Green D M
Department of Psychology, University of Florida, Gainesville 32611, USA.
J Acoust Soc Am. 1995 Jun;97(6):3749-60. doi: 10.1121/1.412390.
In most experimental situations, it is expected that observers will achieve perfect detection at extremely high signal levels. Technically, it is assumed that the asymptote of the psychometric function is unity. In many practical psychophysical tests, such as those involving children, patients, or nonhuman animals, the observers are occasionally inattentive. Using computer simulations, it was assumed that inattention can be modeled as a stationary stochastic process whose major effect is to produce a psychometric function having an asymptote less than unity. A maximum-likelihood procedure was used to estimate threshold, because it has been shown to provide reasonably stable threshold estimates using very few observations. Inattention increases the variability of the threshold estimate, as would be expected, because inattention reduces the slope of the psychometric function. The simulations also show that the maximum-likelihood procedure poorly estimates the amount of inattention, and can, thereby, produce a strong bias in the threshold estimates, overestimating or underestimating the true values under different circumstances. Inattention appears to affect the two-alternative forced-choice procedure more strongly than the yes-no (go/nogo) procedure.
在大多数实验情境中，预计观察者在极高信号水平下能实现完美检测。从技术角度讲，假定心理测量函数的渐近线为1。在许多实际的心理物理学测试中，比如涉及儿童、患者或非人类动物的测试，观察者偶尔会注意力不集中。通过计算机模拟，假定注意力不集中可被建模为一个平稳随机过程，其主要影响是产生一个渐近线小于1的心理测量函数。使用最大似然程序来估计阈值，因为已经表明它使用很少的观测值就能提供相当稳定的阈值估计。正如预期的那样，注意力不集中会增加阈值估计的变异性，因为注意力不集中会降低心理测量函数的斜率。模拟还表明，最大似然程序对注意力不集中程度的估计很差，因此可能在阈值估计中产生强烈偏差，在不同情况下高估或低估真实值。与是/否（去/不去）程序相比，注意力不集中似乎对二择一迫选程序的影响更大。
