Biology subjects

Rucci, M.

Publications and source records attributed to Rucci, M..

17 recordsLinked to original sources

bioRxiv2026

Eye movements enhance stereoscopic 3D vision

In moving organisms, sensory systems must recover spatial properties of the world from signals continually altered by their own movements. These self-generated temporal signals carry useful spatial information across various sensory modalities, but it remains unclear whether they also contribute to fine visual computations traditionally thought to rely on the spatial structure of the retinal images. In humans, stereopsis estimates depth from differences between the images in the two eyes with extraordinary precision. Yet fixational eye movements continually alter these differences, causing binocular disparity to fluctuate over time. Here we show that stereopsis critically depends on these oculomotor-induced input changes. Using high-resolution binocular eye tracking and gaze-contingent display control, we selectively manipulated the retinal consequences of the differential (vergence) and common (version) components of binocular eye movements. Suppressing eye-movement-induced disparity modulations severely impairs stereopsis, even when retinal image motion in each eye is preserved. Across viewing conditions, the strength of disparity modulations closely predicts performance, regardless of whether they are generated by vergence or version. These findings establish stereopsis as a spatiotemporal process and reveal disparity dynamics induced by eye movements as a critical resource for fine depth perception.

neuroscience↗

bioRxiv2026

Active sensing explains cortical variability and improves visual information

Active vision is often considered at the scale of saccades, with each fixation treated as a static visual sample. Yet the eyes continue to move during fixation, continually transforming the retinal input. Here we measured these movements at high precision while recording neuronal populations in the foveal primary visual cortex of awake marmosets viewing repeated flashed natural images. Fixational eye movements accounted for most conditional firing-rate variability and nearly all shared variability not explained by the trial-averaged response. An image-computable model captured this modulation largely from gaze-dependent retinal input; explicit eye-position and eye-velocity signals added little predictive power. Under natural viewing, retinal motion redistributed image power across temporal frequencies, and motion effects grew when this power engaged spatiotemporal tuning. In model-derived populations, fixational motion increased the spatial information carried per spike relative to stabilized input, with sharpening growing across successive nonlinear stages. Thus, activity commonly assigned to cortical noise is not just structured visual reafference generated by the movement of the observer, but is beneficial signal which sharpens spatial representations.

neuroscience↗

bioRxiv2025

High-resolution mapping of foveal vision

Human vision critically relies on the foveola, a tiny region of the retina with the highest photoreceptors density. Although it spans only[~] 0.1% of the visual field, the foveola accounts for nearly one third of projections to the visual cortex. Accurate assessment of foveal function is therefore essential for monitoring visual processes and visual health. However, probing this region is challenging because of its minute size and the incessant eye movements that humans perform, even when fixating on a single point. Here, we leverage recent advances in eye-tracking and gaze-contingent display control to develop a visual field test capable of mapping foveal sensitivity with high precision and reliability. Applied to healthy observers, this method reveals substantial idiosyncratic variability both across and within individuals, with peak sensitivity consistently shifted toward the temporal visual field. By enabling high-resolution individualized assessment of foveal vision, this approach opens new avenues for both clinical diagnostics and basic research.

neuroscience↗

bioRxiv2025

What one sees depends on how far the eye has moved

Humans explore visual scenes through frequent, rapid gaze shifts known as saccades. These movements redirect the high-acuity region of the retina toward objects of interest, thus selecting information based on location. Here, we show that saccade amplitude provides a separate and complementary form of selection, effectively filtering visual information by spatial frequency rather than location. Specifically, a reduction in saccade amplitude attenuates post-saccadic visual sensitivity in an amplitude-dependent range of low spatial frequencies. This effect is highly robust, so that even minute changes in saccade size considerably affect visibility. We show that this phenomenon arises from the way the magnitude-dependent kinematic characteristics of saccades transform the visual world into a spatiotemporal flow: post-saccadic visibility closely follows theoretical predictions based on the spatial information that saccade transients convey within the temporal bandwidth of retinal sensitivity. Thus, saccades not only guide selection based on location, but also filter visual information based on content, actively shaping perception.

neuroscience↗

bioRxiv2025

Residual Foveal Motion Facilitates Processing of Visually Tracked Objects

Humans and other species visually track moving objects via pursuit eye movements. These movements fail to stabilize the stimulus on the retina, an effect often attributed to errors in oculomotor control. However, it remains unclear whether the resulting residual retinal motion serves visual functions. Using high-resolution eye tracking, we reconstructed foveal motion during discrimination of both stationary and moving stimuli. We show that the retinal motion elicited by pursuit is heavily constrained and strikingly mirrors the motion present during normal active fixation. We then show that this motion performs an important information-compression computational function by equalizing luminance modulations in a low-spatial-frequency range during tracking of natural stimuli. Finally, we show that the resulting visual signals during tracking contribute to perceptual judgments, shifting spatial sensitivity toward lower frequencies relative to fixation. These results suggest that retinal motion during pursuit constitutes an active strategy for encoding space in the joint space-time domain.

neuroscience↗

bioRxiv2025

Subfoveal scotomas trigger fine-scale fixation reorganization: insights from retinal imaging and retinal-contingent stimulation

Fine spatial vision relies on the foveola, the 1-degree retinal region with highest cone density. Despite its importance, the relationship between retinal anatomy, fixational behavior, and visual perception in the foveola is not fully understood. Using an Adaptive Optics Scanning Light Ophthalmoscope for high-resolution retinal imaging and stimulation, we studied the effect of a simulated subfoveolar ({approx}0.03 degrees2) scotoma on fine spatial vision and fixation behavior in healthy observers. Our findings show that the visuomotor system adapts to the scotoma with striking precision by shifting the preferred locus of fixation in a systematic fashion by minute ({approx}5 arcmin) amounts to bring stimuli into a region of visibility. These results reveal an unprecedented level of fine-scale plasticity in the human visuomotor system. Interestingly, this new retinal locus of fixation is characterized by lower cone density among those surrounding the scotoma, indicating that factors beyond spatial sampling maximization influence these fine-scale adjustments.

neuroscience↗

bioRxiv2024

High refresh rate display for natural monocular viewing in AOSLO psychophysics experiments

By combining an external display operating at 360 frames per second with an Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO) for human foveal imaging, we demonstrate color stimulus delivery at high spatial and temporal resolution in AOSLO psychophysics experiments. A custom pupil relay enables viewing of the stimulus through a 3-mm effective pupil diameter and provides refractive error correction from -8 to +4 diopters. Performance of the assembled and aligned pupil relay was validated by measuring the wavefront error across the field of view and correction range, and the as-built Strehl ratio was 0.64 or better. High-acuity stimuli were rendered on the external display and imaged through the pupil relay to demonstrate that spatial frequencies up to 54 cycles per degree, corresponding to 20/11 visual acuity, are resolved. The completed external display was then used to render fixation markers across the field of view of the monitor, and a continuous retinal montage spanning 9.4 by 5.4 degrees of visual angle was acquired with the AOSLO. We conducted eye-tracking experiments during free-viewing and high-acuity tasks with polychromatic images presented on the external display. Sub-arcminute eye position uncertainty was achieved, enabling precise localization of the line of sight on the monitor while simultaneously imaging the fine structure of the human central fovea. This high refresh rate display overcomes the temporal, spectral, and field of view limitations of AOSLO-based stimulus presentation, enabling natural monocular viewing of stimuli in psychophysics experiments conducted with AOSLO.

bioengineering↗

bioRxiv2024

Perceptual consequences of retinal stabilization with a high-frequency LCD display

During natural fixation, ocular drifts continually modulate the input to the retina. Previous studies have shown that this motion enhances sensitivity to fine spatial detail, a conclusion supported by findings of reduced sensitivity to high--but not low--spatial frequencies when stimuli are immobilized on the retina for brief periods of time. Most prior retinal-stabilization studies have relied on fast-phosphor cathode ray tube (CRT) displays or adaptive optics scanning laser ophthalmoscopes (AOSLOs), both of which deliver temporally pulsed stimulation. This raises the question of whether stimulus flicker contributed to the previously observed perceptual impairments under retinal stabilization. Here, we replicate stabilization experiments using two types of fast displays that provide more continuous stimulation: liquid-crystal display (LCD) and organic light-emitting diode (OLED) monitors. We again find an impairment in sensitivity to high spatial frequencies under retinal stabilization. Analyses of the retinal input confirm high-quality stabilization within the temporal bandwidth of human vision. These results show that retinal-stabilization effects are robust across display technologies and are little affected by the specific dynamics of modern displays.

neuroscience↗

bioRxiv2023

Eye Blinks as a Visual Processing Stage

Humans blink their eyes frequently during normal viewing, more often than it seems necessary for keeping the cornea well lubricated. Since the closure of the eyelid disrupts the image on the retina, eye blinks are commonly assumed to be detrimental to visual processing. However, blinks also provide luminance modulations rich in spatial information to neural pathways highly sensitive to temporal changes. Here we report that the luminance transients from blinks enhance visual sensitivity. By coupling high-resolution eye-tracking in human observers with modeling of blink transients and spectral analysis of visual input signals, we show that blinking increases the power of retinal stimulation and that this effect significantly enhances visibility despite the time lost in exposure to the external scene. We further show that, as predicted from the spectral content of input signals, this enhancement is selective for stimuli at low spatial frequencies and occurs irrespective of whether the luminance transients are actively generated or passively experienced. These findings indicate that, like eye movements, blinking acts as a computational tool in a visual processing strategy that uses motor behavior to reformat spatial information in the temporal domain.

neuroscience↗

bioRxiv2022

Alignment, calibration, and validation of an adaptive optics scanning laser ophthalmoscope optimized for resolving human cones in the central fovea

Advances in adaptive optics scanning laser ophthalmoscope (AOSLO) technology have enabled cones in the human fovea to be reliably resolved, providing new insight into human foveal anatomy, visual perception, and retinal degenerative diseases. These high-resolution ophthalmoscopes require careful alignment of each optical subsystem to ensure diffraction-limited imaging performance, which is necessary for resolving the smallest foveal cones. This paper presents a systematic and rigorous methodology for building, aligning, calibrating, and testing an AOSLO designed for imaging the cone mosaic of the central fovea in humans with cellular resolution. This methodology uses a two-stage alignment procedure and thorough system testing to achieve diffraction-limited performance. Results from retinal imaging of healthy human subjects show that the system can resolve cones at the very center of the fovea, the region where the cones are smallest and most densely packed.

bioengineering↗

bioRxiv2022

High-resolution eye-tracking via digital imaging of Purkinje reflections

Reliably measuring eye movements and determining where the observer looks are fundamental needs in vision science. A classical approach to achieve high-resolution oculomotor measurements is the so-called Dual-Purkinje-Image (DPI) method, a technique that relies on the relative motion of the reflections generated by two distinct surfaces in the eye, the cornea and the back of the lens. This technique has been traditionally implemented in fragile and difficult to operate analog devices, which have remained exclusive use of specialized oculomotor laboratories. Here we describe progress on the development of a digital DPI, a system that builds on recent advances in digital imaging to enable fast, highly precise eye-tracking without the complications of previous analog devices. This system integrates an optical setup with no moving components with a digital imaging module and dedicated software on a fast processing unit. Data from both artificial and human eyes demonstrate sub-arcminute resolution at 1 Khz. Furthermore, when coupled with previously developed gaze-contingent calibration methods, this system enables localization of the line of sight within a few arcminutes.

neuroscience↗

bioRxiv2022

Fine-scale measurement of the blind spot borders

The blind spot is both a necessity and a nuisance for seeing. It is the portion of the visual field projecting to where the optic nerve crosses the retina, a region devoid of photoreceptors and hence visual input. The precise way in which vision transitions into blindness at the blind spot border is to date unknown. A chief challenge to map this transition is the incessant movement of the eye, which unavoidably smears measurements across space. In this study, we used high-resolution eye-tracking and state-of-the-art retinal stabilization to finely map the blind spot borders. Participants reported the onset of tiny high-contrast probes that were briefly flashed at precise positions around the blind spot. This method has sufficient resolution to enable mapping of blood vessels from psychophysical measurements. Our data show that, even after accounting for eye movements, the transition zones at the edges of the blind spot are considerable. On the horizontal meridian, the regions with detection rates between 80% and 20% span approximately 25% of the overall width of the blind spot. These borders also vary considerably in size across different axes. These data show that the transition from full visibility to blindness at the blind spot border is not abrupt but occurs over a broad area.

neuroscience↗

bioRxiv2022

Individual differences in eye drift predict visual acuity

Visual acuity is commonly assumed to be determined by the eye optics and spatial sampling in the retina. Unlike a camera, however, the eyes are never stationary during the acquisition of visual information, a jittery motion known as ocular drift, incessantly displaces stimuli over many photoreceptors. Previous studies have shown that acuity is impaired in the absence of retinal image motion caused by eye drift. However, the relation between individual drift characteristics and acuity remains unknown. Here we show that (a) healthy emmetropes exhibit a large variability in their amount of drift; and (b) that these differences profoundly affect the structure of spatiotemporal signals to the retina. We further show that (c) the spectral distribution of the resulting luminance modulations strongly correlates with individual visual acuity; and (d) that natural inter-trial fluctuations in the amount of drift modulate acuity. As a consequence, in healthy emmetropes acuity can be predicted from the motor behavior elicited by a simple fixation task, without directly measuring it. These results shed new light on how oculomotor behavior contributes to fine spatial vision. SignificanceHealthy humans can visually resolve extremely fine patterns, in some cases with the relevant features spanning less than a single photoreceptor on the retina. This accomplishment is particularly remarkable considering that the eyes are never stationary. Ocular drift--a motion that eludes human awareness--shifts the stimulus across many photoreceptors during the acquisition of visual information. Here we show that visual acuity depends on ocular drift. Natural variations in the amount of drift are associated with acuity both within and across subjects, so that individual acuity limits can be directly inferred from the amount of motion during fixation on a marker. Results closely follow the strength of the luminance modulations caused by ocular drift, providing support to long-standing dynamic theories of visual acuity.

neuroscience↗

bioRxiv2022

Fine oculomotor knowledge enhances high-acuity vision

It has long been debated how humans resolve fine details and perceive a stable visual world despite the fixational motion of their eyes, the incessant ocular jitter that occurs in the intervals between voluntary gaze shifts. Current theories assume these processes to rely solely on the visual input to the retina, without contributions from motor and/or proprioceptive sources. Here we show that contrary to this widespread assumption, the visual system has access to high-resolution extra-retinal knowledge of fixational eye motion and uses it to deduce spatial relations. Building on recent advances in gaze-contingent display control, we created a spatial discrimination task in which the stimulus configuration was entirely determined by oculomotor activity. Our results show that humans correctly infer geometrical relations even when no spatial information is delivered to the retina and accurately combine high-resolution extraretinal monitoring of gaze displacement with retinal signals. These findings reveal a multimodal strategy for encoding spatial details, in which fine oculomotor knowledge is used to interpret the fixational input to the retina.

neuroscience↗

bioRxiv2021

Beyond Fixation: detailed characterization of neural selectivity in free-viewing primates

Virtually all vision studies use a fixation point to stabilize gaze, rendering stimuli on video screens fixed to retinal coordinates. This approach requires trained subjects, is limited by the accuracy of fixational eye movements, and ignores the role of eye movements in shaping visual input. To overcome these limitations, we developed a suite of hardware and software tools to study vision during natural behavior in untrained subjects. We show this approach recovers receptive fields and tuning properties of visual neurons from multiple cortical areas of marmoset monkeys. Combined with high-precision eye-tracking, it achieves sufficient resolution to recover the receptive fields of foveal V1 neurons. These findings demonstrate the power of free viewing to characterize neural response while simultaneously studying the dynamics of natural behavior. HighlightsO_LIWe introduce a free-viewing paradigm for studying neural mechanisms of visual processing during active vision C_LIO_LIReceptive fields (RFs) and neural selectivity in primary visual cortex (V1) and area MT can be extracted during free-viewing in minimally-trained subjects C_LIO_LINovel high-resolution eye tracking in this context supports detailed measurements of receptive fields in foveal V1 C_LI

neuroscience↗

bioRxiv2021

Foveal vision at the time of microsaccades

Humans use rapid eye movements (saccades) to inspect stimuli with the foveola, the region of the retina where receptors are most densely packed. It is well established that visual sensitivity is generally attenuated during these movements, a phenomenon known as saccadic suppression. This effect is commonly studied with large, often peripheral, stimuli presented during instructed saccades. However, little is known about how saccades modulate the foveola and how the resulting dynamics unfold during natural visual exploration. Here we measured the foveal dynamics of saccadic suppression in a naturalistic high-acuity task, a task designed after primates social grooming, which--like most explorations of fine patterns--primarily elicits minute saccades (microsaccades). Leveraging on recent advances in gaze-contingent display control, we were able to systematically map the peri-saccadic time-course of sensitivity across the foveola. We show that contrast sensitivity is not uniform across this region and that both the extent and dynamics of saccadic suppression vary within the foveola. Suppression is stronger and faster in the most central portion, where sensitivity is generally higher and selectively rebounds at the onset of a new fixation. These results shed new light on the modulations experienced by foveal vision during the saccade-fixation cycle and explain some of the benefits of microsaccades.

neuroscience↗

bioRxiv2018

Contrast sensitivity reveals an oculomotor strategy for temporally encoding space

The contrast sensitivity function (CSF), how sensitivity varies with the spatial frequency of the stimulus, is a fundamental assessment of visual performance. The CSF is generally assumed to be determined by low-level sensory processes. However, the sensitivities of neurons in the early visual pathways, as measured in experiments with immobilized eyes, diverge from psychophysical CSF measurements in primates. Under natural viewing conditions, as in typical psychophysical measurements, humans continually move their eyes, drifting in a seemingly erratic manner even when looking at a fixed point. Here, we show that the resulting transformation of the visual scene into a spatiotemporal flow on the retina constitutes a processing stage that reconciles human CSF and the response characteristics of retinal ganglion cells under a broad range of conditions. Our findings suggest a fundamental integration between perception and action: eye movements work synergistically with the sensitivities of retinal neurons to encode spatial information.

neuroscience↗