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

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.     

Scale-model comprehension by chimpanzees (Pan troglodytes)

The ability of chimpanzees (Pan troglodytes) to recognize the correspondence between a scale model and its real-world referent was examined. In Experiments 1 and 2, an adult female and a young adult male watched as an experimenter hid a miniature model food in 1 of 4 sites in a scale model. Then, the chimpanzees were given the opportunity to find the real food item that had been hidden in the analogous location in the real room. The female performed significantly above chance, whereas the male performed at chance level. Experiments 3 and 4 tested 5 adult and 2 adolescent chimpanzees in a similar paradigm, using a scale model of the chimpanzees' outdoor area. Results indicate that some adult chimpanzees were able to reliably demonstrate an understanding of the relationship between a scale model and the larger space it represented, whereas other subjects were constrained by inefficient and unsuccessful search patterns.     

Tie strength and family formation: Which personal relationships are influential?

On the basis of the analysis of qualitative interviews in Western Germany, it has been argued that personal relationships have a strong impact on individuals' family formation processes and childbearing intentions. Persons who influence individuals' childbearing choices were identified. Strong ties, such as among core family members (i.e., parents and siblings), are an important contributing factor, but the authors are also able to show that weak ties, such as those among colleagues and acquaintances, need to be considered when examining social influence on family formation processes. Apart from single network partners, influential groups of persons have been identified. Such groups serve as a comparative standard regarding the timing of having one's first child and subsequent children.