Figure 2.

Human performance on the distance reproduction task exhibits central tendency and bias. (A) Example reproduction data from a representative subject. Open green circles represent individual trials, with blue circles indicating average reproduction distance for a given sample distance and blue lines indicating the best fitting logarithmic curve. If subjects performed the task ideally, without any reliance on the prior, then reproduced distances should lie along the identity line, indicated by (μ Likelihood). Conversely, if subjects rely entirely on the mean of the prior distribution, then responses should lie entirely along the mean of the stimulus set, indicated by (μ Prior). The optimal tradeoff between measurement noise and prior experience results in human responses lying between these two, with an overestimation of the shortest distance and underestimation of the longest distance. Additionally, subjects may also exhibit non‐optimal bias, as the prior distribution for a given subject (μ Subj Prior) may not be veridical to the actual stimulus set. In this example, subject performance matches the actual stimulus set quite well. (B) A second representative subject, who exhibits a large bias in performance. If performance were measured entirely against the stimulus set, then the subject would appear to overestimate every distance. However, this subject may still be exhibiting central tendency, when measured against their own, individual prior distribution (μ Subj Prior). Here, μ Subj Prior is calculated as the mean of the stimulus set, offset by the average reproduced distance; μ Subj Likelihood is calculated as the sample distance, offset by the average reproduced distance. (C) Dependence and independence of performance indices. Mean R _prior correlates well with the slope of the logarithmic curve (m), whereas BIAS correlates with the intercept (b). Crucially, both indices do not correlate with one another, indicating independence. Displayed r values represent Pearson correlation coefficients. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]