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1.
Cell ; 184(14): 3748-3761.e18, 2021 07 08.
Artigo em Inglês | MEDLINE | ID: mdl-34171308

RESUMO

Lateral intraparietal (LIP) neurons represent formation of perceptual decisions involving eye movements. In circuit models for these decisions, neural ensembles that encode actions compete to form decisions. Consequently, representation and readout of the decision variables (DVs) are implemented similarly for decisions with identical competing actions, irrespective of input and task context differences. Further, DVs are encoded as partially potentiated action plans through balance of activity of action-selective ensembles. Here, we test those core principles. We show that in a novel face-discrimination task, LIP firing rates decrease with supporting evidence, contrary to conventional motion-discrimination tasks. These opposite response patterns arise from similar mechanisms in which decisions form along curved population-response manifolds misaligned with action representations. These manifolds rotate in state space based on context, indicating distinct optimal readouts for different tasks. We show similar manifolds in lateral and medial prefrontal cortices, suggesting similar representational geometry across decision-making circuits.


Assuntos
Tomada de Decisões , Percepção de Movimento/fisiologia , Lobo Parietal/fisiologia , Animais , Comportamento Animal , Julgamento , Macaca mulatta , Masculino , Modelos Neurológicos , Neurônios/fisiologia , Estimulação Luminosa , Córtex Pré-Frontal/fisiologia , Psicofísica , Análise e Desempenho de Tarefas , Fatores de Tempo
2.
Nature ; 591(7851): 604-609, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-33473215

RESUMO

In dynamic environments, subjects often integrate multiple samples of a signal and combine them to reach a categorical judgment1. The process of deliberation can be described by a time-varying decision variable (DV), decoded from neural population activity, that predicts a subject's upcoming decision2. Within single trials, however, there are large moment-to-moment fluctuations in the DV, the behavioural significance of which is unclear. Here, using real-time, neural feedback control of stimulus duration, we show that within-trial DV fluctuations, decoded from motor cortex, are tightly linked to decision state in macaques, predicting behavioural choices substantially better than the condition-averaged DV or the visual stimulus alone. Furthermore, robust changes in DV sign have the statistical regularities expected from behavioural studies of changes of mind3. Probing the decision process on single trials with weak stimulus pulses, we find evidence for time-varying absorbing decision bounds, enabling us to distinguish between specific models of decision making.


Assuntos
Tomada de Decisões/fisiologia , Modelos Neurológicos , Animais , Comportamento de Escolha/fisiologia , Discriminação Psicológica , Julgamento , Macaca/fisiologia , Movimento (Física) , Percepção de Movimento , Estimulação Luminosa , Fatores de Tempo
3.
Annu Rev Physiol ; 85: 191-215, 2023 02 10.
Artigo em Inglês | MEDLINE | ID: mdl-36343603

RESUMO

Neural mechanisms of perceptual decision making have been extensively studied in experimental settings that mimic stable environments with repeating stimuli, fixed rules, and payoffs. In contrast, we live in an ever-changing environment and have varying goals and behavioral demands. To accommodate variability, our brain flexibly adjusts decision-making processes depending on context. Here, we review a growing body of research that explores the neural mechanisms underlying this flexibility. We highlight diverse forms of context dependency in decision making implemented through a variety of neural computations. Context-dependent neural activity is observed in a distributed network of brain structures, including posterior parietal, sensory, motor, and subcortical regions, as well as the prefrontal areas classically implicated in cognitive control. We propose that investigating the distributed network underlying flexible decisions is key to advancing our understanding and discuss a path forward for experimental and theoretical investigations.


Assuntos
Mapeamento Encefálico , Tomada de Decisões , Humanos , Tempo de Reação , Imageamento por Ressonância Magnética , Encéfalo
4.
J Neurosci ; 44(16)2024 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-38413233

RESUMO

Technical advances in artificial manipulation of neural activity have precipitated a surge in studying the causal contribution of brain circuits to cognition and behavior. However, complexities of neural circuits challenge interpretation of experimental results, necessitating new theoretical frameworks for reasoning about causal effects. Here, we take a step in this direction, through the lens of recurrent neural networks trained to perform perceptual decisions. We show that understanding the dynamical system structure that underlies network solutions provides a precise account for the magnitude of behavioral effects due to perturbations. Our framework explains past empirical observations by clarifying the most sensitive features of behavior, and how complex circuits compensate and adapt to perturbations. In the process, we also identify strategies that can improve the interpretability of inactivation experiments.


Assuntos
Aprendizagem , Neurônios , Neurônios/fisiologia , Redes Neurais de Computação , Cognição , Resolução de Problemas
5.
Proc Natl Acad Sci U S A ; 117(40): 25066-25073, 2020 10 06.
Artigo em Inglês | MEDLINE | ID: mdl-32948691

RESUMO

The brain represents and reasons probabilistically about complex stimuli and motor actions using a noisy, spike-based neural code. A key building block for such neural computations, as well as the basis for supervised and unsupervised learning, is the ability to estimate the surprise or likelihood of incoming high-dimensional neural activity patterns. Despite progress in statistical modeling of neural responses and deep learning, current approaches either do not scale to large neural populations or cannot be implemented using biologically realistic mechanisms. Inspired by the sparse and random connectivity of real neuronal circuits, we present a model for neural codes that accurately estimates the likelihood of individual spiking patterns and has a straightforward, scalable, efficient, learnable, and realistic neural implementation. This model's performance on simultaneously recorded spiking activity of >100 neurons in the monkey visual and prefrontal cortices is comparable with or better than that of state-of-the-art models. Importantly, the model can be learned using a small number of samples and using a local learning rule that utilizes noise intrinsic to neural circuits. Slower, structural changes in random connectivity, consistent with rewiring and pruning processes, further improve the efficiency and sparseness of the resulting neural representations. Our results merge insights from neuroanatomy, machine learning, and theoretical neuroscience to suggest random sparse connectivity as a key design principle for neuronal computation.


Assuntos
Potenciais de Ação/fisiologia , Encéfalo/fisiologia , Redes Neurais de Computação , Neurônios/fisiologia , Algoritmos , Humanos , Aprendizado de Máquina , Modelos Neurológicos , Rede Nervosa/fisiologia , Plasticidade Neuronal/fisiologia
6.
J Neurosci ; 41(37): 7876-7893, 2021 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-34326145

RESUMO

Visual object recognition relies on elaborate sensory processes that transform retinal inputs to object representations, but it also requires decision-making processes that read out object representations and function over prolonged time scales. The computational properties of these decision-making processes remain underexplored for object recognition. Here, we study these computations by developing a stochastic multifeature face categorization task. Using quantitative models and tight control of spatiotemporal visual information, we demonstrate that human subjects (five males, eight females) categorize faces through an integration process that first linearly adds the evidence conferred by task-relevant features over space to create aggregated momentary evidence and then linearly integrates it over time with minimum information loss. Discrimination of stimuli along different category boundaries (e.g., identity or expression of a face) is implemented by adjusting feature weights of spatial integration. This linear but flexible integration process over space and time bridges past studies on simple perceptual decisions to complex object recognition behavior.SIGNIFICANCE STATEMENT Although simple perceptual decision-making such as discrimination of random dot motion has been successfully explained as accumulation of sensory evidence, we lack rigorous experimental paradigms to study the mechanisms underlying complex perceptual decision-making such as discrimination of naturalistic faces. We develop a stochastic multifeature face categorization task as a systematic approach to quantify the properties and potential limitations of the decision-making processes during object recognition. We show that human face categorization could be modeled as a linear integration of sensory evidence over space and time. Our framework to study object recognition as a spatiotemporal integration process is broadly applicable to other object categories and bridges past studies of object recognition and perceptual decision-making.


Assuntos
Tomada de Decisões/fisiologia , Reconhecimento Facial/fisiologia , Movimentos Oculares/fisiologia , Feminino , Humanos , Masculino , Testes Neuropsicológicos , Reconhecimento Visual de Modelos/fisiologia , Estimulação Luminosa , Tempo de Reação/fisiologia
7.
J Neurophysiol ; 128(2): 310-325, 2022 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-35792500

RESUMO

An integral feature of human memory is the ability to recall past events. What distinguishes such episodic memory from semantic or associative memory is the joint encoding and retrieval of "what," "where," and "when" (WWW) for such events. Surprisingly, little work has addressed whether all three components of WWW are retrieved with equal fidelity when remembering episodes. To study this question, we created a novel task where human participants identified matched or mismatched still images sampled from recently viewed synthetic movies. The mismatch images only probe one of the three WWW components at a time, allowing us to separately test accuracies for each component of the episodes. Crucially, each WWW component in the movies is easily distinguishable in isolation, thereby making any differences in accuracy between components due to how they are joined in memory. We find that memory for "when" has the lowest accuracy, with it being the component most influenced by primacy and recency. Furthermore, the memory of "when" is most susceptible to interference due to changes in task load. These findings suggest that episodes are not stored and retrieved as a coherent whole but instead their components are either stored or retrieved differentially as part of an active reconstruction process. NEW & NOTEWORTHY When we store and subsequently retrieve episodes, does the brain encode them holistically or in separate parts that are later reconstructed? Using a task where participants study abstract episodes and on any given trial are probed on the what, where, and when components, we find mnemonic differences between them. Accuracy for "when" memory is the lowest, as it is most influenced by primacy, recency, and interference, suggesting that episodes are not treated holistically by the brain.


Assuntos
Memória Episódica , Rememoração Mental , Encéfalo , Humanos , Semântica
8.
Proc Natl Acad Sci U S A ; 113(31): E4531-40, 2016 08 02.
Artigo em Inglês | MEDLINE | ID: mdl-27432960

RESUMO

Decision-making in a natural environment depends on a hierarchy of interacting decision processes. A high-level strategy guides ongoing choices, and the outcomes of those choices determine whether or not the strategy should change. When the right decision strategy is uncertain, as in most natural settings, feedback becomes ambiguous because negative outcomes may be due to limited information or bad strategy. Disambiguating the cause of feedback requires active inference and is key to updating the strategy. We hypothesize that the expected accuracy of a choice plays a crucial rule in this inference, and setting the strategy depends on integration of outcome and expectations across choices. We test this hypothesis with a task in which subjects report the net direction of random dot kinematograms with varying difficulty while the correct stimulus-response association undergoes invisible and unpredictable switches every few trials. We show that subjects treat negative feedback as evidence for a switch but weigh it with their expected accuracy. Subjects accumulate switch evidence (in units of log-likelihood ratio) across trials and update their response strategy when accumulated evidence reaches a bound. A computational framework based on these principles quantitatively explains all aspects of the behavior, providing a plausible neural mechanism for the implementation of hierarchical multiscale decision processes. We suggest that a similar neural computation-bounded accumulation of evidence-underlies both the choice and switches in the strategy that govern the choice, and that expected accuracy of a choice represents a key link between the levels of the decision-making hierarchy.


Assuntos
Encéfalo/fisiologia , Comportamento de Escolha/fisiologia , Tomada de Decisões/fisiologia , Rede Nervosa/fisiologia , Adaptação Psicológica/fisiologia , Algoritmos , Retroalimentação Psicológica , Feminino , Humanos , Modelos Logísticos , Masculino , Percepção de Movimento/fisiologia , Desempenho Psicomotor/fisiologia , Incerteza
9.
J Vis ; 18(6): 9, 2018 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-30029220

RESUMO

When the visual system analyzes distributed patterns of sensory inputs, what features of those distributions does it use? It has been previously demonstrated that higher-order statistical moments of luminance distributions influence perception of static surfaces and textures. Here, we tested whether the brain also represents higher-order moments of dynamic stimuli. We constructed random dot kinematograms, where dots moved according to probability distributions that selectively differed in terms of their mean, variance, skewness, or kurtosis. When viewing these stimuli, human observers were sensitive to the mean direction of coherent motion and to the variance of dot displacement angles, but they were insensitive to skewness and kurtosis. Observer behavior accorded with a model of directional motion energy, suggesting that information about higher-order moments is discarded early in the visual processing hierarchy. These results demonstrate that use of higher-order moments is not a general property of visual perception.


Assuntos
Percepção de Movimento/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Percepção Visual/fisiologia , Adulto , Feminino , Humanos , Masculino , Probabilidade , Movimentos Sacádicos/fisiologia , Adulto Jovem
10.
J Vis ; 18(8): 10, 2018 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-30140892

RESUMO

Perceptual systems adapt to their inputs. As a result, prolonged exposure to particular stimuli alters judgments about subsequent stimuli. This phenomenon is commonly assumed to be sensory in origin. Changes in the decision-making process, however, may also be a component of adaptation. Here, we quantify sensory and decision-making contributions to adaptation in a facial expression paradigm. As expected, exposure to happy or sad expressions shifts the psychometric function toward the adaptor. More surprisingly, response times show both an overall decline and an asymmetry, with faster responses opposite the adapting category, implicating a substantial change in the decision-making process. Specifically, we infer that sensory changes from adaptation are accompanied by changes in how much sensory information is accumulated for the two choices. We speculate that adaptation influences implicit expectations about the stimuli one will encounter, causing modifications in the decision-making process as part of a normative response to a change in context.


Assuntos
Adaptação Ocular/fisiologia , Tomada de Decisões/fisiologia , Expressão Facial , Células Receptoras Sensoriais/fisiologia , Adolescente , Adulto , Comportamento de Escolha , Feminino , Humanos , Julgamento , Masculino , Pessoa de Meia-Idade , Psicometria , Tempo de Reação , Adulto Jovem
11.
J Neurophysiol ; 116(2): 587-601, 2016 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-27169503

RESUMO

Object categories are recognized at multiple levels of hierarchical abstractions. Psychophysical studies have shown a more rapid perceptual access to the mid-level category information (e.g., human faces) than the higher (superordinate; e.g., animal) or the lower (subordinate; e.g., face identity) level. Mid-level category members share many features, whereas few features are shared among members of different mid-level categories. To understand better the neural basis of expedited access to mid-level category information, we examined neural responses of the inferior temporal (IT) cortex of macaque monkeys viewing a large number of object images. We found an earlier representation of mid-level categories in the IT population and single-unit responses compared with superordinate- and subordinate-level categories. The short-latency representation of mid-level category information shows that visual cortex first divides the category shape space at its sharpest boundaries, defined by high/low within/between-group similarity. This short-latency, mid-level category boundary map may be a prerequisite for representation of other categories at more global and finer scales.


Assuntos
Mapeamento Encefálico , Neurônios/fisiologia , Dinâmica não Linear , Reconhecimento Visual de Modelos/fisiologia , Lobo Temporal/citologia , Animais , Simulação por Computador , Macaca , Masculino , Modelos Neurológicos , Estimulação Luminosa , Análise de Componente Principal , Curva ROC , Tempo de Reação , Máquina de Vetores de Suporte , Lobo Temporal/fisiologia , Fatores de Tempo , Vias Visuais/fisiologia
12.
Nature ; 461(7261): 263-6, 2009 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-19693010

RESUMO

A decision is a commitment to a proposition or plan of action based on evidence and the expected costs and benefits associated with the outcome. Progress in a variety of fields has led to a quantitative understanding of the mechanisms that evaluate evidence and reach a decision. Several formalisms propose that a representation of noisy evidence is evaluated against a criterion to produce a decision. Without additional evidence, however, these formalisms fail to explain why a decision-maker would change their mind. Here we extend a model, developed to account for both the timing and the accuracy of the initial decision, to explain subsequent changes of mind. Subjects made decisions about a noisy visual stimulus, which they indicated by moving a handle. Although they received no additional information after initiating their movement, their hand trajectories betrayed a change of mind in some trials. We propose that noisy evidence is accumulated over time until it reaches a criterion level, or bound, which determines the initial decision, and that the brain exploits information that is in the processing pipeline when the initial decision is made to subsequently either reverse or reaffirm the initial decision. The model explains both the frequency of changes of mind as well as their dependence on both task difficulty and whether the initial decision was accurate or erroneous. The theoretical and experimental findings advance the understanding of decision-making to the highly flexible and cognitive acts of vacillation and self-correction.


Assuntos
Tomada de Decisões/fisiologia , Computadores , Sinais (Psicologia) , Feminino , Mãos/fisiologia , Humanos , Masculino , Modelos Neurológicos , Modelos Psicológicos , Movimento (Física) , Movimento , Estimulação Luminosa , Desempenho Psicomotor , Tempo de Reação , Fatores de Tempo
13.
Cereb Cortex ; 24(12): 3350-64, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23921785

RESUMO

Episodic recollection entails the conscious remembrance of event details associated with previously encountered stimuli. Recollection depends on both the establishment of cortical representations of event features during stimulus encoding and the cortical reinstatement of these representations at retrieval. Here, we used multivoxel pattern analyses of functional magnetic resonance imaging data to examine how cortical and hippocampal activity at encoding and retrieval drive recollective memory decisions. During encoding, words were associated with face or scene source contexts. At retrieval, subjects were cued to recollect the source associate of each presented word. Neurally derived estimates of encoding strength and pattern reinstatement in occipitotemporal cortex were computed for each encoding and retrieval trial, respectively. Analyses demonstrated that (1) cortical encoding strength predicted subsequent memory accuracy and reaction time, (2) encoding strength predicted encoding-phase hippocampal activity, and (3) encoding strength and retrieval-phase hippocampal activity predicted the magnitude of cortical reinstatement. Path analyses further indicated that cortical reinstatement partially mediated both the effect of cortical encoding strength and the effect of retrieval-phase hippocampal activity on subsequent source memory performance. Taken together, these results indicate that memory-guided decisions are driven in part by a pathway leading from hippocampally linked cortical encoding of event attributes to hippocampally linked cortical reinstatement at retrieval.


Assuntos
Mapeamento Encefálico , Córtex Cerebral/fisiologia , Imagens, Psicoterapia , Rememoração Mental/fisiologia , Adolescente , Córtex Cerebral/irrigação sanguínea , Feminino , Hipocampo/irrigação sanguínea , Hipocampo/fisiologia , Humanos , Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética , Masculino , Vias Neurais/irrigação sanguínea , Vias Neurais/fisiologia , Testes Neuropsicológicos , Oxigênio/sangue , Desempenho Psicomotor , Análise de Regressão , Adulto Jovem
14.
J Neurosci ; 33(42): 16483-9, 2013 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-24133253

RESUMO

Many decisions involve integration of evidence conferred by discrete cues over time. However, the neural mechanism of this integration is poorly understood. Several decision-making models suggest that integration of evidence is implemented by a dynamic system whose state evolves toward a stable point representing the decision outcome. The internal dynamics of such point attractor models render them sensitive to the temporal gaps between cues because their internal forces push the state forward once it is dislodged from the initial stable point. We asked whether human subjects are as sensitive to such temporal gaps. Subjects reported the net direction of stochastic random dot motion, which was presented in one or two brief observation windows (pulses). Pulse strength and interpulse interval varied randomly from trial to trial. We found that subjects' performance was largely invariant to the interpulse intervals up to at least 1 s. The findings question the implementation of the integration process via mechanisms that rely on autonomous changes of network state. The mechanism should be capable of freezing the state of the network at a variety of firing rate levels during temporal gaps between the cues, compatible with a line of stable attractor states.


Assuntos
Tomada de Decisões/fisiologia , Modelos Neurológicos , Percepção de Movimento/fisiologia , Adulto , Sinais (Psicologia) , Feminino , Humanos , Masculino , Tempo de Reação/fisiologia , Fatores de Tempo
15.
Neural Comput ; 26(10): 2135-62, 2014 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-25058707

RESUMO

We have calculated the intrinsic dimensionality of visual object representations in anterior inferotemporal (AIT) cortex, based on responses of a large sample of cells stimulated with photographs of diverse objects. Because dimensionality was dependent on data set size, we determined asymptotic dimensionality as both the number of neurons and number of stimulus image approached infinity. Our final dimensionality estimate was 93 (SD: ± 11), indicating that there is basis set of approximately 100 independent features that characterize the dimensions of neural object space. We believe this is the first estimate of the dimensionality of neural visual representations based on single-cell neurophysiological data. The dimensionality of AIT object representations was much lower than the dimensionality of the stimuli. We suggest that there may be a gradual reduction in the dimensionality of object representations in neural populations going from retina to inferotemporal cortex as receptive fields become increasingly complex.


Assuntos
Potenciais de Ação/fisiologia , Percepção de Forma/fisiologia , Neurônios/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Lobo Temporal/citologia , Algoritmos , Animais , Macaca mulatta , Estimulação Luminosa , Análise de Componente Principal , Vias Visuais/fisiologia
16.
ArXiv ; 2024 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-39279840

RESUMO

Non-sensory thalamic nuclei interact with the cortex through thalamocortical and cortico-basal ganglia-thalamocortical loops. Reciprocal connections between the mediodorsal thalamus (MD) and the prefrontal cortex are particularly important in cognition, while the reciprocal connections of the ventromedial (VM), ventral anterior (VA), and ventrolateral (VL) thalamus with the prefrontal and motor cortex are necessary for sensorimotor information processing. However, limited and often oversimplified understanding of the connectivity of the MD, VA, and VL nuclei in primates have hampered development of accurate models that explain their contribution to cognitive and sensorimotor functions. The current prevalent view suggests that the MD connects with the prefrontal cortex, while the VA and VL primarily connect with the premotor and motor cortices. However, past studies have also reported diverse connections that enable these nuclei to integrate information across a multitude of brain systems. In this review, we provide a comprehensive overview of the anatomical connectivity of the primate MD, VA, and VL with the cortex. By synthesizing recent findings, we aim to offer a valuable resource for students, newcomers to the field, and experts developing new theories or models of thalamic function. Our review highlights the complexity of these connections and underscores the need for further research to fully understand the diverse roles of these thalamic nuclei in primates.

17.
J Neurosci ; 31(49): 17887-91, 2011 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-22159103

RESUMO

As we shift our gaze to explore the visual world, information enters cortex in a sequence of successive snapshots, interrupted by phases of blur. Our experience, in contrast, appears like a movie of a continuous stream of objects embedded in a stable world. This perception of stability across eye movements has been linked to changes in spatial sensitivity of visual neurons anticipating the upcoming saccade, often referred to as shifting receptive fields (Duhamel et al., 1992; Walker et al., 1995; Umeno and Goldberg, 1997; Nakamura and Colby, 2002). How exactly these receptive field dynamics contribute to perceptual stability is currently not clear. Anticipatory receptive field shifts toward the future, postsaccadic position may bridge the transient perisaccadic epoch (Sommer and Wurtz, 2006; Wurtz, 2008; Melcher and Colby, 2008). Alternatively, a presaccadic shift of receptive fields toward the saccade target area (Tolias et al., 2001) may serve to focus visual resources onto the most relevant objects in the postsaccadic scene (Hamker et al., 2008). In this view, shifts of feature detectors serve to facilitate the processing of the peripheral visual content before it is foveated. While this conception is consistent with previous observations on receptive field dynamics and on perisaccadic compression (Ross et al., 1997; Morrone et al., 1997; Kaiser and Lappe, 2004), it predicts that receptive fields beyond the saccade target shift toward the saccade target rather than in the direction of the saccade. We have tested this prediction in human observers via the presaccadic transfer of the tilt-aftereffect (Melcher, 2007).


Assuntos
Atenção/fisiologia , Movimentos Sacádicos/fisiologia , Transferência de Experiência/fisiologia , Campos Visuais/fisiologia , Humanos , Estimulação Luminosa/métodos , Psicometria
18.
J Neurosci ; 31(17): 6339-52, 2011 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-21525274

RESUMO

Decisions are often based on a combination of new evidence with prior knowledge of the probable best choice. Optimal combination requires knowledge about the reliability of evidence, but in many realistic situations, this is unknown. Here we propose and test a novel theory: the brain exploits elapsed time during decision formation to combine sensory evidence with prior probability. Elapsed time is useful because (1) decisions that linger tend to arise from less reliable evidence, and (2) the expected accuracy at a given decision time depends on the reliability of the evidence gathered up to that point. These regularities allow the brain to combine prior information with sensory evidence by weighting the latter in accordance with reliability. To test this theory, we manipulated the prior probability of the rewarded choice while subjects performed a reaction-time discrimination of motion direction using a range of stimulus reliabilities that varied from trial to trial. The theory explains the effect of prior probability on choice and reaction time over a wide range of stimulus strengths. We found that prior probability was incorporated into the decision process as a dynamic bias signal that increases as a function of decision time. This bias signal depends on the speed-accuracy setting of human subjects, and it is reflected in the firing rates of neurons in the lateral intraparietal area (LIP) of rhesus monkeys performing this task.


Assuntos
Tomada de Decisões/fisiologia , Discriminação Psicológica/fisiologia , Percepção de Movimento/fisiologia , Probabilidade , Tempo de Reação/fisiologia , Percepção do Tempo/fisiologia , Potenciais de Ação/fisiologia , Animais , Viés , Feminino , Humanos , Macaca mulatta , Masculino , Modelos Psicológicos , Neurônios/fisiologia , Lobo Parietal/citologia , Estimulação Luminosa/métodos , Psicofísica , Análise de Regressão
19.
Nature ; 442(7103): 692-5, 2006 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-16878143

RESUMO

The inferior temporal cortex (IT) of primates is thought to be the final visual area in the ventral stream of cortical areas responsible for object recognition. Consistent with this hypothesis, single IT neurons respond selectively to highly complex visual stimuli such as faces. However, a direct causal link between the activity of face-selective neurons and face perception has not been demonstrated. In the present study of macaque monkeys, we artificially activated small clusters of IT neurons by means of electrical microstimulation while the monkeys performed a categorization task, judging whether noisy visual images belonged to 'face' or 'non-face' categories. Here we show that microstimulation of face-selective sites, but not other sites, strongly biased the monkeys' decisions towards the face category. The magnitude of the effect depended upon the degree of face selectivity of the stimulation site, the size of the stimulated cluster of face-selective neurons, and the exact timing of microstimulation. Our results establish a causal relationship between the activity of face-selective neurons and face perception.


Assuntos
Face/anatomia & histologia , Macaca mulatta/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Lobo Temporal/fisiologia , Envelhecimento , Animais , Viés , Estimulação Elétrica , Modelos Neurológicos , Neurônios/fisiologia , Estimulação Luminosa , Lobo Temporal/citologia , Fatores de Tempo
20.
Nat Neurosci ; 11(6): 693-702, 2008 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-18488024

RESUMO

Simple perceptual tasks have laid the groundwork for understanding the neurobiology of decision-making. Here, we examined this foundation to explain how decision-making circuitry adjusts in the face of a more difficult task. We measured behavioral and physiological responses of monkeys on a two- and four-choice direction-discrimination decision task. For both tasks, firing rates in the lateral intraparietal area appeared to reflect the accumulation of evidence for or against each choice. Evidence accumulation began at a lower firing rate for the four-choice task, but reached a common level by the end of the decision process. The larger excursion suggests that the subjects required more evidence before making a choice. Furthermore, on both tasks, we observed a time-dependent rise in firing rates that may impose a deadline for deciding. These physiological observations constitute an effective strategy for handling increased task difficulty. The differences appear to explain subjects' accuracy and reaction times.


Assuntos
Tomada de Decisões/fisiologia , Discriminação Psicológica/fisiologia , Neurônios/fisiologia , Lobo Parietal/citologia , Comportamento Espacial/fisiologia , Potenciais de Ação/fisiologia , Animais , Comportamento Animal , Movimentos Oculares/fisiologia , Haplorrinos , Movimento (Física) , Tempo de Reação/fisiologia , Análise de Regressão , Análise e Desempenho de Tarefas
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