Effect of Probe-Item Similarity

<div><p>(A) A schematic diagram of four stimulus conditions. These examine effects of summed probe-item similarity on participants' report of having seen a stimulus. Conditions a–d keep inter-item homogeneity constant (pairs a & b and c & d) while changing summed probe-item similarity. These diagrams show the relationships between conditions, rather than the actual values stimuli may take. Throughout, summed probe-item similarity is denoted in green, whereas inter-item similarity is denoted in blue. Conditions in the first row have high summed similarity (indicated by the shorter green solid bars). These are identical to their pairs (b and d, respectively) in the second row in terms of inter-item homogeneity (indicated by the length of the blue dashed bar), and similarity of the probe to the closest item (shorter of the two green solid bars). The second row shows cases of lower summed similarity (longer green solid bars).</p> <p>(B) The results of the experiment. For each pair of otherwise matched stimuli, when summed similarity is larger, participants are more likely to indicate that a probe has been seen before (<i>p</i> < 0.01). These box plots show the median (thick bar), and boxes include the middle 50% of data. The whiskers include all data points that are not outliers. Outliers are shown as circles, and defined as those points more than 1.5 times the interquartile range from the median. Light and dark green indicate high (conditions a & c) and low (conditions b & d) summed similarity, respectively.</p>