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. 2012 Jan 12;367(1585):48–58. doi: 10.1098/rstb.2011.0189

Figure 4.

Figure 4.

Experiment 2. (a) The apparatus with the dowel in the 0° orientation. This set-up was used in the demonstration and criterion phase, as well as during the 0° trials of the testing phase. (b) An ape grasps the dowel in preparation to insert and dislodge the goal/reward.