Vision Research

Filling-in occurs during the perceptual disappearance of a blank figure presented on a textured background. Current models of perceptual filling-in are based on a two-stage model where the figure boundary weakens after a period of adaptation, followed by the spreading of the background representation into the region representing the figure. This suggests a competition between figure boundary and background representations whereby filling-in is facilitated by a weaker boundary representation and a stronger background representation. Here, we test this interpretation, by using the oblique effect and surround-modulation suppression, which are functional properties of early visual cortex that modulate the expected strengths of the responses to the background texture and to the figure boundary. In a sample of N=58 participants, we found more filling-in with background textures of cardinal compared to oblique orientations (earlier onset time, with more and longer episodes of filling-in per trial), in line with a known, stronger neuronal response for cardinal than for oblique orientation in early visual cortex. We found more filling-in when the main axis of the rectangular figure was iso-oriented rather than cross-oriented with the background texture (more and longer episodes of filling-in per trial, but no change in onset time), in line with a lower response to oriented stimuli when surrounded by iso-oriented flankers compared to cross-oriented flankers. Overall, our results support the two-stage model and suggest the involvement of early visual cortical areas characterized by the oblique effect and orientation- tuned surround-suppression.

Visual signals from the two eyes merge gradually as they pass through the primary visual cortex (V1). Here we use a computational model of Macaque V1 to study the first stage of this integration along the magnocellular pathway, in layer 4C, aiming to infer neuroanatomical origins of binocular response. It is known that neurons in layer 4C are predominantly monocular, though some do exhibit varying degrees of binocularity. We find (1) the emergence of narrow binocular strips along borders of ocular dominance columns (ODC), a finding that aligns with experiments; (2) most consistent with data is when 10 - 30% of interactions near ODC boundaries are cross-columnar; and (3) feedback from layer 6 is largely monocular. These results were obtained through systematic hypothesis testing using a multiscale model that is orders of magnitude faster than its biologically-detailed predecessors. We propose that multiscale modeling can be an effective tool for bridging anatomy and function.

During active vision, the brain must coordinate where to move the eyes with predictions about upcoming sensory input. Before each saccade, perception is enhanced at the upcoming fixation location, but whether this enhancement depends on expectations about target features remains unknown. Here, participants prepared a saccade to a cued location while reporting the presence and orientation of a brief visual target that appeared either at the saccade goal or at the opposite location. Feature expectation was manipulated across blocks by varying the probability of the two target orientations. Perceptual sensitivity (d') increased when targets were presented at the saccade goal, consistent with presaccadic enhancement, and was also higher for less expected features. However, these effects were independent: feature probability did not alter the magnitude of presaccadic enhancement. Moreover, presaccadic enhancement increased near saccade onset, whereas the advantage for less expected features weakened as movement onset approached. Saccade latency revealed a contrasting pattern. Visual targets presented at the saccade goal delayed movement initiation. This delay depended on feature probability, with longer latencies for unexpected than for expected features only when saccades were directed towards the target. This location-specific effect persisted after accounting for perceptual report, and the latency cost for unexpected features was reproduced in a follow-up experiment. Together, these findings show that feature probability enhanced sensitivity to unexpected information independently of presaccadic enhancement, while selectively delaying saccade initiation towards targets with unexpected features. This dissociation suggests that feature expectation modulates perception and action through functionally distinct forms of visual processing.

Numerosity adaptation (the underestimation of number after exposure to a numerous adaptor) is reduced when adaptor and test differ in color, suggesting that the numerosity system parses items into color-defined categories. Here we ask whether this chromatic selectivity is organized into multiple narrowly tuned chromatic channels, and whether its expression depends on individual chromatic sensitivity. Twenty observers (aged 22-61) completed two psychophysical tasks. First, chromatic discrimination was measured for five hues spaced in 5{degrees} CIE L*a*b* steps ({Delta}H = 0{degrees}, 5{degrees}, 10{degrees}, 15{degrees}, 20{degrees}) from a red reference (LCh: 54, 118, 38), yielding an individual just-noticeable difference (JND). Second, numerosity adaptation was measured across the same five chromatic distances between a 48-dot adaptor and the test. Observers with superior discrimination (JND < 2.5{degrees}) showed robust chromatic tuning, adaptation declining as the test moved away from the adaptor hue, whereas poorer discriminators showed none. Using an interindividual-covariance / factor-analytic approach, we found that adaptation strengths at neighboring chromatic distances were highly correlated and fell off with chromatic separation. Principal component analysis extracted two factors, one loading on the larger chromatic distances and one on the smaller; under oblique (promax) rotation the two factors were substantially correlated (r = .66), implying at least two dissociable but overlapping chromatically tuned mechanisms. These results suggest that numerosity adaptation is mediated by multiple, comparatively narrow chromatic channels, resembling the higher-order color mechanisms inferred from color scaling, SSVEP, and fMRI, rather than the two early cardinal axes (L-M, S-(L+M)).

A critical step in visual cortical maturation is refinement of receptive field (RF) size, producing higher acuity vision. This was previously studied using species with well-developed vision (e.g., carnivores, primates), in which visual experience was necessary for refinement but not maintenance of RFs in visual cortex. In contrast, in Syrian hamsters, a crepuscular species with low visual acuity, dark rearing had no effect on RF refinement in juveniles, but RFs re-enlarged in adulthood, resulting in reduced acuity. These inter-species differences raise the question of whether the need for visual experience is primarily related to the phylogenetic position of the species or to its ecological niche. Here we report that dark rearing had no effect on development or maintenance of RF properties of visual cortical neurons in nocturnal mice. Mice with lifelong visual deprivation refined and maintained their RF size over time. Furthermore, the development of stimulus direction tuning was unaffected by dark rearing. In contrast, surround suppression, orientation tuning and the sharpness of direction tuning were abnormal in dark reared mice. These and our previous results from hamsters show that species living in an ecological niche with minimal daylight exposure require little to no visual experience to develop and maintain refined RFs. This study is an important step in developing a better understanding of the role of visual experience in the development of visual processing circuitry and suggests that diurnal mammals may be a better model for human visual cortical development than mice.

PurposeOculocutaneous albinism type 1 (OCA1) is an inherited disorder caused by tyrosinase (TYR) gene mutations. Affected individuals experience visual impairment and severe photosensitivity from ocular hypomelanosis, with no current treatments. We evaluated the safety and efficacy of a TYR-encoding adeno-associated virus (AAV) vector in healthy rhesus macaques as a potential OCA1 treatment. MethodsA novel AAV2-based capsid (ATX002) was packaged with the human VMD2 promoter and TYR (hTYR) fused with mGreenLantern (mGL). Two adult rhesus macaques were injected with ATX002-hVMD2-hTYR-mGL subretinally (OD) and intravitreally (OS). Safety and efficacy were assessed via comprehensive ophthalmic examination, fundus photography, spectral-domain optical coherence tomography (SD-OCT), and full-field electroretinography at baseline and defined timepoints up to 12 weeks post-injection, followed by post-mortem immunohistochemistry (IHC). ResultsBoth subretinal doses induced localized hypermelanosis by 3 weeks post-injection, which persisted through the study endpoint and was accompanied by measurable thickening of the retinal pigment epithelium (RPE) on SD-OCT. Histological IHC confirmed successful RPE transduction via robust mGL fluorescence, corroborating in vivo findings by revealing localized RPE hyperplasia and transgene-expressing cells adjacent to regions of de novo hypermelanosis. Intravitreal delivery did not induce any changes to the RPE. Transient uveitis was observed but successfully managed with anti-inflammatory treatment. ConclusionsSubretinal AAV-TYR delivery is a safe and effective approach with the potential to induce RPE pigmentation. These findings support the use of AAV-TYR gene therapy for OCA1, demonstrating efficacy and a manageable safety profile in a large-animal model, and provide a critical bridge toward human clinical translation.

Current debates regarding the relative contribution of saliency versus semantics to gaze control often rely on comparing the predictive power of saliency and meaning maps. We argue that such indirect, global approaches are fundamentally limited because fixations arise from heterogeneous, local causes that are conflated in whole-scene comparisons. To substantiate this claim, we used a direct method where participants explicitly identified the reasons for fixation at specific clusters of high fixation density, distinguishing between low-level saliency and various semantic categories, as well as the most important one. The obtained judgments revealed that multiple factors contribute simultaneously to gaze control. Although their influence varied across fixation clusters, semantics generally dominated saliency. Notably, abstract semantic categories, particularly "unknown/unusual," proved important, highlighting the role of prior knowledge and novelty besides personal relevance in guiding attention. To interpret these findings in the context of existing models, we propose a framework distinguishing between processes highlighting interesting locations in the image from a sampling strategy translating this information into scanpaths. Within this framework, classic saliency and meaning maps are viewed as restricted inputs to the strategy, whereas deep learning-based models (e.g., DeepGaze IIE) are more general and may also implicitly encode aspects of the strategy itself. Consistent with this, we found that the predictive performance of DeepGaze IIE varied less significantly with the specific reasons for fixation than that of classic saliency and meaning map approaches.

Object representations in the human ventral occipitotemporal cortex (VOTC) are organized along multiple dimensions, including shape (rectilinear vs. curvilinear), real-world size (large vs. small), and mobility (stationary vs. mobile). However, these dimensions are strongly correlated in naturalistic vision, making their separate contributions to VOTC organization unclear. For example, large objects (e.g., a wardrobe, a house) are typically rectilinear and stationary, while small objects (e.g., a ball, a cup) are more curvilinear and mobile. Here, we used fMRI, together with a new stimulus set that orthogonally manipulates shape, size, and mobility, to investigate the separate influences of these dimensions on VOTC organization. Example stimuli include air balloon (large, curvilinear, mobile), radar dish (large, curvilinear, stationary), and mailbox (small, rectilinear, stationary). Contrasts revealed that large (vs. small), rectilinear (vs. curvilinear), and stationary (vs. mobile) dimensions all independently evoked strong and overlapping activity in medio-anterior VOTC. This overlapping activity was at the intersection of the parahippocampal place area (PPA) and the ventral place-memory area (VPMA). Similar results were found at the intersection of the scene-selective occipital place area and the lateral place-memory area (LPMA). Finally, large (vs. small), but not rectilinear (vs. curvilinear) or stationary (vs. mobile) activity, was found in additional posterior ventral scene-selective regions, as well as in early visual cortex. Overall, these results indicate that object shape, real-world size, and mobility dimensions all independently activate scene-selective PPA and OPA, showing joint selectivity for distinct low- and high-level object properties that are highly correlated in naturalistic vision.

Blinks are a ubiquitous yet largely unnoticed aspect of human vision, despite causing frequent interruptions of visual input that can amount to up to 10% of waking time. By leveraging a large dataset of unconstrained gaze behavior during two natural tasks, we found a novel behavioral strategy to limit the impact of blinks: blinks were strategically coupled with head movements, which minimizes information loss due to unreliable visual input during head movements. Specifically, blink probability increased with higher head velocities and showed strong temporal modulation relative to head movement onset. Blink probability was reduced before head movement initiation and then peaked during the head movement. The strength of this coupling was tailored to the individual needs of participants, with participants with higher baseline blink showing a stronger synchronization. This indicates that blinks are a part of an individually coordinated strategy when orchestrating eye and head movements during unconstrained natural behavior.

Working memory (WM) is a core cognitive function that supports goal-directed behavior by temporarily maintaining and manipulating information. One of the most widely used paradigms for investigating WM function is the N-back task, and numerous neuroimaging studies have examined load-dependent neural responses using a variety of analytical approaches. However, most previous studies have focused on low-to-moderate load ranges (primarily 0-3-back), and it remains unclear how whole-brain activity patterns reconfigure across a broader range of WM demands, including conditions approaching capacity limits. In the present study, we investigated behavioral performance and whole-brain activity patterns across an extended N-back task ranging from 0-back to 7-back. Behavioral analyses revealed that discrimination sensitivity (d') decreased nonlinearly with increasing WM load, whereas reaction time (RT) exhibited an inverted-U pattern, peaking at intermediate load conditions. To characterize load-dependent whole-brain activity patterns, we computed relative activation maps by subtracting the participant-wise mean activation map across all conditions from each condition-specific activation map. Spatial similarity analyses with the Yeo 7-network templates revealed that low-load conditions showed relatively high similarity to default mode network (DMN)-related patterns. Similarity to the dorsal attention network (DAN) and frontoparietal network (FPN) was maximal at intermediate load levels, indicating load-dependent changes in network similarity profiles. High-load conditions were characterized by partial re-emergence of DMN-related patterns, accompanied by reduced DAN/FPN similarity. In addition, semantic similarity analysis using Neurosynth-derived semantic maps revealed relatively high similarity to default mode-related and self-referential representations under low-load conditions. Intermediate-load conditions showed strong correspondence with working memory- and executive control-related representations, whereas high-load conditions exhibited increased similarity to salience-, aversive/interoceptive-, and inhibitory-control-related representations. Together, these findings suggest that increasing WM load is associated not merely with stronger activation, but with changes in whole-brain activity patterns accompanied by nonlinear changes in network similarity profiles across levels of cognitive demand. Furthermore, the relative activation map-based whole-brain pattern analysis used in this study may provide a useful approach for evaluating changes in whole-brain state representations associated with cognitive load.

The ability to mentally rotate objects is a fundamental feature of human cognition, and humans can use this ability to make choices about objects based on their geometry. However, remarkably little is known about how such choices are reached, and what sort of visual information might facilitate them. We devised an experiment where participants had to mentally simulate an object's rotation to choose which of two objects was better for a subsequent task based on its shape alone. We also tracked their gaze while they made their choice, to see which visual information they were using to facilitate this mental simulation. We found that participants were consistently able to choose the most suitable object for the task, and, remarkably, the visual information they sampled was directly linked to their choices. Put simply, participants made better choices when they looked at more informative regions of the objects, and participants who sampled regions that were better for facilitating mental simulation made better choices overall. These findings reveal a direct link between fixations, simulation, and decision-making, suggesting that to perform any fine-grained mental simulation people need to direct their gaze at specific, informative points of an object to simulate its two-dimensional proximal image displacement.

Mutations in MYO7A result in the most severe subtype of Usher syndrome, the leading genetic cause of deafblindness. The large size of MYO7A requires dual adeno-associated virus (AAV) vectors for gene transfer or alternative methods to treat retinal defects. Here, we evaluated two treatment approaches: i) Supplementation of the human MYO7A gene via dual mRNA trans-splicing AAVs, and ii) CRISPR/Cas-mediated activation of the related murine Myo7b gene. Upon MYO7A supplementation, the transgenic MYO7A transcript and protein were expressed and correctly localized in retinal pigment epithelial (RPE) and photoreceptors of mice, pigs, and human retinal organoids. In RPE-and photoreceptor-specific Myo7a knockout mice, we could restore MYO7A expression and localization of melanosomes in RPE cells to wild-type levels. Myo7b activation led to partial restoration of melanosome localization, and the localization of MYO7B protein was largely comparable to MYO7A. These findings indicate that both approaches are in principle suitable for the therapy of Usher syndrome.

Representations of the same physical stimulus vary between individuals. Characterizing individual differences has practical implications, but is challenging because these representations are not directly observable. Given a model of how representations vary within a population, we propose a Bayesian adaptive procedure for estimating an individual observer's representation from a series of targeted perceptual discrimination judgments. A key component of our approach is using Fisher information to identify stimulus distortions that efficiently differentiate observers in the population. As a proof of concept, we focus on individual differences in color perception and simulate observers with cone fundamentals drawn from an individual colorimetric observer model. We demonstrate that our approach can recover key aspects of a sampled observer's cone fundamentals using simulated three-alternative forced-choice oddity judgments with approximately 500 trials, corresponding to an experimental duration of approximately one hour. Our Bayesian adaptive framework provides a promising and generalizable approach to efficiently link behavioral measurements to individual differences in sensory representations.

During sideways movement of an observer, optic flow parsing - in which an objects speed in the world is extracted from all the other visual movement present in the scene, self-generated and otherwise - has been shown to be incomplete, leading to biases in speed perception, particularly when object and observer are moving in opposite directions. Here, we assess how judgements about the speed of objects moving in depth (judged relative to the world) towards or away from an observer (6 m/s) are affected by simultaneous movement of the observer either in the same or opposite direction as the object. In a virtual reality display, participants (n = 25) viewed a sphere simulated as moving in a corridor either while they were stationary or during visually simulated self-motion in the same or opposite direction as the object. They judged the spheres movement relative to the world by comparing its motion to a probe sphere that travelled laterally across the corridor in front of them. In a second experiment (n = 28) participants performed the same task but during faster self-motion (10 m/s). The second cohort also judged the direction in which the object was perceived to move during the same combinations of self and object speeds. Object speed was overestimated when the object travelled in the direction opposite to the observer compared to how objects motion was judged when the observer was stationary. However, object speed was also overestimated during self-motion in the same direction as the object where participants were also much more likely to misjudge the direction of motion of the object. Precision of judgements was lower when self-motion was simulated than it was for stationary observers. A simple arithmetic model of flow parsing fails to capture these results satisfactorily, suggesting that different mechanisms may be at play when the observer travels in the same direction as a moving object and is vulnerable to misperceiving its direction of travel.

The advancement in deep learning techniques has made Convolutional Neural Networks (CNNs) a powerful tool for the fully automated classification of zooplankton images. In this study, we systematically investigate how network selection, colour information and differences in imaging instruments affect the classification of zooplankton images by comparing multiple state-of-the-art CNNs on images of zooplankton and marine snow from the in situ Continuous Particle Imaging and Classification Sensor (CPICS), Video Plankton Recorder (VPR), In Situ Ichtyoplankton Imaging System (ISIIS), and the on-board Plankton Imager (Pi-10). With differences between models of 7.8 to 19% in F1-score, we find that model selection strongly affects the classification performance, with EfficientNetV2S showing the most reliable overall performance. Moreover, differences between model architectures are largest for the least abundant classes (<100 labeled images), which implies that when these are present, careful model selection is most beneficial. The high image quality of the Pi-10 strongly increases the performance for the least abundant classes compared to the other instruments. In addition, we find a significant correlation (r = 0.597) between ImageNet the performance and F1-score on zooplankton images, which implies that more generally, a model that performs well on ImageNet will perform well for zooplankton classification. Colour information increases the F1-score of the best performing classifier with 2.8%, but provides a stronger benefit (25% F1-score) for classes with <100 images. The overall performance increase of colour information is less than expected and questions the advantage of recording colour information for zooplankton.

Upright postural control during movement relies on multisensory integration. Yet, the frequency-specific contribution of vision remains poorly characterized in virtual reality (VR). This study investigated how multi-sine visual stimulation amplitude delivered in VR influences standing postural responses. Fifteen healthy adults stood on a force plate wearing a VR headset. Visuo-postural coupling was assessed through coherence and gain analyses between a multi-sine signal (10 sinusoids, 0.12 to 1 Hz) oscillating a virtual environment in one of four amplitudes (0.5, 1, 2, 4 degrees peak-to-peak) and the anteroposterior whole-body angle. All amplitudes elicited measurable postural responses. Increasing amplitude significantly increased postural oscillation and tended to increase coherence, while gain significantly decreased. These results are consistent with a nonlinear control system. The 2 degrees amplitude elicited the largest gain with significant coherence across all stimulated frequencies, suggesting it is suitable for studying visual contributions to postural control during movement execution.

Oculocutaneous albinism type 1 (OCA1) is a pigmentation disorder caused by biallelic tyrosinase (TYR) mutations, an essential enzyme for melanin synthesis. TYR inactivity results in loss of hair, skin, and eye pigment, which is detrimental for ocular function. Hypopigmentation of iris, retinal pigment epithelium (RPE), and choroid results in severe photosensitivity and low visual acuity. There are currently no FDA-approved pigment restoring therapies for OCA1, making therapeutic development an unmet clinical need. To address this gap, we have advanced an adeno-associated viral (AAV)-mediated Tyr replacement approach for OCA1 ocular pigment restoration. We evaluated the optimal viral delivery strategy and vector cell-type specificity for iris, RPE, and choroid pigmentation in an OCA1 mouse model, testing intraocular and systemic viral delivery methods in conjunction with viral constructs of varying RPE-specificity. Early, systemic delivery of an RPE-directed AAV-Tyr construct, AAV9.2yf-VMD2-Tyr, achieved widespread ocular pigment rescue with minimal off-target expression in non-ocular tissues. Animals treated with AAV9.2yf-VMD2-Tyr demonstrated reduced photophobic behavior compared to untreated controls, indicating that ocular pigmentation restores a debilitating functional consequence of OCA1. Our findings establish a foundation for clinical translation of an AAV-TYR therapy aimed at improving light sensitivity, glare, and low vision through pigment restoration in patients with OCA1.

Fixational eye movements (FEMs) comprise the involuntary small scale eye motion conducted during fixation on a stationary stimulus. As a consequence, the visual information can be spread across multiple photoreceptors reducing the local signal-to-noise ratio. Yet, the signals transmitted by individual photoreceptors adapt to constant stimulation so that an entirely still scene would eventually fade from view. Because FEMs convert a stationary stimulus in the world to a temporally varying one on the retina, they can act to prevent this stimulus fading. Thus, FEMs can be understood as a sampling protocol than needs to be adjusted to the underlying processing circuitry. We analyse the impact of FEMs on the rate of information acquisition at the level of the retina for two common tasks of the human eye that typically go hand in hand: detection and localization. Here, we build a simple analytical model of visual perception, i.e. we subject a continuous receptor array to a stimulus moving across the retina as a consequence of FEMs with receptor excitations depending on past stimulation through a linear response function. Using Bayesian inference we quantify both the probability of detection and the accuracy of localization as a function of parameters controlling eye movements and stimulus. We find that localization of a stimulus is equivalent to the detection of the stimulus gradient. This allows us to discern optimal properties of eye movements for the respective tasks and provides a link between two typical psychophysical observables: detection thresholds and Vernier acuity. Our analysis suggests that typical human FEMs tend to facilitate localization at the expense of detection. Simply put, if you can see a stimulus you also know where it is. Finally, we propose a variety of experimental protocols to investigate the interplay between FEMs, detection, and localization with the potential of inferring intrinsic properties of an individuals visual system.

Purpose: Photoreceptor Kv2.1/Kv8.2 voltage-gated potassium channels carry an outward potassium current, helping to set the resting membrane potential and to shape dim light responses. Because potassium flux in the outer retina influences extracellular osmolarity and fluid distribution, we hypothesized that Kv2.1/Kv8.2 channels also contribute to fluid homeostasis in this region of the retina. Methods: OCT imaging was performed in Kv8.2 heterozygous (Het) and knockout (KO) mice aged 4-7 weeks under dark- and light-adapted conditions. Light-dark differences in the distance between the external limiting membrane (ELM) and retinal pigment epithelium (RPE) ({Delta}ELM-RPE) were calculated to quantify light-evoked expansion of the subretinal space (SRS). As a secondary outcome, outer nuclear layer (ONL) thickness was also measured under both lighting conditions. Retinal gene expression was assessed by RNA-seq and droplet digital RT-PCR. Retinal protein expression was determined by western blotting and immunolabeling. Results: {Delta}ELM-RPE was significantly reduced in Kv8.2 KO mice compared with Het controls, indicating reduced SRS hydration. ONL thickness exhibited a small but significant light-dark change that was different between genotypes. Transcriptomic analyses revealed upregulation of osmosensitive genes, including osmolyte transporters and aquaporins. AQP1 protein expression in photoreceptors increased. Conclusions: These findings reveal a previously unrecognized role for Kv2.1/Kv8.2 channels in outer retinal fluid homeostasis and support a model in which photoreceptor potassium efflux contributes to osmotic water movement into the subretinal space.

Context effects are ubiquitous across sensory systems and reflect a general encoding principle for both simple and complex stimuli. One simple context effect, contraction bias, manifests in two-interval perception tasks as a bias of the perceived magnitude of the first stimulus toward the center of the overall magnitude range. The underlying cause of contraction bias is unclear. One explanation is that a listeners magnitude estimate of the first stimulus is combined with a perceptual anchor, usually the mean stimulus magnitude, biasing it toward the anchor (sensory model). An alternative explanation is that a listeners response criterion shifts, based on the magnitude of the stimulus pair, relative to the mean magnitude of the stimuli range (decision model). Two pitch-discrimination experiments were performed to test these hypotheses in the auditory domain. The first was a forced-choice discrimination task, where listeners were asked to identify the higher or lower tone in a pair. The second was a same-different task where listeners indicated whether or not the two tones in a pair differed in frequency. Contraction bias was observed in the higher-lower discrimination task, even after extensive perceptual training with feedback. In contrast, no contraction bias was observed in the same-different task. Computational models of the sensory and decision hypotheses were fit to data from both experiments. The sensory model captured the pattern of results the higher-lower experiment but erroneously predicted a contraction bias in the same-different task. The decision model produced similar predictions to the sensory model in the higher-lower task but correctly predicted no contraction bias in the same-different task, and produced lower prediction errors and more stable parameter estimates in both paradigms. Overall, the results suggest that the underlying nature of the contraction bias may reflect decision, rather than sensory, biases based on the context.