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1.
Nat Commun ; 12(1): 1149, 2021 02 19.
Artigo em Inglês | MEDLINE | ID: mdl-33608533

RESUMO

An outstanding challenge for consciousness research is to characterize the neural signature of conscious access independently of any decisional processes. Here we present a model-based approach that uses inter-trial variability to identify the brain dynamics associated with stimulus processing. We demonstrate that, even in the absence of any task or behavior, the electroencephalographic response to auditory stimuli shows bifurcation dynamics around 250-300 milliseconds post-stimulus. Namely, the same stimulus gives rise to late sustained activity on some trials, and not on others. This late neural activity is predictive of task-related reports, and also of reports of conscious contents that are randomly sampled during task-free listening. Source localization further suggests that task-free conscious access recruits the same neural networks as those associated with explicit report, except for frontal executive components. Studying brain dynamics through variability could thus play a key role for identifying the core signatures of conscious access, independent of report.


Assuntos
Encéfalo/fisiologia , Estado de Consciência/fisiologia , Estimulação Acústica , Adolescente , Adulto , Percepção Auditiva/fisiologia , Comportamento , Neurociência Cognitiva , Eletroencefalografia , Feminino , Humanos , Masculino , Percepção Visual/fisiologia , Adulto Jovem
2.
Artigo em Inglês | MEDLINE | ID: mdl-33211531

RESUMO

Eye blinks strongly attenuate visual input, yet we perceive the world as continuous. How this visual continuity is achieved remains a fundamental and unsolved problem. A decrease in luminance sensitivity has been proposed as a mechanism but is insufficient to mask the even larger decrease in luminance because of blinks. Here we put forward a different hypothesis: visual continuity can be achieved through shortening of perceived durations of the sensory consequences of blinks. Here we probed the perceived durations of the blackouts caused by blinks and visual stimuli interrupted by blinks. We found that the perceived durations of blackouts because of blinks are about half as long as artificial blackouts immediately preceding or following the blink. Stimuli interrupted by blinks were perceived as briefer than uninterrupted stimuli, by about the same duration as the interruption-but so were stimuli interrupted by optically simulated blinks. There was a difference between real and simulated blinks, however: The decrease in perceived duration depended on the duration of the interruption for simulated, but not for real, blinks. These profound modifications in time perception during blinks show a way in which temporal processing contributes to the solution of an essential perceptual problem. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

4.
Sci Rep ; 8(1): 13550, 2018 09 10.
Artigo em Inglês | MEDLINE | ID: mdl-30202116

RESUMO

The shape of objects is typically identified through active touch. The accrual of spatial information by the hand over time requires the continuous integration of tactile and movement information. Sensory inputs arising from one single sensory source gives rise to an infinite number of possible touched locations in space. This observation raises the question of the determination of a common reference frame that might be employed by humans to resolve spatial ambiguity. Here, we employ a paradigm where observers reconstruct the spatial attributes of a triangle from tactile inputs applied to a stationary hand correlated with the voluntary movements of the other hand. We varied the orientation of the hands with respect to one another and to the trunk, and tested three distinct hypotheses regarding a reference frame used for integration: a hand-centred, a trunk-centred or an allocentric reference frame. The results indicated strongly that the integration of movement information and tactile inputs was performed in a radial trunk-centred reference frame.

5.
J Vis ; 18(5): 7, 2018 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-29904782

RESUMO

When ambiguous visual stimuli are presented continuously, they often lead to oscillations between usually two perceptions. Because of these oscillations, it has been thought that the underlying neural dynamics also arises from a binary or two-state system. Contradicting the binary assumption, it has been shown recently that the perception of some ambiguous stimuli is governed by continuously varying internal states, measured as biases that differ considerably from one observer to the next and that can also evolve over time (Wexler, Duyck, & Mamassian, 2015). Here I study bias patterns in the motion quartet, an ambiguous apparent motion stimulus, as the quartet's orientation is varied. The bias patterns are robustly idiosyncratic, and are even more complex than those that have been described previously. There are two qualitatively different bias types: Some observers prefer a translation axis, while others show preference for a rotation direction. Each type also varies parametrically: the orientation of the preferred axis, and the direction of preferred rotation. There are also clear cases of combination of the two bias types. When measured repeatedly over 9 hr, the bias patterns usually remain stable, but also sometimes evolve both parametrically (e.g., change of preferred axis), as well as across bias type (change from axial to rotational bias). Control experiments revealed that the variety of bias patterns observed across subjects, and their changes over time, are not due to voluntary decisions. Overall, these results exhibit the multidimensional complexity of internal states underlying the perception of even simple stimuli.


Assuntos
Percepção de Movimento/fisiologia , Orientação , Rotação , Adolescente , Adulto , Idoso , Viés , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estimulação Luminosa , Adulto Jovem
6.
Iperception ; 9(3): 2041669518773111, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29780569

RESUMO

Saccades are crucial to visual information intake by re-orienting the fovea to regions of interest in the visual scene. However, they cause drastic disruptions of the retinal input by shifting the retinal image at very high speeds. The resulting motion and smear are barely noticed, a phenomenon known as saccadic omission. Here, we studied the perception of motion during simulated saccades while observers fixated, moving naturalistic visual scenes across the retina with saccadic speed profiles using a very high temporal frequency display. We found that the mere presence of static pre- and post-saccadic images significantly reduces the perceived amplitude of motion but does not eliminate it entirely. This masking of motion perception could make the intra-saccadic stimulus much less salient and thus easier to ignore.

7.
J Exp Psychol Hum Percept Perform ; 43(3): 581-595, 2017 03.
Artigo em Inglês | MEDLINE | ID: mdl-28080111

RESUMO

The extraction of spatial information by touch often involves exploratory movements, with tactile and kinesthetic signals combined to construct a spatial haptic percept. However, the body has many tactile sensory surfaces that can move independently, giving rise to the source binding problem: when there are multiple tactile signals originating from sensory surfaces with multiple movements, are the tactile and kinesthetic signals bound to one another? We studied haptic signal combination by applying the tactile signal to a stationary fingertip while another body part (the other hand or a foot) or a visual target moves, and using a task that can only be done if the tactile and kinesthetic signals are combined. We found that both direction and speed of movement transfer across limbs, but only direction transfers between visual target motion and the tactile signal. In control experiments, we excluded the role of explicit reasoning or knowledge of motion kinematics in this transfer. These results demonstrate the existence of 2 motion representations in the haptic system-one of direction and another of speed or amplitude-that are both source-free or unbound from their sensory surface of origin. These representations may well underlie our flexibility in haptic perception and sensorimotor control. (PsycINFO Database Record


Assuntos
Generalização Psicológica/fisiologia , Cinestesia/fisiologia , Percepção de Movimento/fisiologia , Percepção do Tato/fisiologia , Adulto , Feminino , Humanos , Masculino , Atividade Motora , Acompanhamento Ocular Uniforme/fisiologia , Adulto Jovem
8.
J Vis ; 16(10): 1, 2016 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-27479918

RESUMO

Static visual stimuli are smeared across the retina during saccades, but in normal conditions this smear is not perceived. Instead, we perceive the visual scene as static and sharp. However, retinal smear is perceived if stimuli are shown only intrasaccadically, but not if the stimulus is additionally shown before a saccade begins, or after the saccade ends (Campbell & Wurtz, 1978). This inhibition has been compared to forward and backward metacontrast masking, but with spatial relations between stimulus and mask that are different from ordinary metacontrast during fixation. Previous studies of smear masking have used subjective measures of smear perception. Here we develop a new, objective technique for measuring smear masking, based on the spatial localization of a gap in the smear created by very quickly blanking the stimulus at various points during the saccade. We apply this technique to show that smear masking survives dichoptic presentation (suggesting that it is therefore cortical in origin), as well as separations of as much as 6° between smear and mask.


Assuntos
Mascaramento Perceptivo/fisiologia , Retina/fisiologia , Movimentos Sacádicos/fisiologia , Percepção Visual/fisiologia , Humanos
9.
Proc Natl Acad Sci U S A ; 112(48): 14990-5, 2015 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-26627250

RESUMO

Studies of perception usually emphasize processes that are largely universal across observers and--except for short-term fluctuations--stationary over time. Here we test the universality and stationarity assumptions with two families of ambiguous visual stimuli. Each stimulus can be perceived in two different ways, parameterized by two opposite directions from a continuous circular variable. A large-sample study showed that almost all observers have preferred directions or biases, with directions lying within 90 degrees of the bias direction nearly always perceived and opposite directions almost never perceived. The biases differ dramatically from one observer to the next, and although nearly every bias direction occurs in the population, the population distributions of the biases are nonuniform, featuring asymmetric peaks in the cardinal directions. The biases for the two families of stimuli are independent and have distinct population distributions. Following external perturbations and spontaneous fluctuations, the biases decay over tens of seconds toward their initial values. Persistent changes in the biases are found on time scales of several minutes to 1 hour. On scales of days to months, the biases undergo a variety of dynamical processes such as drifts, jumps, and oscillations. The global statistics of a majority of these long-term time series are well modeled as random walk processes. The measurable fluctuations of these hitherto unknown degrees of freedom show that the assumptions of universality and stationarity in perception may be unwarranted and that models of perception must include both directly observable variables as well as covert, persistent states.


Assuntos
Modelos Neurológicos , Percepção Visual/fisiologia , Feminino , Humanos , Masculino
10.
Sci Rep ; 5: 14584, 2015 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-26412592

RESUMO

We continually move our body and our eyes when exploring the world, causing our sensory surfaces, the skin and the retina, to move relative to external objects. In order to estimate object motion consistently, an ideal observer would transform estimates of motion acquired from the sensory surface into fixed, world-centered estimates, by taking the motion of the sensor into account. This ability is referred to as spatial constancy. Human vision does not follow this rule strictly and is therefore subject to perceptual illusions during eye movements, where immobile objects can appear to move. Here, we investigated whether one of these, the Filehne illusion, had a counterpart in touch. To this end, observers estimated the movement of a surface from tactile slip, with a moving or with a stationary finger. We found the perceived movement of the surface to be biased if the surface was sensed while moving. This effect exemplifies a failure of spatial constancy that is similar to the Filehne illusion in vision. We quantified this illusion by using a Bayesian model with a prior for stationarity, applied previously in vision. The analogy between vision and touch points to a modality-independent solution to the spatial constancy problem.


Assuntos
Teorema de Bayes , Ilusões , Modelos Psicológicos , Percepção de Movimento , Percepção do Tato , Adulto , Algoritmos , Feminino , Humanos , Masculino , Psicometria , Adulto Jovem
11.
Proc Natl Acad Sci U S A ; 112(2): 619-24, 2015 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-25548179

RESUMO

Although motor actions can profoundly affect the perceptual interpretation of sensory inputs, it is not known whether the combination of sensory and movement signals occurs only for sensory surfaces undergoing movement or whether it is a more general phenomenon. In the haptic modality, the independent movement of multiple sensory surfaces poses a challenge to the nervous system when combining the tactile and kinesthetic signals into a coherent percept. When exploring a stationary object, the tactile and kinesthetic signals come from the same hand. Here we probe the internal structure of haptic combination by directing the two signal streams to separate hands: one hand moves but receives no tactile stimulation, while the other hand feels the consequences of the first hand's movement but remains still. We find that both discrete and continuous tactile and kinesthetic signals are combined as if they came from the same hand. This combination proceeds by direct coupling or transfer of the kinesthetic signal from the moving to the feeling hand, rather than assuming the displacement of a mediating object. The combination of signals is due to perception rather than inference, because a small temporal offset between the signals significantly degrades performance. These results suggest that the brain simplifies the complex coordinate transformation task of remapping sensory inputs to take into account the movements of multiple body parts in haptic perception, and they show that the effects of action are not limited to moving sensors.


Assuntos
Mãos/fisiologia , Cinestesia/fisiologia , Percepção do Tato/fisiologia , Feminino , Humanos , Masculino , Modelos Psicológicos , Percepção de Movimento/fisiologia , Movimento/fisiologia , Adulto Jovem
12.
J Vis ; 14(2)2014 02 17.
Artigo em Inglês | MEDLINE | ID: mdl-24534883

RESUMO

Although the retinal position of objects changes with each saccadic eye movement, we perceive the visual world to be stable. How this visual stability or constancy arises is debated. Cancellation accounts propose that the retinal consequences of eye movements are compensated for by an equal-but-opposite eye movement signal. Assumption accounts propose that saccade-induced retinal displacements are ignored because we have a prior belief in a stable world. Saccadic suppression of displacement-the fact that small displacements of the visual targets during saccades go unnoticed-argues in favor of assumption accounts. Extinguishing the target before the displacement unmasks it, arguing in favor of cancellation accounts. We show that an irrelevant displacement of the target orthogonal to saccade direction unmasks displacements parallel to saccade direction, and therefore relieves saccadic suppression of displacement. This result suggests that visual stability arises from the interplay between cancellation and assumption mechanisms: When the post-saccadic target position falls within an elliptic region roughly equivalent to habitual saccadic variability, displacements are not seen and stability is assumed. When the displacements fall outside this region, as with our orthogonal steps, displacements are seen and positions are remapped.


Assuntos
Retina/fisiologia , Movimentos Sacádicos/fisiologia , Percepção Visual/fisiologia , Humanos , Estimulação Luminosa/métodos
13.
Proc Natl Acad Sci U S A ; 110(17): 7080-5, 2013 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-23572578

RESUMO

When human observers are exposed to even slight motion signals followed by brief visual transients--stimuli containing no detectable coherent motion signals--they perceive large and salient illusory jumps. This visually striking effect, which we call "high phi," challenges well-entrenched assumptions about the perception of motion, namely the minimal-motion principle and the breakdown of coherent motion perception with steps above an upper limit called dmax. Our experiments with transients, such as texture randomization or contrast reversal, show that the magnitude of the jump depends on spatial frequency and transient duration--but not on the speed of the inducing motion signals--and the direction of the jump depends on the duration of the inducer. Jump magnitude is robust across jump directions and different types of transient. In addition, when a texture is actually displaced by a large step beyond the upper step size limit of dmax, a breakdown of coherent motion perception is expected; however, in the presence of an inducer, observers again perceive coherent displacements at or just above dmax. In summary, across a large variety of stimuli, we find that when incoherent motion noise is preceded by a small bias, instead of perceiving little or no motion--as suggested by the minimal-motion principle--observers perceive jumps whose amplitude closely follows their own dmax limits.


Assuntos
Percepção de Movimento/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Limiar Sensorial , Humanos , Estimulação Luminosa , Psicofísica , Fatores de Tempo
14.
J Vis ; 13(2): 15, 2013 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-23397040

RESUMO

Perceiving three-dimensional object motion while moving through the world is hard: not only must optic flow be segmented and parallax resolved into shape and motion, but also observer motion needs to be taken into account in order to perceive absolute, rather than observer-relative motion. In order to simplify the last step, it has recently been suggested that if the visual background is stationary, then foreground object motion, computed relative to the background, directly yields absolute motion. A series of studies with immobile observers and optic flow simulating observer movement have provided evidence that observers actually utilize this so-called "flow parsing" strategy (Rushton & Warren, 2005). We test this hypothesis by using mobile observers (as well as immobile ones) who judge the motion in depth of a foreground object in the presence of a stationary or moving background. We find that background movement does influence motion perception but not as much as predicted by the flow-parsing hypothesis. Thus, we find evidence that, in order to perceive absolute motion, observers partly use flow-parsing but also compensate egocentric motion by a global self-motion estimate.


Assuntos
Percepção de Movimento/fisiologia , Movimento (Física) , Movimento/fisiologia , Fluxo Óptico/fisiologia , Adulto , Feminino , Humanos , Masculino , Estimulação Luminosa/métodos
15.
J Vis ; 12(7)2012 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-22829658

RESUMO

Different attention and saccade control areas contribute to space constancy by remapping target activity onto their expected post-saccadic locations. To visualize this dynamic remapping, we used a technique developed by Honda (2006) where a probe moved vertically while participants made a saccade across the motion path. Observers do not report any large excursions of the trace at the time of the saccade that would correspond to the classical peri-saccadic mislocalization effect. Instead, they reported that the motion trace appeared to be broken into two separate segments with a shift of approximately one-fifth of the saccade amplitude representing an overcompensation of the expected retinal displacement caused by the saccade. To measure the timing of this break in the trace, we introduced a second, physical shift that was the same size but opposite in direction to the saccade-induced shift. The trace appeared continuous most frequently when the physical shift was introduced at the midpoint of the saccade, suggesting that the compensation is in place when the saccade lands. Moreover, this simple linear shift made the combined traces appear continuous and linear, with no curvature. In contrast, Honda (2006) had reported that the pre- and post-saccadic portion of the trace appeared aligned and that there was often a small, visible excursion of the trace at the time of the saccade. To compare our results more directly, we increased the contrast of our moving probe in a third experiment. Now some observers reported seeing a deviation in the motion path but the misalignment remained present. We conclude that the large deviations at the time of saccade are generally masked for a continuously moving target but that there is nevertheless a residual misalignment between pre- and post-saccadic coordinates of approximately 20% of the saccade amplitude that normally goes unnoticed.


Assuntos
Atenção/fisiologia , Percepção de Movimento/fisiologia , Movimentos Sacádicos/fisiologia , Percepção Espacial/fisiologia , Adulto , Feminino , Humanos , Masculino , Estimulação Luminosa/métodos , Psicometria , Tempo de Reação/fisiologia , Retina/fisiologia , Percepção do Tempo/fisiologia , Campos Visuais/fisiologia , Adulto Jovem
16.
Front Psychol ; 3: 136, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22582050

RESUMO

People often perform spontaneous body movements during spatial tasks such as giving complex directions or orienting themselves on maps. How are these spontaneous gestures related to spatial problem-solving? We measured spontaneous movements during a perspective-taking task inspired by map reading. Analyzing the motion data to isolate rotation and translation components of motion in specific geometric relation to the task, we found out that most participants executed spontaneous miniature rotations of the head that were significantly related to the main task parameter. These head rotations were as if participants were trying to align themselves with the orientation on the map either in the image plane or on the ground plane, but with tiny amplitudes, typically below 1% of the actual movements. Our results are consistent with a model of sensorimotor prediction driving spatial reasoning. The efference copy of planned movements triggers this prediction mechanism. The movements themselves may then be mostly inhibited; the small spontaneous gestures that we measure are the visible traces of these planned but inhibited actions.

17.
Psychol Sci ; 21(5): 667-75, 2010 May.
Artigo em Inglês | MEDLINE | ID: mdl-20483845

RESUMO

It is commonly assumed that size constancy-invariance of perceived size of objects as they change retinal size because of changes in distance-depends solely on retinal stimulation and vergence, but on no other action-related signals. Distance to an object can change through displacement of either the observer or the object. The common assumption predicts that the two types of displacement should lead to the same degree of size constancy. We measured size constancy while observers viewed stationary stimuli at different distances. Changes in distance between trials were either actively produced by the observer or generated by real or simulated object displacement, with retinal stimulation held constant across the movement conditions. Responses were always closer to perfect constancy for observer than for object movement. Thus, size constancy is enhanced by information from observer displacement, and, more generally, processes thought to be purely perceptual may have unexpected components related to action.


Assuntos
Percepção de Distância , Orientação , Percepção de Tamanho , Atenção , Percepção de Cores , Humanos , Julgamento , Ilusões Ópticas , Psicofísica
18.
J Vis ; 10(1): 8.1-13, 2010 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-20143901

RESUMO

Perceptual aftereffects provide a sensitive tool to investigate the influence of eye and head position on visual processing. There have been recent indications that the TAE is remapped around the time of a saccade to remain aligned to the adapting location in the world. Here, we investigate the spatial frame of reference of the TAE by independently manipulating retinal position, gaze orientation, and head orientation between adaptation and test. The results show that the critical factor in the TAE is the correspondence between the adaptation and test locations in a retinotopic frame of reference, whereas world- and head-centric frames of reference do not play a significant role. Our results confirm that adaptation to orientation takes place at retinotopic levels of visual processing. We suggest that the remapping process that plays a role in visual stability does not transfer feature gain information around the time of eye (or head) movements.


Assuntos
Pós-Efeito de Figura/fisiologia , Movimentos da Cabeça/fisiologia , Orientação/fisiologia , Movimentos Sacádicos/fisiologia , Percepção Visual/fisiologia , Adaptação Fisiológica/fisiologia , Adulto , Humanos , Estimulação Luminosa/métodos , Psicofísica , Adulto Jovem
19.
J Vis ; 9(7): 1, 2009 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-19761316

RESUMO

To perceive object motion when the eyes themselves undergo smooth movement, we can either perceive motion directly-by extracting motion relative to a background presumed to be fixed-or through compensation, by correcting retinal motion by information about eye movement. To isolate compensation, we created stimuli in which, while the eye undergoes smooth movement due to inertia, only one object is visible-and the motion of this stimulus is decoupled from that of the eye. Using a wide variety of stimulus speeds and directions, we rule out a linear model of compensation, in which stimulus velocity is estimated as a linear combination of retinal and eye velocities multiplied by a constant gain. In fact, we find that when the stimulus moves in the same direction as the eyes, there is little compensation, but when movement is in the opposite direction, compensation grows in a nonlinear way with speed. We conclude that eye movement is estimated from a combination of extraretinal and retinal signals, the latter based on an assumption of stimulus stationarity. Two simple models, in which the direction of eye movement is computed from the extraretinal signal and the speed from the retinal signal, account well for our results.


Assuntos
Movimentos Oculares/fisiologia , Percepção de Movimento/fisiologia , Dinâmica não Linear , Adaptação Fisiológica , Adulto , Feminino , Humanos , Masculino , Modelos Biológicos , Estimulação Luminosa/métodos , Acompanhamento Ocular Uniforme/fisiologia , Retina/fisiologia
20.
Curr Biol ; 18(23): 1872-6, 2008 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-19062283

RESUMO

Understanding how we spontaneously scan the visual world through eye movements is crucial for characterizing both the strategies and inputs of vision. Despite the importance of the third or depth dimension for perception and action, little is known about how the specifically three-dimensional aspects of scenes affect looking behavior. Here we show that three-dimensional surface orientation has a surprisingly large effect on spontaneous exploration, and we demonstrate that a simple rule predicts eye movements given surface orientation in three dimensions: saccades tend to follow surface depth gradients. The rule proves to be quite robust: it generalizes across depth cues, holds in the presence or absence of a task, and applies to more complex three-dimensional objects. These results not only lead to a more accurate understanding of visuo-motor strategies, but also suggest a possible new oculomotor technique for studying three-dimensional vision from a variety of depth cues in subjects--such as animals or human infants--that cannot explicitly report their perceptions.


Assuntos
Percepção de Profundidade , Movimentos Oculares/fisiologia , Visão Ocular/fisiologia , Humanos , Movimentos Sacádicos , Visão Binocular/fisiologia , Visão Monocular/fisiologia
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