CRCNS:Investigating perceptual processing speed and its impact on choice behavior

描述(由申请人提供)：选择行为的神经生物学已经通过实验室任务进行了深入的研究，在实验室任务中，受试者做出知觉判断，并用运动动作指示结果。因此，心理物理和神经生理学的联合实验已经将知觉决策能力表征为信号质量、强度和主观价值的函数，并揭示了许多潜在的神经回路及其特定的作用。然而，时间的根本问题要难得多：与执行运动动作来报告判断相比，做出感性判断需要多长时间？受试者在什么时间点致力于特定的选择，是什么神经机制决定了这一点？这些问题与许多需要快速选择的现实情况有关；例如，当司机看到红绿灯时，必须根据灯的颜色迅速决定是踩刹车还是踩油门。但准确的计时测量是复杂的，因为它们受到许多感觉和运动因素的影响，例如准备好、动机、任务难度和速度与准确性的权衡。因此，目前关于知觉决策的时间动态的知识相当粗糙。该项目中的PI最近开发了一项消除这些混淆的任务，并产生了一种新的心理物理测量--测速曲线，它分离出受试者的感知处理能力，并以前所未有的时间分辨率对其进行量化。他们还构建了一个计算模型，非常详细地再现了受试者的行为。新的范式和模型将共同用于研究知觉判断的时机及其神经基础。具体的模型预测将通过单神经元记录和猴子额叶眼场(FEF)内的微刺激来测试，这些猴子被训练成在各种条件下执行这项任务。有三个具体目标。目的1：检验知觉加工速度的变化表现为测速曲线斜率的变化(心理上)和眼球运动活动的加速(神经上)的假设。根据该模型，与眼跳选择相关的测速曲线和眼球运动活动应该以特定的方式取决于知觉困难。为了测量这种依赖性，受试者将执行同一选择任务的3个版本，根据要区分的不同刺激特征，这些版本的知觉难度会有所不同。目的2：检验一种假设，即当知觉加工速度保持不变时，即使其他心理物理性能指标发生变化，测速曲线的斜率和眼动活动的加速度也将保持不变。因此，这些实验是对目标1的补充。受试者将执行四种不同的选择任务，其中知觉难度将被固定，但与两种可能的运动反应相关的可能性和奖励将有所不同。受试者的表现水平、反应时间和选择比例预计会在四种情况下发生巨大变化，但感知加工速度的测量相关性不应如此。目的3：检验这样一种假设，即FEF中激活水平的整体增加会改变受试者做出选择的时间和准确性，但不会改变观察到的知觉加工速度。亚阈值微刺激电流将在任务执行过程中的不同时间点注入FEF。问题是，被唤起的活动是否被解释为纯粹的运动信号，或者它是否对受试者的感知处理能力有直接影响。智力优势：拟议的实验跟踪受试者的知觉表现是如何及时展开的，并为研究选择是如何做出的开辟了一条全新的途径。这将有可能(1)确定各种认知因素，如注意力、动机、运动准备和知觉处理速度对受试者测量的心理物理表现的具体贡献，(2)调查在选择任务中神经元活动如何与这些因素中的每一个相关，以及(3)揭示这种神经元活动的时间进程如何与受试者选择准确性的时间进程相关。更广泛的影响：(1)教学。这项研究的结果会纳入督导主任所教授的课程。(2)教育。辅修神经科学的本科生将在PIS的实验室获得研究学术学分。一名研究生和一名博士后将发展电生理学和计算的综合技能。(3)科学认识。预计结果将得到广泛讨论和传播。(4)加强研究基础设施。将购买尖端设备，用于这一项目和未来的项目。(五)社会效益。这种新颖的任务设计有可能适用于人类受试者，并成为一种强大的诊断工具，可以用来阐明特定的神经回路或大脑‘模块’是如何受到特定精神障碍的影响的。

DESCRIPTION (provided by applicant): The neurobiology of choice behavior has been intensely studied with laboratory tasks in which a subject makes a perceptual judgement and indicates the result with a motor action. Combined psychophysical and neurophysiological experiments have thus characterized perceptual decision-making capacity as a function of signal quality, strength, and subjective value, and have revealed many of the underlying neural circuits and their specific roles. However, the fundamental question of timing has been much harder to tackle: how long does it take to make a perceptual judgment, versus executing a motor action to report that judgment? At what point in time is a subject committed to a particular choice, and what neural mechanisms determine that? These issues are relevant to many real-life situations that require quick choices; for instance, when a driver sees a traffic light and must rapidly decide whether to step on the brake or the accelerator, depending on the light's color. But making accurate timing measurements is complicated because they are affected by numerous sensory and motor factors, such as readiness, motivation, task difficulty and speed-accuracy trade-offs. Consequently, current knowledge about the temporal dynamics of perceptual decision-making is rather crude. The PIs in this project recently developed a task that eliminates these confounds and produces a new psychophysical measure, the tachometric curve, which isolates a subject's perceptual processing capacity and quantifies it with unprecedented temporal resolution. They have also constructed a computational model that reproduces the subjects' behavior with great detail. The new paradigm and the model will be used jointly to investigate the timing of perceptual judgments and its neural basis. Specific model predictions will be tested via single-neuron recording and microstimulation within the Frontal Eye Field (FEF) of monkeys trained to perform the task under a variety of conditions. There are three specific aims. Aim 1: To test the hypothesis that changes in perceptual processing speed are manifested as changes in the slope of the tachometric curve (psychophysically) and in the acceleration of the oculomotor activity associated with a saccadic choice (neurally). According to the model, the tachometric curve and the oculomotor activity associated with saccadic choices should depend in specific ways on perceptual difficulty. To measure this dependency, subjects will perform 3 versions of the same choice task that will vary in perceptual difficulty according to different stimulus features to be discriminated. Aim 2: To test the hypothesis that when perceptual processing speed remains constant, both the slope of the tachometric curve and the acceleration of the oculomotor activity will stay constant as well, even if other measures of psychophysical performance do change. These experiments are thus complementary to those of Aim 1. Subjects will perform 4 variants of the choice task in which perceptual difficulty will be fixed but the likelihoods and rewards associated with the two possible motor responses will vary. The subject's performance level, reaction times and proportions of choices are expected to change drastically across the 4 conditions, but the measured correlates of perceptual processing speed should not. Aim 3: To test the hypothesis that an overall increase in the level of activation in FEF alters the timing and accuracy of a subject's choices, but not the observed perceptual processing speed. Subthreshold microstimulation current will be injected into the FEF at different points in time during task performance. The question is whether the evoked activity is interpreted as a purely motor signal or if it has a direct impact on the subject's perceptual processing capacity. Intellectual merit: The proposed experiments track how a subject's perceptual performance unfolds in time, and open up an entirely new avenue for investigating how choices are made. It will be possible (1) to determine the specific contributions of various cognitive factors such as attention, motivation, motor preparation, and perceptual processing speed to a subject's measured psychophysical performance, (2) to investigate how neuronal activity is related to each of these factors during a choice task, and (3) to reveal how the time course of this neuronal activity correlates with the time course of a subject's choice accuracy. Broader impacts: (1) Teaching. The results of this study will be incorporated into courses taught by the PIs. (2) Education. Undergraduate students with a minor in neuroscience will be hosted for research academic credit in the PIs' laboratories. A graduate student and a postdoctoral fellow will develop combined electrophysiological and computational skills. (3) Scientific understanding. The results are expected to be widely discussed and disseminated. (4) Enhancement of infrastructure for research. Cutting-edge equipment will be acquired for use in this and future projects. (5) Benefits to society. The novel task design has the potential to be adapted to human subjects and become a powerful diagnostic tool for elucidating how specific neural circuits or brain 'modules' are compromised by a given mental disorder.