Biology subjects

Lacquaniti, F.

Publications and source records attributed to Lacquaniti, F..

8 recordsLinked to original sources

bioRxiv2025

Task demands and visual context naturalness modulate gravitational expectation during ocular tracking of temporarily occluded ballistic trajectories

During ocular tracking of a target, contextual information provides useful cues to account for motion features the visual system is poorly sensitive to, like its acceleration. For example, the brain can rely on an internal model of gravity to intercept and track accelerated targets under gravity, and cues about the visual environment naturalness can facilitate its recruitment. Notably, in real life, these two tasks are often associated. Experimental evidence suggests that predictive information may be shared between the two tasks, albeit their concurrent execution can, in turn, affect the oculomotor performance. To gain further insight on how task demands and the naturalness of the visual context affect the weighting of sensory feedback and predictive feedforward information in ocular tracking, subjects tracked targets either congruent with gravity or perturbed during the trajectory with altered gravity. Targets were projected on either pictorial or neutral background, and, to enforce prediction, were occluded for variable intervals 550 ms after the perturbation. Sixty-nine participants were divided into two groups: one group performed only ocular tracking, the other also intercepted the targets. In general, subjects ocular tracking performance depended on the target acceleration level and the visual context, with effects of gravitational expectations being more evident with the pictorial naturalistic environment. This result reinforced the idea that gravity a priori information can be weighted based on the naturalness of the visual context. Another striking finding was that participants who only tracked the target showed systematic changes of the oculomotor performance with the acceleration level right after the perturbation, compatible with a strong reliance on gravitational expectation; instead, participants that also intercepted the target showed such systematic changes primarily after the targets occlusion, perhaps weighting more sensory information until then. Thus, concurrence of ocular tracking and manual interception seemingly influenced the temporal recruitment of internalized gravity information.

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bioRxiv2024

Incomplete adaptation to surface movement during hand reaching

Humans can effectively adapt to changes in the environment to maintain adequate motor performance in a vast range of situations. However, residual errors tend to persist when strong a priori assumptions about the statistical regularities of the environment are violated. In our study, we challenged the expectation that inanimate objects are usually at rest. To this end, we used a robotic interface to move a plate over which participants slid their finger while reaching towards a target. We found limited evidence of adaptation after prolonged exposure to this perturbation, and only when visual feedback about hand position was provided. Although participants were aware of the motion of the contact surface, explicit knowledge about its direction was limited. Our results provide important insights on the limits of adaptation to motion perturbation in the somatosensory system, which can inform the design of technology applications such as haptic interfaces and collaborative robots.

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bioRxiv2024

Visual and vestibular processing of vertical motion: a psychophysical study

The motion of objects and ourselves along the vertical is affected by gravitational acceleration. However, the visual system is poorly sensitive to accelerations, and the vestibular otoliths do not disassociate gravitational and inertial accelerations of ego-motion. Here, we tested the hypothesis that the brain resolves visual and vestibular ambiguities about vertical motion with internal models of gravity, which predict that downward motions are accelerated and upward motions are decelerated by gravity. In visual sessions, a target moved up or down while participants remained stationary. In vestibular sessions, participants were moved up or down, while they fixated an imaginary target moving along. In visual-vestibular sessions, participants were moved up or down while the visual target remained fixed. We found that downward motions of either the visual target or the participant were systematically perceived as lasting less than upward motions of the same duration, and vice-versa for the opposite direction of motion, consistent with the prior assumption that downward motion is accelerated and upward motion is decelerated by gravity. In visual-vestibular sessions, there was no significant difference in the average estimates of duration of downward and upward motion of the participant. However, there was large inter-subject variability of these estimates.

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bioRxiv2023

Rhythmic tapping to a moving beat: motion kinematics overrules motion naturalness.

Beat induction is the cognitive ability that allow humans to listen to a regular pulse in music and move in synchrony with it. Although auditory rhythmic cues are known to induce more consistent synchronization than flashing visual metronomes, this asymmetry can be canceled out by visual moving metronomes. Here, we investigated whether the naturalness of the visual motion or its kinematics could provide a synchronization advantage over flashing metronomes. Subjects tap in sync with visual isochronous metronomes defined by vertically or horizontally accelerating and decelerating motion, either congruent or not with natural gravity, and then continue tapping with no metronome. We found that motion kinematics was the predominant factor determining rhythm synchronization, as accelerating moving metronomes in either cardinal direction produced more precise and predictive tapping than decelerating or flashing conditions. Notably, a Bayesian observer model revealed that error correction during tapping synchronization and regression towards the mean in accuracy during tapping continuation in the absence of external cues are optimal control strategies independently of the moving properties of the visual metronomes. Our results support the notion that accelerating visual metronomes convey a strong sense of beat as seen in the cueing movements of an orchestra director.

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bioRxiv2022

Independent synaptic inputs to motor neurons driving antagonist muscles

The CNS may produce the same endpoint trajectory or torque profile with different muscle activation patterns. What differentiates these patterns is the presence of co-contraction, which does not contribute to joint torque generation but allows to modulate mechanical impedance. Whether co-contraction is controlled through the same synaptic input to motor neurons involved in generating joint torque is still unclear. We hypothesized that co-contraction is controlled through a specific synaptic input, independent from that underlying the control of torque. To test this hypothesis, we asked participants to concurrently generate multi-directional isometric forces at the hand and to modulate the co-contraction of arm muscles to displace and stabilize a virtual end-effector. The firings of motor units were identified through decomposition of High-Density EMGs collected from two antagonist muscles, Biceps Brachii and Triceps Brachii. We found significant peaks in the coherence between the neural drive to the two muscles, suggesting the existence of a common input modulating co-contraction across different exerted forces. Moreover, the within-muscle coherence computed after removing the component synchronized with the drive to the antagonist muscle or with the exerted force revealed two subsets of motor neurons that were selectively recruited to generate joint torque or modulate co-contraction. This study is the first to directly investigate the extent of shared versus independent control of antagonist muscles at the motor neuron level in a task involving concurrent force generation and modulation of co-contraction. Significance StatementHow the CNS coordinates the activity of antagonist muscles to modulate limb mechanical impedance is still unclear. We hypothesized that a common synaptic input, shared by the motor neurons pools of antagonist muscles, and independent from the inputs underlying force generation, regulates co-contraction. We then analyzed the coherence between the firing trains of motor neurons to assess whether a common input drives antagonist muscles only during tasks requiring co-activation for impedance but not for force generation. Results highlighted the existence of separate neural pathways underlying the control of joint torque or impedance. Scientifically, this study addressed an important gap in understanding how neural drive is delivered to antagonist muscles, disentangling the control of muscles for joint torque or impedance modulation.

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bioRxiv2022

Enhancement of vestibular motion discrimination by small stochastic whole-body perturbations in young healthy humans

Noisy galvanic vestibular stimulation has been shown to improve vestibular perception in healthy subjects. Here, we sought to obtain similar results using more natural stimuli consisting of small-amplitude motion perturbations of the whole body. Thirty participants were asked to report the perceived direction of antero-posterior sinusoidal motion on a MOOG platform. We compared the baseline perceptual thresholds with those obtained by applying small, stochastic perturbations at different power levels along the antero-posterior axis, symmetrically distributed around a zero-mean. At the population level, we found that the thresholds for all but the highest level of noise were significantly lower than the baseline threshold. At the individual level, the threshold was lower with at least one noise level than the threshold without noise in 87% of participants. Thus, small, stochastic oscillations of the whole body can increase the probability of detecting subthreshold vestibular signals, possibly due to stochastic resonance mechanisms. We suggest that, just as the external noise of the present experiments, also the spontaneous random oscillations of the body associated with standing posture are beneficial by enhancing vestibular thresholds with a mechanism similar to stochastic resonance. The results are also relevant from a clinical perspective, since they raise the possibility of improving motion perception in people with elevated thresholds due to aging or vestibulopathy by means of small-amplitude motion perturbations. HIGHLIGHTSO_LISmall-amplitude motion perturbations of the whole body improve vestibular perceptual thresholds of motion discrimination in young healthy people C_LIO_LIImprovements occur at optimal levels of noise amplitude, idiosyncratic to each subject C_LIO_LIThe findings are consistent with the phenomenon of stochastic resonance C_LIO_LIThe new method can applied to people with elevated thresholds due to aging or vestibulopathy C_LI

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bioRxiv2019

A Hessian-based decomposition to characterize how performance in complex motor skills depends on individual strategy and variability

In complex real-life motor skills such as unconstrained throwing, performance depends on how accurate is on average the outcome of noisy, high-dimensional, and redundant actions. What characteristics of the action distribution relate to performance and how different individuals select specific action distributions are key questions in motor control. Previous computational approaches have highlighted that variability along the directions of first order derivatives of the action-to-outcome mapping affects performance the most, that different mean actions may be associated to regions of the actions space with different sensitivity to noise, and that action covariation in addition to noise magnitude matters. However, a method to relate individual high-dimensional action distribution and performance is still missing. Here we introduce a de-composition of performance into a small set of indicators that compactly and directly characterize the key performance-related features of the distribution of high-dimensional redundant actions. Central to the method is the observation that, if performance is quantified as a mean score, the Hessian (second order derivatives) of the action-to-score function determines how the noise of the action distribution affects the average score. We can then approximate the mean score as the sum of the score of the mean action and a tolerance-variability index which depends on both Hessian and action covariance. Such index can be expressed as the product of three terms capturing noise magnitude, noise sensitivity, and alignment of the most variable and most noise sensitive directions. We apply this method to the analysis of unconstrained throwing actions by non-expert participants and show that, consistently across four different throwing targets, each participant shows a specific selection of mean action score and tolerance-variability index as well as specific selection of noise magnitude and alignment indicators. Thus, participants with different strategies may display the same performance because they can trade off suboptimal mean action for better tolerance-variability and higher action variability for better alignment with more tolerant directions in action space. Author summaryWhy do people differ in their performance of complex motor skills? In many real-life motor tasks achieving a goal requires selecting an appropriate high-dimensional action out of infinitely many goal-equivalent actions. Because of sensorimotor noise, we are unable to execute the exact same movement twice and our performance depends on how accurate we are on average. Thus, to understand why people perform differently we need to characterize how their action distribution relates to their mean task score. While better performance is often associated to smaller variability around a more accurate mean action, performance also depends on the relationship between the directions of highest variability in action space and the directions in which action variability affects the most the outcome of the action. However, characterizing such geometric relationship when actions are high dimensional is challenging. In this work we introduce a method that allows to characterize the key performance-related features of the distribution of high-dimensional actions by a small set of indicators. We can then compare such indicators in different people performing a complex task (such as unconstrained throwing) and directly characterize the most skilled ones but also identify different strategies that distinguish people with similar performance.

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bioRxiv2019

The discrimination of tactile speed in absence of texture elements: Role of deformation and vibratory cues

Motion encoding in touch relies on multiple cues, such as displacements of traceable texture elements, friction-induced vibrations, and gross fingertip deformations by shear force. We evaluated the role of deformation and vibration cues in tactile speed discrimination. To this end, we tested the discrimination of speed of a moving smooth glass plate, and compared the precision of the responses when the same task was performed with a plate having a fine texture. Participants performed the task with and without masking vibrations. Speed discrimination was nearly as precise among the two surface types, as assessed by the steep slope of the psychometric function. Consistent with our previous work, high-frequency vibrations impaired the ability of the participants in discriminating surface speed. Results of the current study showed that it is possible to discriminate motion speed even in absence of a raised texture. HighlightsO_LIOn a smooth surface, humans are able to discriminate the speed of a moving surface by frictional motion cues C_LIO_LIThe precision of speed discrimination is nearly the same with smooth and fine-textured surface types C_LIO_LIHigh frequency vibrations impair the ability to discriminate speed of moving surfaces C_LI

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