We screened a larger number of participants (N = 15, seven female) with a shorter version of the experiment, before the above described training was given. The data from these screening sessions can be found in Appendix B (Figure A2 and Figure A3). Performance was highly variable and frequently very poor. The first six of these participants (three female, chosen by order of recruitment only) went on to complete the training blocks and then the main experiment. Two participants (S1, S2) were lab members and experienced participants in psychophysical experiments, and although not naive as to the purpose of the experiment, they had no prior experience with the specific stimuli used. The other participants were naive volunteers, who were compensated at £5/h for their time. Some of them had prior experience with psychophysical experiments using depth and motion but no exposure to this particular type of experiment or understanding of its purpose. All participants had normal or corrected to normal vision and passed the TNO test. The experimental procedures used were in accordance with the declaration of Helsinki and approved by the St Andrews University Teaching and Research Ethics Committee (Ethics code: PS11472). All participants provided written informed consent before participating in the study