What do Arabic numerals mean to macaques (Macaca mulatta)?

In the past, rhesus macaques (Macaca mulatta) have demonstrated an ability to use Arabic numerals to facilitate performance in a variety of tasks. However, it remained unclear whether they understood the absolute and relative values of numerals. In Experiment 1, numeral-trained macaques picked the larger stimuli when presented with pairwise comparisons involving numerals and analog quantities.

Perception of Food Amounts by Chimpanzees Based on the Number, Size, Contour Length and Visibility of Items.

Nonhuman animals reliably select the largest of two or more sets of discrete items, particularly if those items are food items. However, many studies of these numerousness judgments fail to control for confounds between amount of food e.g.

When in doubt, chimpanzees rely on estimates of past reward amounts.

Many animals can repeatedly judge the larger of two sets of food items. However, it remains unclear as to what information might accrue regarding the relative rates of return from these repeated responses. Information about overall rates of return is, in fact, unnecessary to perform well at the task itself.

Quantity judgments of sequentially presented food items by capuchin monkeys (Cebus apella).

Recent assessments have shown that capuchin monkeys, like chimpanzees and other Old World primate species, are sensitive to quantitative differences between sets of visible stimuli. In the present study, we examined capuchins' performance in a more sophisticated quantity judgment task that required the ability to form representations of food quantities while viewing the quantities only one piece at a time. In three experiments, we presented monkeys with the choice between two sets of discrete homogeneous food items and allowed the monkeys to consume the set of their choice.

Ordinal judgments of symbolic stimuli by capuchin monkeys (Cebus apella) and rhesus monkeys (Macaca mulatta): the effects of differential and nondifferential reward.

Ordinal learning was investigated in capuchin monkeys (Cebus apella) and rhesus monkeys (Macaca mulatta). In Experiment 1, both species were presented with pairings of the Arabic numerals 0 to 9. Some monkeys were given food rewards equal to the value of the numeral selected and some were rewarded with a single pellet only for choosing the higher numeral within the pair.

Summation and quantity judgments of sequentially presented sets by capuchin monkeys (Cebus apella).

Capuchin monkeys (Cebus apella) were presented with two sets of food items, identical in food type but differing in number. Animals selected one set and were permitted to consume their choice. Set sizes ranged from 1 to 6 items.

Rhesus monkeys (Macaca mulatta) select Arabic numerals or visual quantities corresponding to a number of sequentially completed maze trials.

Four number-trained rhesus monkeys were trained to enumerate their sequential responses. After completing a series of computerized maze trials, the monkeys were given a same/different discrimination involving a numerical stimulus (an Arabic numeral or a visual quantity) and the letter D. The goal was to choose the numerical stimulus if it matched the number ofjust-completed maze trials, and to choose the letter D if it did not.

Ordinal-list integration for symbolic, arbitrary, and analog stimuli by rhesus macaques (Macaca mulatta).

Two numeral-trained monkeys learned to produce 3 5-item lists of Arabic numerals, colors, and arbitrary signs in the correct sequence. The monkeys then responded at above-chance levels when the authors tested them with nonrewarded pair-wise comparisons of items from different lists, indicating their use of ordinal-position information. The authors also tested the monkeys with nonrewarded pair-wise comparisons of an analog quantity and an item from 1 of the 3 learned lists.

Ordinal judgments and summation of nonvisible sets of food items by two chimpanzees and a rhesus macaque.

Two chimpanzees and a rhesus macaque rapidly learned the ordinal relations between 5 colors of containers (plastic eggs) when all containers of a given color contained a specific number of identical food items. All 3 animals also performed at high levels when comparing sets of containers with sets of visible food items. This indicates that the animals learned the approximate quantity of food items in containers of a given color.

Macaques' (Macaca mulatta) use of numerical cues in maze trials.

We tested the ability of number-trained rhesus monkeys to use Arabic numeral cues to discriminate between different series of maze trials and anticipate the final trial in each series. The monkeys' prior experience with numerals also allowed us to investigate spontaneous transfer between series. A total of four monkeys were tested in two experiments.