Attention and Interhemispheric Communication: Implications for Language Dominance.

Dominance of the left hemisphere for language processing is a prominent feature of brain organisation. Whereas structural models clarify the functional asymmetry due to direct access to local language circuits, dynamic models propose functional states of intrahemispheric activation and interhemispheric inhibition that are coupled with attentional processes. Real word settings often require modulations of lateralised neural processing and further express individual heterogeneity. In this research, we tested left- and right-handers, and used a behavioural paradigm with presentation of lateralised cue-target pairs to the same or opposite visual field. We observed that handedness distinctly affected word processing in the left hemisphere following contralateral cueing. Moreover, left-hemispheric dominance strengthened for right-handers vs abolished for left-handers, influencing behavioural efficiency. In combination with eye dominance recordings, these data suggest that attentional biases guided the processing strategies of both groups and in turn their achievements. Therefore, hand and eye dominance are both essential factors with a functional role in directing the communication of visual information between both hemispheres. Overall, the findings underline the importance of interacting hand-eye control systems in contributing to interhemispheric patterns in the context of language processing.

The interactive functional biases of manual, language and attention systems.

Hemispheric lateralisation is a fundamental principle of functional brain organisation. We studied two core cognitive functions-language and visuospatial attention-that typically lateralise in opposite cerebral hemispheres. In this work, we tested both left- and right-handed participants on lexical decision-making as well as on symmetry detection by means of a visual half-field paradigm with various target-distractor combinations simultaneously presented to opposite visual fields. Laterality indexes were analysed using a behavioural metrics in single individuals as well as between individuals. We observed that lateralisation of language and visuospatial attention as well as their relationship generally followed a left-right profile, albeit with differences as a function of handedness and target-distractor combination. In particular, right-handed individuals tended towards a typical pattern whereas left-handed individuals demonstrated increased individual variation and atypical organisation. That the atypical variants varied as a function of target-distractor combination and thus interhemispheric communication underlines its dynamic role in characterising lateralisation properties. The data further revealed distinctive relationships between right-handedness and left-hemispheric dominance for language together with right-hemispheric dominance for visuospatial processing. Overall, these findings illustrate the role of broader mechanisms in supporting hemispheric lateralisation of cognition and behaviour, relying on common principles but controlled by internal and external factors.

Space, time and number: common coding mechanisms and interactions between domains.

Space, time and number are key dimensions that underlie how we perceive, identify and act within the environment. They are interconnected in our behaviour and brain. In this study, we examined interdependencies between these dimensions. To this end, left- and right-handed participants performed an object collision task that required space-time processing and arithmetic tests that involved number processing. Handedness of the participants influenced collision detection with left-handers being more accurate than right-handers, which is in line with the premise that hand preference guides individual differences as a result of sensorimotor experiences and distinct interhemispheric integration patterns. The data further showed that successful collision detection was a predictor for arithmetic achievement, at least in right-handers. These findings suggest that handedness plays a mediating role in binding information processing across domains, likely due to selective connectivity properties within the sensorimotor system that is guided by hemispheric lateralisation patterns.

Stability and flexibility in cognitive control: Interindividual dynamics and task context processing.

Adaptive behaviour requires cognitive control for shielding current goals from distractors (stability) but at the same time for switching between alternative goals (flexibility). In this behavioural study, we examine the stability-flexibility balance in left- and right-handers during two types of decision-making, instructed (sensory cued) and voluntary (own choice), by means of distractor inhibition and hand/task switching. The data revealed that both groups showed opposite tendencies for instructed decision-making. Moreover, right-handers resisted distracting information more efficiently whereas left-handers showed superior switching abilities. When participants were involved in voluntary decision-making, no effects of handedness were noted, which suggests that free-choice processing alters the balance between stability and flexibility. These data illustrate that handedness is an index of individual variation during instructed decision-making, biasing the proficiency of cognitive control towards stability and flexibility of information processing. These biases can however be overruled by top-down strategies that dominate during voluntary decision-making. Overall, the research underlines the antagonistic functions of stability and flexibility in decision-making, and offers an approach for examining cognitive control and the role of internal and external factors in balancing the stability-flexibility trade-off.

Individual Differences and Hemispheric Asymmetries for Language and Spatial Attention.

Language and spatial processing are cognitive functions that are asymmetrically distributed across both cerebral hemispheres. In the present study, we compare left- and right-handers on word comprehension using a divided visual field paradigm and spatial attention using a landmark task. We investigate hemispheric asymmetries by assessing the participants' behavioral metrics; response accuracy, reaction time and their laterality index. The data showed that right-handers benefitted more from left-hemispheric lateralization for language comprehension and right-hemispheric lateralization for spatial attention than left-handers. Furthermore, left-handers demonstrated a more variable distribution across both hemispheres, supporting a less focal profile of functional brain organization. Taken together, the results underline that handedness distinctively modulates hemispheric processing and behavioral performance during verbal and nonverbal tasks. In particular, typical lateralization is most prevalent for right-handers whereas atypical lateralization is more evident for left-handers. These insights contribute to the understanding of individual variation of brain asymmetries and the mechanisms related to changes in cerebral dominance.

Motor Timing and Covariation with Time Perception: Investigating the Role of Handedness.

Time is a fundamental dimension of our behavior and enables us to guide our actions and to experience time such as predicting collisions or listening to music. In this study, we investigate the regulation and covariation of motor timing and time perception functions in left- and right-handers who are characterized by distinct brain processing mechanisms for cognitive-motor control. To this purpose, we use a combination of tasks that assess the timed responses during movements and the perception of time intervals. The results showed a positive association across left- and right-handers between movement-driven timing and perceived interval duration when adopting a preferred tempo, suggesting cross-domain coupling between both abilities when an intrinsic timescale is present. Handedness guided motor timing during externally-driven conditions that required cognitive intervention, which specifies the relevance of action expertise for the performance of timed-based motor activities. Overall, our results reveal that individual variation across domain-general and domain-specific levels of organization plays a steering role in how one predicts, perceives and experiences time, which accordingly impacts on cognition and behavior.

Manual dexterity: Functional lateralisation patterns and motor efficiency.

Manual tasks are an important goal-directed ability. In this EEG work, we studied how handedness affects the hemispheric lateralisation patterns during performance of visually-driven movements with either hand. The neural correlates were assessed by means of EEG coherence whereas behavioural output was measured by motor error. The EEG data indicated that left- and right-handers showed distinct recruitment patterns. These involved local interactions between brain regions as well as more widespread associations between brain systems. Despite these differences, brain-behaviour correlations highlighted that motor efficiency depended on left-sided brain regions across groups. These results suggest that skilled hand motor control relies on different neural patterns as a function of handedness whereas behavioural efficiency is linked with the left hemisphere. In conclusion, the present findings add to our understanding about principles of lateralised organisation as a function of handedness.

Hemispheric asymmetries and the control of motor sequences.

Sequencing of finger positions reflects a prototype of skilled behaviour. In order to perform sequencing, cognitive control supports the requirements and postural transitions. In this electroencephalography (EEG) study, we evaluate the effects of hand dominance and assess the neural correlates of unimanual and bimanual sequencing in left- and right-handers. The behavioural measurements provided an index of response planning (response time to first key press) and response execution (time between successive key presses, taps/s and percentage of correct responses), whereas the neural dynamics was determined by means of EEG coherence, expressing the functional connectivity between brain areas. Correlations between brain activity and behaviour were calculated for exploring the neural correlates that are functionally relevant for sequencing. Brain-behavioural correlations during response planning and execution revealed the significance of circuitry in the left hemisphere, underlining its significant role in the organisation of goal-directed behaviour. This lateralisation profile was independent of intrinsic constraints (hand dominance) and extrinsic demands (task requirements), suggesting essential higher-order computations in the left hemisphere. Overall, the observations highlight that the left hemisphere is specialised for sequential motor organisation in left- and right-handers, suggesting an endogenous hemispheric asymmetry for compound actions and the representation of skill; processes that can be separated from those that are involved in hand dominance.

Developmental changes in motor control: insights from bimanual coordination.

Manual dexterity is known to gradually progress with developmental age. In this study, we evaluate the performance of unimanual and bimanual actions under perturbed and unperturbed conditions in children between 4 and 10 years of age. Behavior was assessed by means of trajectory measurements and degree of bimanual coupling. The results showed that the younger children performed less successfully than the older children in the unimanual and bimanual tasks, with a plateau occurring around the age of 8 years. The SWAN rating scale of inattention and hyperactivity/impulsivity correlated with bimanual behavior at this particular age, suggesting that these traits are predictors of intricate skill performance during a critical developmental phase when significant refinement of control mechanisms occurs. The data furthermore revealed that a rebalancing of the between-hand performance asymmetries enabled superior bimanual coordination patterns in the older children. This suggests that progress in bimanual behavior relies on essential changes in unimanual processing and points to a dynamic interplay of circuitry. Overall, the data highlight a progressive change and integration of control systems due to developmental age with behavioral performance being guided by the existing constraints.

Cognitive control of response inhibition and switching: hemispheric lateralization and hand preference.

Changing environmental constraints often make already prepared responses unnecessary or inappropriate. Under such circumstances, cognitive control enables to suppress the response or switch to alternative behavior. Here, we examine the neural dynamics of both functions in left- and right-handers who performed two variants of a paradigm that required either inhibition of the response or switching the response between hands. The EEG coherence data showed strengthening of interregional coupling in the alpha band (8-12 Hz) following the target cues with an essential contribution of fronto-medial circuitry and a specific involvement of parietal areas in response switching. Brain-behavioral correlations revealed the functional significance of left-sided regions for successful response inhibition and switching, underlining the significant role of the left hemisphere for the organization of goal-directed activities. This lateralization pattern was observed for both left- and right-handers and suggests dominance of higher-order aspects of action planning in the left hemisphere.

Bimanual control processes and the role of handedness.

OBJECTIVE: Bimanual movements are a fundamental motor skill. Whereas substantial research is available from right-handers, much less is known from left-handers. Accordingly, in the present electroencephalography (EEG) study we evaluated bimanual behavior in left- versus right-handers. METHOD: Thirteen left-handers and 13 right-handers took part in the experiment. Cortical dynamics were evaluated by means of EEG coherence in the beta frequency band (14-28 Hz), and behavioral performance was measured using motor error. RESULTS: The EEG data revealed that right-handers showed a left-sided lateralization pattern whereas left-handers demonstrated a bilateral organization pattern during symmetrical actions. Asymmetry of the bimanual task demands modified the hemispheric profile for both groups and resulted in an additional involvement of the motor-nondominant hemisphere. Brain-behavioral correlations underlined that response planning strongly relied on the left hemisphere irrespective of handedness whereas the motor-dominant hemisphere drove response execution. CONCLUSION: The findings suggest that skilled motor planning may develop preferentially in the left hemisphere.

Subliminal priming and effects of hand dominance.

In the masked priming paradigm, motor responses to targets are influenced by previously presented subliminal primes, and are guided by facilitatory and inhibitory mechanisms that depend on prime-target compatibility/duration. In this study, we evaluate subliminal-driven priming in right- and left-handers during unimanual as well as bimanual tasks. The data from the unimanual tasks confirmed that prime-target compatibility affects performance as a function of prime-target duration. In a bimanual setting, the preferred hand benefitted from facilitation in both handedness groups whereas the non-preferred hand showed a positive priming effect only in left-handers. This denotes that left-handers are more susceptible to response activation of either hand. In addition, inhibitory priming had a stronger effect on the non-preferred than preferred hand, independent of handedness group. Overall, the findings suggest that subliminal-driven mechanisms that assist adaptive motor behavior are sensitive not only to extrinsic (task-related) factors such as prime-target compatibility but also to intrinsic (performer-related) factors such as hand dominance. The data further provide support for handedness-specific effects in motor functions and underline a significant role of hand dominance in the control of bimanual actions.

Handedness and the excitability of cortical inhibitory circuits.

Inhibitory processes play a significant role in the control of goal-directed actions. To increase insights into these mechanisms as a function of handedness, we measured the transient inhibition of volitional motor activity induced by single pulse transcranial magnetic stimulation during bimanual isometric contractions with symmetrical and asymmetrical force demands. Here, we assess the cortical silent period (cSP), which associates with intrahemispheric inhibition, and the ipsilateral silent period (iSP), which provides an estimation of interhemispheric inhibition. The data showed that inhibitory processes support the functional regulation of bimanual motor output. Furthermore, right-handers demonstrated asymmetries in intra- and interhemispheric inhibition due to asymmetrical force requirements and hand dominance, whereas left-handers did not show marked differences. In particular, right-handers demonstrated increased inhibitory processing that favoured control of the dominant (left) hemisphere whereas both motor cortices exhibited equal capabilities in left-handers. These observations were specific to the bimanual nature of the task. The present results underline distinct organisational mechanisms of coordinated behaviour in right- and left-handers.

Motor awareness and dissociable levels of action representation.

The present study evaluated the performance of a tracking task during which no, a small (subliminal: 20°) or a large (conscious: 60°) rotational perturbation was implemented. The instantaneous as well as carry-over effects of the perturbations were assessed. The subjective reports revealed that the subjects did not discriminate between the 0° and 20° perturbation conditions, despite increased trajectory error and directional trajectory changes in the latter than former condition, which suggests augmented error processing and task monitoring. Conversely, the 60° perturbation condition was characterized by subjective awareness in association with objective performance changes. Furthermore, a carry-over effect for the 60° but not for the 20° perturbation was observed when the distortion was removed midway into the trajectory. Together, the data underline distinct functioning of motor control and motor awareness with implications across time scales.

Prediction of collision events: an EEG coherence analysis.

OBJECTIVE: A common daily-life task is the interaction with moving objects for which prediction of collision events is required. To evaluate the sources of information used in this process, this EEG study required participants to judge whether two moving objects would collide with one another or not. In addition, the effect of a distractor object is evaluated. METHODS: The measurements included the behavioural decision time and accuracy, eye movement fixation times, and the neural dynamics which was determined by means of EEG coherence, expressing functional connectivity between brain areas. RESULTS: Collision judgment involved widespread information processing across both hemispheres. When a distractor object was present, task-related activity was increased whereas distractor activity induced modulation of local sensory processing. Also relevant were the parietal regions communicating with bilateral occipital and midline areas and a left-sided sensorimotor circuit. CONCLUSIONS: Besides visual cues, cognitive and strategic strategies are used to establish a decision of events in time. When distracting information is introduced into the collision judgment process, it is managed at different processing levels and supported by distinct neural correlates. SIGNIFICANCE: These data shed light on the processing mechanisms that support judgment of collision events; an ability that implicates higher-order decision-making.

Coupling between perception and action timing during sensorimotor synchronization.

Time is an important parameter in behaviour, especially when synchronization with external events is required. To evaluate the nature of the association between perception and action timing, this study introduced pitch accented tones during performance of a sensorimotor tapping task. Furthermore, regularity of the pacing cues was modified by small (subliminal) or large (conscious) timing perturbations. A global analysis across the intervals showed that repeated accented tones increased the tap-tone asynchrony in the regular (control) and irregular (subliminal) trials but not in the irregular trials with awareness of the perturbations. Asynchrony variability demonstrated no effect of accentuation in the regular and subliminal irregular trials, whereas it increased in the conscious irregular trials. A local analysis of the intervals showed that pitch accentuation lengthened the duration of the tapping responses, but only in the irregular trials with large timing perturbations. These data underline that common timing processes are automatically engaged for perception and action, although this arrangement can be overturned by cognitive intervention. Overall, the findings highlight a flexible association between perception and action timing within a functional information processing framework.