Stochastic designs in event-related fMRI
Stochastic designs in event-related fMRI
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DOI：
10.1006/nimg.1999.0498
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发表时间：
1999-11-01
期刊：
影响因子：
5.7
通讯作者：
Dale, AM
中科院分区：
文献类型：
--
作者：
Friston, KJ;Zarahn, E;Dale, AM
本文从刺激或试验呈现的最佳时间模式的角度考虑了与事件相关的fMRI设计的效率。“随机”和“确定性”之间的区别用于区分根据事件在一系列时间点发生的概率来指定的设计（随机）和事件总是在预先指定的时间发生的设计（确定性）。随机设计可能是“平稳的”，其中概率是恒定的，或者是非平稳的，其中概率随时间变化。所有这些设计都可以用一个发生概率向量和一个原型设计矩阵来参数化，原型设计矩阵体现了约束条件（如最小刺激开始的异步性）和血流动力学响应模型。给出了这些参数的一个简单函数，并用于比较不同设计的相对效率。缓慢调制发生概率的设计通常比平稳设计更有效。有趣的是，最有效的设计是传统的块设计。本文提出的一个关键点是，对一种效果最有效的设计可能对另一种效果并不最有效。在考虑诱发反应和反应之间的差异时，这一点尤为重要。与差异反应相反，最有效的诱发反应设计要求在达到基线水平的无试验期。在随机、快速呈现设计的背景下，这相当于包含“零事件”。(C) 1999学术出版社。
This article considers the efficiency of event-related fMRI designs in terms of the optimum temporal pattern of stimulus or trial presentations. The distinction between "stochastic" and "deterministic" is used to distinguish between designs that are specified in terms of the probability that an event will occur at a series of time points (stochastic) and those in which events always occur at prespecified time (deterministic). Stochastic designs may be "stationary," in which the probability is constant, or nonstationary, in which the probabilities change with time. All these designs can be parameterized in terms of a vector of occurrence probabilities and a prototypic design matrix that embodies constraints (such as the minimum stimulus onset asynchrony) and the model of hemodynamic responses. A simple function of these parameters is presented and used to compare the relative efficiency of different designs. Designs with slow modulation of occurrence probabilities are generally more efficient than stationary designs. Interestingly the most efficient design is a conventional block design. A critical point, made in this article, is that the most efficient design for one effect may not be the most efficient for another. This is particularly important when considering evoked responses and the differences among responses. The most efficient designs for evoked responses, as opposed to differential responses, require trial-free periods during which baseline levels can be attained. In the context of stochastic, rapid-presentation designs this is equivalent to the inclusion of "null events." (C) 1999 Academic Press.