporal targets always present with varying spatial targets, and combined and separate spatial and temporal targets. Not only the physical features, but also how the targets were represented as movement goals, were important. Thus, movement kinematics do not simply reflect stimulus properties, but rather the representation of the intended goal.     

Orienting to targets by looking and pointing: Parallels and interactions in ocular and manual performance

Orienting to a target by looking and pointing is examined for parallels between the control of the two systems and interactions due to movement of the eyes and limb to the same target. Parallels appear early in orienting and may be due to common processing of spatial information for the ocular and manual systems. The eyes and limb both have shorter response latency to central visual and peripheral auditory targets. Each movement also has shorter latency and duration when the target presentation is short enough (200 msec) that no analysis of feedback of the target position is possible during the movement. Interactions appear at many stages of information processing for movement. Latency of ocular movement is much longer when the subject also points, and the eye and limb movement latencies are highly correlated for orienting to auditory targets. Final position of eyes and limb are significantly correlated only when target duration is short (200 msec). This illustrates that sensory information obtained before the movement begins is an important, but not the only, source of input about target position. Additional information that assists orienting may be passed from one system to another, since visual information gained by looking aided pointing to lights and proprioceptive information from the pointing hand seemed to assist the eyes in looking to sounds. Thus the production of this simple set of movements may be partly described by a cascade-type process of parallel analysis of spatial information for eye and hand control, but is also, later in the movement, assisted by cross-system interaction.     

Training for the production of novel timing movements: Contextual considerations

Summary The present study represented an attempt to determine the extent to which transfer performance on a novel timing task is influenced by contextual similarity (i.e., similar instructions, task requirements, etc.) between training and transfer phases of performance. All subjects were given trials on a task which involved a linear ballistic arm movement. The length of the movement was defined as the distance between a start button and a hinged target, which was knocked over by the subject at the end of the response. During training subjects attempted to produce their movements in a time of 550 ms and were given knowledge of results regarding timing error after each trial. During transfer trials a 300 ms movement time was attempted and no knowledge of results was given. Context was defined by the number of different movement distances performed during training and transfer. Half of the subjects received training trials with a single distance (constant context) while the other half received an equal number of trials with each of three distances (varied context). During the transfer stage of the experiment, subjects either performed in the same movement distance context experienced during training (i.e., constant to constant; varied to varied) or in the opposite context (i.e., constant to varied; varied to constant). The results of the transfer analysis suggested that similariy of context between training and transfer phases of performance was not crucial to the accurate production of a novel closed-timing movement. Implications of the present results for recent theories of memory development are discussed.     

The utilization of visual information in the control of rapid sequential aiming movements.

Two experiments were conducted to examine the role of vision in the execution of a movement sequence. Experiment 1 investigated whether individual components of a sequential movement are controlled together or separately. Participants executed a rapid aiming movement to two targets in sequence. A full vision condition was compared to a condition in which vision was eliminated while in contact with the first target. The size of the first target was constant, while the second target size was varied. Target size had an influence on movement time and peak velocity to the first target. Vision condition and target size did not affect the time spent on the first target. These results suggest that preparation of the second movement is completed before the first movement is terminated. Experiment 2 examined when this preparation occurred. A full vision condition was compared to a condition in which vision was occluded during the flight phase of the first movement. Movement initiation times were shorter when vision was continually available. Total movement time was reduced with vision in two-target condition, but not in a control one-target condition. The time spent on the first target was greater when vision was not available during the first movement component. The results indicate that vision prior to movement onset can be used to formulate a movement plan to both targets in the sequence [Fischman & Reeve (1992).     

Goal-directed aiming under restricted viewing conditions with confirmatory sensory feedback

A substantial body of research has examined the speed-accuracy tradeoff captured by Fitts’ law, demonstrating increases in movement time that occur as aiming tasks are made more difficult by decreasing target width and/or increasing the distance between targets. Yet, serial aiming movements guided by internal spatial representations, rather than by visual views of targets have not been examined in this manner, and the value of confirmatory feedback via different sensory modalities within this paradigm is unknown. Here we examined goal-directed serial aiming movements (tapping back and forth between two targets), wherein targets were visually unavailable during the task. However, confirmatory feedback (auditory, haptic, visual, and bimodal combinations of each) was delivered upon each target acquisition, in a counterbalanced, within-subjects design. Each participant performed the aiming task with their pointer finger, represented within an immersive virtual environment as a 1 cm white sphere, while wearing a head-mounted display. Despite visual target occlusion, movement times increased in accordance with Fitts’ law. Though Fitts’ law captured performance for each of the sensory feedback conditions, the slopes differed. The effect of increasing difficulty on movement times was least influential in the haptic condition, suggesting more efficient processing of confirmatory haptic feedback during aiming movements guided by internal spatial representations.     

The preparation of reach to grasp movements in adults with Down syndrome.

The aim of this study was to determine the extent to which adults with Down syndrome (DS) are able to utilise advance information to prepare reach to grasp movements. The study comprised ten adults with DS; ten children matched to an individual in the group with DS on the basis of their intellectual ability, and twelve adult controls. The participants used their right hand to reach out and grasp illuminated perspex blocks. Four target blocks were positioned on a table surface, two to each side of the midsagittal plane. In the complete precue condition, participants were provided with information specifying the location of the target. In the partial precue condition, participants were given advance information indicating the location of the object relative to the midsagittal plane (left or right). In the null condition, advance information concerning the position of the target object was entirely ambiguous. It was found that both reaction times and movement times were greater for the participants with DS than for the adults without DS. The reaction times exhibited by individuals with DS in the complete precue condition were lower than those observed in the null condition, indicating that they had utilised advance information to prepare their movements. In the group with DS, when advance information specified only the location of the target object relative to the midline, reaction times were equivalent to those obtained when ambiguous information was given. In contrast, the adults without DS exhibited reaction times that were lower in both the complete and partial precue conditions when compared to the null condition. The pattern of results exhibited by the children was similar to that of the adults without DS. The movement times exhibited by all groups were not influenced by the precue condition. In summary, our findings indicate that individuals with DS are able to use advance information if it specifies precisely the location of the target object in order to prepare a reach to grasp movement. The group with DS were unable, however, to obtain the normal advantage of advance information specifying only one dimension of the movement goal (i.e., the position of an object relative to the body midline).