Figure 1.  Rote memory categorization experiment by Heinemann, Ionescu, Stevens and Neiderbach. The pictures were randomly assigned to two categories without a unifying “concept” on which key choice could be based. Sessions were 80 trials in length with the pictures presented in a different random order within each session. Training began with 80 pictures. When errors fell below a proportion of 0.15 the number of pictures in the set was increased to 160, then to 320 and finally to 640. The final set of 640 pictures required eight sessions for a single exposure.