On the limits of the matching concept in monkeys (Cebus apella).
Capuchin monkeys can learn a matching rule, yet fail the moment the pictures start to move.
01Research in Context
What this study did
Three capuchin monkeys with years of matching practice learned a same-different rule with still pictures.
Next the team switched to moving shapes on a screen. They gave the monkeys 12 000 extra trials to see if the old rule would carry over.
What they found
The monkeys never transferred the rule. They scored no better than chance when the pictures started to move.
Even long training could not make the leap from static to dynamic stimuli.
How this fits with other research
Ghosh et al. (2004) saw the opposite with pigeons. The birds learned a dog-versus-cat rule and then passed tests with blended morphs.
Ribeiro et al. (2024) also got good news. College students expanded equivalence classes when they solved quick math problems during the delay.
The three studies line up to show a gap: pigeons and people generalize, but monkeys stall when the physical format changes.
Why it matters
When you teach a new discrimination, do not assume the learner sees the same "concept" you do. Test with many formats—still, moving, color, black-and-white—before you call it mastered. A quick probe trial with altered stimuli can save weeks of retraining later.
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02At a glance
03Original abstract
Two cebus monkeys, with many years of experience matching a variety of static visual stimuli (forms and colors) within a standard matching-to-sample paradigm, were trained to press a left lever when a pair of displayed static stimuli were the same and to press a right lever when they were different. After learning the same/different task, the monkeys were tested for transfer to dynamic visual stimuli (flashing versus steady green disks), with which they had no previous experience. Both failed to transfer to the dynamic stimuli. A third monkey, also with massive past experience matching static visual stimuli, was tested for transfer to the dynamic stimuli within our standard matching paradigm, and it, too, failed. All 3 subjects were unable to reach a moderate acquisition criterion despite as many as 52 sessions of training with the dynamic stimuli. These results provide further evidence that, in monkeys, the matching (or identity) concept has a very limited reach; they consequently do not support the view held by some theorists that an abstract matching concept based on physical similarity is a general endowment of animals.
Journal of the experimental analysis of behavior, 1989 · doi:10.1901/jeab.1989.52-225