The decision to stop "counting" explains numerical underproduction in primates.

In two trained rhesus macaques, instructed numerical production shows a systematic underproduction bias (more often than overproduction), with longer reaction times for underproduced sequences.

• Why it matters: The mechanisms that decide when counting sequences stop are unclear, yet they shape how accurately animals generate target numbers of actions.
• What they did: The monkeys produced instructed numerosities from sign numerals or dot arrays while action timing was controlled; accuracy and reaction times were fit with a stochastic accumulation-to-bound stopping model.
• The result: The model explains both the underproduction-overproduction asymmetry and the reaction-time differences, supporting a sequential stopping process underlying numerical production.

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