Abstract
Over the past few decades, researchers have firmly established that a wide range of nonhuman animals exhibit some form of numerical competence. The focus of this research was to define further the extent of numerical ability in rhesus monkeys, and specifically to determine whether the animals possess a symbolic understanding of Arabic numerals. This required examining the stimulus attributes (e.g., number vs. hedonic value) represented by the numerals, as well as the precision (e.g., absolute vs. relative) and generality of those representations. In chapters 2 and 3, monkeys were required to compare and order numerals and were rewarded with either proportional or probabilistic rewards. The results indicated that monkeys were relying on the ordinal or absolute numerical values associated with each numeral and not hedonic value or learned 2-choice discriminations. The studies in chapters 4 and 5 indicated that monkeys can use numerals to symbolize an approximate number of sequential motor responses. The study in Chapter 6 tested the generality of the monkeys’ symbolic number concept using transfer tests. The results indicated that some monkeys are able to abstract number across presentation mode, but this ability is only exhibited under limited conditions. Collectively, these studies provide evidence that rhesus monkeys view Arabic numerals as more than sign-stimuli associated with specific response-reward histories, but that numerals do not have the same precise symbolic meaning as they do for humans.
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