School of Psychology, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
Chem Senses. 2014 Mar;39(3):229-41. doi: 10.1093/chemse/bjt073. Epub 2013 Dec 27.
Psychometric functions are predominately used for estimating detection thresholds in vision and audition. However, the requirement of large data quantities for fitting psychometric functions (>30 replications) reduces their suitability in olfactory studies because olfactory response data are often limited (<4 replications) due to the susceptibility of human olfactory receptors to fatigue and adaptation. This article introduces a new method for fitting individual-judge psychometric functions to olfactory data obtained using the current standard protocol-American Society for Testing and Materials (ASTM) E679. The slope parameter of the individual-judge psychometric function is fixed to be the same as that of the group function; the same-shaped symmetrical sigmoid function is fitted only using the intercept. This study evaluated the proposed method by comparing it with 2 available methods. Comparison to conventional psychometric functions (fitted slope and intercept) indicated that the assumption of a fixed slope did not compromise precision of the threshold estimates. No systematic difference was obtained between the proposed method and the ASTM method in terms of group threshold estimates or threshold distributions, but there were changes in the rank, by threshold, of judges in the group. Overall, the fixed-slope psychometric function is recommended for obtaining relatively reliable individual threshold estimates when the quantity of data is limited.
心理物理函数主要用于估计视觉和听觉中的检测阈值。然而，拟合心理物理函数的要求大量数据（>30 次重复）降低了它们在嗅觉研究中的适用性，因为由于人类嗅觉受体对疲劳和适应的敏感性，嗅觉反应数据通常有限（<4 次重复）。本文介绍了一种新的方法，用于拟合使用当前标准协议 - 美国测试与材料协会（ASTM）E679 获得的嗅觉数据的个体判断心理物理函数。个体判断心理物理函数的斜率参数固定为与组函数相同；仅使用截距拟合相同形状的对称 S 形函数。本研究通过与两种可用方法进行比较来评估所提出的方法。与传统心理物理函数（拟合斜率和截距）的比较表明，固定斜率的假设不会影响阈值估计的精度。在组阈值估计或阈值分布方面，提出的方法与 ASTM 方法之间没有系统差异，但在组中，按阈值划分的法官的等级发生了变化。总体而言，当数据量有限时，建议使用固定斜率的心理物理函数来获得相对可靠的个体阈值估计。
