Lugtigheid Arthur J, Welchman Andrew E
School of Psychology, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
Vision Res. 2011 Oct 15;51(20):2234-41. doi: 10.1016/j.visres.2011.08.019. Epub 2011 Aug 31.
Many every-day activities necessitate an estimate of the time remaining until an object will hit us: the time-to-contact (TTC). Observers' skill in estimating TTC has been studied by considering the use and combination of key visual signals (e.g. looming and disparity). However, establishing observers' proficiency in estimating TTC can be complicated, as the variable of interest (time) is typically highly correlated with other signals (e.g. target velocity or displacement). As a result, observers' responses may be based on correlates of TTC rather than on TTC itself. Here we evaluate two widely-used TTC tasks: one absolute task in which observers pressed a button to indicate the estimated TTC, and a relative task in which TTC was judged relative to a reference. We test how a wide range of experimental variables that co-vary with TTC contribute to observers' judgments. We systematically vary the correlation between TTC and its covariates and test how psychophysical judgments are affected. We show that for both absolute and relative estimation tasks, observers' responses are best explained on the basis that they judge TTC rather than one (or more) of its covariates. Our results suggest that relative tasks are preferable when assessing TTC, and we suggest a number of analyses methods to ensure that participants' judgements correspond to the variable under investigation.
即接触时间（TTC）。通过考虑关键视觉信号（如逼近和视差）的使用和组合，研究了观察者估计TTC的技能。然而，确定观察者估计TTC的熟练程度可能会很复杂，因为感兴趣的变量（时间）通常与其他信号（如目标速度或位移）高度相关。因此，观察者的反应可能基于TTC的相关因素而非TTC本身。在此，我们评估了两种广泛使用的TTC任务：一种是绝对任务，观察者按下按钮以指示估计的TTC；另一种是相对任务，其中TTC是相对于一个参考值进行判断的。我们测试了与TTC共同变化的各种实验变量如何影响观察者的判断。我们系统地改变TTC与其协变量之间的相关性，并测试心理物理学判断是如何受到影响的。我们表明，对于绝对和相对估计任务，观察者的反应最好基于他们判断的是TTC而非其一个（或多个）协变量来解释。我们的结果表明，在评估TTC时相对任务更可取，并且我们提出了一些分析方法以确保参与者的判断与所研究的变量相对应。
