Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 62
Filtrar
1.
J Vis ; 21(3): 15, 2021 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-33704373

RESUMO

Divided attention has little effect for simple tasks, such as luminance detection, but it has large effects for complex tasks, such as semantic categorization of masked words. Here, we asked whether the semantic categorization of visual objects shows divided attention effects as large as those observed for words, or as small as those observed for simple feature judgments. Using a dual-task paradigm with nameable object stimuli, performance was compared with the predictions of serial and parallel models. At the extreme, parallel processes with unlimited capacity predict no effect of divided attention; alternatively, an all-or-none serial process makes two predictions: a large divided attention effect (lower accuracy for dual-task trials, compared to single-task trials) and a negative response correlation in dual-task trials (a given response is more likely to be incorrect when the response about the other stimulus is correct). These predictions were tested in two experiments examining object judgments. In both experiments, there was a large divided attention effect and a small negative correlation in responses. The magnitude of these effects was larger than for simple features, but smaller than for words. These effects were consistent with serial models, and rule out some but not all parallel models. More broadly, the results help establish one of the first examples of likely serial processing in perception.

2.
Psychon Bull Rev ; 27(2): 315-321, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31907851

RESUMO

Spatial cues help participants detect a visual target when it appears at the cued location. One hypothesis for this cueing effect, called selective perception, is that cueing a location enhances perceptual encoding at that location. Another hypothesis, called selective decision, is that the cue has no effect on perception, but instead provides prior information that facilitates decision-making. We distinguished these hypotheses by comparing a simultaneous display with two spatial locations to sequential displays with two temporal intervals. The simultaneous condition had a partially valid spatial cue, and the sequential condition had a partially valid temporal cue. Selective perception predicts no cueing effect for sequential displays given there is enough time to switch attention. In contrast, selective decision predicts cueing effects for sequential displays regardless of time. We used endogenous cueing of a detection-like coarse orientation discrimination task with clear displays (no external noise or postmasks). Results showed cueing effects for the sequential condition, supporting a decision account of selective attention for endogenous cueing of detection-like tasks.


Assuntos
Atenção/fisiologia , Sinais (Psicologia) , Tomada de Decisões/fisiologia , Percepção Espacial/fisiologia , Percepção Visual/fisiologia , Adulto , Feminino , Humanos , Masculino
3.
Atten Percept Psychophys ; 82(4): 2000-2017, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-31832892

RESUMO

Reading is a demanding task, constrained by inherent processing capacity limits. Do those capacity limits allow for multiple words to be recognized in parallel? In a recent study, we measured semantic categorization accuracy for nouns presented in pairs. The words were replaced by post-masks after an interval that was set to each subject's threshold, such that with focused attention they could categorize one word with ~80% accuracy. When subjects tried to divide attention between both words, their accuracy was so impaired that it supported a serial processing model: on each trial, subjects could categorize one word but had to guess about the other. In the experiments reported here, we investigated how our previous result generalizes across two tasks that require lexical access but vary in the depth of semantic processing (semantic categorization and lexical decision), and across different masking stimuli, word lengths, lexical frequencies and visual field positions. In all cases, the serial processing model was supported by two effects: (1) a sufficiently large accuracy deficit with divided compared to focused attention; and (2) a trial-by-trial stimulus processing tradeoff, meaning that the response to one word was more likely to be correct if the response to the other was incorrect. However, when the task was to detect colored letters, neither of those effects occurred, even though the post-masks limited accuracy in the same way. Altogether, the results are consistent with the hypothesis that visual processing of words is parallel but lexical access is serial.

4.
eNeuro ; 6(6)2019.
Artigo em Inglês | MEDLINE | ID: mdl-31772033

RESUMO

Model-based analyses open exciting opportunities for understanding neural information processing. In a commentary published in eNeuro, Gardner and Liu (2019) discuss the role of model specification in interpreting results derived from complex models of neural data. As a case study, they suggest that one such analysis, the inverted encoding model (IEM), should not be used to assay properties of "stimulus representations" because the ability to apply linear transformations at various stages of the analysis procedure renders results "arbitrary." Here, we argue that the specification of all models is arbitrary to the extent that an experimenter makes choices based on current knowledge of the model system. However, the results derived from any given model, such as the reconstructed channel response profiles obtained from an IEM analysis, are uniquely defined and are arbitrary only in the sense that changes in the model can predictably change results. IEM-based channel response profiles should therefore not be considered arbitrary when the model is clearly specified and guided by our best understanding of neural population representations in the brain regions being analyzed. Intuitions derived from this case study are important to consider when interpreting results from all model-based analyses, which are similarly contingent upon the specification of the models used.


Assuntos
Encéfalo , Neuroimagem
5.
Trends Cogn Sci ; 23(10): 812-814, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31477387

Assuntos
Atenção , Leitura
6.
Cortex ; 121: 44-59, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31542467

RESUMO

Interacting with a cluttered and dynamic environment requires making decisions about visual information at relevant locations while ignoring irrelevant locations. Typical adults can do this with covert spatial attention: prioritizing particular visual field locations even without moving the eyes. Deficits of covert spatial attention have been implicated in developmental dyslexia, a specific reading disability. Previous studies of children with dyslexia, however, have been complicated by group differences in overall task ability that are difficult to distinguish from selective spatial attention. Here, we used a single-fixation visual search task to estimate orientation discrimination thresholds with and without an informative spatial cue in a large sample (N = 123) of people ranging in age from 5 to 70 years and with a wide range of reading abilities. We assessed the efficiency of attentional selection via the cueing effect: the difference in log thresholds with and without the spatial cue. Across our whole sample, both absolute thresholds and the cueing effect gradually improved throughout childhood and adolescence. Compared to typical readers, individuals with dyslexia had higher thresholds (worse orientation discrimination) as well as smaller cueing effects (weaker attentional selection). Those differences in dyslexia were especially pronounced prior to age 20, when basic visual function is still maturing. Thus, in line with previous theories, literacy skills are associated with the development of selective spatial attention.


Assuntos
Atenção/fisiologia , Orientação/fisiologia , Leitura , Percepção Espacial/fisiologia , Adolescente , Adulto , Criança , Tomada de Decisões/fisiologia , Dislexia/fisiopatologia , Feminino , Fixação Ocular/fisiologia , Humanos , Masculino , Campos Visuais/fisiologia , Percepção Visual/fisiologia , Adulto Jovem
7.
Sci Rep ; 9(1): 9199, 2019 06 24.
Artigo em Inglês | MEDLINE | ID: mdl-31235711

RESUMO

Degenerative retinal diseases such as retinitis pigmentosa and macular degeneration cause irreversible vision loss in more than 10 million people worldwide. Retinal prostheses, now implanted in over 250 patients worldwide, electrically stimulate surviving cells in order to evoke neuronal responses that are interpreted by the brain as visual percepts ('phosphenes'). However, instead of seeing focal spots of light, current implant users perceive highly distorted phosphenes that vary in shape both across subjects and electrodes. We characterized these distortions by asking users of the Argus retinal prosthesis system (Second Sight Medical Products Inc.) to draw electrically elicited percepts on a touchscreen. Using ophthalmic fundus imaging and computational modeling, we show that elicited percepts can be accurately predicted by the topographic organization of optic nerve fiber bundles in each subject's retina, successfully replicating visual percepts ranging from 'blobs' to oriented 'streaks' and 'wedges' depending on the retinal location of the stimulating electrode. This provides the first evidence that activation of passing axon fibers accounts for the rich repertoire of phosphene shape commonly reported in psychophysical experiments, which can severely distort the quality of the generated visual experience. Overall our findings argue for more detailed modeling of biological detail across neural engineering applications.


Assuntos
Eletrodos Implantados , Degeneração Macular/cirurgia , Fosfenos , Retinite Pigmentosa/cirurgia , Próteses Visuais , Idoso , Simulação por Computador , Estimulação Elétrica , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Modelos Neurológicos , Células Ganglionares da Retina/citologia , Percepção Visual
8.
Proc Natl Acad Sci U S A ; 116(20): 10087-10096, 2019 05 14.
Artigo em Inglês | MEDLINE | ID: mdl-30962384

RESUMO

In most environments, the visual system is confronted with many relevant objects simultaneously. That is especially true during reading. However, behavioral data demonstrate that a serial bottleneck prevents recognition of more than one word at a time. We used fMRI to investigate how parallel spatial channels of visual processing converge into a serial bottleneck for word recognition. Participants viewed pairs of words presented simultaneously. We found that retinotopic cortex processed the two words in parallel spatial channels, one in each contralateral hemisphere. Responses were higher for attended than for ignored words but were not reduced when attention was divided. We then analyzed two word-selective regions along the occipitotemporal sulcus (OTS) of both hemispheres (subregions of the visual word form area, VWFA). Unlike retinotopic regions, each word-selective region responded to words on both sides of fixation. Nonetheless, a single region in the left hemisphere (posterior OTS) contained spatial channels for both hemifields that were independently modulated by selective attention. Thus, the left posterior VWFA supports parallel processing of multiple words. In contrast, activity in a more anterior word-selective region in the left hemisphere (mid OTS) was consistent with a single channel, showing (i) limited spatial selectivity, (ii) no effect of spatial attention on mean response amplitudes, and (iii) sensitivity to lexical properties of only one attended word. Therefore, the visual system can process two words in parallel up to a late stage in the ventral stream. The transition to a single channel is consistent with the observed bottleneck in behavior.


Assuntos
Atenção/fisiologia , Córtex Cerebral/fisiologia , Leitura , Córtex Cerebral/diagnóstico por imagem , Feminino , Humanos , Imagem por Ressonância Magnética , Masculino , Reconhecimento Psicológico/fisiologia
9.
Psychol Sci ; 29(7): 1062-1071, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-29733752

RESUMO

To test the limits of parallel processing in vision, we investigated whether people can recognize two words at once. Participants viewed brief, masked pairs of words and were instructed in advance to judge both of the words (dual-task condition) or just one of the words (single-task condition). For judgments of semantic category, the dual-task deficit was so large that it supported all-or-none serial processing: Participants could recognize only one word and had to guess about the other. Moreover, participants were more likely to be correct about one word if they were incorrect about the other, which also supports a serial-processing model. In contrast, judgments of text color with identical stimuli were consistent with unlimited-capacity parallel processing. Thus, under these conditions, serial processing is necessary to judge the meaning of words but not their physical features. Understanding the implications of this result for natural reading will require further investigation.


Assuntos
Atenção/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Psicolinguística , Leitura , Reconhecimento Psicológico/fisiologia , Adulto , Feminino , Humanos , Masculino , Adulto Jovem
10.
Front Psychol ; 8: 1983, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-29184522

RESUMO

Here we show that, using functional magnetic resonance imaging (fMRI) blood-oxygen level dependent (BOLD) responses in human primary auditory cortex, it is possible to reconstruct the sequence of tones that a person has been listening to over time. First, we characterized the tonotopic organization of each subject's auditory cortex by measuring auditory responses to randomized pure tone stimuli and modeling the frequency tuning of each fMRI voxel as a Gaussian in log frequency space. Then, we tested our model by examining its ability to work in reverse. Auditory responses were re-collected in the same subjects, except this time they listened to sequences of frequencies taken from simple songs (e.g., "Somewhere Over the Rainbow"). By finding the frequency that minimized the difference between the model's prediction of BOLD responses and actual BOLD responses, we were able to reconstruct tone sequences, with mean frequency estimation errors of half an octave or less, and little evidence of systematic biases.

11.
J Vis ; 17(6): 19, 2017 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-28654964

RESUMO

Performance in many visual tasks is impaired when observers attempt to divide spatial attention across multiple visual field locations. Correspondingly, neuronal response magnitudes in visual cortex are often reduced during divided compared with focused spatial attention. This suggests that early visual cortex is the site of capacity limits, where finite processing resources must be divided among attended stimuli. However, behavioral research demonstrates that not all visual tasks suffer such capacity limits: The costs of divided attention are minimal when the task and stimulus are simple, such as when searching for a target defined by orientation or contrast. To date, however, every neuroimaging study of divided attention has used more complex tasks and found large reductions in response magnitude. We bridged that gap by using functional magnetic resonance imaging to measure responses in the human visual cortex during simple feature detection. The first experiment used a visual search task: Observers detected a low-contrast Gabor patch within one or four potentially relevant locations. The second experiment used a dual-task design, in which observers made independent judgments of Gabor presence in patches of dynamic noise at two locations. In both experiments, blood-oxygen level-dependent (BOLD) signals in the retinotopic cortex were significantly lower for ignored than attended stimuli. However, when observers divided attention between multiple stimuli, BOLD signals were not reliably reduced and behavioral performance was unimpaired. These results suggest that processing of simple features in early visual cortex has unlimited capacity.


Assuntos
Mapeamento Encefálico/métodos , Córtex Visual/fisiologia , Adulto , Atenção/fisiologia , Feminino , Humanos , Imagem por Ressonância Magnética/métodos , Masculino , Orientação , Estimulação Luminosa , Campos Visuais , Adulto Jovem
12.
J Neural Eng ; 14(5): 051003, 2017 10.
Artigo em Inglês | MEDLINE | ID: mdl-28612755

RESUMO

The 'bionic eye'-so long a dream of the future-is finally becoming a reality with retinal prostheses available to patients in both the US and Europe. However, clinical experience with these implants has made it apparent that the visual information provided by these devices differs substantially from normal sight. Consequently, the ability of patients to learn to make use of this abnormal retinal input plays a critical role in whether or not some functional vision is successfully regained. The goal of the present review is to summarize the vast basic science literature on developmental and adult cortical plasticity with an emphasis on how this literature might relate to the field of prosthetic vision. We begin with describing the distortion and information loss likely to be experienced by visual prosthesis users. We then define cortical plasticity and perceptual learning, and describe what is known, and what is unknown, about visual plasticity across the hierarchy of brain regions involved in visual processing, and across different stages of life. We close by discussing what is known about brain plasticity in sight restoration patients and discuss biological mechanisms that might eventually be harnessed to improve visual learning in these patients.


Assuntos
Aprendizagem/fisiologia , Plasticidade Neuronal/fisiologia , Optogenética/métodos , Córtex Visual/fisiologia , Percepção Visual/fisiologia , Próteses Visuais , Humanos , Optogenética/tendências , Próteses Visuais/tendências
13.
Atten Percept Psychophys ; 79(2): 553-562, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27909979

RESUMO

Observers show small but systematic deviations from equal weighting of all elements when asked to localize the center of an array of dots. Counter-intuitively, with small numbers of dots drawn from a Gaussian distribution, this bias results in subjects overweighting the influence of outlier dots - inconsistent with traditional statistical estimators of central tendency. Here we show that this apparent statistical anomaly can be explained by the observation that outlier dots also lie in regions of lower dot density. Using a standard model of V1 processing, which includes spatial integration followed by a compressive static nonlinearity, we can successfully predict the finding that dots in less dense regions of an array have a relatively greater influence on the perceived center.


Assuntos
Movimentos Oculares/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Estimulação Luminosa/métodos , Tempo de Reação/fisiologia , Feminino , Humanos , Masculino , Distribuição Normal , Distribuição Aleatória , Adulto Jovem
14.
Front Hum Neurosci ; 10: 324, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27458357

RESUMO

Early blind subjects exhibit superior abilities for processing auditory motion, which are accompanied by enhanced BOLD responses to auditory motion within hMT+ and reduced responses within right planum temporale (rPT). Here, by comparing BOLD responses to auditory motion in hMT+ and rPT within sighted controls, early blind, late blind, and sight-recovery individuals, we were able to separately examine the effects of developmental and adult visual deprivation on cortical plasticity within these two areas. We find that both the enhanced auditory motion responses in hMT+ and the reduced functionality in rPT are driven by the absence of visual experience early in life; neither loss nor recovery of vision later in life had a discernable influence on plasticity within these areas. Cortical plasticity as a result of blindness has generally be presumed to be mediated by competition across modalities within a given cortical region. The reduced functionality within rPT as a result of early visual loss implicates an additional mechanism for cross modal plasticity as a result of early blindness-competition across different cortical areas for functional role.

15.
Philos Trans R Soc Lond B Biol Sci ; 370(1677): 20140208, 2015 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-26240423

RESUMO

An extraordinary variety of sight recovery therapies are either about to begin clinical trials, have begun clinical trials, or are currently being implanted in patients. However, as yet we have little insight into the perceptual experience likely to be produced by these implants. This review focuses on methodologies, such as optogenetics, small molecule photoswitches and electrical prostheses, which use artificial stimulation of the retina to elicit percepts. For each of these technologies, the interplay between the stimulating technology and the underlying neurophysiology is likely to result in distortions of the perceptual experience. Here, we describe some of these potential distortions and discuss how they might be minimized either through changes in the encoding model or through cortical plasticity.


Assuntos
Transtornos da Visão/terapia , Percepção Visual/fisiologia , Terapia por Estimulação Elétrica/métodos , Humanos , Modelos Biológicos , Optogenética/métodos , Retina/citologia , Retina/fisiologia , Transtornos da Visão/fisiopatologia , Transtornos da Visão/psicologia , Próteses Visuais
16.
J Vis ; 15(4): 5, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26053144

RESUMO

Over the past 15 years, a number of behavioral studies have shown that the human visual system can extract the average value of a set of items along a variety of feature dimensions, often with great facility and accuracy. These efficient representations of sets of items are commonly referred to as summary representations, but very little is known about whether their computation constitutes a single unitary process or if it involves different mechanisms in different domains. Here, we asked participants to report the average value of a set of items presented serially over time in four different feature dimensions. We then measured the contribution of different parts of the information stream to the reported summaries. We found that this temporal weighting profile differs greatly across domains. Specifically, summaries of mean object location (Experiment 1) were influenced approximately 2.5 times more by earlier items than by later items. Summaries of mean object size (Experiment 1), mean facial expression (Experiment 2), and mean motion direction (Experiment 3), however, were more influenced by later items. These primacy and recency effects show that summary representations computed across time do not incorporate all items equally. Furthermore, our results support the hypothesis that summary representations operate differently in different feature domains, and may be subserved by distinct mechanisms.


Assuntos
Expressão Facial , Reconhecimento Visual de Modelos/fisiologia , Estatística como Assunto , Humanos
17.
Psychol Sci ; 26(4): 393-401, 2015 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-25740284

RESUMO

In 2000, monocular vision was restored to M. M., who had been blind between the ages of 3 and 46 years. Tests carried out over 2 years following the surgery revealed impairments of 3-D form, object, and face processing and an absence of object- and face-selective blood-oxygen-level-dependent responses in ventral visual cortex. In the present research, we reexamined M. M. to test for experience-dependent recovery of visual function. Behaviorally, M. M. remains impaired in 3-D form, object, and face processing. Accordingly, we found little to no evidence of the category-selective organization within ventral visual cortex typically associated with face, body, scene, or object processing. We did observe remarkably normal object selectivity within lateral occipital cortex, consistent with M. M.'s previously reported shape-discrimination performance. Together, these findings provide little evidence for recovery of high-level visual function after more than a decade of visual experience in adulthood.


Assuntos
Cegueira/fisiopatologia , Plasticidade Neuronal/fisiologia , Visão Monocular/fisiologia , Córtex Visual/fisiopatologia , Adulto , Cegueira/terapia , Humanos , Masculino , Pessoa de Meia-Idade , Reconhecimento Visual de Modelos/fisiologia
18.
Neuroimage ; 105: 428-39, 2015 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-25449742

RESUMO

Here we describe a method for measuring tonotopic maps and estimating bandwidth for voxels in human primary auditory cortex (PAC) using a modification of the population Receptive Field (pRF) model, developed for retinotopic mapping in visual cortex by Dumoulin and Wandell (2008). The pRF method reliably estimates tonotopic maps in the presence of acoustic scanner noise, and has two advantages over phase-encoding techniques. First, the stimulus design is flexible and need not be a frequency progression, thereby reducing biases due to habituation, expectation, and estimation artifacts, as well as reducing the effects of spatio-temporal BOLD nonlinearities. Second, the pRF method can provide estimates of bandwidth as a function of frequency. We find that bandwidth estimates are narrower for voxels within the PAC than in surrounding auditory responsive regions (non-PAC).


Assuntos
Córtex Auditivo/fisiologia , Percepção Auditiva/fisiologia , Mapeamento Encefálico/métodos , Adulto , Feminino , Humanos , Imagem por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Adulto Jovem
19.
J Neurophysiol ; 110(10): 2426-39, 2013 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-23883860

RESUMO

Contrasting theories of visual attention have emphasized selection by spatial location, individual features, and whole objects. We used functional magnetic resonance imaging to ask whether and how attention to one feature of an object spreads to other features of the same object. Subjects viewed two spatially superimposed surfaces of random dots that were segregated by distinct color-motion conjunctions. The color and direction of motion of each surface changed smoothly and in a cyclical fashion. Subjects were required to track one feature (e.g., color) of one of the two surfaces and detect brief moments when the attended feature diverged from its smooth trajectory. To tease apart the effect of attention to individual features on the hemodynamic response, we used a frequency-tagging scheme. In this scheme, the stimulus features (color and direction of motion) are modulated periodically at distinct frequencies so that the contribution of each feature to the hemodynamics can be inferred from the harmonic response at the corresponding frequency. We found that attention to one feature (e.g., color) of one surface increased the response modulation not only to the attended feature but also to the other feature (e.g., motion) of the same surface. This attentional modulation was evident in multiple visual areas and was present as early as V1. The spread of attention to the behaviorally irrelevant features of a surface suggests that attention may automatically select all features of a single object. Thus object-based attention may be supported by an enhancement of feature-specific sensory signals in the visual cortex.


Assuntos
Atenção/fisiologia , Percepção de Movimento/fisiologia , Córtex Visual/fisiologia , Percepção Visual/fisiologia , Adulto , Mapeamento Encefálico , Percepção de Cores/fisiologia , Feminino , Humanos , Imagem por Ressonância Magnética , Masculino , Estimulação Luminosa , Psicofísica , Lobo Temporal/fisiologia , Adulto Jovem
20.
J Vis ; 13(7): 13, 2013 Jun 20.
Artigo em Inglês | MEDLINE | ID: mdl-23788461

RESUMO

There is substantial interest in using functional magnetic resonance imaging (fMRI) retinotopic mapping techniques to examine reorganization of the occipital cortex after vision loss in humans and nonhuman primates. However, previous reports suggest that standard phase encoding and the more recent population Receptive Field (pRF) techniques give biased estimates of retinotopic maps near the boundaries of retinal or cortical scotomas. Here we examine the sources of this bias and show how it can be minimized with a simple modification of the pRF method. In normally sighted subjects, we measured fMRI responses to a stimulus simulating a foveal scotoma; we found that unbiased retinotopic map estimates can be obtained in early visual areas, as long as the pRF fitting algorithm takes the scotoma into account and a randomized "multifocal" stimulus sequence is used.


Assuntos
Mapeamento Encefálico , Oxigênio/sangue , Retina/fisiopatologia , Escotoma/fisiopatologia , Córtex Visual/fisiopatologia , Percepção Visual/fisiologia , Adulto , Algoritmos , Viés , Feminino , Humanos , Imagem por Ressonância Magnética/métodos , Masculino
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...