Joan Lopez-Moliner

Joan Lopez-Moliner
University of Barcelona | UB · Institut de Neurociències (UBneuro)

Professor
Psychopysics, optic flow

About

126
Publications
12,884
Reads
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1,263
Citations
Additional affiliations
September 2003 - present
University of Barcelona
Position
  • Professor
September 2003 - present
University of Barcelona
Position
  • Professor
September 2001 - September 2003
Erasmus MC
Position
  • PostDoc Position
Education
January 1994 - March 1998
Universitat Politècnica de Catalunya
Field of study
  • Artificial Intelligence - Computer Science

Publications

Publications (126)
Poster
Typically, research in time perception has disregarded the effect that multiple simultaneous elements may have on the duration of an event. However, real life situations are complex, and irrelevant external information can affect our time estimates when we try to assess the duration of specific relevant events. Here, we have examined how the durati...
Article
In this article we present a temporal extension of the slow motion prior model to generate predictions regarding the temporal evolution of the contrast induced speed bias. We further tested these predictions using a novel experimental paradigm that allows us to measure the dynamic perceptual difference between stimuli through a series of manual pur...
Article
Full-text available
We often need to interact with targets that move along arbitrary trajectories in the 3D scene. In these situations, information of parameters like speed, time-to-contact, or motion direction is required to solve a broad class of timing tasks (e.g., shooting, or interception). There is a large body of literature addressing how we estimate different...
Article
Full-text available
Catching a ball in a parabolic flight is a complex task in which the time and area of interception are strongly coupled, making interception possible for a short period. Although this makes the estimation of time-to-contact (TTC) from visual information in parabolic trajectories very useful, previous attempts to explain our precision in interceptiv...
Preprint
Full-text available
We often need to interact with targets that move along arbitrary trajectories in the 3D scene. In these situations, information of parameters like speed, time-to-contact, or motion direction is required to solve a broad class of timing tasks (e.g., shooting, or interception). There is a large body of literature addressing how we estimate different...
Article
Full-text available
Obtaining reliable estimates of the time-to-contact (TTC) in a three-dimensional (3D) parabolic trajectory is still an open issue. A direct analysis of the optic flow cannot make accurate predictions for gravitationally accelerated objects. Alternatively, resorting to prior knowledge of gravity and size can provide accurate estimates of TTC in para...
Article
Full-text available
In a 2-alternative forced-choice protocol, observers judged the duration of ball motions shown on an immersive virtual-reality display as approaching in the sagittal plane along parabolic trajectories compatible with Earth gravity effects. In different trials, the ball shifted along the parabolas with one of three different laws of motion: constant...
Article
Full-text available
Humans expect downwards moving objects to accelerate and upwards moving objects to decelerate. These results have been interpreted as humans maintaining an internal model of gravity. We have previously suggested an interpretation of these results within a Bayesian framework of perception: earth gravity could be represented as a Strong Prior that ov...
Preprint
Full-text available
Every time we use our smartphone, tablet, or other electronic devices we are exposed to temporal delays between our actions and the sensory feedback. We can compensate for such delays by adjusting our motor commands and doing so likely requires establishing new temporal mappings between motor areas and sensory predictions. However, little is known...
Article
Full-text available
People usually follow a moving object with their gaze if they intend to interact with it. What would happen if they did not? We recorded eye and finger movements while participants moved a cursor toward a moving target. An unpredictable delay in updating the position of the cursor on the basis of that of the invisible finger made it essential to us...
Preprint
Humans expect downwards moving objects to accelerate and upwards moving objects to decelerate. These results have been interpreted as humans maintaining an internal model of gravity. We have previously suggested an interpretation of these results within a Bayesian framework of perception: earth gravity could be represented as a Strong Prior that ov...
Article
Full-text available
In order to intercept moving objects, we need to predict the spatiotemporal features of the motion of both the object and our hand. Our errors can result in updates of these predictions to benefit interceptions in the future (adaptation). Recent studies claim that task-relevant variability in baseline performance can help adapt to perturbations, be...
Article
Full-text available
Many daily life situations (e.g. dodging an approaching object or hitting a moving target) require people to correct planning of future movements based on previous temporal errors. However, the actual temporal error can be difficult to perceive: imagine a baseball batter that swings and misses a fastball. Here we show that in such situations people...
Article
Full-text available
There is evidence that humans rely on an earth gravity (9.81 m/s²) prior for a series of tasks involving perception and action, the reason being that gravity helps predict future positions of moving objects. Eye-movements in turn are partially guided by predictions about observed motion. Thus, the question arises whether knowledge about gravity is...
Article
Full-text available
The contribution of sensory and decisional processes to perceptual decision making is still unclear, even in simple perceptual tasks. When decision makers need to select an action from a set of balanced alternatives, any tendency to choose one alternative more often—choice bias—is consistent with a bias in the sensory evidence, but also with a pref...
Preprint
Full-text available
The contribution of sensory and decisional processes to perceptual decision making is still unclear, even in simple perceptual tasks. When decision makers need to select an action from a set of balanced alternatives, any tendency to choose one alternative more often— choice bias—is consistent with a bias in the sensory evidence, but also with a pre...
Preprint
Full-text available
There is evidence that humans rely on an earth gravity (9.81 m/s2) prior for a series of tasks involving perception and action, the reason being that gravity helps predict future positions of moving objects. Eye-movements in turn are partially guided by predictions about observed motion. Thus, the question arises whether knowledge about gravity is...
Article
Full-text available
In daily life, we often need to make accurate and precise movements. However, our movements do not always end up as intended. When we are consistently too late to catch a ball for example, we need to update the predictions of the temporal consequences of our motor commands. These predictions can be improved when the brain evaluates sensory error si...
Preprint
Full-text available
Correction on the basis of previous errors is paramount to sensorimotor learning. While corrections of spatial errors have been studied extensively, little is known about corrections of previous temporal errors. We tackled this problem in different conditions involving arm movements (AM), saccadic eye movements (SM) or button presses (BP). The task...
Article
Full-text available
The increased reliance on electronic devices such as smartphones in our everyday life exposes us to various delays between our actions and their consequences. Whereas it is known that people can adapt to such delays, the mechanisms underlying such adaptation remain unclear. To better understand these mechanisms, the current study explored the role...
Article
Evidence suggests that humans rely on an earth gravity prior for sensory-motor tasks like catching or reaching. Even under earth-discrepant conditions, this prior biases perception and action towards assuming a gravitational downwards acceleration of 9.81 m/s2. This can be particularly detrimental in interactions with virtual environments employing...
Preprint
Full-text available
Evidence suggests that humans rely on an earth gravity prior for sensory-motor tasks like catching or reaching. Even under earth-discrepant conditions, this prior biases perception and action towards assuming a gravitational downwards acceleration of 9.81 m/s ² . This can be particularly detrimental in interactions with virtual environments employi...
Article
Full-text available
In the future, humans are likely to be exposed to environments with altered gravity conditions, be it only visually (Virtual and Augmented Reality), or visually and bodily (space travel). As visually and bodily perceived gravity as well as an interiorized representation of earth gravity are involved in a series of tasks, such as catching, grasping,...
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Full-text available
Experimental work on body ownership illusions showed how simple multisensory manipulation can generate the illusory experience of an artificial limb as being part of the own-body. This work highlighted how own-body perception relies on a plastic brain representation emerging from multisensory integration. The flexibility of this representation is r...
Article
In ball games, one cannot direct ones gaze at the ball all the time because one must also judge other aspects of the game, such as other players' positions. We wanted to know whether there are times at which obtaining information about the ball is particularly beneficial for catching it. We recently found that people could catch successfully if the...
Article
Full-text available
quickpsy is a package to parametrically fit psychometric functions. In comparison with previous R packages, quickpsy was built to easily fit and plot data for multiple groups. Here, we describe the standard parametric model used to fit psychometric functions and the standard estimation of its parameters using maximum likelihood. We also provide exa...
Article
Full-text available
We easily adapt to changes in the environment that involve cross-sensory discrepancies (e.g., between vision and proprioception). Adaptation can lead to changes in motor commands so that the experienced sensory consequences are appropriate for the new environment (e.g., we program a movement differently while wearing prisms that shift our visual sp...
Article
Full-text available
Recent studies have proposed that some cross-modal illusions might be expressed in what were previously thought of as sensory-specific brain areas. Therefore, one interesting question is whether auditory-driven visual illusory percepts respond to manipulations of low-level visual attributes (such as luminance or chromatic contrast) in the same way...
Article
A basic function of the visual system is to estimate the location of objects. Among other sensory inputs, the coding of an object's position involves the integration of visual motion, such as that produced by other moving patterns in the scene. Psychophysical evidence has shown that motion signals can shift, in the direction of motion, both the per...
Article
Full-text available
Previous studies have shown that asynchrony in perceived changes in the visual attributes of an object is attenuated when the object is the target of a manual reaching action (e.g. Corveleyn et al. in J Vis, 2012. doi: 10.1167/12.11.20 ). In the present study, we examined the temporal and spatial constraints associated with the effect of action on...
Article
Humans time their interceptive actions with remarkable precision. This daily-life performance is far too good to be explained by reported experimental perceptual estimates of when an object will arrive at the interception location. One option is that people use general principles to reduce variability such as integrating early estimates from predic...
Article
Full-text available
Hitting a moving target requires that we do not miss the target when it is around the aimed position. The time available for us not to miss the target when it is at the position of interest is usually called the time window and depends on target's speed and size. These variables, among others, have been manipulated in previous studies but kept cons...
Article
Full-text available
When vision of the hand is unavailable, movements drift systematically away from their targets. It is unclear, however, why this drift occurs. We investigated whether drift is an active process, where people deliberately modify their movements based on biased position estimates, causing the real hand to move away from the real target location, or a...
Article
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The mechanisms responsible for the integration of sensory information from different modalities have become a topic of intense interest in psychophysics and neuroscience. Many authors now claim that early, sensory-based cross-modal convergence improves performance in detection tasks. An important strand of supporting evidence for this claim is base...
Article
Full-text available
Previous studies have shown that performing a motor action toward a target decreases the perceptual asynchrony observed in a temporal order judgment (TOJ) of a change in the target's visual attributes. We examined the temporal limit of this effect and whether this temporal limit can be extended through sensorimotor adaptation. Participants performe...
Article
It is known that people can learn to deal with delays between their actions and the consequences of such actions. We wondered whether they do so by adjusting their anticipations about the sensory consequences of their actions or whether they simply learn to move in certain ways when performing specific tasks. To find out, we examined details of how...
Article
Two main components are considered in reaching movements towards a target: the reaction time (RT, the time between target onset and movement initiation) and the movement time (MT, from movement onset to movement offset). RT is often used as a signature of action planning. We are interested in how both components are coupled and whether they can be...
Article
Numeric value seems to be analogically represented in a mental number line, with value increasing from left to right. In traditional number line tasks, participants estimate the position a number would have on a line representing a numerical range. While some views claim a logarithmic or a linear representation, the fact that part/whole decisions a...
Article
In ball games one cannot direct ones gaze at the ball all the time, because one must also judge other aspects of the game, such as other players positions. We wanted to know whether there are times at which obtaining information about the ball is particularly beneficial. We recently occluded vision at random times and found that people could catch...
Article
The integration of vision and proprioception for estimating the hand's starting location prior to a reach has been shown to depend on the modality of the target towards which the reach is planned. Here we investigated whether the processing of online feedback is also influenced by target modality. Participants made reaching movements to a target th...
Article
Full-text available
Many actions involve limb movements toward a target. Visual and proprioceptive estimates are available online, and by optimally combining (Ernst and Banks, 2002) both modalities during the movement, the system can increase the precision of the hand estimate. The notion that both sensory modalities are integrated is also motivated by the intuition t...
Article
The different sources of information that can be used to estimate time-to-contact may have different degrees of reliability across time. For example, after a given presentation or display time, an absolute change of angular size can be more reliable than the corresponding estimation of the rate of angular expansion (e.g. motion information). One co...
Article
People readily intercept moving targets with a delayed visual representation of their hand. Seeing the representation pass the target is enough to perform better on subsequent trials, so they are not just speeding up in response to the visual representation being less far than they expected. Here we examine the specificity of such sensory-motor ada...
Article
Estimating whether an object is reachable is important if one intends to interact with the object. If an object is moving, it will be reachable only within a certain time-window. In such situations, motion of the object relative to the body has to be taken into account to judge the moment at which the target becomes reachable. We know that judgment...
Article
Full-text available
Interception requires precise estimation of time-to-contact (TTC) information. A long-standing view posits that all relevant information for extracting TTC is available in the angular variables, which result from the projection of distal objects onto the retina. The different timing models rooted in this tradition have consequently relied on combin...
Article
Full-text available
Cross-modal enhancement can be mediated both by higher-order effects due to attention and decision making, as well as by detection level stimulus-driven interactions. However, the contribution of each of these sources to behavioural improvements has not been conclusively determined and quantified separately. Here, we apply psychophysical analysis b...
Article
Full-text available
Perceiving a visual object requires binding sensory estimates of its various physical attributes. This process can be facilitated if changes of different attributes are perceived with little asynchronies when they are physically aligned, which is not always the case as revealed by temporal order judgment or perceptual synchronization tasks of visua...
Article
In backward masking, a target stimulus is rendered invisible by the presentation of a second stimulus, the mask. When the mask is effective, neural responses to the target are suppressed. Nevertheless, weak target responses sometimes may produce a behavioural response. It remains unclear whether the reduced target response is a purely feedforward r...
Article
Being able to see the object that you are aiming for is evidently useful for guiding the hand to a moving object. We examined to what extent seeing the moving hand also influences performance. Subjects tried to intercept moving targets while either instantaneous or delayed feedback about the moving hand was provided at certain times. After each att...
Data
Nonlinearity of the m-Tau function. Text S2 is dedicated to the nonlinear character of and how it could be successfully hidden behind noise. The section presents additional figures with random trials (analogous to Figure 3b), and corresponding scatter plots with goodness-of-fit measures as a function of . (PDF)
Data
Full-text available
Fitting m-Tau and -function to neuronal recordings. Text S4 juxtaposes the individual fitting results of and to a variety of previously published neural recording data, which served to compile Figure 2. Further summary results are presented along with fitting results of individual recording traces. (PDF)
Data
Full-text available
Finding parameter values for corrected m-Tau. Text S5 describes the optimization procedure for the corrected m-Tau -model “”, with which we obtained the parameter values for the simulation of our psychophysical experiment (e.g. Figure 8). The -parameters were optimized in three different ways: For achieving a good prediction performance of the psyc...
Data
Full-text available
Properties and extension of modified Tau. Text S1 presents additional mathematical details of the -function. Specifically, it is shown how the -function could be extended to a model which predicts the so-called “linear approach” data. Corresponding simulation results from this model are also shown. (PDF)
Data
Full-text available
Predictions of corrected m-Tau for the psychophysical experiment. Text S7 shows the full set of figures with simulation results of our psychophysical experiment. Whereas Figure 8 shows -predictions that were obtained with the parameter set optimized for the “combined” object diameter according to -score, Text S7 shows analogous figures for the rema...
Data
Full-text available
First order temporal low-pass filter (Equation 4). Text S8 gives a short introduction to the temporal low-pass filter that forms a part of the -model (equation 4), and is also used for the extension of the -model described in Text S1). (PDF)
Data
Full-text available
Noise suppression. Text S3 considers the numerical robustness of , , and , by adding correlated and uncorrelated noise to the angular variables. Similar to Figure 6, it is shown how noise affects these functions (e.g. bigger object diameters are associated with correspondingly less fluctuations), and thus the results presented in this section help...
Data
Full-text available
Time to contact approximation of “Tau” and . Text S6 presents a comprehensive analysis of two alternative functions which have a maximum before ttc, namely “inverse ” () and “angular acceleration” (). The two functions were also fitted to the neuronal recording data (they turn out to be inadequate), and compared to the maximum of the -function. Thi...
Article
Several previous studies in motor control have looked at spatial and temporal precision of arm movements under different conditions. However, none of them have focused on the benefits of giving more time to plan the movement in terms of spatial and temporal precision. With this aim we designed a task in which participants had to point towards stati...