Left hand, but not right hand, reaching is sensitive to visual context

Revisiting the effect of visual illusions on grasping in left and right handers

Visual illusions have provided compelling evidence for a dissociation between perception and action. For example, when two different-sized objects are placed on opposite ends of the Ponzo illusion, people erroneously perceive the physically smaller object to be bigger than the physically larger one, but when they pick up the objects, their grip aperture reflects the real difference in size between the objects. This and similar findings have been demonstrated almost entirely for the right hand in right handers. The scarce research that has examined right and left-handed subjects in this context, has typically used only small samples. Here, we extended this research with a larger sample size (more than 50 in each group) in a version of the Ponzo illusion that allowed us to disentangle the effects of real and illusory size on action and perception in much more powerful way. We also collected a wide range of kinematic measures to assess possible differences in visuomotor control in left and right handers. The results showed that the dissociation between perception and action persisted for both hands in right handers, but only for the right hand in left handers. The left hand of left handers was sensitive to the illusion. Left handers also showed more variable and slower movements, as well as larger safety margins in both hands. These findings suggest that grasping in left handers may require more cognitive supervision, which could lead to greater sensitivity to visual context , particularly with their dominant left hand.

Bilateral arm movements are coordinated via task-dependent negotiations between independent and codependent control, but not by a "coupling" control policy

Prior research has shown that coordination of bilateral arm movements might be attributed to either control policies that minimize performance and control costs regardless of bilateral symmetry or by control coupling, which activates bilaterally homologous muscles as a single unit to achieve symmetric performance. We hypothesize that independent bimanual control (movements of one arm are performed without influence on the other) and codependent bimanual control (two arms are constrained to move together with high spatiotemporal symmetry) are two extremes on a coordination spectrum that can be negotiated to meet infinite variations in task demands. To better understand and distinguish between these views, we designed a task where minimization of either control costs or asymmetry would yield different patterns of coordination. Participants made bilateral reaches with a shared visual cursor to a midline target. We then covertly varied the gain contribution of either hand to the shared cursor's horizontal position. Across two experiments, we show that bilateral coordination retains high task-dependent sensitivity to subtle visual feedback gain asymmetries applied to the shared cursor. Specifically, we found a change from strong spatial covariation between hands during equal gains to more independent control during asymmetric gains, which occurred rapidly and with high specificity to the dimension of gain manipulation. Furthermore, the extent of spatial covariation was graded to the magnitude of perpendicular gain asymmetry between hands. These findings suggest coordination of bilateral arm movements flexibly maneuvers along a continuous coordination spectrum in a task-dependent manner that cannot be explained by bilateral control coupling.NEW & NOTEWORTHY Minimization of performance and control costs and efferent coupling between bilaterally homologous muscle groups have been separately hypothesized to describe patterns of bimanual coordination. Here, we address whether the mechanisms mediating independent and codependent control between limbs can be weighted for successful task performance. Using bilaterally asymmetric visuomotor gain perturbations, we show bimanual coordination can be characterized as a negotiation along a spectrum between extremes of independent and codependent control, but not efferent control coupling.

Force feedback delay affects perception of stiffness but not action, and the effect depends on the hand used but not on the handedness

Interaction with an object often requires the estimation of its mechanical properties. We examined whether the hand that is used to interact with the object and their handedness affected people's estimation of these properties using stiffness estimation as a test case. We recorded participants' responses on a stiffness discrimination of a virtual elastic force field and the grip force applied on the robotic device during the interaction. In half of the trials, the robotic device delayed the participants' force feedback. Consistent with previous studies, delayed force feedback biased the perceived stiffness of the force field. Interestingly, in both left-handed and right-handed participants, for the delayed force field, there was even less perceived stiffness when participants used their left hand than their right hand. This result supports the idea that haptic processing is affected by laterality in the brain, not by handedness. Consistent with previous studies, participants adjusted their applied grip force according to the correct size and timing of the load force regardless of the hand that was used, the handedness, or the delay. This suggests that in all of these conditions, participants were able to form an accurate internal representation of the anticipated trajectory of the load force (size and timing) and that this representation was used for accurate control of grip force independently of the perceptual bias. Thus these results provide additional evidence for the dissociation between action and perception in the processing of delayed information. NEW & NOTEWORTHY Introducing delay to force feedback during interaction with an elastic force field biases the perceived stiffness of the force field. We show that this bias depends on the hand that was used for probing but not on handedness. At the same time, both left-handed and right-handed participants adjusted their applied grip force while using either their left or right hands in anticipation of the correct magnitude and timing despite the delay in load force.

EXTRAVERSION/INTROVERSION AND AGE-RELATED DIFFERENCES IN SPEED-ACCURACY TRADEOFF

ABSTRACT Introduction: Extraversion/introversion and age differences might influence speed-accuracy tradeoff. Objective: The speed-accuracy tradeoff was investigated in extroverted and introverted female children, young adults and older adults. Method: Participants carried out an alternative version of Fitts’ task, which involved making alternate clicks with the mouse held in the dominant hand, moving as fast as possible, on two rectangular targets on a computer screen in order to make twelve attempts at six random levels of difficulty (twelve combinations of target widths and distances between targets). Each of the three groups was composed of 16 introverted and 16 extroverted subjects, based upon Brazilian versions of Eysenck’s questionnaire. Results: Elderly introverts fell short of the target more often and committed more overall errors than the elderly extroverts. Additionally, compared to their younger adult counterparts, the elderly subjects fell short of the target more often and committed more overall errors, besides taking longer to complete the task with higher levels of difficulty. Conclusion: The findings were interpreted in light of theories designed to explain the main processes underlying extroversion/introversion and age-related differences. Level of Evidence II; Lesser quality prospective study.

Action properties of object images facilitate visual search

There is mounting evidence that constraints from action can influence the early stages of object selection, even in the absence of any explicit preparation for action. Here, we examined whether action properties of images can influence visual search, and whether such effects were modulated by hand preference. Observers searched for an oddball target among 3 distractors. The search arrays consisted either of images of graspable "handles" ("action-related" stimuli), or images that were otherwise identical to the handles but in which the semicircular fulcrum element was reoriented so that the stimuli no longer looked like graspable objects ("non-action-related" stimuli). In Experiment 1, right-handed observers, who have been shown previously to prefer to use the right hand over the left for manual tasks, were faster to detect targets in action-related versus non-action-related arrays, and showed a response time (reaction time [RT]) advantage for rightward- versus leftward-oriented action-related handles. In Experiment 2, left-handed observers, who have been shown to use the left and right hands relatively equally in manual tasks, were also faster to detect targets in the action-related versus non-action-related arrays, but RTs were equally fast for rightward- and leftward-oriented handle targets. Together, or results suggest that action properties in images, and constraints for action imposed by preferences for manual interaction with objects, can influence attentional selection in the context of visual search. (PsycINFO Database Record

A philosophical approach to the concept of handedness: The phenomenology of lived experience in left- and right-handers

This paper provides a philosophical evaluation of the concept of handedness prevalent but largely unspoken in the scientific literature. This literature defines handedness as the preference or ability to use one hand rather than the other across a range of common activities. Using the philosophical discipline of phenomenology, I articulate and critique this conceptualization of handedness. Phenomenology shows defining a concept of handedness by focusing on hand use leads to a right hand biased concept. I argue further that a phenomenological model based in spatial orientation rather than hand use provides a more inclusive concept of handedness.

The contributions of vision and haptics to reaching and grasping

This review aims to provide a comprehensive outlook on the sensory (visual and haptic) contributions to reaching and grasping. The focus is on studies in developing children, normal, and neuropsychological populations, and in sensory-deprived individuals. Studies have suggested a right-hand/left-hemisphere specialization for visually guided grasping and a left-hand/right-hemisphere specialization for haptically guided object recognition. This poses the interesting possibility that when vision is not available and grasping relies heavily on the haptic system, there is an advantage to use the left hand. We review the evidence for this possibility and dissect the unique contributions of the visual and haptic systems to grasping. We ultimately discuss how the integration of these two sensory modalities shape hand preference.

Are there right hemisphere contributions to visually-guided movement? Manipulating left hand reaction time advantages in dextrals

Many studies have argued for distinct but complementary contributions from each hemisphere in the control of movements to visual targets. Investigators have attempted to extend observations from patients with unilateral left- and right-hemisphere damage, to those using neurologically-intact participants, by assuming that each hand has privileged access to the contralateral hemisphere. Previous attempts to illustrate right hemispheric contributions to the control of aiming have focussed on increasing the spatial demands of an aiming task, to attenuate the typical right hand advantages, to try to enhance a left hand reaction time advantage in right-handed participants. These early attempts have not been successful. The present study circumnavigates some of the theoretical and methodological difficulties of some of the earlier experiments, by using three different tasks linked directly to specialized functions of the right hemisphere: bisecting, the gap effect, and visuospatial localization. None of these tasks were effective in reducing the magnitude of left hand reaction time advantages in right handers. Results are discussed in terms of alternatives to right hemispheric functional explanations of the effect, the one-dimensional nature of our target arrays, power and precision given the size of the left hand RT effect, and the utility of examining the proportions of participants who show these effects, rather than exclusive reliance on measures of central tendency and their associated null hypothesis significance tests.

Sensitivity analysis of a novel five-degrees-of-freedom user command controller in people with spinal cord injury and non-injured for full upper extremity neuroprosthesis, wearable powered orthoses and prosthetics

Sensitivity analysis for a user command controller monitoring head position for artificial control of the proximal upper limb was performed. The controller was evaluated by having subjects complete target matching tasks manipulating a simulated on-screen hand representation to investigate the effects of target location and target speed on performance. Sixteen subjects took part in the study, 11 of whom had sustained cervical spinal cord injuries. The subjects were able to control the on-screen hand with overall low sensitivity of performance with the controller to target position in its five-degrees-of-freedom. The optimal speed was found to be a compromise between low speed and high accuracy but longer completion time and fast speed for short completion time with lower accuracy. The results demonstrated the robustness of the controller across a population of non-injured subjects and those with tetraplegia.

Is that graspable? Let your right hand be the judge

A right-hand preference for visually-guided grasping has been shown on numerous accounts. Grasping an object requires the integration of both visual and motor components of visuomotor processing. It has been suggested that the left hemisphere plays an integral role in visuomotor functions. The present study serves to investigate whether the visual processing of graspable objects, without any actual reaching or grasping movements, yields a right-hand (left-hemisphere) advantage. Further, we aim to address whether such an advantage is automatically evoked by motor affordances. Two groups of right-handed participants were asked to categorize objects presented on a computer monitor by responding on a keypad. The first group was asked to categorize visual stimuli as graspable (e.g. apple) or non-graspable (e.g. car). A second group categorized the same stimuli but as nature-made (e.g. apple) or man-made (e.g. car). Reaction times were measured in response to the visually presented stimuli. Results showed a right-hand advantage for graspable objects only when participants were asked to respond to the graspable/non-graspable categorization. When participants were asked to categorize objects as nature-made or man-made, a right-hand advantage for graspable objects did not emerge. The results suggest that motor affordances may not always be automatic and might require conscious representations that are appropriate for object interaction.

Increased cortical thickness and altered functional connectivity of the right superior temporal gyrus in left-handers

Altered structure in the temporal cortex has been implicated in the variable language laterality of left-handers (LH). The neuroanatomy of language lateralization and the corresponding synchronous functional connectivity (FC) in handedness cohorts are not, however, fully understood. We used structural and resting-state functional magnetic resonance imaging (fMRI) data to investigate the effect of altered cortical thickness on FC in LH and right-handers (RH). Whole-brain cortical thickness was calculated and compared between the LH and RH. We observed increased cortical thickness in the right superior temporal gyrus (STG) in the LH. A further FC analysis was conducted between the right STG and the remaining voxels in the brain. Compared with RH, the LH showed significantly higher FC in the left STG, right occipital cortex, and lower FC in the left inferior frontal gyrus and supramarginal gyrus. Our findings suggest that LH have atypical connectivity in the language network, with an enhanced role of the STG, findings which provide novel insights into the structural and functional substrates underlying the atypical language development of left-handed individuals.

Effects of direction and index of difficulty on aiming movements after stroke

BACKGROUND

Brain hemispheres play different roles in the control of aiming movements that are impaired after unilateral stroke. It is not clear whether those roles are influenced by the direction and the difficulty of the task.

OBJECTIVE

To evaluate the influence of direction and index of difficulty (ID) of the task on performance of ipsilesional aiming movements after unilateral stroke.

METHODS

Ten individuals with right hemisphere stroke, ten with left hemisphere stroke, and ten age- and gender-matched controls performed the aiming movements on a digitizing tablet as fast as possible. Stroke individuals used their ipsilesional arm. The direction (ipsilateral or contralateral), size (0.8 or 1.6 cm), and distance (9 or 18 cm) of the targets, presented on a monitor, were manipulated and determined to be of different ID (3.5, 4.5, and 5.5). Results. Individuals with right hemisphere lesion were more sensitive to ID of the task, affecting planning and final position accuracy. Left hemisphere lesion generated slower and less smooth movements and was more influenced by target distance. Contralateral movements and higher ID increased planning demands and hindered movement execution.

CONCLUSION

Right and left hemisphere damages are differentially influenced by task constraints which suggest their complementary roles in the control of aiming movements.

Manual asymmetries in the kinematics of a reach-to-grasp action

In the present study, we manipulated the perceived demand of an ecologically valid task to investigate the possible presence of manual asymmetries in a reach-to-grasp action. Participants reached, grasped and sipped from a water glass under low (nearly empty) and high (nearly full) demand conditions. Participants reached to grasp in closed-loop, open-loop and delay visual conditions. Manual asymmetries were found in movement time, peak velocity and maximum grip aperture variability. Consistent with reach-to-point literature: (1) right-handed actions were completed in less time than left-handed actions in visually and memory-guided conditions; (2) right-handed movements were more accurate (i.e., produced more consistent maximum grip apertures) than left-handed movements in visually guided conditions. The results support a theory of left-hemisphere specialization for visual control of action.

Left, right, left, right, eyes to the front! Müller-Lyer bias in grasping is not a function of hand used, hand preferred or visual hemifield, but foveation does matter

We investigated whether the control of movement of the left hand is more likely to involve the use of allocentric information than movements performed with the right hand. Previous studies (Gonzalez et al. in J Neurophys 95:3496–3501, 2006; De Grave et al. in Exp Br Res 193:421–427, 2009) have reported contradictory findings in this respect. In the present study, right-handed participants (N = 12) and left-handed participants (N = 12) made right- and left-handed grasps to foveated objects and peripheral, non-foveated objects that were located in the right or left visual hemifield and embedded within a Müller-Lyer illusion. They were also asked to judge the size of the object by matching their hand aperture to its length. Hand apertures did not show significant differences in illusory bias as a function of hand used, handedness or visual hemifield. However, the illusory effect was significantly larger for perception than for action, and for the non-foveated compared to foveated objects. No significant illusory biases were found for reach movement times. These findings are consistent with the two-visual system model that holds that the use of allocentric information is more prominent in perception than in movement control. We propose that the increased involvement of allocentric information in movements toward peripheral, non-foveated objects may be a consequence of more awkward, less automatized grasps of nonfoveated than foveated objects. The current study does not support the conjecture that the control of left-handed and right-handed grasps is predicated on different sources of information.

The A Theory Of Magnitude (ATOM) model in temporal perception and reproduction tasks

According to the A Theory of Magnitude (ATOM) model, time, numbers and space are processed by a common analog magnitude system. The model proposes that time, numbers and space are influenced by each other. Indeed, spatial-temporal (STEARC effect), spatial-numerical (SNARC effect) and temporal-numerical (TiNARC effect) interactions have been observed. However, the processing of time, numbers and space has not yet been studied within the same experimental procedure. The goal of this study is to test the ATOM model using a procedure in which time, numbers and space are all present. The participants were asked to perform temporal estimation (Experiment 1) and reproduction (Experiment 2) tasks in two different conditions, with either numbers or letters as stimuli. In Experiment 1, significant STEARC, SNARC and TiNARC effects were found in general and when numbers were presented. Moreover, a significant triple interaction between space, time and magnitude was observed, indicating associations between the left key, short duration and small magnitudes, as well as between the right key, long duration and large magnitudes. These results were similar in reaction times and accuracy. In Experiment 2, the results of reproduction times mirrored the previous data but the triple interaction was not found on reproduction times. Considering the temporal accuracy, the STEARC, SNARC and TiNARC effects as well as triple interaction were found. The results seem to partially confirm the ATOM model, even if differences between temporal tasks should be posited.

Network asymmetry of motor areas revealed by resting-state functional magnetic resonance imaging

There are ample functional magnetic resonance imaging (fMRI) studies on functional brain asymmetries, and the asymmetry of cerebral network in the resting state may be crucial to brain function organization. In this paper, a unified schema of voxel-wise functional connectivity and asymmetry analysis was presented and the network asymmetry of motor areas was studied. Twelve healthy male subjects with mean age 29.8 ± 6.4 were studied. Functional network in the resting state was described by using functional connectivity magnetic resonance imaging (fcMRI) analysis. Motor areas were selected as regions of interest (ROIs). Network asymmetry, including intra- and inter-network asymmetries, was formulated and analyzed. The intra-network asymmetry was defined as the difference between the left and right part of a particular functional network. The inter-network asymmetry was defined as the difference between the networks for a specific ROI in the left hemisphere and its homotopic ROI in the right hemisphere. Primary motor area (M1), primary sensory area (S1) and premotor area (PMA) exhibited higher functional correlation with the right parietal-temporal-occipital circuit and the middle frontal gyrus than they did with the left hemisphere. Right S1 and right PMA exhibited higher functional correlation with the ipsilateral precentral and supramarginal areas. There exist the large-scale hierarchical network asymmetries of the motor areas in the resting state. These asymmetries imply the right hemisphere dominance for predictive motor coding based on spatial attention and higher sensory processing load for the motor performance of non-dominant hemisphere.