Biology subjects

Ahissar, E.

Publications and source records attributed to Ahissar, E..

7 recordsLinked to original sources

bioRxiv2025

The dynamics of episodic recall

The mechanistic understanding of memory recall, a process long known to be influenced by environmental context, has posed a persistent challenge to neuron-centric models. In this study, we approached recall by shifting the focus from internal neuronal representations to brain-environment interactions, employing precise tracking of gaze dynamics within a well-controlled virtual reality (VR) setting. We found that each verbal report of recalled event was consistently preceded by a gradual process of brain-environment coupling: fixational pauses became progressively longer, while gaze direction slowly converged on a specific spatial location associated with the memorized object--a recall-specific location (RSL). Upon the initiation of the verbal report, gaze rapidly diverged from the RSL. Chunked verbal reports were associated with convergence onto shared or spatially clustered RSLs. Moreover, when recall occurred in the same spatial context as encoding, participants recalled objects in the order they were encountered and RSLs were more correlated with gaze locations during encoding. These findings reveal a direct mechanistic dependence of memory recall on the environment and support the view that the environment is not merely a context for memory, but an integral component of the memory itself.

neuroscience↗

bioRxiv2025

Object detection through dynamic motor-sensory convergence

To interact effectively with the world, animals coordinate how they move and how they sense. In natural settings, perceivers adapt their motor-sensory strategies as they approach and explore objects, dynamically shaping both the generation and interpretation of sensory cues. Previous attempts to explain this process by reducing it solely to neuronal representations have failed to capture the mechanisms underlying dynamic perception. In this study, we use precise behavioral tracking to investigate the initial phase of object interaction, asking: What motor-sensory strategies support object detection during natural approach? Using high resolution video tracking of rats freely exploring objects under infrared illumination, we analyzed how head and whisker dynamics evolved across sequential contacts. We found that whisker-object interactions converged toward a distinct line, *, within a motor-sensory plane, where small changes in voluntary whisker movements produced large changes in whisker curvature, a sensory correlate of contact force. This convergence was actively controlled, predicted head movements and marked the completion of object approach. Convergence to * was consistent across different objects, suggesting it serves as an invariant motor-sensory contingency for object detection. Proximity to *predicted the emergence of touch-induced pumps, a rapid motor-sensory reflex that further facilitated convergence within a single whisking cycle. Together, these results reveal that object detection is a closed-loop dynamic process, in which animals actively steer motor-sensory dynamics toward a robust detection-optimized state.

animal behavior and cognition↗

bioRxiv2025

Temporal coding enables hyperacuity in event based vision

The fact that the eyes are constantly in motion, even during fixation, entails that the spike times of retinal outputs carry information about the visual scene even when the scene is static. Moreover, this motion implies that fine details of the visual scene could not be decoded from pure spatial retinal representations due to smearing. Understanding the interplay of temporal and spatial information in visual processing is thus pivotal for both biological research and bio-inspired computer-vision applications. In this study, we consider data from a popular event-based camera that was designed to emulate the function of a biological retina in hardware. Similarly to biological eye, and in contrast to standard frame-based cameras, this camera outputs an asynchronous sequence of "spike" events. We used this camera to obtain dataset of event streams of tiny images, i.e., images whose recognition is impaired by photosensors pixelization and thus their recognition requires hyperacuity. Using these datasets we demonstrate here the superiority of event-based spatio-temporal coding over frame-based spatial coding in the recognition of tiny images by artificial neural networks (ANNs). We further demonstrate the benefits of event sequences for unsupervised learning. Interestingly, Vernier hyperacuity, which is a standard measure of shape hyperacuity, emerged in ANNs following training on tiny images, resembling the natural hyperacuity observed in humans. Our findings underscore the essential role of precise temporal information in visual processing, offering insights for advancing both biological understanding and bio-inspired engineering of visual perception.

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↗

bioRxiv2020

Active palpation underlying shape perception is shaped by physiological thresholds and experience.

Hand movements are essential for tactile perception of objects. However, why different individuals converge on specific movement patterns is not yet clear. Focusing on planar shape perception, we tracked the hands of 11 participants while they practiced shape recognition. Our results show that planar shape perception is mediated by contour-following movements, either tangential to the contour or spatially-oscillating perpendicular to it, and by scanning movements, crossing between distant parts of the shapes contour. Both strategies exhibited non-uniform coverage of the shapes contours. We found that choice of strategy during the first experimental session was strongly correlated with two idiosyncratic parameters: participants with lower tactile resolution tended to move faster; and faster-adapting participants tended to employ oscillatory movements more often. In addition, practicing on isolated geometric features increased the tendency to use the contour-following strategy. These results provide insights into the processes of strategy selection in tactile perception. SIGNIFICANCE STATMENTHand movements are integral components of tactile perception. Yet, the specific motion strategies used to perceive specific objects and features, and their dependence on physiological features and on experience, are understudied. Focusing on planar shape perception and using high-speed hand tracking we show that human participants employ two basic palpation strategies: Contour-following and scanning. We further show that the strategy chosen by each participant and its kinematics depend strongly on the participants physiological thresholds - indicative of spatial resolution and temporal adaptation - and on their perceptual experience.

neuroscience↗

bioRxiv2019

Predictive whisker kinematics reveal context-dependent sensorimotor strategies

Animals actively move their sensory organs in order to acquire sensory information. Some rodents, such as mice and rats, employ cyclic scanning motions of their facial whiskers to explore their proximal surrounding, a behavior known as whisking. Here we investigated the contingency of whisking kinematics on the animals behavioral context that arises from both internal processes (attention and expectations) and external constraints (available sensory and motor degrees of freedom). We recorded rat whisking at high temporal resolution in two experimental contexts - freely moving or head-fixed - and two spatial sensory configurations - a single row or three caudal whiskers on each side of the snout. We found that rapid sensorimotor twitches, called pumps, occurring during free-air whisking carry information about the rats upcoming exploratory direction, as demonstrated by the ability of these pumps to predict consequent head and body locomotion. Specifically, pump behavior during both voluntary motionlessness and imposed head-fixation exposed a backward redistribution of sensorimotor exploratory resources. Further, head-fixed rats employed a wide range of whisking profiles to compensate for the loss of head- and body-motor degrees of freedom. Finally, changing the number of intact vibrissae available to a rat resulted in an alteration of whisking strategy consistent with the rat actively reallocating its remaining resources. In sum, this work shows that rats adapt their active exploratory behavior in a \"homeostatic\" attempt to preserve sensorimotor coverage under changing environmental conditions and changing sensory capacities, including those imposed by various laboratory conditions.

neuroscience↗

bioRxiv2019

Visual closed-loop dynamics via ocular drift

Vision is obtained with a continuous motion of the eyes. The kinematic analysis of eye motion, during any visual or ocular task, typically reveals two (kinematic) components: saccades, which quickly replace the visual content in the retinal fovea, and drifts, which slowly scan the image after each saccade. While the saccadic exchange of regions of interest (ROIs) is commonly considered to be included in motor-sensory closed-loops, it is commonly assumed that drifts function in an open-loop manner, that is, independent of the concurrent visual input. Accordingly, visual perception is assumed to be based on a sequence of open-loop processes, each initiated by a saccade-triggered retinal snapshot. Here we directly challenged this assumption by testing the dependency of drift kinematics on concurrent visual inputs using real-time gaze-contingent-display. Our results demonstrate a dependency of the trajectory on the concurrent visual input, convergence of speed to condition-specific values and maintenance of selected drift-related motor-sensory controlled variables, all strongly indicative of drifts being included in a closed-loop brain-world process, and thus suggesting that vision is inherently a closed-loop process. Author summaryOur eyes do not function like cameras; it has long been known that we are actively scanning our visual environment in order to see. Moreover, it is commonly accepted that our fast eye movements, saccades, are controlled by the brain and are affected by the sensory input. However, our slow eye movements, the ocular drifts, are often ignored when visual acquisition is analyzed. Accordingly, visual processing is typically assumed to be based on computations performed on saccade-triggered snapshots of the retinal state. Our work strongly challenges this model and provides significant evidence for an alternative model, a cybernetic one. We show that the dynamics of the ocular drifts do not allow, and cannot be explained by, open loop visual acquisition. Instead, our results suggest that visual acquisition is part of a closed-loop process, which dynamically and continuously links the brain to its environment.

neuroscience↗