Biology subjects

Sagi, D.

Publications and source records attributed to Sagi, D..

12 recordsLinked to original sources

bioRxiv2026

Artificial light at night reshapes diel brain transcriptomics in Dascyllus aruanus damselfish

Artificial light at night (ALAN) disrupts natural light cycles and interferes with light-dependent biological processes. However, the effect of ALAN on cellular processes in wildlife is unclear. We examined diel brain transcriptomic alterations in the diurnal damselfish Dascyllus aruanus by comparing fish exposed to three consecutive nights of ALAN with control fish, sampled during both the day and night. ALAN partially disrupted circadian regulation transcription, altering diel expression of the core clock regulator bmal1 and glucocorticoid-regulated genes. At night, ALAN triggered activation of genes indicative of neuronal activity and acute neural stress, along with suppression of restorative nocturnal processes. The following day, the transcriptomic divergence between ALAN-exposed and control fish expanded, with widespread downregulation of genes governing vascular homeostasis, coagulation, and immune function. Together, these findings indicate that ALAN reshapes brain transcriptomic programs across the entire diel cycle, identifying molecular signatures of physiological disruption in light-polluted marine environments.

cell biology↗

bioRxiv2025

Serial Dependence Predicts Generalization in Perceptual Learning

Visual perception is shaped by recent experience, but how these momentary influences accumulate to support long-term learning and generalization remains unclear. Here, we asked whether short-term memory traces, attractive serial-dependence effects (SDEs), promote learning generalization. We re-analyzed over 200,000 trials from observers trained on a visual texture-discrimination task under three conditions that differentially modulated generalization. Under certain conditions, SDEs reached further back in time than previously reported and persisted after eight days of practice, despite the non-informative nature of past stimuli. Observers in conditions that promoted generalization displayed larger long-range SDEs, and individual SDE magnitude predicted transfer of learning across locations. We propose that SDE is associated with learning flexibility, providing a principled framework for when and why perceptual learning generalizes, which is central to theories of cognitive flexibility. Attractive serial dependence is not an extra mechanism in this model--it is the behavioral footprint of ongoing template plasticity required for flexibility in changing environments.

neuroscience↗

bioRxiv2024

A Tunable and Druggable Mechanism to Delay Forgetting of Olfactory Memories in C. elegans

The poet W.B Yeats wrote that "All that is personal soon rots, it must be packed in ice or salt". Here we show that in Caenorhabditis elegans nematodes, simple animals with just 302 neurons, memories are preserved on ice and in lithium salt. C. elegans nematodes can form associative memories, which are typically forgotten quickly. We discovered that when placed on ice, worms delay forgetting of specific olfactory memories by at least 8-fold. Delayed forgetting was canceled completely when the worms were gradually adapted to low temperatures, owing to a genetically-encoded program that turns acclimated worms cold-tolerant. RNA-seq, mutant analyses, and pharmacological assays revealed that regulation of membrane properties switches cold-induced delayed forgetting ON and OFF, and, remarkably, that lithium delays forgetting only in cold-sensitive but not cold-tolerant worms. We found that downregulation of the diacylglycerol pathway in the AWC sensory neurons is essential for lithium-mediated delayed forgetting, and using neuronal activity recordings located the memory trace to the downstream AIY interneurons. We suggest that the awesome genetic tractability of C. elegans might be harnessed to study the effects of lithium and cold temperatures on the brain, why it influences psychiatric disorders, and even more fundamentally how memory is stored and lost.

neuroscience↗

bioRxiv2023

Isolating objective and subjective filling-in using the Drift Diffusion Model

Spatial context is known to influence the behavioral sensitivity (d) and the decision criterion (c) for detection of low-contrast targets. Of interest here is the effect on the decision criterion. Polat and Sagi (2007) demonstrated that for a Gabor target positioned between two similar co-aligned high contrast flankers, observers reports of seeing the target (Hit and False-Alarm) decreased with increasing target-flankers distance. This effect was more pronounced when distance was randomized within testing blocks compared to when it was fixed. According to Signal-Detection-Theory (SDT), the latter result suggests that the decision-criterion is adjusted to a specific, distance-dependent combination of signal (S) and Noise (N) when the S and N statistics are fixed, but not when they vary across trials. However, SDT cannot differentiate between changes in the decision-bias (criterion-shift) and changes introduced by variations in S and N (signal-shift). To circumvent this limitation of SDT, we analyze reaction-time data (RT) within the framework of the Drift-Diffusion-Model (DDM). We performed an RT analysis of target-flanker interactions using data from Polat & Sagi (2007) and Zomet et al. (2008; 2016). The analysis revealed a stronger dependence on flankers for faster RTs and a weaker dependence for slower RTs. The results are explained by DDM, where an evidence accumulation process depends on the flankers via a change in the rate of the evidence (signal-shift), and on observers prior via a change in the starting point (criterion-shift), leading to RT-independent and RT-dependent effects, respectively. The RT-independent distance-dependent response-bias is attributed to the observers inability to learn multiple internal distributions required to accommodate the distance-dependent effects of the flankers on both the Signal and Noise.

neuroscience↗

bioRxiv2022

Motion-Induced Blindness as a Noisy Excitable System

Perceptual disappearance of a salient target induced by a moving texture mask (MIB: Motion Induced Blindness) is a striking effect, currently poorly understood. Here, we investigated whether the mechanisms underlying MIB qualify as an excitable system. Excitable systems exhibit fast switches from one state to another (e.g., visible/invisible) induced by an above-threshold perturbation and stimulus-independent dynamics, followed by a refractory period. In the experiments, disappearance was induced by masks consisting of slowly rotating radial bars with a gap at the target location, leading to periodic perturbation of the visual field around the target (a bright parafoveal spot). When passed around the target location, masks frequently induced an abrupt target disappearance, pointing to locality. As expected from excitable systems, the disappearance time was not affected by additional bars crossing the target during invisibility, and there was little dependence on the mask configuration. After the target reappeared, it stayed for at least 0.5-2 seconds (the refractory period). Therefore, the mechanisms governing MIB represent an example of an excitable system, where the transition to the invisible state is induced by the mask, with the dynamics that follow determined mostly by the internal network properties.

neuroscience↗

bioRxiv2021

Contrast adaptation improves spatial integration

The effects of contrast adaptation and contrast area summation were investigated using a contrast discrimination task. The task consisted of a target of variable size, and a pedestal with a fixed base contrast. Discrimination performance was examined for a condition in which the pedestal size was fixed, equal to the largest target size, and for a condition in which the pedestal size matched the target size and thus varied with it. Repeated performance of the task produced rapid within-session improvements for both conditions. For stimuli with a matching size of target and pedestal, the performance improved only for the larger targets, indicating the development of area summation, which was initially absent for these stimuli. However, the improvements were mostly temporary, and were not fully retained between subsequent sessions. The temporary nature of the sensitivity gains implies that they resulted, at least in part, from rapid adaptation to the stimulus contrast. We suggest that adaptation decorrelates and thus reduces the spatial noise generated by a high-contrast pedestal, leading to improved area summation and better contrast sensitivity. A decorrelation model successfully predicted our experimental results.

neuroscience↗

bioRxiv2019

A decision-time account of individual variability in context-dependent orientation estimation

Following exposure to an oriented stimulus, the perceived orientation is slightly shifted, a phenomenon termed the tilt aftereffect (TAE). This estimation bias, as well as other context-dependent biases, is speculated to reflect statistical mechanisms of inference that optimize visual processing. Importantly, although measured biases are extremely robust in the population, the magnitude of individual bias can be extremely variable. For example, measuring different individuals may result in TAE magnitudes that differ by a factor of 5. Such findings appear to challenge the accounts of bias in terms of learned statistics: is inference so different across individuals? Here, we found that a strong correlation exists between reaction time and TAE, with slower individuals having much less TAE. In the tilt illusion, the spatial analogue of the TAE, we found a similar, though weaker, correlation. These findings can be explained by a theory predicting that bias, caused by a change in the initial conditions of evidence accumulation (e.g., prior), decreases with decision time (Dekel & Sagi, 2019b). We contend that the context-dependence of visual processing is more homogeneous in the population than was previously thought, with the measured variability of perceptual bias explained, at least in part, by the flexibility of decision-making. Homogeneity in processing might reflect the similarity of the learned statistics. HighlightsO_LIThe tilt aftereffect (TAE) exhibits large individual differences. C_LIO_LIReduced TAE magnitudes are found in slower individuals. C_LIO_LIReduced TAE in slower decisions can be explained by the reduced influence of prior. C_LIO_LITherefore, individual variability can reflect decision making flexibility. C_LI

neuroscience↗

bioRxiv2019

Interaction of contexts in context-dependent orientation estimation

The processing of a visual stimulus is known to be influenced by the statistics in recent visual history and by the stimulus visual surround. Such contextual influences lead to perceptually salient phenomena, such as the tilt aftereffect and the tilt illusion. Despite much research on the influence of an isolated context, it is not clear how multiple, possibly competing sources of contextual influence interact. Here, using psychophysical methods, we compared the combined influence of multiple contexts to the sum of the isolated context influences. The results showed large deviations from linear additivity for adjacent or overlapping contexts, and remarkably, clear additivity when the contexts were sufficiently separated. Specifically, for adjacent or overlapping contexts, the combined effect was often lower than the sum of the isolated component effects (sub-additivity), or was more influenced by one component than another (selection). For contexts that were separated in time (600 ms), the combined effect measured the exact sum of the isolated component effects (in degrees of bias). Overall, the results imply an initial compressive transformation during visual processing, followed by selection between the processed parts. HighlightsO_LINon-linear sub-additivity for increased context area or contrast C_LIO_LINon-linear selection between overlapping or adjacent, dissimilar contexts C_LIO_LILinear additivity for combinations of temporally separated contexts C_LI

neuroscience↗

bioRxiv2019

Seeing, fast and slow: the effects of processing time on perceptual bias

Fast and slow decisions exhibit distinct behavioral properties, such as the presence of decision bias in faster but not slower responses. This dichotomy is currently explained by assuming that distinct cognitive processes map to separate brain mechanisms. Here, we suggest an alternative, single-process account based on the stochastic properties of decision processes. Our experimental results show perceptual biases in a variety of tasks (specifically: learned priors, tilt illusion, and tilt aftereffect) that were much reduced with increasing reaction time. To account for this, we consider a simple yet general explanation: prior and noisy decision-related evidence are integrated serially, with evidence and noise accumulating over time (as in the standard drift diffusion model). With time, owing to noise accumulation, the prior effect is predicted to diminish. This illustrates that a clear behavioral separation - presence vs. absence of bias - may reflect a simple stochastic mechanism. HighlightsO_LIPerceptual and decisional biases are reduced in slower decisions. C_LIO_LISimple mechanistic single-process account for slow bias-free decisions. C_LIO_LISignal detection theory criterion is ~zero in decision times>median. C_LI

neuroscience↗

bioRxiv2019

Orientation-selective adaptation improves perceptual grouping

The role of visual pattern adaptation, and learning, in spatial integration was investigated. Observers performed a perpetual grouping task in which they reported whether a grid of identical tilted bars (45{degrees} counterclockwise from the vertical) is perceived as rows or columns. Performance was measured multiple times during a testing session to determine the effects of repeated exposure to the stimuli. To test for possible effects of learning on the within-session dynamics, observers repeated the experiment on five different days. We found that repeated performance produced rapid within-day improvements, which were largely transient, and were not retained when tested on subsequent days. In addition, exposure to stimuli with equal orientation contributed to the within-session improvement, whereas stimuli having an orientation differing by 45{degrees} from the orientation used in the grouping task diminished the improvement previously obtained in the same session. Practice with the task, over days, resulted in faster improvements. The transient nature of these exposure-driven improvements and their susceptibility to interference by stimuli designed to reduce adaptation suggests that adaptation was the main cause for the observed improvements. Finally, to investigate the effects of adaptation on internal noise and on spatial integration, we employed an external noise paradigm, showing that internal noise reduction resulted from adaptation. Internal noise was reduced only when spatial integration was effective, suggesting that adaptation improved perception of global stimulus properties. Overall, our results suggest that the grouping task benefits from an adaptation process that rapidly adjusts the visual system to the statistics of the visual stimuli. We suggest that this effect is achieved through spatial decorrelation of neural responses. With practice, the visual system is able to adjust faster to changes in the statistics of the environment.

neuroscience↗

bioRxiv2017

Real-time visual interactions across the boundary of awareness

The relationship between our conscious experiences of the visual world and the neuronal processes involved in the processing of visual information is a central theme of current research. However, it is not yet known whether conscious experiences possess unique quantitative or qualitative processing features. Recently we have shown that two visual stimuli, one consciously experienced and one not, interact as function of features and objects similarity, pointing to preserved visual representations in the absence of perceptual awareness. Here we ask whether these representations can be modified in the absence of perceptual awareness by testing interactions while the unperceived stimulus is being modified outside of ones awareness. Observers performed a Motion Induced Blindness task, wherein a plaid Target was morphed into a Gabor patch once disappearance was reported. Reappearances of the morphed target were induced by a visible Cue. Our results indicate that the effectiveness of the cue depends on the target representation during the time of suppression. Reappearance rates were highest when the morphed target and the cue share the same orientations. Our findings indicate that the target-cue interactions do not depend on memory-stored representations, but rather on the current state of the consciously unavailable target. We conclude that visual representations can be modified in the absence of conscious perception.

neuroscience↗

bioRxiv2017

AWARENESS OF THE OUTCOME OF SELF-INITIATED POINTING ACTIONS

Are we aware of the outcome of our actions? The participants pointed rapidly at a screen location marked by a transient visual target (T), with and without seeing their hand, and were asked to estimate (E) their landing location (L) using the same finger but without time constraints. We found that L and E are systematically and idiosyncratically shifted away from their corresponding targets (T, L), suggesting unawareness. Moreover, E was biased away from L, toward T (21% and 37%, with and without visual feedback), in line with a putative Bayesian account of the results, assuming a strong prior in the absence of vision. However, L (the assumed prior) and E (the assumed posterior) precisions were practically identical, arguing against such an account of the results. Instead, the results are well accounted for by a simple model positing that the participants E is set to the planned rather than the actual L. When asked to estimate their landing location, participants appeared to reenact their original motor plan.

animal behavior and cognition↗