Size matters: Impact of item size and quantity on array choice by chimpanzees (Pan troglodytes).

Abstract

The authors previously reported that chimpanzees (Pan troglodytes) showed a striking bias to select the larger of 2 candy arrays, despite a reversed reward contingency in which the animals received the smaller, nonselected array as a reward, except when Arabic numerals were used as stimuli. A perceptual or incentive-based interference occurred that was overcome by symbolic stimuli. The authors of the present study examined the impact of element size in choice arrays, using 1 to 5 large and small candies. Five test-sophisticated chimpanzees selected an array from the 2 presented during each trial. Their responses were not optimal, as animals generally selected arrays with larger total mass; thus, they received the smaller remaining array as a reward. When choice stimuli differed in size and quantity, element size was more heavily weighted, although choices reflected total candy mass. These results replicate previous findings showing chimpanzees' difficulties with quantity judgments under reverse reward contingencies and also show that individual item size exerts a more powerful interference effect.

Elephant cognition in primate perspective

“…All elephants chose the basket containing the larger amount, significantly more often than expected by chance, performing at 72-82% accuracy. As in the first experiment, the elephants did not exhibit disparity or magnitude effects, in which performance declines with a smaller difference between quantities, or the total quantity increases, respectively, in striking contrast to the performance of great apes and even human infants in similar relative quantity judgement tests (see Anderson, Stoinski, Bloomsmith, & Maple, 2007;Beran, 2001;Boysen, Bernston, & Mukobi, 2001;Feigenson, Carey, & Hauser, 2002;Xu & Spelke, 2000). It is not yet known what cognitive mechanisms underlie the Asian elephants' numerical ability, but it may be that elephants are able to keep track of a larger number of items in immediate, working memory than can great apes including humans, and that when relative quantity judgements of larger numbers of items are explored then disparity and magnitude effects will emerge.…”

Sometimes area counts more than number

“…Cue salience may be highly specific to the situation at hand; the literature suggests there is not one stable preference for volume, number, or size that transcends situational factors (35)(36)(37)(38)(39)(40)(41). For example, Boysen et al (41) tested chimpanzees in an interference task that required them to choose one of two trays of candy.…”

“…For example, Boysen et al (41) tested chimpanzees in an interference task that required them to choose one of two trays of candy. The animals were rewarded with the contents of the nonchosen tray; hence the optimal choice was to choose the tray that contained a smaller number of objects to receive the greatest food reward.…”

Rudiments of mind: Insights through the chick model on number and space cognition in animals.

“…Such an ability would conceivably be the basis for efficient foraging strategies (Krebs, 1974). Several species prefer the larger amount of food in a spontaneous forced-choice discrimination task (Anderson, 2003;Call, 2000;Boysen, Bertson & Mukobi, 2001). For example, rhesus monkeys (Macaca mulatta) can discriminate between 1 vs. 2; 2 vs. 3; 3 vs. 4, and 3 vs. 5 (in this instance referring to pieces of apple) but not between 4 vs. 5; 4 vs. 6; 4 vs. 8, and 3 vs. 8 (Hauser, Carey & Hauser, 2000).…”