Wang Penghan, Reynaud Alexandre
McGill Vision Research Unit, Department of Ophthalmology & Visual Sciences, McGill University, Montreal, QC H3G 1A4, Canada.
Vision (Basel). 2023 Nov 15;7(4):74. doi: 10.3390/vision7040074.
Points of Subjective Equality (PSE) are commonly measured using staircase or constant stimuli methods. However, the staircase method is highly dependent on the step size, and the constant stimuli method is time-consuming. Thus, we wanted to develop an efficient and quick method to estimate both the PSE and the slope of the psychometric function. We developed a random-step algorithm in which a one-up-one-down rule is followed but with a random step size in a pre-defined range of test levels. Each stimulus would be chosen depending on the previous response of the subject. If the subject responded "up", any random level in the lower range would be picked for the next trial. And if the subject responded "down", any random level in the upper range would be picked for the next trial. This procedure would result in a bell-shaped distribution of the test levels around the estimated PSE, while a substantial amount of trials would still be dispersed at both bounds of the range. We then compared this method with traditional constant stimuli procedure on a task based on the Pulfrich phenomenon while the PSEs of participants could be varied using different neutral density filters. Our random-step method provided robust estimates of both the PSE and the slope under various noise levels with small trial counts, and we observed a significant correlation between the PSEs obtained with the two methods. The random-step method is an efficient way to measure the full psychometric function when testing time is critical, such as in clinical settings.
主观相等点（PSE）通常使用阶梯法或恒定刺激法进行测量。然而，阶梯法高度依赖于步长，而恒定刺激法耗时较长。因此，我们希望开发一种高效快速的方法来估计PSE和心理测量函数的斜率。我们开发了一种随机步长算法，该算法遵循一上一下规则，但步长在预先定义的测试水平范围内是随机的。每个刺激将根据受试者的先前反应来选择。如果受试者回答“向上”，则在下一次试验中从较低范围内选择任何随机水平。如果受试者回答“向下”，则在下一次试验中从较高范围内选择任何随机水平。这个过程将导致测试水平围绕估计的PSE呈钟形分布，而大量试验仍将分散在范围的两端。然后，我们在基于普费里希现象的任务中，将这种方法与传统的恒定刺激程序进行了比较，同时可以使用不同的中性密度滤光片来改变参与者的PSE。我们的随机步长法在各种噪声水平下，只需少量试验就能对PSE和斜率提供可靠的估计，并且我们观察到两种方法获得的PSE之间存在显著相关性。当测试时间至关重要时，例如在临床环境中，随机步长法是测量完整心理测量函数的有效方法。
