- Nijmegen, Gelderland, Netherlands
Luc Selen
Radboud University Nijmegen, Psychology, Post-Doc
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Motor costs influence movement selection. These costs could change when movements are adapted in response to errors. When the motor system attributes the encountered errors to an external cause, appropriate movement selection requires an... more
Motor costs influence movement selection. These costs could change when movements are adapted in response to errors. When the motor system attributes the encountered errors to an external cause, appropriate movement selection requires an update of the movement goal, which prompts the selection of a different control policy. However, when errors are attributed to an internal cause, the initially selected control policy could remain unchanged, but the internal forward model of the body needs to be updated, resulting in an online correction of the movement. We hypothesized that external attribution of errors leads to the selection of a different control policy, and thus to a change in the expected cost of movements. This should also affect subsequent motor decisions. Conversely, internal attribution of errors may (initially) only evoke online corrections, and thus is expected to leave the motor decision process unchanged. We tested this hypothesis using a saccadic adaptation paradigm, designed to change the relative motor cost of two targets. Motor decisions were measured using a target selection task between the two saccadic targets before and after adaptation. Adaptation was induced by either abrupt or gradual perturbation schedules, which are thought to induce more external or internal attribution of errors, respectively. By taking individual variability into account, our results show that saccadic decisions shift towards the least costly target after adaptation, but only when the perturbation is abruptly, and not gradually, introduced. We suggest that credit assignment of errors not only influences motor adaptation but also subsequent motor decisions.
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Full body-motion biases decisions of hand choice. We examined the signatures of this bias in hand preference in corticospinal excitability before a reach target was presented. Our results show that behavior and corticospinal excitability... more
Full body-motion biases decisions of hand choice. We examined the signatures of this bias in hand preference in corticospinal excitability before a reach target was presented. Our results show that behavior and corticospinal excitability modulate depending on the state of the body in motion. This suggests that information about body motion penetrates deeply within the motor system.
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Contemporary motor control theories propose competition between multiple motor plans before the winning command is executed. While most competitions are completed before movement onset, movements are often initiated before the competition... more
Contemporary motor control theories propose competition between multiple motor plans before the winning command is executed. While most competitions are completed before movement onset, movements are often initiated before the competition has been resolved. An example of this is saccadic averaging, wherein the eyes land at an intermediate location between two visual targets. Behavioral and neurophysiological signatures of competing motor commands have also been reported for reaching movements, but debate remains about whether such signatures attest to an unresolved competition, arise from averaging across many trials, or reflect a strategy to optimize behavior given task constraints. Here, we recorded EMG activity from an upper limb muscle (m. pectoralis) while 12 (8 female) participants performed an immediate response reach task, freely choosing between one of two identical and suddenly presented visual targets. On each trial, muscle recruitment showed two distinct phases of directionally tuned activity. In the first wave, time-locked ∼100 ms of target presentation, muscle activity was clearly influenced by the nonchosen target, reflecting a competition between reach commands that was biased in favor of the ultimately chosen target. This resulted in an initial movement intermediate between the two targets. In contrast, the second wave, time-locked to voluntary reach onset, was not biased toward the nonchosen target, showing that the competition between targets was resolved. Instead, this wave of activity compensated for the averaging induced by the first wave. Thus, single-trial analysis reveals an evolution in how the nonchosen target differentially influences the first and second wave of muscle activity.SIGNIFICANCE STATEMENTContemporary theories of motor control suggest that multiple motor plans compete for selection before the winning command is executed. Evidence for this is found in intermediate reach movements toward two potential target locations, but recent findings have challenged this notion by arguing that intermediate reaching movements reflect an optimal response strategy. By examining upper limb muscle recruitment during a free-choice reach task, we show early recruitment of a suboptimal averaged motor command to the two targets that subsequently transitions to a single motor command that compensates for the initially averaged motor command. Recording limb muscle activity permits single-trial resolution of the dynamic influence of the nonchosen target through time.
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ABSTRACTVoice production can be a whole-body affair: Upper limb movements physically impact the voice in steady-state vocalization, speaking, and singing. This is supposedly due to biomechanical impulses on the chest-wall, affecting... more
ABSTRACTVoice production can be a whole-body affair: Upper limb movements physically impact the voice in steady-state vocalization, speaking, and singing. This is supposedly due to biomechanical impulses on the chest-wall, affecting subglottal pressure. Unveiling such biomechanics is important, as humans gesture with their hands in a synchronized way with speaking. Here we assess biomechanical interactions between arm movements and the voice, by measurement of key (respiratory-related) muscles with electromyography (EMG) during different types of upper limb movement while measuring the bodys center of mass. We show that gesture-related muscle activations scale with positive peaks in the voices amplitude. Some of these muscles also strongly associate with changes in the center mass, confirming that gesture-vocal coupling partly arises due to posture-related muscle activity. If replicated, these results suggest an evolutionary ancient gesture-vocal connection at the level of biomechan...
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Within predictive processing two kinds of learning can be distinguished: parameter learning and structure learning. In Bayesian parameter learning, parameters under a specific generative model are continuously being updated in light of... more
Within predictive processing two kinds of learning can be distinguished: parameter learning and structure learning. In Bayesian parameter learning, parameters under a specific generative model are continuously being updated in light of new evidence. However, this learning mechanism cannot explain how new parameters are added to a model. Structure learning, unlike parameter learning, makes structural changes to a generative model by altering its causal connections or adding or removing parameters. Whilst these two types of learning have recently been formally differentiated, they have not been empirically distinguished. The aim of this research was to empirically differentiate between parameter learning and structure learning on the basis of how they affect pupil dilation. Participants took part in a within-subject computer-based learning experiment with two phases. In the first phase, participants had to learn the relationship between cues and target stimuli. In the second phase, th...
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The endeavor to understand the human brain has seen more progress in the last few decades than in the previous two millennia. Still, our understanding of how the human brain relates to behavior in the real world and how this link is... more
The endeavor to understand the human brain has seen more progress in the last few decades than in the previous two millennia. Still, our understanding of how the human brain relates to behavior in the real world and how this link is modulated by biological, social, and environmental factors is limited. To address this, we designed the Healthy Brain Study (HBS), an interdisciplinary, longitudinal, cohort study based on multidimensional, dynamic assessments in both the laboratory and the real world. Here, we describe the rationale and design of the currently ongoing HBS. The HBS is examining a population-based sample of 1,000 healthy participants (age 30–39) who are thoroughly studied across an entire year. Data are collected through cognitive, affective, behavioral, and physiological testing, neuroimaging, bio-sampling, questionnaires, ecological momentary assessment, and real-world assessments using wearable devices. These data will become an accessible resource for the scientific c...
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Within predictive processing learning is construed as Bayesian model updating with the degree of certainty for different existing hypotheses changing in light of new evidence. Bayesian model updating, however, cannot explain how new... more
Within predictive processing learning is construed as Bayesian model updating with the degree of certainty for different existing hypotheses changing in light of new evidence. Bayesian model updating, however, cannot explain how new hypotheses are added to a model. Model revision, unlike model updating, makes structural changes to a generative model by altering its causal connections or adding or removing hypotheses. Whilst model updating and model revision have recently been formally differentiated, they have not been empirically distinguished. The aim of this research was to empirically differentiate between model updating and revision on the basis of how they affect prediction errors and predictions over time. To study this, participants took part in a within-subject computer-based learning experiment with two phases: updating and revision. In the updating phase, participants had to predict the relationship between cues and target stimuli and in the revision phase, they had to co...
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Behavioral studies have shown that humans account for inertial acceleration in their decisions of hand choice when reaching during body motion. Physiologically, it is unclear at what stage of movement preparation information about body... more
Behavioral studies have shown that humans account for inertial acceleration in their decisions of hand choice when reaching during body motion. Physiologically, it is unclear at what stage of movement preparation information about body motion is integrated in the process of hand selection. Here, we addressed this question by applying transcranial magnetic stimulation over motor cortex (M1) of human participants who performed a preferential reach task while they were sinusoidally translated on a linear motion platform. If M1 only represents a read-out of the final hand choice, we expect the body motion not to affect the MEP amplitude. If body motion biases the hand selection process prior to target onset, we expect corticospinal excitability to modulate with the phase of the motion, with larger MEP amplitudes for phases that show a bias to using the right hand. Behavioral results replicate our earlier findings of a sinusoidal modulation of hand choice bias with motion phase. MEP ampl...
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Contemporary theories of motor control have suggested that multiple motor commands compete for action selection. While most of these competitions are completed prior to movement onset, averaged saccadic eye movements that land at an... more
Contemporary theories of motor control have suggested that multiple motor commands compete for action selection. While most of these competitions are completed prior to movement onset, averaged saccadic eye movements that land at an intermediate location between two visual targets are thought to arise when a movement is initiated prior to the resolution of the competition. In contrast, while averaged reach movements have been reported, there is still debate on whether averaged reach movements are the result of a resolved competition between two potential actions or a strategic behavior that optimally incorporates the current task demands. Here, we use a reach version of the paradigm that has previously shown to elicit saccadic averaging to examine whether similar averaging occurs based on neuromuscular activity of an upper limb muscle. On a single trial basis, we observed a temporal evolution of the two competing motor commands during a free-choice reach task to one of two visual ta...
Recent computational theories and behavioral observations suggest that motor learning is supported by multiple adaptation processes, operating on different timescales, but direct neural evidence is lacking. We tested this hypothesis by... more
Recent computational theories and behavioral observations suggest that motor learning is supported by multiple adaptation processes, operating on different timescales, but direct neural evidence is lacking. We tested this hypothesis by applying transcranial magnetic stimulation over motor cortex in 16 human subjects during a validated reach adaptation task. Motor-evoked potentials (MEPs) and cortical silent periods (CSPs) were recorded from the biceps brachii to assess modulations of corticospinal excitability as indices for corticospinal plasticity. Guided by a two-state adaptation model, we show that the MEP reflects an adaptive process that learns quickly but has poor retention, while the CSP correlates with a process that responds more slowly but retains information well. These results provide a physiological link between models of motor learning and distinct changes in corticospinal excitability. Our findings support the relationship between corticospinal gain modulations and t...
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For the brain to decide on a reaching movement, it needs to select which hand to use. A number of body-centered factors affect this decision, such as the anticipated movement costs of each arm, recent choice success, handedness, and task... more
For the brain to decide on a reaching movement, it needs to select which hand to use. A number of body-centered factors affect this decision, such as the anticipated movement costs of each arm, recent choice success, handedness, and task demands. While the position of each hand relative to the target is also known to be an important spatial factor, it is unclear which reference frames coordinate the spatial aspects in the decisions of hand choice. Here we tested the role of gaze- and head-centered reference frames in a hand selection task. With their head and gaze oriented in different directions, we measured hand choice of 19 right-handed subjects instructed to make unimanual reaching movements to targets at various directions relative to their body. Using an adaptive procedure, we determined the target angle that led to equiprobable right/left hand choices. When gaze remained fixed relative to the body this balanced target angle shifted systematically with head orientation, and wh...
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In daily life, we frequently reach to objects while our body is in motion. We have recently shown that body accelerations influence the decision which hand to use for the reach, possibly by modulating the body-centered computations of the... more
In daily life, we frequently reach to objects while our body is in motion. We have recently shown that body accelerations influence the decision which hand to use for the reach, possibly by modulating the body-centered computations of the expected reach costs. However, head orientation relative to the body was not manipulated, hence it remains unclear whether vestibular signals contribute in their head-based sensory frame or in a transformed body-centered reference frame to these cost calculations. To test this, subjects performed a preferential reaching task to targets at various directions while they were sinusoidally translated along the lateral body axis, with their head either aligned with the body (straight-ahead) or 18° rotated to the left. As a measure of hand preference, we determined the target direction that resulted in equiprobable right/left hand choices. Results show that head orientation affects this balanced target angle when the body is stationary, but does not furt...
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As we age, the acuity of our sensory organs declines, which may affect our lifestyle. Sensory deterioration in the vestibular system is typically bilateral and gradual, and could lead to problems with balance and spatial orientation. To... more
As we age, the acuity of our sensory organs declines, which may affect our lifestyle. Sensory deterioration in the vestibular system is typically bilateral and gradual, and could lead to problems with balance and spatial orientation. To compensate for the sensory deterioration, it has been suggested that the brain reweights the sensory information sources according to their relative noise characteristics. For rehabilitation and training programs, it is important to understand the consequences of this reweighting, preferably at the individual subject level. We psychometrically examined the age-dependent reweighting of visual and vestibular cues used in spatial orientation in a group of 32 subjects (age range: 19–76 yr). We asked subjects to indicate the orientation of a line (clockwise or counterclockwise relative to the gravitational vertical) presented within an oriented square visual frame when seated upright or with their head tilted 30° relative to the body. Results show that su...
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Comparing models facilitates testing different hypotheses regarding the computational basis of perception and action. Effective model comparison requires stimuli for which models make different predictions. Typically, experiments use a... more
Comparing models facilitates testing different hypotheses regarding the computational basis of perception and action. Effective model comparison requires stimuli for which models make different predictions. Typically, experiments use a predetermined set of stimuli or sample stimuli randomly. Both methods have limitations; a predetermined set may not contain stimuli that dissociate the models, whereas random sampling may be inefficient. To overcome these limitations, we expanded the psi-algorithm (Kontsevich & Tyler, 1999) from estimating the parameters of a psychometric curve to distinguishing models. To test our algorithm, we applied it to two distinct problems. First, we investigated dissociating sensory noise models. We simulated ideal observers with different noise models performing a two-alternative forced-choice task. Stimuli were selected randomly or using our algorithm. We found using our algorithm improved the accuracy of model comparison. We also validated the algorithm in...
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DFNA9 is a rare progressive autosomal dominantly inherited vestibulo-cochlear disorder, resulting in a homogeneous group of patients with hearing impairment and bilateral vestibular function loss. These patients suffer from a deteriorated... more
DFNA9 is a rare progressive autosomal dominantly inherited vestibulo-cochlear disorder, resulting in a homogeneous group of patients with hearing impairment and bilateral vestibular function loss. These patients suffer from a deteriorated sense of spatial orientation, leading to balance problems in darkness, especially on irregular surfaces. Both behavioral and functional imaging studies suggest that the remaining sensory cues could compensate for the loss of vestibular information. A thorough model-based quantification of this reweighting in individual patients is, however, missing. Here we psychometrically examined the individual patient’s sensory reweighting of these cues after complete vestibular loss. We asked a group of DFNA9 patients and healthy control subjects to judge the orientation (clockwise or counterclockwise relative to gravity) of a rod presented within an oriented square frame (rod-in-frame task) in three different head-on-body tilt conditions. Our results show a c...
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The vestibular system provides information for spatial orientation. However, this information is ambiguous: because the otoliths sense the gravitoinertial force, they cannot distinguish gravitational and inertial components. As a... more
The vestibular system provides information for spatial orientation. However, this information is ambiguous: because the otoliths sense the gravitoinertial force, they cannot distinguish gravitational and inertial components. As a consequence, prolonged linear acceleration of the head can be interpreted as tilt, referred to as the somatogravic effect. Previous modeling work suggests that the brain disambiguates the otolith signal according to the rules of Bayesian inference, combining noisy canal cues with the a priori assumption that prolonged linear accelerations are unlikely. Within this modeling framework the noise of the vestibular signals affects the dynamic characteristics of the tilt percept during linear whole-body motion. To test this prediction, we devised a novel paradigm to psychometrically characterize the dynamic visual vertical—as a proxy for the tilt percept—during passive sinusoidal linear motion along the interaural axis (0.33 Hz motion frequency, 1.75 m/s2 peak ac...
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In everyday life, we frequently have to decide which hand to use for a certain action. It has been suggested that for this decision the brain calculates expected costs based on action values, such as expected biomechanical costs, expected... more
In everyday life, we frequently have to decide which hand to use for a certain action. It has been suggested that for this decision the brain calculates expected costs based on action values, such as expected biomechanical costs, expected success rate, handedness, and skillfulness. Although these conclusions were based on experiments in stationary subjects, we often act while the body is in motion. We investigated how hand choice is affected by passive body motion, which directly affects the biomechanical costs of the arm movement due to its inertia. With the use of a linear motion platform, 12 right-handed subjects were sinusoidally translated (0.625 and 0.5 Hz). At 8 possible motion phases, they had to reach, using either their left or right hand, to a target presented at 1 of 11 possible locations. We predicted hand choice by calculating the expected biomechanical costs under different assumptions about the future acceleration involved in these computations, being the forthcoming...
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When reaching for an earth-fixed object during self-rotation, the motor system should appropriately integrate vestibular signals and sensory predictions to compensate for the intervening motion and its induced inertial forces. While it is... more
When reaching for an earth-fixed object during self-rotation, the motor system should appropriately integrate vestibular signals and sensory predictions to compensate for the intervening motion and its induced inertial forces. While it is well established that this integration occurs rapidly, it is unknown whether vestibular feedback is specifically processed dependent on the behavioral goal. Here, we studied whether vestibular signals evoke fixed responses with the aim to preserve the hand trajectory in space or are processed more flexibly, correcting trajectories only in task-relevant spatial dimensions. We used galvanic vestibular stimulation to perturb reaching movements toward a narrow or a wide target. Results show that the same vestibular stimulation led to smaller trajectory corrections to the wide than the narrow target. We interpret this reduced compensation as a task-dependent modulation of vestibular feedback responses, tuned to minimally intervene with the task-irreleva...
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The natural world continuously presents us with many opportunities for action, thus a process of target selection must precede action execution. While there has been considerable progress in understanding target selection in stationary... more
The natural world continuously presents us with many opportunities for action, thus a process of target selection must precede action execution. While there has been considerable progress in understanding target selection in stationary environments, little is known about target selection when we are in motion. Here we investigated the effect of self-motion signals on saccadic target selection in a dynamic environment. Human subjects were sinusoidally translated (f=0.6 Hz, 30 cm peak-to-peak displacement) along an inter-aural axis using a vestibular sled. During the motion two visual targets were presented asynchronously but equidistantly on either side of fixation. Subjects had to look at one of these targets as quickly as possible. Using an adaptive approach, the time delay between these targets was adjusted until the subject selected both targets equally often. We determined this balanced time delay for different phases of the motion in order to distinguish the effects of body acc...
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Treisman and Hebb have suggested that "spontaneous," "random," or... more
Treisman and Hebb have suggested that "spontaneous," "random," or "background" activity in the nervous system constitutes "noise" in discrimination and learning; that is, this type of activity has no functional value to the organism. This paper attempts to show that tonic activity, a term including all of the types of activity listed above, is rather the functional substrate of the
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Inferring object orientation in the surroundings heavily depends on our internal sense of direction of gravity. Previous research showed that this sense is based on the integration of multiple information sources, including visual,... more
Inferring object orientation in the surroundings heavily depends on our internal sense of direction of gravity. Previous research showed that this sense is based on the integration of multiple information sources, including visual, vestibular (otolithic) and somatosensory signals. The individual noise characteristics and contributions of these sensors can be studied using spatial orientation tasks, such as the subjective visual vertical (SVV) task. A recent study reported that patients with complete bilateral vestibular loss perform similar as healthy controls on these tasks, from which it was conjectured that the noise levels of both otoliths and body somatosensors are roll-tilt dependent. Here, we tested this hypothesis in ten healthy human subjects by roll-tilting the head relative to the body to dissociate tilt-angle dependencies of otolith and somatosensory noise. Using a psychometric approach, we measured bias and variability in perceived orientation of a briefly flashed line ...
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We continuously adapt our movements in daily life, forming new internal models whenever necessary and updating existing ones. Recent work has suggested that this flexibility is enabled via sensorimotor cues, serving to access the correct... more
We continuously adapt our movements in daily life, forming new internal models whenever necessary and updating existing ones. Recent work has suggested that this flexibility is enabled via sensorimotor cues, serving to access the correct internal model whenever necessary and keeping new models apart from previous ones. While research to date has mainly focused on identifying the nature of such cue representations, here we investigated whether and how these cue representations generalize, interfere, and transfer within and across effector systems. Subjects were trained to make two-stage reaching movements: a premovement that served as a cue, followed by a targeted movement that was perturbed by one of two opposite curl force fields. The direction of the premovement was uniquely coupled to the direction of the ensuing force field, enabling simultaneous learning of the two respective internal models. After training, generalization of the two premovement cues' representations was te...
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We continuously adapt our movements in daily life, forming new internal models whenever necessary and updating existing ones. Recent work has suggested that this flexibility is enabled via sensorimotor cues, serving to access the correct... more
We continuously adapt our movements in daily life, forming new internal models whenever necessary and updating existing ones. Recent work has suggested that this flexibility is enabled via sensorimotor cues, serving to access the correct internal model whenever necessary and keeping new models apart from previous ones. While research to date has mainly focused on identifying the nature of such cue representations, here we investigated whether and how these cue representations generalize, interfere, and transfer within and across effector systems. Subjects were trained to make two-stage reaching movements: a pre-movement that served as a cue, followed by a targeted movement that was perturbed by one of two opposite curl force fields. The direction of the pre-movement was uniquely coupled to the direction of the ensuing force field, enabling simultaneous learning of the two respective internal models. After training, generalization of the two pre-movement cues' representations was...
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Treisman and Hebb have suggested that "spontaneous," "random," or... more
Treisman and Hebb have suggested that "spontaneous," "random," or "background" activity in the nervous system constitutes "noise" in discrimination and learning; that is, this type of activity has no functional value to the organism. This paper attempts to show that tonic activity, a term including all of the types of activity listed above, is rather the functional substrate of the
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... IN DISCRETE MOVEMENTS Luc PJ Selen, Peter J. Beek and Jaap H. van DieÃĢn Institute for Fundamental and Clinical Human Movement Sciences, IFKB, Vrije Universiteit, van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands;... more
... IN DISCRETE MOVEMENTS Luc PJ Selen, Peter J. Beek and Jaap H. van DieÃĢn Institute for Fundamental and Clinical Human Movement Sciences, IFKB, Vrije Universiteit, van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands; email:Luc.Selen@fbw.vu.nl ...