Biology subjects

Heed, T.

Publications and source records attributed to Heed, T..

At least 19 recordsLinked to original sources

bioRxiv2026

Toward naturalistic reaching: Intermediate reaches under uncertainty generalize to walking, but are not obligatory

Highly-constrained laboratory-based experiments have provided important insights into movement planning. When people reach toward one of several stimuli before knowing which to target, their hand trajectories are situated intermediate to direct reaches to each stimulus. Real-world reaching, however, involves a greater decision landscape than typical laboratory tasks. We extended the go-before-you-know paradigm to a walk-to-reach task resembling unconstrained natural behavior. Participants walked three steps toward a touchscreen before reaching for one of two stimuli, marked as the target either at walk onset or after reach onset. Under uncertainty, intermediate reaches occurred, but only for some stimulus layouts and participants. Individual reaches varied considerably; many directly targeted one stimulus and corrected late. Body position at reach onset was anchored to the screen more than the stimuli and was partly intermediate. Thus, intermediate movements generalize beyond the laboratory, but as one flexible strategy among several, not as obligatory motor plan averaging.

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bioRxiv2026

Topographic and somatotopic organization of functional connectivity between the intraparietal sulcus and primary somatosensory cortex in macaque monkeys

The posterior parietal cortex integrates somatosensory information with signals supporting action, spatial cognition, and multisensory processing, yet the fine-scale topographic relationship between the intraparietal sulcus (IPS) and primary somatosensory cortex (S1) remains poorly understood. Here, we used resting-state fMRI in 10 awake rhesus macaques to characterize functional connectivity between four S1 subregions (areas 3a, 3b, 1, and 2) and 223 single-voxel seeds densely sampling an IPS-centered parietal territory. Across S1 subregions and hemispheres, IPS-S1 connectivity exhibited a highly structured spatial organization characterized by systematic anteroposterior and mediolateral gradients and a prominent semi-oval topology following the geometry of the intraparietal sulcus. Connectivity was generally stronger toward the cortical banks and convexities and weaker near the sulcal fundus, a pattern that could not be explained by reduced local temporal signal-to-noise ratio. Unsupervised hierarchical clustering independently recovered this spatial organization and identified connectivity-defined subdivisions that only partially corresponded to classical cytoarchitectonic boundaries. Along the S1 mediolateral axis, prominent troughs in cluster-averaged connectivity profiles corresponded to several previously described somatotopic transitions, allowing to consistently map putative boundaries between tongue and face representations and between hand and trunk-leg representations. Based on these boundaries, individual IPS clusters exhibited connectivity with multiple S1 body-part sectors, with the pattern of connectivity across these sectors varying across IPS clusters and S1 subregions. Together, our findings reveal that IPS-S1 functional connectivity is organized by a large-scale sulcal topology while preserving fine-grained features of S1 somatotopic organization. These findings suggest that the functional organization of the IPS is shaped by multiple spatial dimensions, including large-scale sulcal topology and the organization of S1 subregions and body-part representations, which may together contribute to the functional specialization of individual IPS regions.

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bioRxiv2026

Motor planning and execution establish distinct feedforward and feedback motor histories

Movements are systematically affected by the recent motor history. These history effects may be induced either by reused motor plans or from lingering tuning of the previous movements' execution. We dissociated planning and execution using four experimental manipulations across two complementary motor paradigms. We isolated planning by preventing execution with stop signals and mechanical blocks, and execution by moving participants' hand passively using a robot manipulandum. History effects emerged in feedforward movement aspects - reaction time and early movement kinematics - following isolated planning. In contrast, they were absent or markedly reduced for isolated execution. History effects emerged also in late movement aspect that involves sensory feedback during execution - movement accuracy and precision - but only when movements were both planned and executed. Feedforward effects generalized across hands, whereas feedback effects were effector specific. Thus, prior motor planning and execution make distinct and complementary contributions in shaping future motor behavior.

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bioRxiv2026

Distinct contributions of motor imagery and execution to history-dependent biases in reaching

The recent movement history shapes motor performance, that is, previous movements can affect current movement characteristics such as trajectory shape. History effects are commonly attributed to carryover of motor-related activity. However, action execution entails sensory feedback; therefore, an alternative is that history effects stem from the sensory information produced by previous movements. To dissociate motor and sensory contributions, we assessed whether history effects emerge from imagined movements, which involve movement planning but not sensory feedback. Overt reaches around an obstacle led to systematic adjustment of the initial reach direction of following reaches - a hallmark of motor history. Imagined reaches around obstacles induced similar biases, albeit with smaller magnitude, presumably due to the need to inhibit overt execution during imagery. By contrast, execution but not imagery induced biases in late, feedback-related measures, suggesting that these history effects depended on sensory rather than motor aspects of the movement history. Thus, motor and sensory signals make distinct and complementary contributions to movement history: recent motor states shape feedforward planning, whereas recent sensory states shape feedback-related movement refinement.

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bioRxiv2026

From Head to Toe: Efficient Somatosensory Mapping with Fast Stimulation and Multivariate Pattern Analysis

BackgroundSomatosensory evoked potentials (SEPs) measured with electroencephalography (EEG) are widely used to study cortical responses to touch but most research has limited the focus on few body parts, typically a finger, and applied time-consuming testing protocols. Multivariate pattern analysis (MVPA) provides a complementary approach that may increase sensitivity and allow faster stimulation, yet its relationship to classical SEP analysis in somatosensory research remains largely unexplored. MethodsFifteen participants received vibrotactile stimulation on the finger, hand, cheek, and foot while EEG was recorded. We compared a traditional "slow" stimulation protocol (800-1200 ms inter-stimulus intervals) with a "fast" protocol (300-500 ms). We compared temporal and topographical aspects between SEP and MVPA. ResultsBoth stimulation protocols produced highly similar SEP components (P100, N140, P200), topographies, and classification results, while the fast protocol reduced testing time by about 60%. SEPs revealed systematic body-part differences, with earlier components for cheek stimulation and delayed responses for the foot. Multivariate classification distinguished body parts with accuracies up to [~]50-55% (chance: 25%), peaking around 100 ms after stimulus onset. Classifier weight maps closely matched SEP topographies over centroparietal electrodes, indicating that classification relied on physiologically meaningful somatosensory signals. Classification accuracy peaked around 100 ms after stimulus onset, coinciding with the SEP P100 component, but declined gradually thereafter, suggesting that early somatosensory responses contain particularly informative multivariate patterns that generalize over time. ConclusionsFaster stimulation protocols substantially increase efficiency without compromising interpretability. Combining classical SEP analysis with multivariate classification provides complementary insights and offers a powerful framework for mapping somatosensory representations across the body.

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bioRxiv2025

Crossing effects in the tactile temporal order judgment task: A meta-analysis

The tactile temporal order judgment (TOJ) task is widely used in multisensory neuroscience. Participants judge which of two tactile stimuli, one on each hand, came first. A key finding is that TOJ performance declines when the arms are crossed, likely due to interactions between tactile, proprioceptive, and visual information. The TOJ crossing effect has been widely reported. However, studies have used different analysis methods, leaving open whether the choice of method influences the effects magnitude. Some studies have also reported that the crossing effect is modulated by moderators such as the analysis method, availability of visual information, response modality, or speeded response requirements. Through a systematic, exhaustive literature search, we identified 85 experiments in 51 publications that investigated the TOJ crossing effect, of which 39 experiments from 29 publications reported sufficient information for inclusion in a meta-analysis and fit the focus of our study. This analysis estimated the crossing effects size at approximately 1.45. Checks for potential publication bias indicated that this estimate may be inflated, with a corrected estimate of 0.97 using a regression-based adjustment for small-study effects (Ruckers method), and 1.4 based on p-curve analysis of the reported p-values. Although analysis method and response mode were identified as significant moderators, most moderators and specific contrasts were not statistically significant, likely because too few studies were available to achieve adequate statistical power. The large effect size supports the TOJ tasks use in other research, e.g. developmental and clinical. However, the lack of significant moderation suggests caution when applying the task to questions beyond the crossing effect itself. Public Significance StatementWe provide an effect size estimate of a well-known tactile-spatial measure, the tactile temporal order judgment crossing effect, based on a PRISMA-guided literature review. This measure will help planning for sufficient power in future studies.

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bioRxiv2024

Effector selection precedes movement specification: evidence from repetition effects in motor planning

Motor performance is influenced by movements that were performed shortly prior. For example, reaction times (RTs) for successive movements are reduced when executed with the same effector, even if the specifics of the consecutive movements differ. These findings have been taken to support the notion that repetition effects in motor planning reflect the involvement of effector-specific motor plans. However, previous studies have confounded motor and visual aspects of repetition: movements have typically been instructed via visual cues, and movement repetition, therefore, implied repeating also the visual cue, so that the latter may be (at least partly) responsible for the observed RT effects. In the present study, participants performed two movements in succession, a prime and a probe action, either with their left or right hand and in one of two directions, inward or outward relative to the body midline. We used different cues for prime and probe actions, so that movement repetitions did not involve repetition of the visual cue. Participants initiated successive same-limb movements faster than different-limb movements, but this RT advantage was smaller than observed in previous work. Moreover, repeating movement direction also led to a decrease in RT, though only in combination with hand repetition. Whereas these findings imply that visual cue repetition can contribute to accelerated RTs in movement repetition, they confirm that the recent motor history affects motor planning. Furthermore, they support the idea of a hierarchical framework of motor planning in which effector selection precedes specification of motor parameters.

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bioRxiv2024

Motor Imagery Enhances Performance Beyond the Imagined Action

Motor imagery is frequently utilized to improve the performance of specific target movements in sports and rehabilitation. In this study, we show that motor imagery can facilitate learning of not only the imagined target movements but also sequentially linked overt movements. Hybrid sequences comprising imagined and physically executed segments allowed participants to learn specific movement characteristics of the executed segments when they were consistently associated with specific imagined segments. Electrophysiological recordings revealed that the degree of event-related synchronization in the alpha and beta bands during a basic motor imagery task was correlated with imagery-evoked motor learning. Thus, both behavioral and neural evidence indicate that motor imagerys benefits extend beyond the imagined movements, improving performance in linked overt movements. This provides new evidence for the functional equivalence of imagined and overt movements and suggests new applications for imagery in sports and rehabilitation.

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bioRxiv2024

The macaque ventral intraparietal functional connectivity patterns reveal an anterio-posterior specialization mirroring that described in human ventral intraparietal area

The macaque monkeys ventral intraparietal area (VIP) in the intraparietal sulcus (IPS) responds to visual, vestibular, tactile and auditory signals and is involved in higher cognitive functions including the processing of peripersonal space. In humans, VIP appears to have expanded into three functionally distinct regions. Macaque VIP has been divided cytoarchitonically into medial and lateral parts; however, no functional specialization has so far been associated with this anatomical division. Functional MRI suggests a functional gradient along the anterior-posterior axis of the macaque IPS: anterior VIP shows visio-tactile properties and face preference, whereas posterior VIP responds to large-field visual dynamic stimuli. This functional distinction matches with functional differences among the three human VIP regions, suggesting that a regional specialization may also exist within macaque VIP. Here, we characterized the ipsilateral, whole-brain functional connectivity, assessed during awake resting state, along VIPs anterior-posterior axis by dividing VIP into three regions of interest (ROIs). The functional connectivity profiles of the three VIP ROIs resembled anatomical connectivity profiles obtained by chemical tracing. Anterior VIP was functionally connected to regions associated with motor, tactile, and proprioceptive processing and with regions involved in reaching, grasping, and processing peripersonal space. Posterior VIP had the strongest functional connectivity to regions involved in motion processing and eye movements. These profiles are consistent with the connectivity profiles of the anterior and posterior VIP areas identified in humans. Viewed together, resting state functional connectivity, task-related fMRI and anatomical tracing consistently suggest specific functional specializations of macaque anterior and posterior VIP. This specialization corroborates the distinction of VIP into three anatomically and functionally separate VIP areas in humans.

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bioRxiv2024

Limb, not touch location, is coded in 3D space

Reduced tactile-spatial accuracy with crossed versus uncrossed limbs is considered key evidence for automatic remapping of touch location from skin-based to 3D-spatial codes. Yet, typical tasks use only few stimuli, potentially confounding categorical choice of a touched limb with precise stimulus location. Over five experiments, participants judged whether two touches occurred on the same limb (anatomical) or on the same side of space (external-spatial). Crossing consistently impaired performance, but more under external-spatial than anatomical instructions - contrary to what automatic remapping predicts. Limb assignment errors occurred equally frequent for arm-leg as arm-arm pairs, implying confusion about limb identity, not spatial position. With mouse-based, precise localization, crossing again impaired limb assignment, mainly for stimuli distal to the crossing point, whereas precision was unaffected: localization scatter did not increase, and showed no bias toward the limb's usual side of space. Crossing effects therefore emerge from choosing a limb, not from localizing touch. We propose that they reflect limb assignment, with touch cueing the region of space it is habitually associated with, followed by selecting a limb whose habitual or current posture occupies that region, constrained by which limbs are task-relevant; precise localization is performed afterwards on the selected limb.

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bioRxiv2023

The role of kinesthetic and visuospatial cues in pain-induced movement avoidance

BackgroundAvoidance of movements is an important factor in chronic pain. Previous experiments have investigated the involved learning mechanisms by pairing movements with painful stimuli but, usually, other visuospatial cues are concurrently presented during learning. Therefore, participants might primarily avoid these visuospatial rather than the movement-related cues, potentially invalidating related interpretations of pain-induced movement avoidance. Here, we separated kinesthetic from visuospatial cues to investigate their respective contribution to avoidance learning. MethodsParticipants used a hand-held robotic manipulandum and, during an acquisition phase, received painful stimuli when performing center-out movements. Pain stimuli could be avoided by choosing a curved rather than direct movement trajectories. To distinguish the contribution of kinesthetic vs. visuospatial cues we used two generalization contexts: either participants executed novel movements passing through the same location at which pain had previously been presented in the acquisition phase; or they executed the same pain-associated movements after having been reseated, so that the hand did not pass through the pain-associated location. ResultsAvoidance generalization was comparable in both contexts, and remarkably, highly correlated between them. Our findings suggest that both visuospatial and kinesthetic cues available during acquisition were associated with pain and led to avoidance. ConclusionsOur research corroborates the fear-avoidance pain model and previous studies findings that pain can become associated with movements. However, our study indicates that visuospatial cues also play a critical role. Future studies should distinguish movement-related and space-related associations in pain learning. SignificanceChronic pain is a significant health issue typically attributed to maladaptive learning of pain-movement associations and movement avoidance. We demonstrate that visual cues can play a similarly important role as movement cues in pain learning. This aspect has not previously been considered and has likely confounded previous research findings.

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bioRxiv2022

Variance (un)explained: Experimental conditions and temporal dependencies explain similarly small proportions of reaction time variability in perceptual and cognitive tasks

Any series of sensorimotor actions shows fluctuations in speed and accuracy from repetition to repetition, even when the sensory input and motor output requirements remain identical over time. Such fluctuations are particularly prominent in reaction time (RT) series from laboratory neurocognitive tasks. Despite their omnipresent nature, trial-to-trial fluctuations remain poorly understood. Here, we systematically analysed RT series from various neurocognitive tasks, quantifying how much of the total trial-to-trial RT variance can be explained with general linear models (GLMs) by three sources of variability that are frequently investigated in behavioural and neuroscientific research: 1) experimental conditions, employed to induce systematic patterns in variability, 2) short-term temporal dependencies as the autocorrelation between subsequent trials, and 3) long-term temporal trends over experimental blocks and sessions. Furthermore, we examined to what extent the explained variances by these sources are shared or unique. We analysed 1913 unique RT series from 30 different cognitive control and perception-based tasks. On average, the three sources together explained [~]8-17% of the total variance. The experimental conditions explained on average [~]2.5-3.5% but did not share explained variance with temporal dependencies. Thus, the largest part of the trial-to-trial fluctuations in RT remained unexplained by these three sources. Unexplained fluctuations may take on non-linear forms that are not picked up by GLMs. They may also be partially attributable to observable endogenous factors such as fluctuations in brain activity and bodily states. Still, some extent of randomness may be a feature of the neurobiological system rather than just nuisance. Public significance statementWhen we perform stereotyped repetitive sensorimotor actions, these nevertheless exhibit remarkable variability over time even under laboratory conditions. We show that most of this variability is not explained by linear models including two factors frequently studied in experimental psychology or cognitive neuroscience: the manipulations introduced by the experimenters and endogenous temporal dependencies that arise over multiple timescales. This implies that moment-to-moment fluctuations in typical behavioural data are largely unpredictable by linear models. Endogenous processes may also influence these fluctuations even in highly stable environments. It remains an empirical question to what extent exogenous and endogenous sources influence fluctuations non-linearly.

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bioRxiv2022

Prior movement of one arm facilitates motor adaptation in the other

Many movements in daily life are embedded in motion sequences that involve more than one limb, demanding the motor system to monitor and control different body parts in quick succession. During such movements, systematic changes in the environment or the body might require motor adaptation of specific segments. However, previous motor adaptation research has focused primarily on motion sequences produced by a single limb, or on simultaneous movements of several limbs. For example, adaptation to opposing force fields is possible in unimanual reaching tasks when the direction of a prior or subsequent movement is predictive of force field direction. It is unclear, however, whether multi-limb sequences can support motor adaptation processes in a similar way. In the present study, we investigated whether reaches can be adapted to different force fields in a bimanual motor sequence when the information about the perturbation is associated with the prior movement direction of the other arm. In addition, we examined whether prior perceptual (visual or proprioceptive) feedback of the opposite arm contributes to force field-specific motor adaptation. Our key finding is that only active participation in the bimanual sequential task supports pronounced adaptation. This result suggests that active segments in bimanual motion sequences are linked across limbs. If there is a consistent association between movement kinematics of the linked and goal movement, the learning process of the goal movement can be facilitated. More generally, if motion sequences are repeated often, prior segments can evoke specific adjustments of subsequent movements. Significance statementMovements in a limbs motion sequence can be adjusted based on linked movements. A prerequisite is that kinematics of the linked movements correctly predict which adjustments are needed. We show that use of kinematic information to improve performance is even possible when a prior linked movement is performed with a different limb. For example, a skilled juggler might have learned how to correctly adjust his catching movement of the left hand when the right hand performed a throwing action in a specific way. Linkage is possibly a key mechanism of the human motor system for learning complex bimanual skills. Our study emphasizes that learning of specific movements should not be studied in isolation but within their motor sequence context.

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bioRxiv2022

Dynamic spatial coding in parietal cortex mediates hand movement planning towards touch

Movements towards touch on the body require integrating tactile location and body posture information. Tactile processing and movement planning both rely on posterior parietal cortex (PPC) but their interplay is not understood. Here, human participants received tactile stimuli on their crossed and uncrossed feet, dissociating stimulus location relative to anatomy versus external space. Participants pointed to the touch or the equivalent location on the other foot, which dissociates sensory and motor locations. Multi-voxel pattern analysis of concurrently recorded fMRI signals revealed that tactile location was coded anatomically in anterior PPC but spatially in posterior PPC during sensory processing. After movement instructions were specified, PPC exclusively represented the movement goal in space, in regions associated with visuo-motor planning and with regional overlap for sensory, rule-related, and movement coding. Thus, PPC flexibly updates its spatial codes to accommodate rule-based transformation of sensory input to generate movement to environment and own body alike.

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bioRxiv2022

Modulation of implicitly perceived hand size by visuotactile recalibration

When concurrent visual and tactile stimuli are repeatedly presented with a spatial offset, even unisensory tactile stimuli are afterwards perceived with a spatial bias towards the previously presented visual stimuli. This so-called visuotactile ventriloquism aftereffect reflects visuotactile recalibration. It is unknown whether this recalibration occurs within a bodily map and interacts with perceived features like shape and size of body parts. Here, we applied tactile stimuli to participants hidden left hand and simultaneously presented visual stimuli with spatial offsets that - if integrated with the tactile stimuli - implied an enlarged hand size. We either used a fixed spatial mapping between tactile and visual positions ("congruent"), or a scrambled ("incongruent") mapping. We assessed implicitly perceived hand size via two independent behavioral assessments: pointing movements to unisensory tactile stimuli and tactile distance judgments. Moreover, we assessed explicitly perceived change in hand size with perceptual self-reports. Especially after congruent recalibration, participants localized unimodal tactile stimuli as if they were aiming at an enlarged hand. They also reported tactile distance as shorter after congruent than incongruent recalibration. These modulations resemble those obtained after using tools that prolong the arm and extend reaching space; they suggest that recalibration affected a common, implicit hand representation that underlies both tasks. In contrast, explicit perceptual self-reports did not differ significantly between congruent and incongruent recalibration. Thus, simple visuotactile stimuli are sufficient to modify implicitly perceived body size, indicating a tight link of low-level multisensory processes such as the visuotactile ventriloquism aftereffect and body representation.

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bioRxiv2022

Allocation of visuospatial attention indexes evidence accumulation for reach decisions

Visuospatial attention is a prerequisite for the performance of visually guided movements: Perceptual discrimination is regularly enhanced at target locations prior to movement initiation. It is known that this attentional prioritization evolves over the time of movement preparation; however, it is not clear whether this build-up simply reflects a time requirement of attention formation or whether, instead, attention build-up reflects the emergence of the movement decision. To address this question, we combined behavioral experiments, psychophysics, and computational decision-making models to characterize the time course of attention build-up during motor preparation. Participants (n = 46, 29 female) executed center-out reaches to one of two potential target locations and reported the identity of a visual discrimination target that occurred concurrently at one of various time-points during movement preparation and execution. Visual discrimination increased simultaneously at the two potential target locations but was modulated by the experiment-wide probability that a given location would become the final goal. Attention increased further for the location that was then designated as the final goal location, with a time course closely related to movement initiation. A sequential sampling model of decision-making predicted key temporal characteristics of attentional allocation. Together, these findings provide evidence that visuospatial attentional prioritization during motor preparation does not simply reflect that a spatial location has been selected as movement goal, but rather indexes the time-extended, cumulative decision that leads to selection, hence constituting a link between perceptual and motor aspects of sensorimotor decisions. Significance statementWhen humans perform a goal-directed movement such as a reach, attention shifts towards the goal location already before movement initiation, indicating that motor goal selection relies on the use of attention. Here, we demonstrate that key temporal aspects of visuospatial attention are predicted by a well-known computational model of decision-making. These findings suggest that visual attention signals much more than simply that a motor goal has been selected: instead, the time-course of emergent, visuospatial attention reflects the time-extended, cumulative decision that leads to goal selection, offering a window onto the tight link of perceptual and motor aspects in sensorimotor decision-making.

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bioRxiv2021

Repetition effects in action selection reflect effector- but not hemisphere-specific coding

Action choices are influenced by future and recent past action states. For example, when performing two actions in succession, response times (RT) to initiate the second action are reduced when the same hand is used. These findings suggest the existence of effector-specific processing for action planning. However, given that each hand is primarily controlled by the contralateral hemisphere, the RT benefit might actually reflect effector-independent, hemisphere-specific rather than effector-specific repetition effects. Here, participants performed two consecutive movements, each with a hand or a foot, in one of two directions. Direction was specified in an egocentric reference frame (inward, outward) or in an allocentric reference frame (left, right). Successive actions were initiated faster when the same limb (e.g., left hand - left hand), but not when the other limb of the same body side (e.g., left foot - left hand) executed the second action. The same-limb advantage was evident even when the two movements involved different directions, whether specified egocentrically or allocentrically. Corroborating evidence from computational modeling lends support to the claim that repetition effects in action planning reflect persistent changes in baseline activity within neural populations that encode effector-specific action plans.

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bioRxiv2021

Illusory tactile movement crosses arms and legs and is coded in external space

Humans often misjudge where on the body a touch occurred. Theoretical accounts have ascribed such misperceptions to local interactions in peripheral and primary somatosensory neurons, positing that spatial-perceptual mechanisms adhere to limb boundaries and skin layout. Yet, perception often reflects integration of sensory signals with prior experience. On their trajectories, objects often touch multiple limbs; therefore, body-environment interactions should manifest in perceptual mechanisms that reflect external space. Here, we demonstrate that humans perceived the cutaneous rabbit illusion - the percept of multiple identical stimuli as hopping across the skin - along the Euclidian trajectory between stimuli on two body parts and regularly mislocalized stimuli from one limb to the other. A Bayesian model based on Euclidian, as opposed to anatomical, distance faithfully reproduced key aspects of participants localization behavior. Our results suggest that prior experience of touch in space critically shapes tactile spatial perception and illusions beyond anatomical organization.

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