Fig 3.

Comparison pecks/sec (± 1 SEM) on the baseline arbitrary matching trials (open circles) and nonreinforced hue–hue probe trials (filled circles) averaged over the eight test sessions for the 3 Group TRANS pigeons in Experiment 1 that did exhibit emergent A–A matching. Positive  =  reinforced arbitrary baseline trials and test trials on which the hue comparison matched the preceding hue sample. Negative  =  nonreinforced arbitrary baseline trials and test trials on which the hue comparison did not match the preceding hue sample. Note that ordinates differ across pigeons.