Lateralized effects of target location on reaction times when preparing for manual aiming at a visual target

To elucidate the temporal characteristics of information processing for motor action differing in complexity in relation to both perceptual and cognitive information processing, we investigated whether the reaction times (RTs) to a visual target would be affected by task complexity (finger lifting or manual aiming), pre-cueing (with a pre-cue or without a pre-cue), or target location (five horizontal positions). Using the right hand, seven right-handed subjects performed two tasks, finger lifting and manual aiming at a target, with or without a pre-cue. The pre-cue announced the location of the target to be presented. An ANOVA showed significant interactions between task and location and between pre-cue and location with no significant interaction between task and pre-cue, indicating that the task-location interaction does not depend on whether or not a pre-cue is given. The manual-aiming RTs were longer than the finger-lifting RTs, and the effects of the target location on the RTs differed for finger lifting and manual aiming. It can be assumed that the longer RTs of manual aiming reflect the time for information processing that is needed when preparing for the aiming action per se, which is an extra movement performed in addition to the simple initiation of finger lifting. Differential RTs (DRTs) calculated by subtracting the finger-lifting RTs from the aiming RTs were therefore examined. The DRTs significantly differed for target locations (i.e., a lateralized effect), with the DRTs for an ipsilateral target appearing to be significantly shorter than those for contralateral and central targets. The lateralized effect appearing on the DRTs may be mediated by the processing of visual-spatial information about visual targets as motor preparations are made for manual aiming.     

Object-based processes in the planning of goal-directed hand movements

Theories in motor control suggest that the parameters specified during the planning of goal-directed hand movements to a visual target are defined in spatial parameters like direction and amplitude. Recent findings in the visual attention literature, however, argue widely for early object-based selection processes. The present experiments were designed to examine the contributions of object-based and space-based selection processes to the preparation time of goal-directed pointing movements. Therefore, a cue was presented at a specific location. The question addressed was whether the initiation of responses to uncued target stimuli could benefit from being either within the same object (object based) or presented at the same direction (space based). Experiment 1 replicated earlier findings of object-based benefits for non-goal-directed responses. Experiment 2 confirmed earlier findings of space-based benefits for goal-directed hand pointing movements. In Experiments 3 and 4, space-based and object-based manipulations were combined while requiring goal-directed hand pointing movements. The results clearly favour the notion that the selection processes for goal-directed pointing movements are primarily object based. Implications for theories on selective attention and action planning are discussed.     

Is there manual asymmetry in movement preparation?

Manual asymmetry in response preparation was investigated in simple and complex movements by using simple reaction-time tasks. The simple movement consisted of lifting the index finger, while in the complex one subjects reversed direction of movement to hit a switch after reaching for and grasping a tennis ball. Analysis showed that performance with either the right or the left hand was equivalent, with longer latencies for reacting on the complex task in comparison to the simple one. These findings indicate similar capabilities of the right and the left cerebral hemispheres to prepare the motor system for action independently of the spatial requirements of movement.     

Asymmetries in the spatial localization of transformed targets

This study was designed to examine the contribution of the right cerebral hemisphere in the spatial localization of visual targets for manual aiming. Visual targets were briefly presented to the right and left fields and subjects were required to point either to the target location, or a "mirror" image of the target location with their right or left index finger. Whereas reaction times were faster for left-hand pointing than for right-hand pointing, there was no differential effect of the mirror image transformation. This suggests that left-hand reaction time advantages are more related to right hemisphere involvement in the spatial parameterization of the movement than spatial localization of the target.     

Action matters: The role of action plans and object affordances in selection for action

In a series of three experiments requiring selection of real objects for action, we investigated whether characteristics of the planned action and/or the “affordances” of target and distractor objects affected interference caused by distractors. In all ofthe experiments, the target object was selectedon the basis of colour and was presented alone or with a distractor object. We examined the effect of type of response (button press, grasping, or pointing), object affordances (compatibility with the acting hand, affordances for grasping or pointing), and target/distractor positions (left or right) on distractor interference (reaction time differences between trials with and without distractors). Different patterns of distractor interference were associated with different motor responses. In the button-press conditions of each experiment, distractor interference was largely determined by perceptual salience (e.g., proximity to initial visual fixation). In contrast, in tasks requiring action upon the objects in the array, distractors with handles caused greater interference than those without handles, irrespective of whether the intended action was pointing or grasping. Additionally, handled distractors were relatively more salient when their affordances for grasping were strong (handle direction compatible with the acting hand) than when affordances were weak. These data suggest that attentional highlighting of specific target and distractor features is a function of intended actions.     

Action for perception: a motor-visual attentional effect

Five experiments investigated whether preparation of a grasping movement affects detection and discrimination of visual stimuli. Normal human participants were required to prepare to grasp a bar and then to grasp it as fast as possible on presentation of a visual stimulus. On the basis of the degree of sharing of their intrinsic properties with those of the to-be-grasped bar, visual stimuli were categorized as "congruent" or "incongruent." Results showed that grasping reaction times to congruent visual stimuli were faster than reaction times to incongruent ones. These data indicate that preparation to act on an object produces faster processing of stimuli congruent with that object. The same facilitation was present also when, after the preparation of hand grasping, participants were suddenly instructed to inhibit the prepared grasping movement and to respond with a different motor effector. The authors suggest that these findings could represent an extension of the premotor theory of attention, from orienting of attention to spatial locations to orienting of attention to graspable objects.     

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.     

Grasping remaps the distribution of visuospatial attention and enhances competing action activation

We examined how action goals influence the distribution of visuospatial attention near the body (Experiment 1) and how the temporal relationship between distractors and targets modifies shifts in visuospatial attention (Experiment 2). Targets were light emitting diodes (LEDs) in the left and right hemispace of a visual display. Following left or right target illumination, participants reached to point-to or grasp target object in blocked trials. Coincident with target onset, a distractor LED illuminated in the same or opposite hemispace between the initiation point and target, or no distractor appeared. In Experiment 1, during grasping there was a larger temporal interference effect (slower reach initiation) than with pointing. When grasping versus pointing, participants deviated more towards same-side distractors and away from opposite-side distractors. In Experiment 2, distractors onset 200ms prior to (?200-ms), coincident with (0 ms), or 200ms following (+200 ms) the target. For both reach types, ?200-ms distractors had greater onset temporal interference than 0 ms and +200-ms distractors. For grasping, +200 ms distractors had larger temporal interference than 0 ms distractors. For ?200-ms, reach trajectories deviated more towards opposite-side distractors and away from same-side distractors, the reverse of the pattern for 0 ms and +200-ms distractors.     

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.     

What is special about the index finger?: The index finger advantage in manipulating reflexive attentional shift1

Pointing with the index finger is a universal behavior. However, the functional significance of indexical pointing has not been examined empirically. We examined the efficacy of various pointing gestures in evoking viewer's attentional shifts. After viewing the gesture cue, observers quickly reported the location of a visual target. With a short cue‐target delay, reaction times were generally shorter for the target at the location where gesture cues pointed, but not with a long cue‐target delay. Moreover, the indexical pointing gesture produced a significantly larger cueing effect than the other gestures. Our control experiments indicated that the index‐finger advantage is tightly linked to the proper morphological shape (i.e. length and position of the index finger) of the indexical pointing and is not explained by the directional discriminability of the gesture. The visual system seems to use mechanisms that are partially independent of the directional discrimination of gestures, in order to quickly modulate the viewer's attention.     

Visual search is modulated by action intentions

The influence of action intentions on visual selection processes was investigated in a visual search paradigm. A predefined target object with a certain orientation and color was presented among distractors, and subjects had to either look and point at the target or look at and grasp the target. Target selection processes prior to the first saccadic eye movement were modulated by the different action intentions. Specifically, fewer saccades to objects with the wrong orientation were made in the grasping condition than in the pointing condition, whereas the number of saccades to an object with the wrong color was the same in the two conditions. Saccadic latencies were similar under the different task conditions, so the results cannot be explained by a speed-accuracy trade-off. The results suggest that a specific action intention, such as grasping, can enhance visual processing of action-relevant features, such as orientation. Together, the findings support the view that visual attention can be best understood as a selection-for-action mechanism.     

The temporal organization of hand, eye, and head movements during reaching and pointing

Two experiments are reported that address the issue of coordination of the eyes, head, and hand during reaching and pointing. Movement initiation of the eyes, head, and hand were monitored in order to make inferences about the type of movement control used. In the first experiment, when subjects pointed with the finger to predictable or unpredictable locations marked by the appearance of a light, no differences between head and eye movement initiation were found. In the second experiment, when subjects pointed very fast with the finger, the head started to move before the eyes did. Conversely, when subjects pointed accurately, and thus more slowly, with the finger, the eyes started to move first, followed by the head and finger. When subjects were instructed to point to the same visual target only with their eyes and head, both fast and accurately, however, eye movement always started before head movement, regardless of speed-accuracy instructions. These results indicate that the behavior of the eye and head system can be altered by introducing arm movements. This, along with the variable movement initiation patterns, contradicts the idea that the eye, head, and hand system is controlled by a single motor program. The time of movement termination was also monitored, and across both experiments, the eyes always reached the target first, followed by the finger, and then the head. This finding suggests that movement termination patterns may be a fundamental control variable.     

Motor imagery may incorporate trial-to-trial error

The authors tested for 1/f noise in motor imagery (MI). Participants pointed and imagined pointing to a single target (Experiment 1), to targets of varied size (Experiment 2), and switched between pointing and grasping (Experiment 3). Experiment 1 showed comparable patterns of serial correlation in actual and imagined movement. Experiment 2 suggested increased correlation for MI and performance with increased task difficulty, perhaps reflecting adaptation to a more complex environment. Experiment 3 suggested a parallel decrease in correlation with task switching, perhaps reflecting discontinuity of mental set. Although present results do not conclusively reveal 1/f fluctuation, the emergent patterns suggest that MI could incorporate trial-to-trial error across a range of constraints.     

How do we know what we are doing? Time, intention and awareness of action

Time is a fundamental dimension of consciousness. Many studies of the "sense of agency" have investigated whether we attribute actions to ourselves based on a conscious experience of intention occurring prior to action, or based on a reconstruction after the action itself has occurred. Here, we ask the same question about a lower level aspect of action experience, namely awareness of the detailed spatial form of a simple movement. Subjects reached for a target, which unpredictably jumped to the side on some trials. Participants (1) expressed their expectancy of a target shift during the upcoming movement, (2) pointed at the target as quickly and accurately as possible before returning to the start posiment to the target shift if required and (3) reproduced the spatial path of the movement they had just made, as accurately as possible, to give an indication of their awareness of the pointing movement. We analysed the spatial disparity between the initial and the reproduced movements on those with a target shift. A negative disparity value, or undershoot, suggests that motor awareness merely reflects a sluggish record of coordinated motor performance, while a positive value, or overshoot, suggests that participants' intention to point to the shifting target contributes more to their awareness of action than their actual pointing movement. Undershoot and overshoot thus measure the reconstructive (motoric) and the preconstuctive (intentional) aspects of action awareness, respectively. We found that trials on which subjects strongly expected a target shift showed greater overshoot and less undershoot than trials with lower expectancy. Conscious expectancy therefore strongly influences the experience of the detailed motor parameters of our actions. Further, a delay inserted either between the expectancy judgement and the pointing movement, or between the pointing movement and the reproduction of the movement, had no effect on visuomotor adjustment but strongly influenced action awareness. Delays during either interval boosted undershoots, suggesting increased reliance on a time-limited sensory memory for action. The experience of action is thus strongly influenced by prior thoughts and expectations, but only over a short time period. Thus, awareness of our actions is a dynamic and relatively flexible mixture of what we intend to do, and what our motor system actually does.     

Response competition: a major source of interference in a tactile identification task.

Two experiments investigated the ability of subjects to identify a moving, tactile stimulus. In both experiments, the subjects were presented with a target to their left index fingerpad and a nontarget (also moving) to their left middle fingerpad. Subjects were instructed to attend only to the target location and to respond "1" if the stimulus moved either to the left or up the finger, and to respond "2" if the stimulus moved either right or down the finger. The results showed that accuracy was better and reaction times were faster when the target and nontarget moved in the same direction than when they moved in different directions. When the target and nontarget moved in different directions, accuracy was significantly better and reaction times were significantly faster when the two stimuli had the same assigned response than when they had different responses. The results provide support for the conclusion that movement information is processed across adjacent fingers to the level of incipient response activation, even when subjects attempt to focus their attention on one location on the skin.     

Response competition: A major source of interference in a tactile identification task

Two experiments investigated the ability of subjects to identify a moving, tactile stimulus. In both experiments, the subjects were presented with a target to their left index fingerpad and a nontarget (also moving) to their left middle fingerpad. Subjects were instructed to attend only to the target location and to respond “1” if the stimulus moved either to the left or up the finger, and to respond “2” if the stimulus moved either right or down the finger. The results showed that accuracy was better and reaction times were faster when the target and nontarget moved in the same direction than when they moved in different directions. When the target and nontarget moved in different directions, accuracy was significantly better and reaction times were significantly faster when the two stimuli had the same assigned response than when they had different responses. The results provide support for the conclusion that movement information is processed across adjacent fingers to the level of incipient response activation, even when subjects attempt to focus their attention on one location on the skin.     

Brief bimanual force pulses: correlations between the hands in force and time.

Three experiments assessed coupling phenomena in the coordination of bimanual force pulses. Experiment 1 required symmetric force pulses (equal target forces and rise times for both hands) using the index finger of each hand. As the authors expected, on the basis of bimanual pointing movement results, this experiment revealed positive correlations between both the force rise times and the force amplitudes of the two hands. Experiments 2 and 3 included asymmetric conditions with different target force amplitudes (Experiment 2) or target rise times (Experiment 3). In Experiment 2 force amplitudes but not rise times were fully decoupled in the asymmetric condition. In the asymmetric condition of Experiment 3, however, neither rise times nor force amplitudes were fully decoupled. The results suggest a hierarchical control structure with temporal control dominating nontemporal control of bimanual force coordination.     

Human inferior parietal cortex ‘programs’ the action class of grasping

If one writes with a pen grasped between the toes, or a pencil held in the mouth, the handwriting style may be of poor quality but can be identified as belonging to a particular individual. Like other actions, such as grasping or pointing, different body parts can be used to produce the movement. These findings, of reasonably consistent spatial and temporal productions by different effectors, have been used to argue for the concept of motor equivalence and the existence of motor programs abstracted from particular effectors. In this study subjects were required to perform an action (grasping a sweet) with different effectors (the mouth or the hand) while the brain was scanned. Activation of the inferior parietal lobe during real and imagined mouth grasping, and during real hand grasping actions was demonstrated. Primate neurophysiological research has implicated this region in a movement-planning role. Our results confirm the importance of the inferior parietal lobe in integrating converging multimodal sensory information for coding of general action patterns in humans.     

Object-based control of attention is sensitive to recent experience

How is attention guided by past experience? In visual search, numerous studies have shown that recent trials influence responses to the current trial. Repeating features such as color, shape, or location of a target facilitates performance. Here we examine whether recent experience also modulates a more abstract dimension of attentional control, object-based and location-based control. Participants performed a cued target discrimination task with stimuli presented on 2 rectangles. Response times to targets appearing in an uncued location on a cued rectangle were faster than to targets on the uncued rectangle, demonstrating an object-based attentional benefit. We investigated the object-based benefit on the current trial contingent on the cue-target relationship on the previous trial. The object-based benefit was significant only when the cued object contained the target on the previous trial, not when the uncued object contained the target. This effect of recent experience was not due to either the repetition of spatial cue-target location or the repetition of the response, but to adaptation to contingencies in the environment. Our results suggest a unifying view of attentional control that spans the concrete dimensions of control (e.g., determining the relative importance of red vs. blue) to the abstract (determining the relative importance of objects vs. locations in space). Attention closely tracks the short time scale structure of the environment and automatically adapts to optimize performance to this structure.     

Control of goal-directed movements: the contribution of orienting of visual attention and motor preparation.

Three experiments investigated the role of attention and motor preparation for the control of goal-directed movements. In Experiment 1 (double step paradigm), a movement correction was required on 25% of the trials towards the left or right of the initial target. Within these 25% of trials, the probability of location of the second target was manipulated. The efficiency of movement control increased when increasing the probability of correcting the movement in a given direction. In Experiment 2, attentional processes were isolated by asking the subjects to verbally detect the more or less probable target displacement, without correcting their movement. Subjects were able to orient visual attention during movement execution, thus improving the processing of visual feedbacks from target displacement. In Experiment 3, motor preparation processes were isolated by asking the subjects to correct their movement towards a fixed target in response to a more or less probable mechanical perturbation. It was shown that motor preparation not only specifies the initial movement parameters but may also include some parameters of the most probable movement modulations. Overall, these results highlight the role of both attentional and motor preparation processes in the control of goal-directed movements and suggest that the feedback-based corrections of the movement are modulated by a feedforward control.