Perception of food amounts by chimpanzees based on the number, size, contour length and visibility of items

Abstract

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., mass or volume) and number of food items. Stimulus dimensions other than number of items also may play a role in how animals perceive sets and make choices. Four chimpanzees (Pan troglodytes) completed a variety of tasks that involved comparisons of food items (graham crackers) that varied in terms of their number, size, and orientation. In Experiment 1, chimpanzees chose between two alternative sets of visible cracker pieces. In Experiment 2, the experimenters presented one set of crackers in a vertical orientation (stacked) and the other in a horizontal orientation. In Experiment 3, the experimenters presented all food items one-at-a-time by dropping them into opaque containers. Chimpanzees succeeded overall in choosing the largest amount of food. They did not rely on number or contour length as cues when making these judgments but instead primarily responded to the total amount of food in the sets. However, some errors reflected choices of the set with the smaller total amount of food but the individually largest single food item. Thus, responses were not optimal because of biases that were not related to the total amount of food in the sets.

Quantitative abilities in a reptile ( Podarcis sicula )

“…Hence, we could hypothesize an advantage for the individual that detects and consumes the largest prey first. As suggested in other species [2,5], natural selection might have favoured decision mechanisms that prioritize the search for larger prey instead of the search for patches containing more overall prey.…”

“…However, there is no reason to believe that the selective pressures in favour of the ability to estimate different quantities should not have acted on this vertebrate group. To fill this gap, we investigated quantitative abilities in ruin lizards (Podarcis sicula) using the most common procedure adopted in this field, a free choice test in the presence of food items differing in quantity [2][3][4][5]9]. In detail, in Experiment 1 we tested whether lizards attempt to maximize the amount of food intake.…”

“…hyenas, Crocuta crocuta, [1]) and provides an advantage in foraging decisions as several mammals, birds, amphibians and fish maximize their energy intake by selecting the larger group of food items available (e.g. chimpanzees, Pan troglodytes, [2]; pigeons, Columba livia, [3]; salamanders, Plethodon cinereus, [4]; and guppies, Poecilia reticulata, [5]). Quantitative abilities are essential for both prey and predator survival.…”

Numerical assessment in the wild: insights from social carnivores

“…Researchers in these fields have found that the ability to discriminate between different numbers of objects appears to be a foundational cognitive ability and have documented this ability in numerous species across the Animal Kingdom. For example, quantity discrimination has been demonstrated experimentally in several species of fish [5,11,[19][20][21], amphibians [8,22,23], birds [18,[24][25][26][27][28][29][30][31][32][33][34][35], mammals [9,[36][37][38][39][40][41], primates [42][43][44][45], human infants [46][47][48][49] and even some invertebrates [50][51][52]. The only study testing quantity discrimination in a reptile found that although ruin lizards (Podarcis sicula) do spontaneously select the larger quantity of food, they do not spontaneously select the option with a higher number of food items [53].…”

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

“…The primates are particularly well studied in these kinds of tests, and they accurately judge discrete quantities and continuous quantities (e.g. Boysen & Berntson 1995;Brannon & Terrace 2000;Hauser et al 2000;Beran & Beran 2004;Cantlon & Brannon 2006;Suda & Call 2006;vanMarle et al 2006;Hanus & Call 2007;Tomonaga 2007;Beran et al 2008a).…”