Biology subjects

Lopez-Moliner, J.

Publications and source records attributed to Lopez-Moliner, J..

8 recordsLinked to original sources

bioRxiv2026

Torsion in motion: the visual system as a three-axis gimbal

Rigorously tracking eye and head behavior in space is key to building realistic models of the stimulus that reaches our retina. The motion structure of this stimulus or retinal flow - the substrate for self-motion processing - is created by the relative movement of the eyes with respect to the world. Characterizing this stimulus requires tracking the eye's three degrees of freedom in the head and the head's six degrees of freedom in the world. While vertical and horizontal eye rotations have been described during locomotion in the context of gaze stabilization, the component around the line of sight - torsion - has remained difficult to quantify, and how all three rotational components jointly contribute to retinal flow during self-motion remains largely unexplored. Here, we leveraged head-mounted technology to estimate eye torsion in ten subjects as they walked towards a distant target (from 14 to 4 meters away from the target). More specifically, we combined automatic feature tracking with gaze-constrained simulations of eye rotations and camera projection to recover torsion from image data. We then estimated the curl present in the optic-flow field in head and retina centered frames in two scenarios: torsion as estimated from our data and with no torsion. We show that the eye's torsional component compensates for the roll component of head's angular displacement, altering the incoming visual flow in ways that are relevant for the extraction of self-motion parameters from retinal flow.

animal behavior and cognition↗

bioRxiv2026

Magnitude estimation reveals Poisson-like noise underlying perception

Understanding how physical stimuli map onto perceptual experience is the founding goal of psychophysics. Insights into this process have primarily relied on measurements of sensitivity, how finely people tell stimuli apart, but these cannot identify the internal noise distribution underlying perception because they cannot separate it from signal amplification. Here, using visual contrast, we show that the trial-to-trial variability of subjective ratings derived from magnitude estimation, where people rate stimulus intensity with numbers, provides access to this noise. We validated this estimate by demonstrating that the analysis of this variability alongside mean responses reveals an internal representation comprising a sigmoidal response function and Poisson-like noise that quantitatively predicts sensitivity without free parameters. These predictions include the classic phenomena of the pedestal effect and Weber's law, which we can now trace back to the response nonlinearities and signal-dependent noise. These findings establish subjective rating variability as a behavioral measure of internal noise.

neuroscience↗

bioRxiv2026

Beyond the Focus of Expansion: Retinal curl as a functional signal for heading estimation

Prevailing models aiming at explaining heading assume that humans need to recover the Focus of Expansion (FoE) while accounting for eye-movement-induced rotation. We propose an alternative: the visual system utilizes mean retinal curl from fixations as a surrogate signal for heading, rendering the explicit recovery of the FoE unnecessary. Stationary participants viewed simulated walking paths on a large screen while fixating on points on the projected ground texture at varying eccentricities --a natural behavior inducing sustained retinal curl. Participants continuously reported perceived heading in 3D scene coordinates. To isolate the role of retinal curl, we employed a real-time manipulation that kept translational flow constant while the foveal curl component was either unaltered, cancelled, or overcancelled. Under natural conditions (unaltered), participants exhibited systematic heading biases opposite the direction of gaze. Crucially, these biases vanished when we cancelled the expected curl, and flipped when we overcancelled it, identifying retinal curl as the specific driver of perceptual bias. We modeled these results using a simple feedback controller and a ring-attractor neural network featuring gaze-contingent inhibition and a straight-ahead prior. These findings suggest the brain exploits the geometry of gaze stabilization to simplify navigation, treating retinal curl as a functional signal rather than noise to be filtered.

neuroscience↗

bioRxiv2024

The predictive outfielder: a critical test across gravities

Intercepting moving targets, like fly balls, is a common challenge faced by several species. Historically, models attempting to explain this behavior in humans have relied on optical variables alone. Such models, while insightful, fall short in several respects, particularly in their lack of predictive capabilities. This absence of prediction limits the ability to plan movements or compensate for inherent sensorimotor delays. Moreover, these traditional models often imply that an outfielder must maintain a constant gaze on the target throughout to achieve successful interception. In this study, we present a new model that continuously updates its predictions, not just on the immediate trajectory of the ball, but also on its eventual landing position in the 3D scene and remaining flight time based on the outfielders real time movements. A distinct feature is the models adaptability to different gravitational scenarios, making its predictions inherently tailored to specific environmental conditions. By actively integrating gravity, our model produces trajectory predictions that can be validated against actual paths, providing a significant departure from previous models. To compare our model to the traditional ones, we conducted experiments within a virtual reality setting, strategically varying simulated gravity among other parameters. This gravity variation yielded qualitatively distinct predictions between error-nulling optical-based heuristics and our model. The trajectories, kinematic patterns and timing responses produced by participants were in good agreement with the predictions of our proposed model, suggesting a paradigm shift in our understanding of interceptive actions. Significance statementCatching a moving target, a challenge consistently faced across various species, exemplifies the complex interplay between perception, prediction, and motor action in dynamic environments. Prevailing models have been largely rooted in optical cues, often overlooking the predictive capacities essential for understanding real-world human behaviors and sidestepping crucial physical variables such as gravity. Our research introduces a novel model that emphasizes both the predictive component and the broader gravitational dynamics allowing for a more holistic understanding of interception tasks. This innovative approach not only holds implications for refining existing models of interception but also carries broader significance for training platforms, ensuring relevance across diverse settings, from Earth to altered gravity environments.

neuroscience↗

bioRxiv2020

Visuomotor temporal adaptation is tuned to gamma brain oscillatory coherence

Every time we use our smartphone, tablet, or other electronic devices we are exposed to temporal delays between our actions and the sensory feedback. We can compensate for such delays by adjusting our motor commands and doing so likely requires establishing new temporal mappings between motor areas and sensory predictions. However, little is known about the neural underpinnings that would support building new temporal correspondences between different brain areas. We here address the possibility that communication through coherence, which is thought to support neural interareal communication, lies behind the neural processes accounting for how humans cope with additional delays between motor and sensory areas. We recorded EEG activity while participants intercepted moving targets while seeing a cursor that followed their hand with a delay rather than their own hand. Participants adjusted their movements to the delayed visual feedback and intercepted the target with the cursor. The EEG data shows a significant increase in coherence of beta and gamma bands between visual and motor areas during the hand on-going movement towards interception. However, when looking at differences between participants depending on the level of adaptation, only the increase in gamma band correlated with the level of temporal adaptation. We are able to describe the time course of the coherence using coupled oscillators showing that the times at which high coherence is achieved are within useful ranges to solve the task. Altogether, these results evidence the functional relevance of brain coherence in a complex task where adapting to new delays is crucial. AUTHOR SUMMARYHumans are often exposed to delays between their actions and the incoming sensory feedback caused by actions. While there have been advances in the understanding of the conditions at which temporal adaptation can occur, little is known about the neural mechanisms enabling temporal adaptation. In the present study we measure brain activity (EEG) to investigate whether communication through coherence between motor and sensory areas might be responsible for ones ability to cope with externally imposed delays in an interception task. We show evidence that neural coherence at gamma band between visual and motor areas is related to the degree of adaptation to temporal delays.

neuroscience↗

bioRxiv2019

Earth-Gravity Congruent Motion Benefits Visual Gain For Parabolic Trajectories

TThere is evidence that humans rely on an earth gravity (9.81 m/s2) prior for a series of tasks involving perception and action, the reason being that gravity helps predict future positions of moving objects. Eye-movements in turn are partially guided by predictions about observed motion. Thus, the question arises whether knowledge about gravity is also used to guide eye-movements: If humans rely on a representation of earth gravity for the control of eye movements, earth-gravity-congruent motion should lead to improved visual pursuit. In a pre-registered experiment, we presented participants (n=10) with parabolic motion governed by six different gravities (-1/0.7/0.85/1/1.15/1.3g), two initial vertical velocities and two initial horizontal velocities in a 3D environment. Participants were instructed to follow the target with their eyes. We tracked their gaze and computed the visual gain (velocity of the eyes divided by velocity of the target) as proxy for the quality of pursuit. An LMM analysis with gravity condition as fixed effect and intercepts varying per subject showed that the gain was lower for -1g than for 1g (by -0.13, SE = 0.005). This model was significantly better than a null model without gravity as fixed effect (p<0.001), supporting our hypothesis. A comparison of 1g and the remaining gravity conditions revealed that 1.15g (by 0.043, SE=0.005) and 1.3g (by 0.065, SE=0.005) were associated with lower gains, while 0.7g (by 0.054, SE=0.005) and 0.85g (by 0.029, SE=0.005) were associated with higher gains. This model was again significantly better than a null model (p<0.001), contradicting our hypothesis. Post-hoc analyses reveal that confounds in the 0.7/0.85/1/1.15/1.3g condition may be responsible for these contradicting results. Despite these discrepancies, our data thus provide some support for the hypothesis that internalized knowledge about earth gravity guides eye movements.

neuroscience↗

bioRxiv2018

Prediction and final temporal errors are used for trial-to-trial motor corrections

Many daily life situations (e.g. dodging an approaching object or hitting a moving target) require people to correct planning of future movements based on previous temporal errors. However, the actual temporal error can be difficult to perceive: imagine a baseball batter that swings and misses a fastball. Here we show that in such situations people can use an internal error signal to make corrections in the next trial. This signal is based on the discrepancy between the actual and the planned action onset time: the prediction error. In this study, we used three interception tasks: reaching movements, saccadic eye movements and a button press that released a cursor moving ballistically for a fixed time. We found that action onset depended on the previous temporal error in the arm movement experiment only and not in the saccadic and button press experiments. However, this dependency was modulated by the movement time: faster arm movements depended less on the previous actual temporal error. An analysis using a Kalman filter confirmed that people used the prediction error rather than the previous temporal error for trial-by-trial corrections in fast arm movements, saccades and button press.

neuroscience↗

bioRxiv2018

The Use of Visual Cues in Gravity Judgements on Parabolic Motion.

Evidence suggests that humans rely on an earth gravity prior for sensory-motor tasks like catching or reaching. Even under earth-discrepant conditions, this prior biases perception and action towards assuming a gravitational downwards acceleration of 9.81 m/s2. This can be particularly detrimental in interactions with virtual environments employing earth-discrepant gravity conditions for their visual presentation. The present study thus investigates how well humans discriminate visually presented gravities and which cues they use to extract gravity from the visual scene. To this end, we employed a Two-Interval Forced-Choice Design. In Experiment 1, participants had to judge which of two presented parabolas had the higher underlying gravity. We used two initial vertical velocities, two horizontal velocities and a constant target size. Experiment 2 added a manipulation of the reliability of the target size. Experiment 1 shows that participants have generally high discrimination thresholds for visually presented gravities, with weber fractions of 13 to beyond 30 %. We identified the rate of change of the elevation angle ([y]) and the visual angle ({theta}) as major cues. Experiment 2 suggests furthermore that size variability has a small influence on discrimination thresholds, while at the same time larger size variability increases reliance on[y] and decreases reliance on{theta} . All in all, even though we use all available information, humans display low precision when extracting the governing gravity from a visual scene, which might further impact our capabilities of adapting to earth-discrepant gravity conditions with visual information alone.

neuroscience↗