-
[show abstract]
[hide abstract]
ABSTRACT: Efficient cognitive decisions should be adjustable to incoming novel information. However, most current models of decision making have so far neglected any potential interaction between intentional and stimulus-driven decisions. We report here behavioral results and a new model on the interaction between a perceptual decision and non-predictable novel information. We asked participants to anticipate their response to an external stimulus and presented this stimulus with variable delay. Participants were clearly able to adjust their initial decision to the new stimulus if this latter appeared sufficiently early. To account for these results, we present a two-stage model in which two systems, an intentional and a stimulus-driven, interact only in the second stage. In the first stage of the model, the intentional and stimulus-driven processes race independently to reach a transition threshold between the two stages. The model can also account for results of a second experiment where a response bias is introduced. Our model is consistent with some physiological results that indicate that both parallel and interactive processing take place between intentional and stimulus-driven information. It emphasizes that in natural conditions, both types of processing are important and it helps pinpoint the transition between parallel and interactive processing.
PLoS Computational Biology 04/2013; 9(4):e1003013. · 5.22 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Recent work has shown that humans can learn or detect complex dependencies among variables. Even learning a simple dependency involves the identification of an underlying model and the learning of its parameters. This process represents learning a structured problem. We are interested in an empirical assessment of some of the factors that enable humans to learn such a dependency over time. More specifically, we look at how the statistics of the presentation of samples from a given structure influence learning. Participants engage in an experimental task where they are required to predict the timing of a target. At the outset, they are oblivious to the existence of a relationship between the position of a stimulus and the required temporal response to intercept it. Different groups of participants are either presented with a Random Walk where consecutive stimuli were correlated or with stimuli that were uncorrelated over time. We find that the structural relationship implicit in the task is only learned in the conditions where the stimuli are independently drawn. This leads us to believe that humans require rich and independent sampling to learn hidden structures among variables.
PLoS ONE 01/2013; 8(4):e62276. · 4.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Binocular rivalry is an intriguing phenomenon: when different images are displayed to the two eyes, perception alternates between these two images. What determines whether two monocular images engage in fusion or in rivalry: the physical difference between these images or the difference between the percepts resulting from the images? We investigated that question by measuring the interocular difference of grid orientation needed to produce a transition from fusion to rivalry and by changing those transitions by means of a superimposed tilt illusion. Fusion was attested by a correct stereoscopic slant perception of the grid. The superimposed tilt illusion was achieved in displaying small segments on the grids. We found that the illusion can change the fusion-rivalry transitions indicating that rivalry and fusion are based on the perceived orientations rather than the displayed ones. In a second experiment, we confirmed that the absence of binocular rivalry resulted in fusion and stereoscopic slant perception. We conclude that the superimposed tilt illusion arises at a level of visual processing prior to those stages mediating binocular rivalry and stereoscopic depth extraction.
Vision research 05/2012; 63:63-8. · 2.29 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In natural audio-visual environments, a change in depth is usually correlated with a change in loudness. In the present study, we investigated whether correlating changes in disparity and loudness would provide a functional advantage in binding disparity and sound amplitude in a visual search paradigm. To test this hypothesis, we used a method similar to that used by van der Burg et al. to show that non-spatial transient (square-wave) modulations of loudness can drastically improve spatial visual search for a correlated luminance modulation. We used dynamic random-dot stereogram displays to produce pure disparity modulations. Target and distractors were small disparity-defined squares (either 6 or 10 in total). Each square moved back and forth in depth in front of the background plane at different phases. The target’s depth modulation was synchronized with an amplitude-modulated auditory tone. Visual and auditory modulations were always congruent (both sine-wave or square-wave). In a speeded search task, five observers were asked to identify the target as quickly as possible. Results show a significant improvement in visual search times in the square-wave condition compared to the sine condition, suggesting that transient auditory information can efficiently drive visual search in the disparity domain. In a second experiment, participants performed the same task in the absence of sound and showed a clear set-size effect in both modulation conditions. In a third experiment, we correlated the sound with a distractor instead of the target. This produced longer search times, indicating that the correlation is not easily ignored.
PLoS ONE 05/2012; 7(5-7):e37190. · 4.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Decision makers typically overweight small probabilities and underweight large probabilities. However, there are recent reports that when probability is presented in the form of relative frequencies, this typical pattern reverses. We tested this hypothesis by comparing decision making in two tasks: In one task, probability was stated numerically, and in the other task, it was conveyed through a visual representation. In the visual task, participants chose whether a "stochastic bullet" should be fired at either a large target for a small reward or a small target for a large reward. Participants' knowledge of probability in the visual task was the result of extensive practice firing bullets at targets. In the classical numerical task, participants chose between pairs of lotteries with probabilities and rewards matched to the probabilities and rewards in the visual task. We found that participants' probability-weighting functions were significantly different in the two tasks, but the pattern for the visual task was the typical, not the reversed, pattern.
Psychological Science 03/2012; 23(4):419-26. · 4.43 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: What humans perceive depends in part on what they have previously experienced. After repeated exposure to one stimulus, adaptation takes place in the form of a negative correlation between the current percept and the last displayed stimuli. Previous work has shown that this negative dependence can extend to a few minutes in the past, but the precise extent and nature of the dependence in vision is still unknown. In two experiments based on orientation judgments, we reveal a positive dependence of a visual percept with stimuli presented remotely in the past, unexpectedly and in contrast to what is known for the recent past. Previous theories of adaptation have postulated that the visual system attempts to calibrate itself relative to an ideal norm or to the recent past. We propose instead that the remote past is used to estimate the world's statistics and that this estimate becomes the reference. According to this new framework, adaptation is predictive: the most likely forthcoming percept is the one that helps the statistics of the most recent percepts match that of the remote past.
Current biology: CB 02/2012; 22(7):622-6. · 10.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A study was conducted to examine the time required to process lateral motion and motion-in-depth for luminance- and disparity-defined stimuli. In a 2 × 2 design, visual stimuli oscillated sinusoidally in either 2D (moving left to right at a constant disparity of 9 arcmin) or 3D (looming and receding in depth between 6 and 12 arcmin) and were defined either purely by disparity (change of disparity over time [CDOT]) or by a combination of disparity and luminance (providing CDOT and interocular velocity differences [IOVD]). Visual stimuli were accompanied by an amplitude-modulated auditory tone that oscillated at the same rate and whose phase was varied to find the latency producing synchronous perception of the auditory and visual oscillations. In separate sessions, oscillations of 0.7 and 1.4 Hz were compared. For the combined CDOT + IOVD stimuli (disparity and luminance [DL] conditions), audiovisual synchrony required a 50 ms auditory lag, regardless of whether the motion was 2D or 3D. For the CDOT-only stimuli (disparity-only [DO] conditions), we found that a similar lag (∼60 ms) was needed to produce synchrony for the 3D motion condition. However, when the CDOT-only stimuli oscillated along a 2D path, the auditory lags required for audiovisual synchrony were much longer: 170 ms for the 0.7 Hz condition, and 90 ms for the 1.4 Hz condition. These results suggest that stereomotion detectors based on CDOT are well suited to tracking 3D motion, but are poorly suited to tracking 2D motion.
Journal of Vision 01/2012; 12(11). · 3.38 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The majority of natural scenes contains zones that are visible to one eye only. Past studies have shown that these monocular regions can be seen at a precise depth even though there are no binocular disparities that uniquely constrain their locations in depth. In the so-called da Vinci stereopsis configuration, the monocular region is a vertical line placed next to a binocular rectangular occluder. The opacity of the occluder has been mentioned to be a necessary condition to obtain da Vinci stereopsis. However, this opacity constraint has never been empirically tested. In the present study, we tested whether da Vinci stereopsis and perceptual transparency can interact using a classical da Vinci configuration in which the opacity of the occluder varied. We used two different monocular objects: a line and a disk. We found no effect of the opacity of the occluder on the perceived depth of the monocular object. A careful analysis of the distribution of perceived depth revealed that the monocular object was perceived at a depth that increased with the distance between the object and the occluder. The analysis of the skewness of the distributions was not consistent with a double fusion explanation, favoring an implication of occlusion geometry in da Vinci stereopsis. A simple model that includes the geometry of the scene could account for the results. In summary, the mechanism responsible to locate monocular regions in depth is not sensitive to the material properties of objects, suggesting that da Vinci stereopsis is solved at relatively early stages of disparity processing.
Vision research 08/2011; 51(20):2186-97. · 2.29 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Two sets of dots moving in opposite directions are usually seen as two transparent surfaces. Deciding which surface is in front of the other is bistable and observers exhibit strong biases to see one particular motion direction in front. Surprisingly, biases are dependent on stimulus orientation in a persistent, idiosyncratic, and irrelevant manner. We investigated here whether this preferred direction is arbitrarily fixed or can instead be updated from the context. Observers performed two tasks alternately. One task was to report the surface seen in front in a transparent motion stimulus. The other task was a visual search for a slow dot. Unknown to the observers, we systematically paired the target dot with one surface direction in an attempt to make that surface appear preferentially in front. This manipulation was sufficient to change the observer's preferred direction for the surface seen in front. Attentional explanations did not account for the results. Observers modified their idiosyncratic preference in motion transparency depth rivalry only because it was useful to perform well in an auxiliary task.
Journal of Vision 01/2011; 11(7):18. · 3.38 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In bistable perception, several interpretations of the same physical stimulus are perceived in alternation. If one interpretation appears to help the observer to be successful in an auxiliary task, will that interpretation be seen more often than the other? We addressed this question using rivalrous stimuli. One of the elicited percepts presented an advantage for a separate visual search task that was run in close temporal proximity to the rivalry task. We found that the percept that was useful for the search task became dominant over the alternate percept. Observers were not aware of the manipulation that made one percept more useful, which suggests that usefulness was learned implicitly. The learning influenced only the first percept of each rivalrous presentation, but the bias persisted even when the useful percept was no longer useful. The long-lasting aspect of the effect distinguishes it from other documented attentional effects on bistable perception. Therefore, using implicit learning, we demonstrated that task usefulness can durably change the appearance of a stimulus.
Psychological Science 12/2010; 21(12):1886-93. · 4.43 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The systematic association of an action that a person performs with its sensory effects is thought to attenuate that person's perception of the effect of the action. However, whether learned sensorimotor contingencies truly affect perception, rather than just inducing a response bias, has yet to be determined. The experiment presented in this article comprised two parts: an action-effect association phase and a test phase, during which the actions' perceptual effects were tested. During the association phase, specific actions (left-key and right-key presses) were associated with specific visual effects (tilted Gabor patches). In the test phase, participants' left-key presses and right-key presses triggered the onset of a low-contrast tilted Gabor patch in 50% of trials (no stimulus was presented on the remaining 50% of trials). Participants were required to report the presence or absence of this tilted Gabor patch. Our results showed that participants' sensitivity (d') to the Gabor patches was reduced by 10% when the patches were triggered by the action they had previously been associated with. This finding indicates that a person's action does not induce a response bias (c), but changes the perception (d') of the learned action effect.
Psychological Science 12/2010; 21(12):1740-5. · 4.43 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Visual processing is fraught with uncertainty: The visual system must attempt to estimate physical properties despite missing information and noisy mechanisms. Sometimes high visual uncertainty translates into lack of confidence in our visual perception: We are aware of not seeing well. The mechanism by which we achieve this awareness--how we assess our own visual uncertainty--is unknown, but its investigation is critical to our understanding of visual decision mechanisms. The simplest possibility is that the visual system relies on cues to uncertainty, stimulus features usually associated with visual uncertainty, like blurriness. Probabilistic models of the brain suggest a more sophisticated mechanism, in which visual uncertainty is explicitly represented as probability distributions. In two separate experiments, observers performed a visual discrimination task in which confidence could be determined by the cues available (contrast and crowding or eccentricity and masking) or by their actual performance, the latter requiring a more sophisticated mechanism than cue monitoring. Results show that observers' confidence followed performance rather than cues, indicating that the mechanisms underlying the evaluation of visual confidence are relatively complex. This result supports probabilistic models, which imply the existence of sophisticated mechanisms for evaluating uncertainty.
Proceedings of the National Academy of Sciences 11/2010; 107(48):20834-9. · 9.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In perceiving 3D shape from ambiguous shading patterns, humans use the prior knowledge that the light is located above their head and slightly to the left. Although this observation has fascinated scientists and artists for a long time, the neural basis of this "light from above left" preference for the interpretation of 3D shape remains largely unexplored. Combining behavioral and functional MRI measurements coupled with multivoxel pattern analysis, we show that activations in early visual areas predict best the light source direction irrespective of the perceived shape, but activations in higher occipitotemporal and parietal areas predict better the perceived 3D shape irrespective of the light direction. These findings demonstrate that illumination is processed earlier than the representation of 3D shape in the visual system. In contrast to previous suggestions, we propose that prior knowledge about illumination is processed in a bottom-up manner and influences the interpretation of 3D structure at higher stages of processing.
Proceedings of the National Academy of Sciences 09/2010; 107(37):16309-14. · 9.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: How do we estimate the duration of a temporal interval in a familiar context? A new study finds that it is appropriate, perhaps even advantageous, to tolerate a small bias in our estimate to reduce the overall temporal uncertainty.
Nature Neuroscience 08/2010; 13(8):914-6. · 15.53 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In spite of being one of the most elementary visual effects, the vertical-horizontal illusion is still poorly understood. We provide here a simple quantitative model to describe the overestimation of the vertical segment relative to the horizontal one. The model also includes a necessary factor related to the effect of bisecting a line on the under-estimation of its length. These two factors, orientation anisotropy and length bisection, provide a very good account of various configurations of the illusion when the stimulus looks like a 'T', an 'L', or a '+'-sign, and for different stimulus orientations. The orientation anisotropy bias is on average 6% while the length bisection bias amounts to about 16%. In addition, when uncertainty about line estimation is included, new predictions on the sensitivity of different configurations are obtained and confirmed. In particular, we find that the '+'-sign figure suffers from a loss of sensitivity in comparing their vertical and horizontal segments when compared to the 'L'-figure. This difference can only be accounted for by a late-noise model where uncertainty is at the decision stage rather than on the image measurements.
Vision research 03/2010; 50(10):956-62. · 2.29 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The metajudgment of motor responses refers to our ability to evaluate the accuracy of our own actions. Can humans metajudge the duration of their Reaction Times (RTs) to a light-flash and the accuracy of their reproduction of a reference time interval bounded by two light flashes (Anticipatory Response Time, ART)? A series of four distinct experiments shows that RT_Meta and ART_Metajudgments are possible but with accuracies about x2.4 and x3 poorer than the corresponding RT and ART ones. In order to reveal the origin of this drop in performance, we ask whether a visual feedback synchronous with subjects' key-presses could improve performance. We show that overall the presence of a visual feedback does not significantly improve metajudgment accuracy although such a trend is noticeable in ART_Meta. We then compare these performances with the passive perceptual estimation of the played back (Pb) RT and ART time intervals when bounded by two (RT_Pb) and three (ART_Pb) light flashes. We show that RT_Meta and RT_Pb accuracies are close to equal, but that ART_Meta is about x2 less accurate than ART_Pb which in turn is x1.5 less accurate than ART. The latter observation fails however to reach statistical significance hence not sustaining proposals that active time estimation is more reliable than passive one. The whole dataset is accounted for by a clock-type model where duration estimation performance is limited by four noise sources (visual, clock-count, motor and proprioceptive+efference copy) plus one proper to ART_Meta task. It is proposed that the latter reflects the impossibility for the time-counting system to use the same time origin more than once.
Acta psychologica 02/2010; 134(2):142-53. · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In motion transparency, one surface is very often seen on top of the other in spite of no proper depth cue in the display. We investigated the dynamics of depth assignment in motion transparency stimuli composed of random dots moving in opposite directions. Similarly to other bistable percepts, which surface is seen in front is arbitrary and changes over time. In addition, we found that helping the segregation of the two surfaces by giving the same color to all dots of one surface significantly slowed down the initial rate of depth reversals. We also measured preferences to see one particular motion direction in front. Unexpectedly, we found that all of our 34 observers had a strong bias to see a particular motion direction in front, and this preferred direction was usually either downward or rightward. In contrast, there was no consistency in seeing the fastest or slowest surface in front. Finally, the preferred motion direction seen in front for one observer was very stable across several days, suggesting that a trace of this arbitrary motion preference is kept in memory.
Journal of Vision 01/2010; 10(13):23. · 3.38 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The role of sensory systems is to provide an organism with information about its environment. Because sensory information is noisy and insufficient to uniquely determine the environment, natural perceptual systems have to cope with systematic uncertainty. The extent of that uncertainty is often crucial to the organism: for instance, in judging the potential threat in a stimulus. Inducing uncertainty by using visual noise, we had human observers perform a task where they could improve their performance by choosing the less uncertain among pairs of visual stimuli. Results show that observers had access to a reliable measure of visual uncertainty in their decision-making, showing that subjective uncertainty in this case is connected to objective uncertainty. Based on a Bayesian model of the task, we discuss plausible computational schemes for that ability.
PLoS Computational Biology 09/2009; 5(9):e1000504. · 5.22 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Bayesian decision theory (BDT) is a mathematical framework that allows the experimenter to model ideal performance in a wide variety of visuomotor tasks. The experimenter can use BDT to compute benchmarks for ideal performance in such tasks and compare human performance to ideal. Recently, researchers have asked whether BDT can also be treated as a process model of visuomotor processing. It is unclear what sorts of experiments are appropriate to testing such claims and whether such claims are even meaningful. Any such claim presupposes that observers' performance is close to ideal, and typical experimental tests involve comparison of human performance to ideal. We argue that this experimental criterion, while necessary, is weak. We illustrate how to achieve near-optimal performance in combining perceptual cues with a process model bearing little resemblance to BDT. We then propose experimental criteria termed transfer criteria that constitute more powerful tests of BDT as a model of perception and action. We describe how recent work in motor control can be viewed as tests of transfer properties of BDT. The transfer properties discussed here comprise the beginning of an operationalization (Bridgman, 1927) of what it means to claim that perception is or is not Bayesian inference (Knill & Richards, 1996). They are particularly relevant to research concerning natural scenes since they assess the ability of the organism to rapidly adapt to novel tasks in familiar environments or carry out familiar tasks in novel environments without learning.
Visual Neuroscience 02/2009; 26(1):147-55. · 2.23 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To compare the timing of perceptual and motor decisions, distinct tasks have been designed, all of which have yielded systematic differences between these two moments. These observations have been taken as evidence of a sensorimotor dissociation. Inasmuch as the distinction between perceptual and motor decision moments is conceptually warranted, this conclusion remains debatable, since the observed differences may reflect the dissimilarity between the stimulations/tasks used to assess them. Here, we minimize such dissimilarities by comparing response time (RT) and anticipatory RT (ART), an alternative technique with which to infer the relative perceptual decision moments. Observers pressed a key either in synchrony with the third of a sequence of three stimuli appearing at a constant pace (ART) or in response to the onset of this third stimulus presented at a random interval after the second (RT). Hence, the two stimulation sequences were virtually identical. Both the mean and the variance of RT were affected by stimulus intensity about 1.5 times more than were the mean and the variance of ART. Within the framework of two simple integration-to-bound models, these findings are compatible with the hypothesis that perceptual and motor decisions operate on the same internal signal but are based on distinct criteria, with the perceptual criterion lower than the motor one.
Attention Perception & Psychophysics 02/2009; 71(1):82-94. · 2.04 Impact Factor
