Biology subjects

Otero-Millan, J.

Publications and source records attributed to Otero-Millan, J..

7 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↗

bioRxiv2025

Behavioral and Modeling Evidence that Eye Movements Bias Self-motion Perception

To navigate the world, humans must integrate what they see with how they move. As the body moves, for example, the eyes rotate to explore the environment; these eye rotations, in turn, alter the visual signals used to judge body motion. Yet the practical impact of gaze dynamics on self-motion perception remains poorly understood. We tested how gaze position and gaze velocity shape self-motion perception--specifically heading direction--from visual signals in two behavioral experiments. In Experiment 1, we directly manipulated gaze position and velocity; in Experiment 2, a range of task demands evoked distinct gaze patterns. Across both experiments, heading estimates showed systematic, gaze-dependent errors: these estimates shifted toward the direction of eye motion and grew with horizontal gaze eccentricity and speed. A Bayesian ideal observer reproduced these error patterns across participants and tasks when it included three known features of visuomotor processing: (i) encoding retinal motion with eccentricity-dependent noise, (ii) underestimating eye-rotation speed, and (iii) a prior for moving straight ahead. These results reveal a lawful coupling between oculomotor behavior and heading perception. They further suggest that natural gaze strategies, such as keeping gaze near the optic-flow singularity and limiting pursuit speed, help mitigate gaze-dependent biases during navigation.

neuroscience↗

bioRxiv2025

Illusory tilt does not induce optostatic torsion

Viewing tilted images that contain spatial information about gravity and verticality, such as rotated landscapes, or leaning buildings, produces an eye movement response known as optostatic torsion (OST). OST consists of a small-amplitude rotation [~]1{o} of the eyes around the line of sight, in the same direction of image tilt. Here we aimed to determine whether illusory perceptions of visual tilt were sufficient to produce OST. The illusory stimulus was a variation of the Cafe Wall illusion, applied to four "walls" to approximate the appearance of a tilted room. In a first experiment we determined the perceived magnitude of tilt of the illusory stimulus using a two-alternative forced choice (2AFC) task, measuring the amount of tilt required to cancel the perceived illusory tilt for clockwise (CW) or counterclockwise (CCW) configurations. We found an illusory tilt of +3.67{+/-}0.57{degrees} and -3.80{+/-}0.93{degrees}, respectively. Then, in a second experiment, we recorded 3 dimensions of binocular eye movements in ten healthy subjects viewing one of four possible stimuli: 1) illusory, 2) non-illusory with small tilt, 3) landscape with small tilt, and 4) landscape with large tilt. Both the landscape ({+/-}4{o} tilt: 0.4{+/-}0.1, p<0.05; {+/-}30{degrees} tilt: 0.5{+/-}0.1, p<0.01;) and control stimulus (0.2{degrees}{+/-}0.1{degrees}, p<0.05) produced a significant amount of OST when comparing left tilt and right tilt configurations while the illusory stimulus (0.11{degrees}{+/-}0.07{degrees}, p=0.15) did not. This indicates a potential dissociation between our perception of tilt and the processing of tilt that drives the motor response of OST.

neuroscience↗

bioRxiv2025

A discontinuity in motion perception during fixational drift

The human visual system is tasked with perceiving stable and moving objects despite ever-present eye movements. Normally, our visual system performs this task exceptionally well; indeed, under conditions with frames of reference, our ability to detect relative motion exceeds the sampling limits of foveal cones. However, during fixational drift, if an image is programmed to move in a direction consistent with retinal slip, little to no motion is perceived, even if this motion is amplified. We asked: Would a stimulus moving in a direction consistent with retinal slip, but with a smaller magnitude across the retina, also appear relatively stable? We used an adaptive optics scanning light ophthalmoscope to deliver stimuli that moved contingent to retinal motion and measured subjects perceived motion, under conditions with world-fixed background content. We also tested under conditions with background content closer and farther from the stimuli. We found a sharp discontinuity in motion perception. Stimuli moving in a direction consistent with retinal slip, no matter how small, appear to have relatively little to no motion; while, stimuli moving in the same direction as eye motion appear to be moving. Displacing background content to greater than 4{degrees} from the stimuli diminishes the effects of this phenomenon.

neuroscience↗

bioRxiv2025

Horizontal saccade bias results from combination of saliency anisotropies and egocentric biases

Saccadic eye movements shift the fovea between objects of interest to build a visual percept. In humans, saccades are predominantly executed along the cardinal axes, particularly in the horizontal direction. It is unknown how this horizontal saccade bias could arise mechanistically, though previous work suggests contributions from neural, image-based, and ocular motor factors. Here we used two publicly available eye movement datasets to first investigate which image features-spatial frequency, saliency, and structural content-relate to the horizontal saccade bias. Among the three image features, we found that orientation anisotropies in saliency content best predicted the strength of the horizontal saccade bias. Based on this result, we next implemented a saccade target selection model combining allocentric biases aligned with image orientation and egocentric biases aligned with eye or head orientation, independent of image content. As in prior work, this combination successfully replicated human saccade distributions during free viewing of upright images. When applied to tilted images, the model produced effects of image tilt and saccade size that were correlated with prior empirical findings, though with reduced amplitude, suggesting that current saliency models do not fully capture image effects. Taken together, these results suggest that saccade generation reflects both the allocentric biases present in the structure of natural scenes and the egocentric biases present in the saccade generation system itself. An open question is why the egocentric saccade bias exists, but our results suggest that it is adaptive in response to regularities in the world and our typical upright orientation.

neuroscience↗

bioRxiv2025

OpenIrisDPI: An Open-Source Digital Dual Purkinje Image Eye Tracker for Visual Neuroscience

BackgroundVideo-based eye trackers are widely used in vision science, psychology, clinical assessment, and neurophysiology. Many such systems track the pupil center and corneal reflection (P-CR) and compare their positions to estimate the direction of gaze. However, P-CR eye trackers are often too imprecise for applications with stringent eye tracking quality requirements. New methodWe present OpenIrisDPI, an open-source plugin for the OpenIris frame-work that implements dual Purkinje image (DPI) tracking. OpenIrisDPI supports simultaneous pupillography, a technique widely used in perceptual psychology and neuroscience, and it enables direct comparison between P-CR and DPI signals. ResultsData collected from macaque monkeys using OpenIrisDPI show that the P-CR method overestimates the amount of fixational drift between saccades compared to DPI. The accuracy of the DPI signal was further validated using high-density extracellular recording of neurons in the lateral geniculate nucleus. Compensating for the effects of fixational eye movements using DPI signals produced sharper estimates of neuronal receptive fields than using simultaneously collected P-CR signals. Comparison with existing methodsOpenIrisDPI is provided as open-source software and operates on consumer-grade hardware, making it more accessible than previously described DPI eye trackers and less costly than many P-CR systems. To our knowledge, OpenIrisDPI is the first eye tracker to perform both pupillography and DPI eye tracking. ConclusionOpenIrisDPI makes high-precision eye tracking readily available to the research community. It is well suited for visual neuroscience applications, where accurate knowledge of the retinal image during experiments is critical. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=105 SRC="FIGDIR/small/649589v2_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@596dd2org.highwire.dtl.DTLVardef@139027borg.highwire.dtl.DTLVardef@1d1e526org.highwire.dtl.DTLVardef@11b321c_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIOpenIrisDPI is a new open-source eye tracking system. C_LIO_LIOpenIrisDPI tracks the pupil, corneal reflection, & fourth Purkinje image at 500 Hz. C_LIO_LIDual Purkinje image-based eye tracking is more precise than pupilbased tracking. C_LIO_LIDPI improves receptive field characterization of LGN neurons in fixating macaques. C_LI

neuroscience↗

bioRxiv2024

Open Iris - An Open Source Framework for Video-Based Eye-Tracking Research and Development

Eye-tracking is an essential tool in many fields, yet existing solutions are often limited for customized applications due to cost or lack of flexibility. We present OpenIris, an adaptable and user-friendly open-source framework for video-based eye-tracking. OpenIris is developed in C# with modular design that allows further extension and customization through plugins for different hardware systems, tracking, and calibration pipelines. It can be remotely controlled via a network interface from other devices or programs. Eye movements can be recorded online from camera stream or offline post-processing recorded videos. Example plugins have been developed to track eye motion in 3-D, including torsion. Currently implemented binocular pupil tracking pipelines can achieve frame rates of more than 500Hz. With the OpenIris framework, we aim to fill a gap in the research tools available for high-precision and high-speed eye-tracking, especially in environments that require custom solutions that are not currently well-served by commercial eye-trackers. CCS CONCEPTSO_LIApplied computing [->] Life and medical sciences. C_LI

bioengineering↗