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Appendix

Discrimination task

Proportion of ‘different’ responses in the successive discrimination task for each stepsize, trial type (i.e., between-category vs. within-category), and morph series separately, averaged across participants. Bars indicate the empirical proportions for responding ‘different’. The black dots indicate the mean posterior predictions from the model and the error bars indicate the 95% highest density continuous intervals (HDCI) of the posterior predictive distributions. In this figure, the difference between the darker and the lighter bars (i.e., the category boundary effect: more ‘different’ responses for between-category compared to within-category pairs, keeping stepsize equal) is on average higher for the recognizable than for the non-recognizable morph series. Note. In the interactive version of this figure, you can hover over the colored bars to see the exact percentage different responses, the mean and 95% HDCI of the posterior predictive distributions, and the number of trials related to each bar.




Posterior distributions for the intercept (A) and the effect of stepsize (B) on the probability of responding ‘different’ in the successive discrimination task, for each morph series separately, in logodds units. Black dots and intervals indicate the mean, 66%, and 95% highest density continuous interval (HDCI) for each intercept or slope value. The colored dashed vertical lines indicate the estimated mean value per type of morph series (recognizable vs. non-recognizable). In this figure, the estimated effect of stepsize is larger for the recognizable than for the non-recognizable morph series. Note. In the interactive version of this figure, you can hover over the intervals to see the related mean and 95% HDCI for each distribution.




Estimated pairwise differences between the posterior distributions for the effect of stepsize on the probability of responding ‘different’ in the successive discrimination task for each of the different recognizable and non-recognizable morph series combinations, in logodds units. Black dots and intervals indicate the mean, 66%, and 95% highest density continuous interval (HDCI) for each slope or difference value. The black vertical line indicates a difference in slope of zero. In this figure, the estimated effect of stepsize is larger for the recognizable than for the non-recognizable morph series. Note. In the interactive version of this figure, you can hover over the intervals to see the related mean and 95% HDCI for each distribution.




Posterior distributions for the intercept (A), effect of stepsize (B), effect of trial type (C), and interaction between stepsize and trial type (D) on the probability of responding ‘different’ in the successive discrimination task, for each morph series separately, in logodds units. Black dots and intervals indicate the mean, 66%, and 95% highest density continuous interval (HDCI) for each intercept or slope value. The colored dashed vertical lines indicate the estimated mean value per type of morph series (recognizable vs. non-recognizable). The black vertical line indicates a difference in slope of zero. In this figure, the estimated effect of stepsize is larger for the recognizable than for the non-recognizable morph series (B). The main effect of trial type is larger for the recognizable series car-tortoise and penguin-child than for all non-recognizable morph series (C). The interaction effect between stepsize and trial type is more negative for the recognizable series penguin-child than for all non-recognizable series (D). Note. In the interactive version of this figure, you can hover over the intervals to see the related mean and 95}% HDCI for each distribution.




Proportion of ‘different’ responses in the successive discrimination task for each stepsize, ordered stimulus pair, and morph series separately, averaged across participants. Stimulus pairs are ordered per stepsize and from left to right in the morph series as presented in Figure 3. Bars indicate the empirical proportions for responding ‘different’. The black dots indicate the mean posterior predictions from the model and the grey error bars indicate the 95% highest density continuous intervals (HDCI) of the posterior predictive distributions. In this figure, no clear directional asymmetries (i.e., differences in discrimination performance based on the presentation order of the stimuli in the pair) are present. Note. In the interactive version of this figure, you can hover over the colored bars to see the stimuli involved in the pair (in the presented order from left to right), the exact percentage different responses, the mean and 95% HDCI of the posterior predictive distributions, and the number of trials related to each bar.




Similarity judgment task

Standardized similarity scores for each stepsize, trial type (i.e., between-category vs. within-category), and morph series separately, averaged across participants. Grey dots indicate the raw standardized similarity scores. For the conditions that contain less trials, these grey dots are not always clearly visible. The colored dots and error bars indicate the mean posterior predictions from the model and the 95% highest density continuous interval (HDCI) of the posterior predictive distributions. In this figure, the difference between the darker and the lighter intervals (i.e., the category boundary effect: between-category pairs rated as less similar than within-category pairs, keeping stepsize equal) is on average larger for the recognizable than for the non-recognizable morph series. Note. In the interactive version of this figure, you can hover over the intervals to see the exact similarity score, the mean and 95% HDCI of the posterior predictive distributions, and the number of trials related to each interval.




Posterior distributions for the intercept (A) and the effect of stepsize (B) on the standardized similarity scores, for each morph series separately. Black dots and intervals indicate the mean, 66%, and 95% highest density continuous interval (HDCI) for each intercept or slope value. The colored dashed vertical lines indicate the estimated mean value per type of morph series (recognizable vs. non-recognizable). In this figure, the estimated effect of stepsize is larger (i.e., more different from zero) for the recognizable than for the non-recognizable morph series. Note. In the interactive version of this figure, you can hover over the intervals to see the related mean and 95% HDCI for each distribution.




Estimated pairwise differences between the posterior distributions for the effect of stepsize on the standardized similarity scores for each of the different recognizable and non-recognizable morph series combinations. Black dots and intervals indicate the mean, 66%, and 95% highest density continuous interval (HDCI) for each slope or difference value. The black vertical line indicates a difference in slope of zero. In this figure, the estimated effect of stepsize is larger (i.e., more different from zero) for the recognizable than for the non-recognizable morph series. Note. In the interactive version of this figure, you can hover over the intervals to see the related mean and 95% HDCI for each distribution.




Posterior distributions for the intercept (A), effect of stepsize (B), effect of trial type (C), and interaction between stepsize and trial type (D) on the standardized similarity scores, for each morph series separately. Black dots and intervals indicate the mean, 66%, and 95% highest density continuous interval (HDCI) for each intercept or slope value. The colored dashed vertical lines indicate the estimated mean value per type of morph series (recognizable vs. non-recognizable). The black vertical line indicates a difference in slope of zero. In this figure, the estimated effect of stepsize is larger (i.e., more different from zero) for the recognizable than for the non-recognizable morph series (B). The main effect of trial type is larger (i.e., more different from zero) for the recognizable series car-tortoise and penguin-child than for all non-recognizable morph series (C). The interaction effect between stepsize and trial type is larger (i.e., more different from zero) for the recognizable series watch-seahorse than for all non-recognizable series (D). Note. In the interactive version of this figure, you can hover over the intervals to see the related mean and 95% HDCI for each distribution.




Posterior predictive distributions for the responses to the successive similarity judgment task, for each morph series, stepsize, and ordered stimulus pair separately. Colored dots and error bars indicate the mean posterior predictions from the model and the 95% highest density continuous intervals of the posterior predictive distributions. In this figure, no clear directional asymmetries (i.e., differences in perceived similarity based on the presentation order of the stimuli in the pair) are present. Note. In the interactive version of this figure, you can hover over the mean posterior predictions to see the exact percentage different responses and the number of trials related to each data point.