Grasping with the eyes of your hands: Hapsis and vision modulate hand preference

Healthy adults favor stable left/right hand choices over performance at an unconstrained reach-to-grasp task

Reach-to-grasp actions are fundamental to the daily activities of human life, but few methods exist to assess individuals' reaching and grasping actions in unconstrained environments. The Block Building Task (BBT) provides an opportunity to directly observe and quantify these actions, including left/right hand choices. Here we sought to investigate the motor and non-motor causes of left/right hand choices, and optimize the design of the BBT, by manipulating motor and non-motor difficulty in the BBT's unconstrained reach-to-grasp task. We hypothesized that greater motor and non-motor (e.g. cognitive/perceptual) difficulty would drive increased usage of the dominant hand. To test this hypothesis, we modulated block size (large vs. small) to influence motor difficulty, and model complexity (10 vs. 5 blocks per model) to influence non-motor difficulty, in healthy adults (n = 57). Our data revealed that increased motor and non-motor difficulty led to lower task performance (slower task speed), but participants only increased use of their dominant hand only under the most difficult combination of conditions: in other words, participants allowed their performance to degrade before changing hand choices, even though participants were instructed only to optimize performance. These results demonstrate that hand choices during reach-to grasp actions are more stable than motor performance in healthy right-handed adults, but tasks with multifaceted difficulties can drive individuals to rely more on their dominant hand.

Visual Attention and Cognitive Archaeology: An Eye-Tracking Study of Palaeolithic Stone Tools

The study of lithic technology can provide information on human cultural evolution. This article aims to analyse visual behaviour associated with the exploration of ancient stone artefacts and how this relates to perceptual mechanisms in humans. In Experiment 1, we used eye tracking to record patterns of eye fixations while participants viewed images of stone tools, including examples of worked pebbles and handaxes. The results showed that the focus of gaze was directed more towards the upper regions of worked pebbles and on the basal areas for handaxes. Knapped surfaces also attracted more fixation than natural cortex for both tool types. Fixation distribution was different to that predicted by models that calculate visual salience. Experiment 2 was an online study using a mouse-click attention tracking technique and included images of unworked pebbles and 'mixed' images combining the handaxe's outline with the pebble's unworked texture. The pattern of clicks corresponded to that revealed using eye tracking and there were differences between tools and other images. Overall, the findings suggest that visual exploration is directed towards functional aspects of tools. Studies of visual attention and exploration can supply useful information to inform understanding of human cognitive evolution and tool use.

Getting to grips with endoscopy - Learning endoscopic surgical skills induces bi-hemispheric plasticity of the grasping network

Endoscopic surgery requires skilled bimanual use of complex instruments that extend the peri-personal workspace. To delineate brain structures involved in learning such surgical skills, 48 medical students without surgical experience were randomly assigned to five training sessions on a virtual-reality endoscopy simulator or to a non-training group. Brain activity was probed with functional MRI while participants performed endoscopic tasks. Repeated task performance in the scanner was sufficient to enhance task-related activity in left ventral premotor cortex (PMv) and the anterior Intraparietal Sulcus (aIPS). Simulator training induced additional increases in task-related activation in right PMv and aIPS and reduced effective connectivity from left to right PMv. Skill improvement after training scaled with stronger task-related activation of the lateral left primary motor hand area (M1-HAND). The results suggest that a bilateral fronto-parietal grasping network and left M1-HAND are engaged in bimanual learning of tool-based manipulations in an extended peri-personal space.

Sensorimotor lateralization scaffolds cognitive specialization

In this chapter, we review hemispheric differences for sensorimotor function and cognitive abilities. Specifically, we examine the left-hemisphere specialization for visuomotor control and its interplay with language, executive function, and musical training. Similarly, we discuss right-hemisphere lateralization for haptic processing and its relationship to spatial and numerical processing. We propose that cerebral lateralization for sensorimotor functions served as a foundation for the development of higher cognitive abilities and their hemispheric functional specialization. We further suggest that sensorimotor and cognitive functions are inextricably linked. Based on the studies discussed in this chapter our view is that sensorimotor control serves as a loom upon which the fibers of language, executive function, spatial, and numerical processing are woven together to create the fabric of cognition.

Wait wait, don't tell me: Handedness questionnaires do not predict hand preference for grasping

Handedness questionnaires are a common screening tool in psychology and neuroscience, used whenever a participant's performance on a given task may conceivably be affected by their laterality. Two widely-used examples of such questionnaires are the Edinburgh Handedness Inventory and the Waterloo Handedness Questionnaire. Both instruments ask respondents to report their hand preference for performing a variety of common tasks (e.g., throwing a ball, or opening a drawer). Here we combined questions from the two instruments (E-WHQ; 22 questions total) and asked participants to report their preferred hand for each via a five-point scale. The purpose of this study was to determine whether responses on the E-WHQ are accurate, reliable, and/or predictive of hand-preference for a simple grasp-to-construct task. Regarding accuracy, handedness scores were 5% lower when participants used a scrambled response key versus a consistent one. Test-retest reliability of the questionnaire was weak, with any given inventory item eliciting a different response from 34% of respondents upon retesting. Neither was the E-WHQ predictively useful-although both left- and right-handers preferred their dominant hands, E-WHQ score did not correlate with overall percentage of dominant-hand grasps in either group. We conclude that the E-WHQ is unsuited for predicting hand preference for grasping.

Modulating Children’s Manual Preference Through Spontaneous Nondominant Hand Use

We evaluated the effect of repeated use of the nonpreferred hand on young children’s manual preference by positioning toys in the left hemifield in egocentric coordinates to induce right-handed 4–5-year-olds to use their left hands spontaneously. We induced motor activities in the laterally biased workspace by presenting tasks in a ludic context over different days, similar to their daily kindergarten experience. Preceding and following these lateralized experiences, the children were tested on a task requiring reaching, grasping, and inserting cards into a slot. In the 1-day retention assessment, we found that repeated use of the nonpreferred left hand in the previous phase led to increased use of the left hand to perform the probing task. Following 14 days of rest, the children with induced left-hand experiences used exclusively their left hands to manipulate the leftmost card positions. We propose that repeated use of the nonpreferred left hand leads to increased confidence to plan left-handed movements for subsequent tasks.

Age-related changes in hand dominance and functional asymmetry in older adults

The aim of the study was to investigate fine motor performance and ascertain age-related changes in laterality between the dominant and non-dominant hand. A representative sample of 635 adults (144 males and 491 females) aged 50 years and over completed a test battery MLS (Motor Performance Series) to assess a broad range of hand functions. Functional asymmetry was observed in all four motor tests (postural tremor, aiming, tapping, and inserting long pins). Significant differences between the dominant and non-dominant hand were obtained in both sexes across all age groups, except in the oldest female group (age >70) for the aiming (number of hits and errors) and postural tremor (number of errors) tasks. These differences in age-related changes may be attributed to hemispheric asymmetry, environmental factors, or use-dependent plasticity. Conflicting evidence in the literature warrants additional research to better explain age-related alterations of hand dominance and manual performance in old age.

Handedness and Graspability Modify Shifts of Visuospatial Attention to Near-Hand Objects

We examined how factors related to the internal representation of the hands (handedness and grasping affordances) influence the distribution of visuospatial attention near the body. Left and right handed participants completed a covert visual cueing task, discriminating between two target shapes. In Experiment 1, participants responded with either their dominant or non-dominant hand. In Experiment 2, the non-responding hand was positioned below one of two target placeholders, aligned with the shoulder. In Experiment 3 the near-monitor hand was positioned under the placeholder in the opposite region of hemispace, crossed over the body midline. For Experiments 2 & 3, in blocked trials the palmar and back-of hand surfaces were directed towards the target placeholder such that targets appeared towards either the graspable or non-graspable space of the hand respectively. In Experiment 2, both left and right handers displayed larger accuracy cueing effects for targets near versus distant from the graspable space of the right hand. Right handers also displayed larger response time cueing effects for objects near the graspable versus non-graspable region of their dominant hand but not for their non-dominant hands. These effects were not evident for left-handers. In Experiment 3, for right handers, accuracy biases for near hand targets were still evident when the hand was crossed over the body midline, and reflected hand proximity but not functional orientation biases. These findings suggest that biased visuospatial attention enhances object identity discrimination near hands and that these effects are particularly enhanced for right-handers.

Temporary Nerve Block at Selected Digits Revealed Hand Motor Deficits in Grasping Tasks

Peripheral sensory feedback plays a crucial role in ensuring correct motor execution throughout hand grasp control. Previous studies utilized local anesthesia to deprive somatosensory feedback in the digits or hand, observations included sensorimotor deficits at both corticospinal and peripheral levels. However, the questions of how the disturbed and intact sensory input integrate and interact with each other to assist the motor program execution, and whether the motor coordination based on motor output variability between affected and non-affected elements (e.g., digits) becomes interfered by the local sensory deficiency, have not been answered. The current study aims to investigate the effect of peripheral deafferentation through digital nerve blocks at selective digits on motor performance and motor coordination in grasp control. Our results suggested that the absence of somatosensory information induced motor deficits in hand grasp control, as evidenced by reduced maximal force production ability in both local and non-local digits, impairment of force and moment control during object lift and hold, and attenuated motor synergies in stabilizing task performance variables, namely the tangential force and moment of force. These findings implied that individual sensory input is shared across all the digits and the disturbed signal from local sensory channel(s) has a more comprehensive impact on the process of the motor output execution in the sensorimotor integration process. Additionally, a feedback control mechanism with a sensation-based component resides in the formation process for the motor covariation structure.

A kinematic examination of hand perception

Previous research has found that the perception of our hands is inaccurate. This distorted representation has several constant characteristics including an overestimation of hand width and an underestimation of finger length. In this study, we further investigate this phenomenon by exploring the boundaries of hand representation. Participants placed one hand underneath a table top so it was occluded from view. Using their free hand, participants were instructed to point to the location where they believed the tips and bases of each of their fingers were. These ten landmarks were recorded using a motion capture system. One group of participants pointed to the landmarks in a random order (as done in previous studies) while another group pointed to them in a systematic fashion (from the tip of the thumb sequentially through to the pinky). Furthermore, to explore if having a frame of reference facilitates hand perception, some participants initiated each of their estimations directly from the previous landmark while others initiated them from a home spot located outside the span of the hand. Results showed that the participants who pointed in the systematic order made numerous accurate judgments of hand size and were overall more precise than participants who pointed in a random order. Including a frame of reference however, had no effect on the judgments. The results also showed asymmetries in hand perception. These findings are discussed in relation to different possible internal body representations and hemispheric asymmetries in body perception.

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.

Manual preferences for visually- and haptically-guided grasping

Studies have shown that individuals exhibit a right-hand preference for grasping during visually-guided tasks. Recently, we have found that when vision is occluded right-hand preference decreases dramatically. It remains unknown however, if this decrease is a result of visual occlusion or the effects of relying only on haptic feedback. Therefore, in the present study, we sought to explore the contributions of vision and haptics (separately and in conjunction) to hand preference for grasping. Right- and left-handed individuals were tested on a block building task under four different visual and haptic conditions: 1) vision/normal haptic feedback (V/H), 2) no vision/normal haptic feedback (NV/H), 3) vision/constrained haptic feedback (V/Constrained-H), and 4) no vision/constrained haptic feedback (NV/Constrained-H). Vision was occluded using a blindfold and haptic feedback was constrained by asking participants to wear textured gloves. Right-handed individuals displayed a right-hand preference when vision was available (V/H and V/Constrained-H groups), but this preference was much greater when haptic feedback was constrained (V/Constrained-H group). When vision was occluded and haptic feedback was used to complete the task (NV/H) no hand preference was found. Finally hand preference was similar between the V/H and the NV/Constrained-H groups. For left-handed individuals, no differences in hand use were found between the different sensory groups, but the NV/H group showed a clear left-hand preference for haptically-guided grasping. The results suggest that haptics plays an important role in hand preference for grasping. Furthermore, they support a left-hand/right-hemisphere specialization for haptically-guided grasping (regardless of handedness) and a right-hand/left-hemisphere specialization for visually-guided grasping (at least in right-handed individuals).

Hand preference across the lifespan: effects of end-goal, task nature, and object location

In the present study we investigate age-related changes in hand preference for grasping and the influence of task demands on such preference. Children (2–11), young-adults (17–28) and older-adults (57–90) were examined in a grasp-to-eat and a grasp-to-construct task. The end-goal of these tasks was different (eat vs. construct) as was the nature of the task (unimanual vs. bimanual). In both tasks, ipsilateral and contralateral grasps were analyzed. Results showed a right-hand preference that did not change with age. Across the three age groups, a more robust right-hand preference was observed for the unimanual, grasp-to-eat task. To disentangle if the nature (unimanual) or the end-goal (grasp-to-eat) was the driver of the robust right-hand preference, a follow up experiment was conducted. Young-adult participants completed a unimanual grasp-to-place task. This was contrasted with the unimanual grasp-to-eat task and the bimanual grasp-to-construct task. Rates of hand preference for the grasp-to-eat task remained the highest when compared to the other two grasping tasks. Together, the results demonstrate that hand preference remains stable from childhood to older adulthood, and they suggest that a left hemisphere specialization exists for grasping, particularly when bringing food to the mouth.

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.

Speech in action: degree of hand preference for grasping predicts speech articulation competence in children

Highlights: Degree of lateralization for grasping predicts the maturity of the language production system in young, typically-developing children.

In this report we provide compelling evidence for the relationship between right hand grasp-to-mouth (i.e., feeding) movements and language development. Specifically, we show that children (4–5 years old) who are more right-hand lateralized in picking up small food items for consumption show enhanced differentiation of the “s” and “sh” sounds. This result suggests that left hemisphere control of hand-to-mouth gestures may have provided an evolutionary platform for the development of language. The current investigation presents the exciting possibility that early right hand-to-mouth training could accelerate the development of articulation skills.

Grasping without sight: insights from the congenitally blind

We reach for and grasp different sized objects numerous times per day. Most of these movements are visually-guided, but some are guided by the sense of touch (i.e. haptically-guided), such as reaching for your keys in a bag, or for an object in a dark room. A marked right-hand preference has been reported during visually-guided grasping, particularly for small objects. However, little is known about hand preference for haptically-guided grasping. Recently, a study has shown a reduction in right-hand use in blindfolded individuals, and an absence of hand preference if grasping was preceded by a short haptic experience. These results suggest that vision plays a major role in hand preference for grasping. If this were the case, then one might expect congenitally blind (CB) individuals, who have never had a visual experience, to exhibit no hand preference. Two novel findings emerge from the current study: first, the results showed that contrary to our expectation, CB individuals used their right hand during haptically-guided grasping to the same extent as visually-unimpaired (VU) individuals did during visually-guided grasping. And second, object size affected hand use in an opposite manner for haptically- versus visually-guided grasping. Big objects were more often picked up with the right hand during haptically-guided, but less often during visually-guided grasping. This result highlights the different demands that object features pose on the two sensory systems. Overall the results demonstrate that hand preference for grasping is independent of visual experience, and they suggest a left-hemisphere specialization for the control of grasping that goes beyond sensory modality.

Getting the right grasp on executive function

Executive Function (EF) refers to important socio-emotional and cognitive skills that are known to be highly correlated with both academic and life success. EF is a blanket term that is considered to include self-regulation, working memory, and planning. Recent studies have shown a relationship between EF and motor control. The emergence of motor control coincides with that of EF, hence understanding the relationship between these two domains could have significant implications for early detection and remediation of later EF deficits. The purpose of the current study was to investigate this relationship in young children. This study incorporated the Behavioral Rating Inventory of Executive Function (BRIEF) and two motor assessments with a focus on precision grasping to test this hypothesis. The BRIEF is comprised of two indices of EF: (1) the Behavioral Regulation Index (BRI) containing three subscales: Inhibit, Shift, and Emotional Control; (2) the Metacognition Index (MI) containing five subscales: Initiate, Working Memory, Plan/Organize, Organization of Materials, and Monitor. A global executive composite (GEC) is derived from the two indices. In this study, right-handed children aged 5-6 and 9-10 were asked to: grasp-to-construct (Lego® models); and grasp-to-place (wooden blocks), while their parents completed the BRIEF questionnaire. Analysis of results indicated significant correlations between the strength of right hand preference for grasping and numerous elements of the BRIEF including the BRI, MI, and GEC. Specifically, the more the right hand was used for grasping the better the EF ratings. In addition, patterns of space-use correlated with the GEC in several subscales of the BRIEF. Finally and remarkably, the results also showed a reciprocal relationship between hand and space use for grasping and EF. These findings are discussed with respect to: (1) the developmental overlap of motor and executive functions; (2) detection of EF deficits through tasks that measure lateralization of hand and space use; and (3) the possibility of using motor interventions to remediate EF deficits.