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1.
Am J Occup Ther ; 73(3): 7303345030p1-7303345030p8, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31120847

RESUMO

IMPORTANCE: Attention deficit hyperactivity disorder (ADHD) is associated with driving deficits. Visual standards for driving define minimum qualifications for safe driving, including acuity and field of vision, but they do not consider the ability to explore the environment efficiently by shifting the gaze, which is a critical element of safe driving. OBJECTIVE: To examine visual exploration during simulated driving in adolescents with and without ADHD. DESIGN: Adolescents with and without ADHD drove a driving simulator for approximately 10 min while their gaze was monitored. They then completed a battery of questionnaires. SETTING: University lab. PARTICIPANTS: Participants with (n = 16) and without (n = 15) ADHD were included. Participants had a history of neurological disorders other than ADHD and normal or corrected-to-normal vision. Control participants reported not having a diagnosis of ADHD. Participants with ADHD had been previously diagnosed by a qualified professional. OUTCOMES AND MEASURES: We compared the following measures between ADHD and non-ADHD groups: dashboard dwell times, fixation variance, entropy, and fixation duration. RESULTS: Findings showed that participants with ADHD were more restricted in their patterns of exploration than control group participants. They spent considerably more time gazing at the dashboard and had longer periods of fixation with lower variability and randomness. CONCLUSIONS AND RELEVANCE: The results support the hypothesis that adolescents with ADHD engage in less active exploration during simulated driving. WHAT THIS ARTICLE ADDS: This study raises concerns regarding the driving competence of people with ADHD and opens up new directions for potential training programs that focus on exploratory gaze control.


Assuntos
Transtorno do Deficit de Atenção com Hiperatividade/diagnóstico , Condução de Veículo , Fixação Ocular , Adolescente , Estudos de Casos e Controles , Humanos , Inquéritos e Questionários
2.
J Vis ; 19(1): 6, 2019 01 02.
Artigo em Inglês | MEDLINE | ID: mdl-30640374

RESUMO

Saccades shift the gaze rapidly every few hundred milliseconds from one fixated location to the next, producing a flow of visual input into the visual system even in the absence of changes in the environment. During fixation, small saccades called microsaccades are produced 1-3 times per second, generating a flow of visual input. The characteristics of this visual flow are determined by the timings of the saccades and by the characteristics of the visual stimuli on which they are performed. Previous models of microsaccade generation have accounted for the effects of external stimulation on the production of microsaccades, but they have not considered the effects of the prolonged background stimulus on which microsaccades are performed. The effects of this stimulus on the process of microsaccade generation could be sustained, following its prolonged presentation, or transient, through the visual transients produced by the microsaccades themselves. In four experiments, we varied the properties of the constant displays and examined the resulting modulation of microsaccade properties: their sizes, their timings, and the correlations between properties of consecutive microsaccades. Findings show that displays of higher spatial frequency and contrast produce smaller microsaccades and longer minimal intervals between consecutive microsaccades; and smaller microsaccades are followed by smaller and delayed microsaccades. We explain these findings in light of previous models and suggest a conceptual model by which both sustained and transient effects of the stimulus have central roles in determining the generation of microsaccades.


Assuntos
Fixação Ocular/fisiologia , Movimentos Sacádicos/fisiologia , Percepção Visual/fisiologia , Adulto , Análise de Variância , Feminino , Humanos , Masculino , Estimulação Luminosa/métodos , Adulto Jovem
3.
Neuroimage ; 184: 279-292, 2019 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-30223059

RESUMO

The accurate extraction of signals out of noisy environments is a major challenge of the perceptual system. Forming temporal expectations and continuously matching them with perceptual input can facilitate this process. In humans, temporal expectations are typically assessed using behavioral measures, which provide only retrospective but no real-time estimates during target anticipation, or by using electrophysiological measures, which require extensive preprocessing and are difficult to interpret. Here we show a new correlate of temporal expectations based on oculomotor behavior. Observers performed an orientation-discrimination task on a central grating target, while their gaze position and EEG were monitored. In each trial, a cue preceded the target by a varying interval ("foreperiod"). In separate blocks, the cue was either predictive or non-predictive regarding the timing of the target. Results showed that saccades and blinks were inhibited more prior to an anticipated regular target than a less-anticipated irregular one. This consistent oculomotor inhibition effect enabled a trial-by-trial classification according to interval-regularity. Additionally, in the regular condition the slope of saccade-rate and drift were shallower for longer than shorter foreperiods, indicating their adjustment according to temporal expectations. Comparing the sensitivity of this oculomotor marker with those of other common predictability markers (e.g. alpha-suppression) showed that it is a sensitive marker for cue-related anticipation. In contrast, temporal changes in conditional probabilities (hazard-rate) modulated alpha-suppression more than cue-related anticipation. We conclude that pre-target oculomotor inhibition is a correlate of temporal predictions induced by cue-target associations, whereas alpha-suppression is more sensitive to conditional probabilities across time.


Assuntos
Antecipação Psicológica/fisiologia , Mapeamento Encefálico/métodos , Medições dos Movimentos Oculares , Movimentos Oculares/fisiologia , Ritmo alfa/fisiologia , Sinais (Psicologia) , Eletroencefalografia , Feminino , Humanos , Masculino , Adulto Jovem
4.
J Neurosci ; 39(2): 353-363, 2019 01 09.
Artigo em Inglês | MEDLINE | ID: mdl-30459223

RESUMO

Our visual input is constantly changing, but not all moments are equally relevant. Visual temporal attention, the prioritization of visual information at specific points in time, increases perceptual sensitivity at behaviorally relevant times. The dynamic processes underlying this increase are unclear. During fixation, humans make small eye movements called microsaccades, and inhibiting microsaccades improves perception of brief stimuli. Here, we investigated whether temporal attention changes the pattern of microsaccades in anticipation of brief stimuli. Human observers (female and male) judged stimuli presented within a short sequence. Observers were given either an informative precue to attend to one of the stimuli, which was likely to be probed, or an uninformative (neutral) precue. We found strong microsaccadic inhibition before the stimulus sequence, likely due to its predictable onset. Critically, this anticipatory inhibition was stronger when the first target in the sequence (T1) was precued (task-relevant) than when the precue was uninformative. Moreover, the timing of the last microsaccade before T1 and the first microsaccade after T1 shifted such that both occurred earlier when T1 was precued than when the precue was uninformative. Finally, the timing of the nearest pre- and post-T1 microsaccades affected task performance. Directing voluntary temporal attention therefore affects microsaccades, helping to stabilize fixation at the most relevant moments over and above the effect of predictability. Just as saccading to a relevant stimulus can be an overt correlate of the allocation of spatial attention, precisely timed gaze stabilization can be an overt correlate of the allocation of temporal attention.SIGNIFICANCE STATEMENT We pay attention at moments in time when a relevant event is likely to occur. Such temporal attention improves our visual perception, but how it does so is not well understood. Here, we discovered a new behavioral correlate of voluntary, or goal-directed, temporal attention. We found that the pattern of small fixational eye movements called microsaccades changes around behaviorally relevant moments in a way that stabilizes the position of the eyes. Microsaccades during a brief visual stimulus can impair perception of that stimulus. Therefore, such fixation stabilization may contribute to the improvement of visual perception at attended times. This link suggests that, in addition to cortical areas, subcortical areas mediating eye movements may be recruited with temporal attention.


Assuntos
Atenção/fisiologia , Fixação Ocular/fisiologia , Antecipação Psicológica/fisiologia , Sinais (Psicologia) , Feminino , Humanos , Masculino , Desempenho Psicomotor/fisiologia , Movimentos Sacádicos/fisiologia , Percepção Espacial/fisiologia , Percepção Visual/fisiologia , Adulto Jovem
5.
Neuropsychologia ; 119: 330-339, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-30125589

RESUMO

Attention affects visual perception at target locations via the amplification of stimuli signal strength, perceptual performance and perceived contrast. Behavioral and neural correlates of attention can be observed when attention is both covertly and overtly oriented (with or without accompanying eye movements). Previous studies have demonstrated that at the grand-average level, lateralization of Event Related Potentials (ERP) is associated with attentional facilitation at cued, relative to un-cued locations. Yet, the correspondence between ERP lateralization and behavior has not been established at the single-subject level. Specifically, it is an open question whether inter-individual differences in the neural manifestation of attentional orienting can predict differences in perception. Here, we addressed this question by examining the correlation between ERP lateralization and visual sensitivity at attended locations. Participants were presented with a cue indicating where a low-contrast grating patch target will appear, following a delay of varying durations. During this delay, while participants were waiting for the target to appear, a task-irrelevant checkerboard probe was presented briefly and bilaterally. ERP was measured relative to the onset of this probe. In separate blocks, participants were requested to report detection of a low-contrast target either by making a fast eye-movement toward the target (overt orienting), or by pressing a button (covert orienting). Results show that in the covert orienting condition, ERP lateralization of individual participants was positively correlated with their mean visual sensitivity for the target. But, no such correlation was found in the overt orienting condition. We conclude that ERP lateralization of individual participants can predict their performance on a covert, but not an overt, target detection task.


Assuntos
Atenção/fisiologia , Encéfalo/fisiologia , Potenciais Evocados Visuais/fisiologia , Lateralidade Funcional , Percepção Visual/fisiologia , Eletroencefalografia , Feminino , Humanos , Masculino , Adulto Jovem
6.
Psychophysiology ; 55(11): e13215, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30094856

RESUMO

Saccades constitute a major source of artifacts and confounds in brain imaging studies. Whereas some artifacts can be removed by omitting segments of data, saccadic artifacts cannot be typically eliminated by this method because of their high occurrence rate even during fixation (1-3 per second). Some saccadic artifacts can be alleviated by offline-correction algorithms, but these methods leave nonnegligible residuals and cannot mitigate the saccade-related visual activity. Here, we propose a novel yet simple approach for diminishing saccadic artifacts and confounds through experimental design. We suggest that specific tasks can lead to substantially less saccade occurrences around the time of stimulus presentation, starting from slightly before its onset and lasting for a few hundred milliseconds. In three experiments, we compared the frequency and size of saccades in a variety of tasks. Results of Experiment 1 showed that a foveal change-detection task reduced the number and sizes of saccades, relative to a parafoveal orientation-discrimination task. Experiment 2 replicated this finding with a parafoveal object recognition task. Experiment 3 showed that both foveal and parafoveal continuous change detection tasks induced fewer and smaller saccades than a discrete orientation-discrimination task. We conclude that adding a foveal or a parafoveal continuous task reduces saccades' number and size. This would lead to better artifact correction and enable the omission of contaminated data segments. This study may be the first step toward developing saccade-free experimental designs.


Assuntos
Artefatos , Eletroencefalografia/normas , Medições dos Movimentos Oculares/normas , Fóvea Central/fisiologia , Neuroimagem/normas , Projetos de Pesquisa/normas , Movimentos Sacádicos/fisiologia , Percepção Visual/fisiologia , Adulto , Feminino , Humanos , Masculino , Adulto Jovem
7.
PLoS One ; 13(6): e0198242, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29933381

RESUMO

BACKGROUND: During visual exploration or free-view, gaze positioning is largely determined by the tendency to maximize visual saliency: more salient locations are more likely to be fixated. However, when visual input is completely irrelevant for performance, such as with non-visual tasks, this saliency maximization strategy may be less advantageous and potentially even disruptive for task-performance. Here, we examined whether visual saliency remains a strong driving force in determining gaze positions even in non-visual tasks. We tested three alternative hypotheses: a) That saliency is disadvantageous for non-visual tasks and therefore gaze would tend to shift away from it and towards non-salient locations; b) That saliency is irrelevant during non-visual tasks and therefore gaze would not be directed towards it but also not away-from it; c) That saliency maximization is a strong behavioral drive that would prevail even during non-visual tasks. METHODS: Gaze position was monitored as participants performed visual or non-visual tasks while they were presented with complex or simple images. The effect of attentional demands was examined by comparing an easy non-visual task with a more difficult one. RESULTS: Exploratory behavior was evident, regardless of task difficulty, even when the task was non-visual and the visual input was entirely irrelevant. The observed exploratory behaviors included a strong tendency to fixate salient locations, central fixation bias and a gradual reduction in saliency for later fixations. These exploratory behaviors were spatially similar to those of an explicit visual exploration task but they were, nevertheless, attenuated. Temporal differences were also found: in the non-visual task there were longer fixations and later first fixations than in the visual task, reflecting slower visual sampling in this task. CONCLUSION: We conclude that in the presence of a rich visual environment, visual exploration is evident even when there is no explicit instruction to explore. Compared to visually motivated tasks, exploration in non-visual tasks follows similar selection mechanisms, but occurs at a lower rate. This is consistent with the view that the non-visual task is the equivalent of a dual-task: it combines the instructed task with an uninstructed, perhaps even mandatory, exploratory behavior.


Assuntos
Comportamento Exploratório/fisiologia , Fixação Ocular/fisiologia , Adulto , Feminino , Humanos , Masculino
8.
Cortex ; 106: 104-119, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-29913382

RESUMO

As you read this text, your brain is busy integrating numerous different processes-perceptual, cognitive and motor. While you acquire the semantic and linguistic contents of this abstract, your eyes traverse its lines with speed and coordination. The oculomotor response to text is so rapid and precise that it is hypothesized it to be partially based on reflexive orienting mechanisms. In this study we examined the hypothesis that the presentation of written text triggers reflexive orienting toward the direction of reading, similarly to the effect of peripheral stimulation or that of symbolic directional cues (arrows or gazing eyes). In three experiments, participants (N = 120) were presented with task-irrelevant text, shortly followed by a left/right pro-saccade task. The first experiment confirmed the hypothesis by showing that saccades which are congruent with the direction of reading are faster than those which are incongruent. This was observed both in right-to-left (Hebrew) and in left-to-right (English) reading-systems and similarly in native-Hebrew and native-English readers. A second experiment showed that this directional bias is found not only for readable text but also for meaningless strings of letters. This confirmed that the bias is driven pre-reading non-lexical processes. The third experiment examined the time-course of this effect. We conclude that text-perception actives early reflexive eye-movements programs and suggest that this link is an essential building-block of fast and effortless reading.


Assuntos
Movimentos Oculares/fisiologia , Orientação Espacial/fisiologia , Orientação/fisiologia , Percepção Visual/fisiologia , Adolescente , Adulto , Atenção/fisiologia , Sinais (Psicologia) , Feminino , Humanos , Masculino , Tempo de Reação/fisiologia , Leitura , Movimentos Sacádicos , Adulto Jovem
9.
Cognition ; 168: 99-109, 2017 11.
Artigo em Inglês | MEDLINE | ID: mdl-28666215

RESUMO

During visual exploration of a scene, the eye-gaze tends to be directed toward more salient image-locations, containing more information. However, while performing non-visual tasks, such information-seeking behavior could be detrimental to performance, as the perception of irrelevant but salient visual input may unnecessarily increase the cognitive-load. It would be therefore beneficial if during non-visual tasks, eye-gaze would be governed by a drive to reduce saliency rather than maximize it. The current study examined the phenomenon of gaze-aversion during non-visual tasks, which is hypothesized to act as an active avoidance mechanism. In two experiments, gaze-position was monitored by an eye-tracker while participants performed an auditory mental arithmetic task, and in a third experiment they performed an undemanding naming task. Task-irrelevant simple motion stimuli (drifting grating and random dot kinematogram) were centrally presented, moving at varying speeds. Participants averted their gaze away from the moving stimuli more frequently and for longer proportions of the time when the motion was faster than when it was slower. Additionally, a positive correlation was found between the task's difficulty and this aversion behavior. When the task was highly undemanding, no gaze aversion behavior was observed. We conclude that gaze aversion is an active avoidance strategy, sensitive to both the physical features of the visual distractions and the cognitive load imposed by the non-visual task.


Assuntos
Atenção , Fixação Ocular , Adulto , Feminino , Humanos , Masculino , Resolução de Problemas , Adulto Jovem
10.
Psychol Sci ; 28(7): 835-850, 2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-28520552

RESUMO

Knowing when to expect important events to occur is critical for preparing context-appropriate behavior. However, anticipation is inherently complicated to assess because conventional measurements of behavior, such as accuracy and reaction time, are available only after the predicted event has occurred. Anticipatory processes, which occur prior to target onset, are typically measured only retrospectively by these methods. In this study, we utilized a novel approach for assessing temporal expectations through the dynamics of prestimulus saccades. Results showed that saccades of neurotypical participants were inhibited prior to the onset of stimuli that appeared at predictable compared with less predictable times. No such inhibition was found in most participants with attention-deficit/hyperactivity disorder (ADHD), and particularly not in those who experienced difficulties in sustaining attention over time. These findings suggest that individuals with ADHD, especially those with sustained-attention deficits, have diminished ability to benefit from temporal predictability, and this could account for some of their context-inappropriate behaviors.


Assuntos
Transtorno do Deficit de Atenção com Hiperatividade/fisiopatologia , Atenção/fisiologia , Percepção do Tempo/fisiologia , Adulto , Transtorno do Deficit de Atenção com Hiperatividade/diagnóstico , Movimentos Oculares/fisiologia , Feminino , Humanos , Masculino , Tempo de Reação/fisiologia , Movimentos Sacádicos/fisiologia , Adulto Jovem
11.
Sci Rep ; 7(1): 886, 2017 04 20.
Artigo em Inglês | MEDLINE | ID: mdl-28428540

RESUMO

Sensory organs are thought to sample the environment rhythmically thereby providing periodic perceptual input. Whisking and sniffing are governed by oscillators which impose rhythms on the motor-control of sensory acquisition and consequently on sensory input. Saccadic eye movements are the main visual sampling mechanism in primates, and were suggested to constitute part of such a rhythmic exploration system. In this study we characterized saccadic rhythmicity, and examined whether it is consistent with autonomous oscillatory generator or with self-paced generation. Eye movements were tracked while observers were either free-viewing a movie or fixating a static stimulus. We inspected the temporal dynamics of exploratory and fixational saccades and quantified their first-order and high-order dependencies. Data were analyzed using methods derived from spike-train analysis, and tested against mathematical models and simulations. The findings show that saccade timings are explained by first-order dependencies, specifically by their refractory period. Saccade-timings are inconsistent with an autonomous pace-maker but are consistent with a "self-paced" generator, where each saccade is a link in a chain of neural processes that depend on the outcome of the saccade itself. We propose a mathematical model parsimoniously capturing various facets of saccade-timings, and suggest a possible neural mechanism producing the observed dynamics.


Assuntos
Geradores de Padrão Central/fisiologia , Modelos Neurológicos , Movimentos Sacádicos , Adulto , Feminino , Fixação Ocular , Humanos , Masculino , Período Refratário Eletrofisiológico
12.
Vision Res ; 118: 70-82, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25645962

RESUMO

Small saccades occur frequently during fixation, and are coupled to changes in visual stimulation and cognitive state. Neurophysiologically, fixational saccades reflect neural activity near the foveal region of a continuous visuomotor map. It is well known that competitive interactions between neurons within visuomotor maps contribute to target selection for large saccades. Here we asked how such interactions in visuomotor maps shape the rate and direction of small fixational saccades. We measured fixational saccades during periods of prolonged fixation while presenting pairs of visual stimuli (parafoveal: 0.8° eccentricity; peripheral: 5° eccentricity) of various contrasts. Fixational saccade direction was biased toward locations of parafoveal stimuli but not peripheral stimuli, ∼100-250ms following stimulus onset. The rate of fixational saccades toward parafoveal stimuli (congruent saccades) increased systematically with parafoveal stimulus contrast, and was suppressed by the simultaneous presentation of a peripheral stimulus. The suppression was best characterized as a combination of two processes: a subtractive suppression of the overall fixational saccade rate and a divisive suppression of the direction bias. These results reveal the nature of suppressive interactions within visuomotor maps and constrain models of the population code for fixational saccades.


Assuntos
Fixação Ocular/fisiologia , Movimentos Sacádicos/fisiologia , Percepção Visual/fisiologia , Adulto , Análise de Variância , Atenção/fisiologia , Feminino , Humanos , Masculino , Neurônios/fisiologia , Estimulação Luminosa , Campos Visuais/fisiologia , Adulto Jovem
13.
J Neurosci ; 34(41): 13693-700, 2014 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-25297096

RESUMO

Microsaccade rate during fixation is modulated by the presentation of a visual stimulus. When the stimulus is an endogenous attention cue, the ensuing microsaccades tend to be directed toward the cue. This finding has been taken as evidence that microsaccades index the locus of spatial attention. But the vast majority of microsaccades that subjects make are not triggered by visual stimuli. Under natural viewing conditions, spontaneous microsaccades occur frequently (2-3 Hz), even in the absence of a stimulus or a task. While spontaneous microsaccades may depend on low-level visual demands, such as retinal fatigue, image fading, or fixation shifts, it is unknown whether their occurrence corresponds to changes in the attentional state. We developed a protocol to measure whether spontaneous microsaccades reflect shifts in spatial attention. Human subjects fixated a cross while microsaccades were detected from streaming eye-position data. Detection of a microsaccade triggered the appearance of a peripheral ring of grating patches, which were followed by an arrow (a postcue) indicating one of them as the target. The target was either congruent or incongruent (opposite) with respect to the direction of the microsaccade (which preceded the stimulus). Subjects reported the tilt of the target (clockwise or counterclockwise relative to vertical). We found that accuracy was higher for congruent than for incongruent trials. We conclude that the direction of spontaneous microsaccades is inherently linked to shifts in spatial attention.


Assuntos
Atenção/fisiologia , Movimentos Sacádicos/fisiologia , Sinais (Psicologia) , Movimentos Oculares/fisiologia , Feminino , Fixação Ocular/fisiologia , Humanos , Masculino , Estimulação Luminosa , Desempenho Psicomotor , Percepção Visual
14.
J Neurosci ; 33(23): 9635-43, 2013 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-23739960

RESUMO

A salient visual stimulus can be rendered invisible by presenting it to one eye while flashing a mask to the other eye. This procedure, called continuous flash suppression (CFS), has been proposed as an ideal way of studying awareness as it can make a stimulus imperceptible for extended periods of time. Previous studies have reported robust suppression of cortical activity in higher visual areas during CFS, but the role of primary visual cortex (V1) is still controversial. In this study, we resolve this controversy on the role of V1 in CFS and also begin characterizing the computational processes underlying CFS. Early visual cortical activity was measured with functional magnetic resonance imaging while human subjects viewed stimuli composed of target and mask, presented to the same or different eyes. Functional MRI responses in early visual cortex were smaller when target and mask were in different eyes compared with the same eye, not only for the lowest contrast target rendered invisible by CFS, but also for higher contrast targets, which were visible even when presented to the eye opposite the mask. We infer that CFS is based on modulating the gain of neural responses, akin to reducing target contrast.


Assuntos
Estimulação Luminosa/métodos , Córtex Visual/fisiologia , Percepção Visual/fisiologia , Feminino , Humanos , Imagem por Ressonância Magnética/métodos , Masculino , Desempenho Psicomotor/fisiologia , Fatores de Tempo
15.
Brain Topogr ; 24(1): 30-9, 2011 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-20665099

RESUMO

We previously showed that the transient broadband induced gamma-band response in EEG (iGBRtb) appearing around 200-300 ms following a visual stimulus reflects the contraction of extra-ocular muscles involved in the execution of saccades, rather than neural oscillations. Several previous studies reported induced gamma-band responses also following auditory stimulation. It is still an open question whether, similarly to visual paradigms, such auditory paradigms are also sensitive to the saccadic confound. In the current study we address this question using simultaneous eye-tracking and EEG recordings during an auditory oddball paradigm. Subjects were instructed to respond to a rare target defined by sound source location, while fixating on a central screen. Results show that, similar to what was found in visual paradigms, saccadic rate displayed typical temporal dynamics including a post-stimulus decrease followed by an increase. This increase was more moderate, had a longer latency, and was less consistent across subjects than was found in the visual case. Crucially, the temporal dynamics of the induced gamma response were similar to those of saccadic-rate modulation. This suggests that the auditory induced gamma-band responses recorded on the scalp may also be affected by saccadic muscle activity.


Assuntos
Estimulação Acústica/métodos , Percepção Auditiva/fisiologia , Ondas Encefálicas/fisiologia , Córtex Cerebral/fisiologia , Músculos Oculomotores/fisiologia , Movimentos Sacádicos/fisiologia , Feminino , Humanos , Masculino , Músculos Oculomotores/inervação , Adulto Jovem
16.
Neuroimage ; 49(3): 2248-63, 2010 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-19874901

RESUMO

Analysis of high-frequency (gamma-band) neural activity by means of non-invasive EEG is gaining increasing interest. However, we have recently shown that a saccade-related spike potential (SP) seriously confounds the analysis of EEG induced gamma-band responses (iGBR), as the SP eludes traditional EEG artifact rejection methods. Here we provide a comprehensive profile of the SP and evaluate methods for its detection and suppression, aiming to unveil true cerebral gamma-band activity. The SP appears consistently as a sharp biphasic deflection of about 22 ms starting at the saccade onset, with a frequency band of approximately 20-90 Hz. On the average, larger saccades elicit higher SP amplitudes. The SP amplitude gradually changes from the extra-ocular channels towards posterior sites with the steepest gradients around the eyes, indicating its ocular source. Although the amplitude and the sign of the SP depend on the choice of reference channel, the potential gradients remain the same and non-zero for all references. The scalp topography is modulated almost exclusively by the direction of saccades, with steeper gradients ipsilateral to the saccade target. We discuss how the above characteristics impede attempts to remove these SPs from the EEG by common temporal filtering, choice of different references, or rejection of contaminated trials. We examine the extent to which SPs can be reliably detected without an eye tracker, assess the degree to which scalp current density derivation attenuates the effect of the SP, and propose a tailored ICA procedure for minimizing the effect of the SP.


Assuntos
Artefatos , Encéfalo/fisiologia , Eletroencefalografia , Movimentos Sacádicos/fisiologia , Potenciais de Ação/fisiologia , Adulto , Mapeamento Encefálico/métodos , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Análise de Componente Principal
17.
Brain Topogr ; 22(1): 3-6, 2009 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-19234781

RESUMO

The contraction of the extra-ocular muscles, during the execution of saccades, produces a strong electric potential in the EEG called the saccadic spike potential (SP). At the frequency spectrum, this SP manifests as a broadband response with most of its power at the gamma-band frequencies. Saccadic activity is known to follow a time-pattern of repression (at around 50-150 ms post stimulus) which is followed by a large increase in saccadic rate at around 200-300 ms post stimulus. Due to this temporal pattern relative to the stimulus, and to the appearance of a SP at each saccade, this increase in saccadic rate shows up after averaging as an increase in gamma-band activity at the time-range of 200-300 ms. Thus, the broadband-transient "induced gamma-band response" frequently reported in the EEG literature, is in fact a "gamma-imposter", due to ocular myographic activity, and not to neural activity. Previous findings regarding the scalp EEG broadband-transient induced gamma-band response, relating it to neural synchronization and to various cognitive functions should be reevaluated considering the systematic contamination by ocular activity.


Assuntos
Encéfalo/fisiologia , Eletroencefalografia , Músculos Oculomotores/metabolismo , Movimentos Sacádicos/fisiologia , Medições dos Movimentos Oculares , Humanos , Couro Cabeludo , Fatores de Tempo
18.
Exp Brain Res ; 193(4): 603-14, 2009 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-19066869

RESUMO

Little is known on cross-modal interaction in complex object recognition. The factors influencing this interaction were investigated using simultaneous presentation of pictures and vocalizations of animals. In separate blocks, the task was to identify either the visual or the auditory stimulus, ignoring the other modality. The pictures and the sounds were congruent (same animal), incongruent (different animals) or neutral (animal with meaningless stimulus). Performance in congruent trials was better than in incongruent trials, regardless of whether subjects attended the visual or the auditory stimuli, but the effect was larger in the latter case. This asymmetry persisted with addition of a long delay after the stimulus and before the response. Thus, the asymmetry cannot be explained by a lack of processing time for the auditory stimulus. However, the asymmetry was eliminated when low-contrast visual stimuli were used. These findings suggest that when visual stimulation is highly informative, it affects auditory recognition more than auditory stimulation affects visual recognition. Nevertheless, this modality dominance is not rigid; it is highly influenced by the quality of the presented information.


Assuntos
Percepção Auditiva , Percepção Visual , Estimulação Acústica , Adolescente , Adulto , Análise de Variância , Animais , Feminino , Humanos , Masculino , Estimulação Luminosa , Tempo de Reação , Análise e Desempenho de Tarefas , Adulto Jovem
19.
Neuron ; 58(3): 429-41, 2008 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-18466752

RESUMO

The induced gamma-band EEG response (iGBR) recorded on the scalp is widely assumed to reflect synchronous neural oscillation associated with object representation, attention, memory, and consciousness. The most commonly reported EEG iGBR is a broadband transient increase in power at the gamma range approximately 200-300 ms following stimulus onset. A conspicuous feature of this iGBR is the trial-to-trial poststimulus latency variability, which has been insufficiently addressed. Here, we show, using single-trial analysis of concomitant EEG and eye tracking, that this iGBR is tightly time locked to the onset of involuntary miniature eye movements and reflects a saccadic "spike potential." The time course of the iGBR is related to an increase in the rate of saccades following a period of poststimulus saccadic inhibition. Thus, whereas neuronal gamma-band oscillations were shown conclusively with other methods, the broadband transient iGBR recorded by scalp EEG reflects properties of miniature saccade dynamics rather than neuronal oscillations.


Assuntos
Encéfalo/fisiologia , Eletroencefalografia , Percepção de Forma/fisiologia , Desempenho Psicomotor/fisiologia , Movimentos Sacádicos/fisiologia , Adulto , Feminino , Fixação Ocular/fisiologia , Humanos , Masculino , Estimulação Luminosa , Tempo de Reação/fisiologia , Couro Cabeludo
20.
J Neurosci ; 27(5): 1090-6, 2007 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-17267563

RESUMO

Gamma-band responses (GBRs) are hypothesized to reflect neuronal synchronous activity related to activation of object representations. However, it is not known whether synchrony in the gamma range is also related to multisensory object processing. We investigated the effect of semantic congruity between auditory and visual information on the human GBR. The paradigm consisted of a simultaneous presentation of pictures and vocalizations of animals, which were either congruent or incongruent. EEG was measured in 17 students while they attended either the auditory or the visual stimulus and performed a recognition task. Behavioral results showed a congruity effect, indicating that information from the unattended modality affected behavior. Irrelevant visual information affected auditory recognition more than irrelevant auditory information affected visual recognition, suggesting a bias toward reliance on visual information in object recognition. Whereas the evoked (phase-locked) GBR was unaffected by congruity, the induced (non-phase-locked) GBR was increased for congruent compared with incongruent stimuli. This effect was independent of the attended modality. The results show that integration of information across modalities, based on semantic congruity, is associated with enhanced synchronized oscillations at the gamma band. This suggests that gamma-band oscillations are related not only to low-level unimodal integration but also to the formation of object representations at conceptual multisensory levels.


Assuntos
Estimulação Acústica/métodos , Percepção Auditiva/fisiologia , Eletroencefalografia , Estimulação Luminosa/métodos , Percepção Visual/fisiologia , Adulto , Potenciais Evocados/fisiologia , Feminino , Humanos , Masculino
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