Biology subjects

Mamassian, P.

Publications and source records attributed to Mamassian, P..

17 recordsLinked to original sources

bioRxiv2026

Disentangling visual and motor contributions to continuous psychophysics

Continuous psychophysics measures visual function by asking observers to track a randomly moving target. Because continuous responses provide more information than traditional discrete judgements, a few minutes of tracking can estimate visual sensitivity, making the approach attractive for testing children and patients. Tracking performance is often summarized by cross-correlating the target and cursor velocities: the resulting cross-correlogram peak, lag and width index how strongly, quickly and sharply the observer responds to the target. Tracking, however, requires both seeing the target and moving the cursor towards it, so poor tracking may reflect impaired vision, impaired motor control, or both. Here, we test whether visual and motor contributions to tracking performance can be told apart. Participants tracked a target with a computer mouse while wearing glasses that simulate two levels of visual impairment, using either their dominant or their non-dominant hand. We find that both manipulations alter the cross-correlogram metrics, lowering the peak correlation and delaying and broadening the response, but in different proportions. Visual impairment mainly delays and broadens the response, and does so in proportion to each participant's loss of visual acuity. The non-dominant hand mainly lowers the peak correlation. Two signatures of motor control explain this difference: with the non-dominant hand, participants pause more often and for longer, and move more noisily between pauses, whereas visual impairment alters neither. Together, response lag, time paused and movement noise reveal whether a change in tracking is visual or motor in almost every participant. Our findings demonstrate that, given a baseline measurement, the same tracking data that measure vision can also reveal whether a change in performance reflects a change in what an individual sees or in how they move.

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bioRxiv2026

Natural scene segmentation dynamics reveal iterative Bayesian inference

The visual system operates by segmenting visual inputs into distinct perceptual objects. Segmentation is dynamic, as revealed by the tempo of perceptual choices and neural activity in visual cortex. Dynamics for natural stimuli however, are poorly understood because natural scene segmentation is ambiguous and subjective. We measured subjective human segmentation maps for natural images using an innovative paradigm, and uncovered richer spatiotemporal dynamics than predicted by current theories of segmentation. To explain these dynamics, we introduced Iterative Bayesian Inference algorithms for segmentation that iteratively integrate visual inputs with the prior expectation that objects are spatially compact. When visual inputs were consistent with such a spatial prior, iterative inference was faster. This predicted relationship between spatial prior and inferential dynamics was evident in our data, and correctly reflected each individual participants spatial biases. We conclude that iterative Bayesian inference sets the tempo for a fundamental function of natural vision.

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bioRxiv2026

Modeling how contextual and structural biases shape duration perception

Human time perception is flexible and shaped by both structural constraints and contextual influences. Disentangling these sources of bias is essential for understanding the predictive mechanisms underlying temporal perception, yet no unified model currently integrates them. Here, we quantified precisely the structural and contextual biases in a duration discrimination task to constrain models of duration perception. Using a two-interval duration discrimination task, participants judged which of the two stimuli lasted longer. Stimuli were both visual, both auditory, or one of each modality. Consistent with previous findings, auditory stimuli were perceived longer than visual stimuli of equal duration, reflecting intrinsic properties of audiovisual neural processing. Contextual biases were manipulated through different duration distributions from which stimuli were drawn, a procedure known to influence temporal judgments. Our results show that duration discrimination relies on distinct representations of each stimulus distribution and is best explained by a combination of Bayesian inference and rescaling. While Bayesian inference accounts for contextual effects that bring perceived durations closer to the mean of each distribution, rescaling mechanisms have the opposite effects. These findings challenge existing accounts of contextual effects in time perception and suggest that the brain normalizes temporal representations to adapt to environmental statistics. FundingsThis work was supported by the FRC and the UNAFAM association, and scientific expertise is provided by the FRCs Scientific Advisory Board, and the Anneliese Maier Award to Pascal Mamassian from the Alexander von Humboldt Foundation. Data availabilityBehavioral data and modeling codes will be open-access upon publication.

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bioRxiv2025

Spatial and temporal contexts drive visual temporal integration via spatiotemporal normalisation

The visual system is known to integrate sensory information across both space and time, but these dimensions are often studied separately. Here we provide novel behavioural evidence for an early integration over space and time, and propose a computational model of this integration that is biologically plausible. We designed a controlled task that forces human participants to integrate information over both space and time to perform well. Stimuli were temporally segmented rings of oriented elements and participants had to detect a missing element in the ring. We found that temporal integration was enhanced when successive visual events were temporally proximate, spatially aligned to form a continuous contour, but also, and more surprisingly, when they were brief. Notably, the spatial effects on integration are temporally asymmetric: integration is facilitated when more events are presented earlier in the sequence, and even more so when they form a collinear contour. These findings indicate that temporal integration is sensitive to both the spatial configuration and the number of visual events presented over time, supporting a continuous rather than discrete process at early visual stages. All of these results are well accounted for by a computational model in which temporal integration arises from the overlap of internal signals generated by individual visual events. These signals are shaped by a spatially and temporally tuned divisive normalisation mechanism and integrated via coincidence detection. Predictions from this model match human performance in seminal past work as well as novel stimulus displays, offering an account of how spatio-temporal interactions determine what we perceive and when.

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bioRxiv2025

Encoding and combining naturalistic motion cues in the ferret higher visual cortex

Natural visual scenes contain rich flows of pattern motion that vary not only in orientation but also in spatial sizes and temporal rhythms. To properly interpret the motion, the brain must extract individual features and integrate them into coherent parts, and sometimes also segregate these parts from each other. Here, we performed single-neuron recordings in the motion-sensitive higher-order visual cortex (PMLS) of awake ferrets to investigate how complex motion signals are encoded and combined. We presented motion clouds--naturalistic stimuli with parametrically controlled spatiotemporal frequency content--and found that motion features were encoded in a temporally ordered sequence: orientation and spatial frequency emerged within 120 ms after stimulus onset, while temporal frequency and direction followed at later latencies. Time-resolved decoding revealed that this selectivity evolved dynamically within neurons and was distributed across the population. To probe motion integration, we introduced compound motion clouds composed of two or three localized frequency components. Neuronal responses were well explained by a linear pooling model, suggesting a simple summation mechanism of the individual components. However, a distinct subset of neurons exhibited late responses sensitive to changes in speed content despite matched marginals, consistent with receptive fields differentiating along the speed gradient. Together, we have uncovered a structured and distributed code for motion in high-level visual cortex, and provide mechanistic insights into how the brain parses complex motion in natural scenes.

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bioRxiv2025

Confidence judgements from fused multisensory percepts

Distinguishing between reliable and unreliable internal sensory representations is crucial for a successful interaction with the environment. Precise estimates of the uncertainty of sensory representations are critical to optimally integrate multiple sensory modalities and produce a coherent interpretation of the world. However, once a multisensory percept is produced, it is not yet known whether humans still have access to the uncertainty of each sensory modality. Here, we asked human participants to perform a series of temporal bisection tasks, in either unimodal visual or auditory conditions, or in bimodal audiovisual conditions where vision and audition could be congruent or not. The validity of their temporal bisection was assessed by asking participants to choose which of two consecutive decisions they felt more confident of being correct, focussing only on the visual modality. We found that once multisensory information is integrated, participants could no longer access the unisensory information to evaluate the validity of their decisions. Comparing three generative models of confidence, we show that confidence judgments are fooled by the fused bimodal percept. These results highlight that some critical information is lost between perceptual and metaperceptual stages of processing in the human brain.

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bioRxiv2025

Given the birds, where is the flock? Visual estimation of the location of collections of points

Many visual tasks resemble statistical judgments, estimating the center of a cloud of identical items for example. In statistical form, the observer sees a sample drawn from an invisible probability density function (PDF) : the observer attempts to estimate the location of the PDF. He receives larger rewards for lower variance. Optimal minimum variance estimators are different for different distributions. We evaluated performance for three location families (Gaussian, Laplacian, and Uniform). How does human perceptual organization stack up against optimal perceptual estimation? We found that observers adopted distinct estimators for distinct distribution families, each approximately minimizing variance for its family. To explain observers ability to adapt to different distributional families, we propose that observers adopt a single estimator based on clusters in the sample. This Visual Cluster Model accounted for performance across distributions, suggesting that perceptual grouping first aggregates parts into clusters and only then into a whole. Significance statementImagine a flock of birds. We can predict where additional birds might appear by estimating the probability density function (PDF) of the birds. We compared performance in estimating the location of PDFs drawn from Gaussian, Laplacian or Uniform location families, rewarding lower variance. The optimal estimators for the three families are different. Observers approximately minimized variance for each condition and used different estimators for different families. How could they do so? We propose that observers use a single estimator based on sample clusters: perceptual grouping first aggregates parts into clusters and only then into a whole.

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bioRxiv2024

The Confidence-Noise Confidence-Boost (CNCB) model of confidence rating data

Over the last decade, different approaches have been proposed to interpret confidence rating judgments obtained after perceptual decisions. One very popular approach is to compute meta-d which is a global measure of the sensibility to discriminate the confidence rating distributions for correct and incorrect perceptual decisions. Here, we propose a generative model of confidence based on two main parameters, confidence noise and confidence boost, that we call CNCB model. Confidence noise impairs confidence judgements above and beyond how sensory noise affects perceptual sensitivity. The confidence boost parameter reflects whether confidence uses the same information that was used for perceptual decisions, or some new information. This CNCB model offers a principled way to estimate a confidence efficiency measure that is a theory-driven alternative to the popular M-ratio. We then describe two scenarios to estimate the confidence boost parameter, one where the experiment uses more than two confidence levels, the other where the experiment uses more than two stimulus strengths. We also extend the model to continuous confidence ratings and describe how a non-linear mapping can be estimated between objective and subjective confidence probabilities. Altogether, the CNCB model should help interpret confidence rating data at a deeper level. This manuscript is accompanied by a toolbox that will allow researchers to estimate all the parameters of the CNCB model in confidence ratings datasets. Some examples of re-analyses of previous datasets are provided in the Appendix. Author SummaryAfter each perceptual decision, humans have the ability to rate how confident they are that their decision is correct. While there is a growing number of models that attempt to explain how confidence judgments are built, there are very few objective measures of the sensitivity of these confidence judgments. We offer here a measure of confidence efficiency whose interpretation is simple. It takes a value of zero when participants are unable to evaluate the validity of their perceptual decision, a value of one when participants use the same information for their perceptual decision and their confidence judgment, and a value larger than one when participants use information for their confidence judgment that was not used for their perceptual decision. This measure of confidence efficiency is based on a generative model called CNCB that has two main parameters, confidence noise and confidence boost. These parameters again have a simple interpretation, and we show under which circumstances they can be estimated on their own. Finally, we extend the model to continuous confidence ratings.

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bioRxiv2024

Long-term perceptual priors drive confidence bias which favors prior-congruent evidence

According to the Bayesian framework, both our perceptual decisions and confidence about those decisions are based on the precision-weighted integration of prior expectations and incoming sensory information. While it is generally assumed that priors influence both decisions and confidence in the same way, previous work has found priors to have a stronger impact at the confidence level, challenging this assumption. However, these patterns were found for high-level probabilistic expectations that are flexibly induced in the task context. It remains unclear whether this generalizes to low-level perceptual priors that are naturally formed through long term exposure. Here we investigated human participants confidence in decisions made under the influence of a long-term perceptual prior: the slow-motion prior. Participants viewed tilted moving-line stimuli for which the slow-motion prior biases the perceived motion direction. On each trial, they made two consecutive motion direction decisions followed by a confidence decision. We contrasted two conditions - one in which the prior impacted discrimination performance, and one in which it did not. We found a confidence bias favoring the condition in which the prior influenced discrimination decisions, even after accounting for performance differences. Computational modeling revealed this effect to be best explained by confidence using the prior-congruent evidence as an additional cue, beyond the posterior evidence used in the perceptual decision. This is in agreement with a confirmatory confidence bias favoring evidence congruent with low-level perceptual priors, revealing that, in line with high-level expectations, even long-term priors have a greater influence on the metacognitive level than on perceptual decisions. Author SummaryPrior expectations play a critical role in shaping not only the perceptual inferences that we make, but also how confident we feel about those inferences. Bayesian confidence models capture that role, but assume priors to influence both decisions and confidence in the same way. Against this assumption, previous work has found dissociations in the influence of priors on decisions and confidence. However, that work has focussed only on high-level probabilistic priors, rather than the low-level perceptual priors that constrain our processing across many naturalistic situations. Here, we examine whether such dissociations arise under the influence of a low-level perceptual prior that naturally affects humans perception of motion, namely, the expectation that objects move slowly. We reveal evidence for such a dissociation: prior-congruent evidence impacts confidence to a greater extent than perceptual decisions. This suggests the existence of an implicit confidence bias favoring information that confirms prior beliefs, even in the case of long-term perceptual priors.

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bioRxiv2023

Sensorimotor Confidence for Tracking Eye Movements

For successful interactions with the world, we often have to evaluate our own performance. Such metacognitive evaluations have been studied with perceptual decisions, but much less with respect to the evaluation of our own actions. While eye movements are one of the most frequent actions we perform, we are typically unaware of them. Here, we investigated if there is any evidence for metacognitive sensitivity for the accuracy of eye movements. Participants tracked a dot cloud as it followed an unpredictable sinusoidal trajectory for six seconds, and then reported if they thought their performance was better or worse than their average tracking performance. Our results show above chance identification of better tracking behavior across all trials and also for repeated attempts of the same target trajectories. While the sensitivity in discriminating performance between better and worse trials was stable across sessions, for their judgements participants relied more on performance in the final seconds of each trial. This behavior matched previous reports when judging the quality of hand movements, although overall metacognitive sensitivity for eye movements was significantly lower. Together, these results provide an additional piece of evidence for sensorimotor confidence, and open interesting questions about why it differs across actions and how it could be related to other instances of confidence. Statement of RelevanceIn everyday life, it is often critical to be able to evaluate the quality of our own cognitive decisions and actions. However, one of our most frequent actions often does not even reach our awareness: eye movements. We investigated whether observers were able to successfully judge the accuracy of their eye movements when tracking a cloud of dots that followed an unpredictable trajectory. We found that observers were able to distinguish good from bad trials, although sensitivity was lower compared to equivalent previous reports when judging the quality of hand movements. These results add an item to the growing list of our metacognitive abilities, but critically for eye movements that we are typically unaware of. They lead to important novel questions about why metacognitive abilities differ across decisions or different types of actions, and what the potential components of metacognitive abilities might be.

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bioRxiv2023

The role of confidence in decision-making and its pupillary correlate during the interaction with a partner

Perceptual confidence reflects the ability to evaluate the evidence that supports perceptual decisions. It is thought to play a critical role in guiding decision-making, but only a few empirical studies have actually investigated the function of confidence. To address this issue, we designed a perceptual task in which participants provided a confidence judgment on the accuracy of their perceptual decision. Then, they viewed the response of a machine or human partner, and they were instructed to decide whether to keep or change their initial response. We observed that confidence predicted participants decision to keep or change their initial responses more than task difficulty and perceptual accuracy. This suggests that confidence, as a subjective evaluation of uncertainty, enables us to weigh our decisions, driving the interaction with a partner. Furthermore, confidence judgments could be predicted by pre-response pupil dynamics, suggesting that arousal changes are linked to confidence computations. This study contributes to our understanding of the function of confidence in decision-making and highlights the possibility of using pupil dynamics as a proxy of confidence.

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bioRxiv2021

Linking individual differences in cognitive control and perception: Meta-perception in older and younger adults

Visual perception is not only shaped by sensitivity, but also by confidence, i.e. the ability to estimate the accuracy of a visual decision. There is robust evidence that younger observers have access to a reliable measure of their own uncertainty when making visual decisions. This metacognitive ability might be challenged during aging due to increasing sensory noise and decreasing cognitive control resources. We investigated age effects on visual confidence using a confidence forced-choice paradigm. We determined discrimination thresholds for trials in which perceptual judgements were indicated as confident and for those in which they were declined as confident. Younger adults (19-38 years) showed significantly lower discrimination thresholds than older adults (60-78 years). In both age groups, perceptual performance was linked to confidence judgements, but overall results suggest reduced confidence efficiency in older adults. However, we observed substantial variability of confidence effects across all particpants. This variability was closely linked to individual differences in cognitive control capacities, i.e. executive function. Our findings provide evidence for age-related differences in meta-perceptual efficiency that present a specific challenge to perceptual performance in old age. We propose that these age effects are primarily mediated by cognitive control resources, supporting their crucial role for metacognitive efficiency.

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bioRxiv2021

Crossmodal metaperception: Visual and tactile confidence share a common scale

Perceptual decisions are typically accompanied by a subjective sense of (un)certainty. There is robust evidence that observers have access to a reliable estimate of their own uncertainty and can judge the validity of their perceptual decisions. However, there is still a debate to what extent these meta-perceptual judgements underly a common mechanism that can monitor perceptual decisions across different sensory modalities. It has been suggested that perceptual confidence can be evaluated on an abstract scale that is not only task-independent but also modality-independent. We aimed to scrutinize these findings by measuring visual contrast and tactile vibration discrimination thresholds in a confidence forced-choice task. A total of 56 participants took part in our study. We determined thresholds for trials in which perceptual decisions were chosen as confident and for those that were declined as confident. Confidence comparisons were made between perceptual decisions either within the visual and tactile modality, respectively, or across both modalities. Furthermore, we assessed executive functions to explore a possible link between cognitive control and meta-perceptual capacities. We found that perceptual performance was a good predictor of confidence judgments and that the threshold modulation was similarly pronounced in both modalities. Most importantly, participants compared their perceptual confidence across visual and tactile decisions with the same precision as within the same modality. Cognitive control capacities were not related to meta-perceptual performance. In conclusion, our findings corroborate that perceptual uncertainty can be accessed on an abstract scale, allowing for confidence comparisons across sensory modalities.

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bioRxiv2021

Separable neural signatures of confidence during perceptual decisions

Perceptual confidence is an evaluation of the validity of perceptual decisions. While there is behavioural evidence that confidence evaluation differs from perceptual decision-making, disentangling these two processes remains a challenge at the neural level. Here we examined the electrical brain activity of human participants in a protracted perceptual decision-making task where observers tend to commit to perceptual decisions early whilst continuing to monitor sensory evidence for evaluating confidence. Premature decision commitments were revealed by patterns of spectral power overlying motor cortex, followed by an attenuation of the neural representation of perceptual decision evidence. A distinct neural representation was associated with the computation of confidence, with sources localised in the superior parietal and orbitofrontal cortices. In agreement with a dissociation between perception and confidence, these neural resources were recruited even after observers committed to their perceptual decisions, and thus delineate an integral neural circuit for evaluating perceptual decision confidence.

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bioRxiv2019

Performance Monitoring for Sensorimotor Confidence: A Visuomotor Tracking Study

To best interact with the external world, humans are often required to consider the quality of their actions. Sometimes the environment furnishes rewards or punishments to signal action efficacy. However, when such feedback is absent or only partial, we must rely on internally generated signals to evaluate our performance (i.e., metacognition). Yet, very little is known about how humans form such judgements of sensorimotor confidence. Do they monitor their performance? Or do they rely on cues to sensorimotor uncertainty to infer how likely it is they performed well? We investigated motor metacognition in two visuomotor tracking experiments, where participants followed an unpredictably moving dot cloud with a mouse cursor as it followed a random trajectory. Their goal was to infer the underlying target generating the dots, track it for several seconds, and then report their confidence in their tracking as better or worse than their average. In Experiment 1, we manipulated task difficulty with two methods: varying the size of the dot cloud and varying the stability of the targets velocity. In Experiment 2, the stimulus statistics were fixed and duration of the stimulus presentation was varied. We found similar levels of metacognitive sensitivity in all experiments, with the temporal analysis revealing a recency effect, where error later in the trial had a greater influence on the sensorimotor confidence. In sum, these results indicate humans predominantly monitor their tracking performance, albeit inefficiently, to judge sensorimotor confidence. HighlightsO_LIParticipants consciously reflected on their tracking performance with some accuracy C_LIO_LISensorimotor confidence was influenced by recent errors C_LIO_LIExpectations of task difficulty did not play a large role in sensorimotor confidence C_LIO_LIMetacognitive sensitivity of binary confidence judgements on continuous performance can be quantified with standard non-parametric techniques C_LI

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bioRxiv2019

Priors and Payoffs in Confidence Judgments

1Priors and payoffs are known to affect perceptual decision-making, but little is understood about how they influence confidence judgments. For optimal perceptual decision-making, both priors and payoffs should be considered when selecting a response. However, for confidence to reflect the probability of being correct in a perceptual decision, priors should affect confidence but payoffs should not. To experimentally test whether human observers follow this normative behavior, we conducted an orientation-discrimination task with varied priors and payoffs, probing both perceptual and metacognitive decision-making. We then examined the placement of discrimination and confidence criteria according to several plausible Signal Detection Theory models. In the normative model, observers use the optimal discrimination criterion (i.e., the criterion that maximizes expected gain) and confidence criteria that shift with the discrimination criterion that maximizes accuracy (i.e., are not affected by payoffs). No observer was consistent with this model, with the majority exhibiting non-normative confidence behavior. One subset of observers ignored both priors and payoffs for confidence, always fixing the confidence criteria around the neutral discrimination criterion. The other group of observers incorrectly incorporated payoffs into their confidence by always shifting their confidence criteria with the same gains-maximizing criterion used for discrimination. Such metacognitive mistakes could have negative consequences outside the laboratory setting, particularly when priors or payoffs are not matched for all the possible decision alternatives.

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bioRxiv2018

When temporal attention lacks confidence

Accurate decision-making requires estimating the uncertainty of perceptual events. Temporal attention is known to enhance the selection of a stimulus at a relevant time, but how does this selective process affect a decisions confidence? Here, we adapted an \"Attentional blink\" paradigm to investigate the effect of temporal attention on confidence judgments. In a RSVP stream of letters, two targets were cued to induce two successive attentional episodes. We found that the confidence ratings given to an item systematically followed the probability with which this item was reported. This coupling made confidence oblivious to selection delays usually observed when the two targets were separated by long intervals (249ms to 747ms). In particular, during this period, confidence was higher for more delayed item selection. One exception to this relationship between confidence and temporal selection was found when the second target appeared soon after (83ms) the first attentional episode. Here, a strong under-confidence bias was observed. Importantly, however, this early confidence bias did not impact confidence sensitivity in discriminating correct and erroneous responses. These results suggest that temporal attention and confidence can operate at different time scales, a difference which seems to reflect high-level heuristic biases rather than segregated processes for decision and confidence evidence.

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