Chimpanzees sometimes see fuller as better: Judgments of food quantities based on container size and fullness

Abstract

The context in which food is presented can alter quantity judgments leading to sub-optimal choice behavior. Humans often over-estimate food quantity on the basis of how food is presented. Food appears larger if plated on smaller dishes than larger dishes and liquid volumes appear larger in taller cups than shorter cups. Moreover, smaller but fuller containers are preferred in comparison to larger, but less full containers with a truly larger quantity. Here, we assessed whether similar phenomena occur in chimpanzees. Four chimpanzees chose between two amounts of food presented in different sized containers, a large (2 oz.) and small (1 oz.) cup. When different quantities were presented in the same-sized cups or when the small cup contained the larger quantity, chimpanzees were highly accurate in choosing the larger food amount. However, when different-sized cups contained the same amount of food or the smaller cup contained the smaller amount of food (but looked relatively fuller), the chimpanzees often showed a bias to select the smaller but fuller cup. These findings contribute to our understanding of how quantity estimation and portion judgment is impacted by the surrounding context in which it is presented.

Defining value through quantity and quality—Chimpanzees (Pan troglodytes) undervalue food quantities when items are broken

“…This effect diminished for some chimpanzees when we introduced a larger discrepancy (2-item difference) between sets in Phase 2. These were clear errors with regard to maximizing intake, and were consistent with previous studies that have reported failures by chimpanzees to select the larger quantity as a function of presentation style or set composition (e.g., Beran et al, 2008; Boysen et al, 2001; Parrish and Beran, 2014b). …”

“…Chimpanzees participated for preferred food rewards and were otherwise maintained on their normal diet of fruit, vegetables, and primate chow (no food or water deprivation was used). All four chimpanzees had extensive prior experience making choices between different quantities of foods (e.g., Beran 2001, 2004, 2012; Beran and Beran 2004; Beran et al, 2009a, b; Parrish and Beran, 2014a, b; Rumbaugh et al, 1987). …”

“…These same chimpanzees were accurate in differentiating food quantities presented in same-sized containers. However, they often showed a bias towards an equal or smaller amount of food when that amount was presented in a smaller, yet seemingly fuller cup (Parrish and Beran, 2014b). Thus, perceptual illusions appear to affect food choice behavior in chimpanzees in many of the same ways as they do for humans (e.g., Van Ittersum and Wansink, 2012; Wansink, 2006; Wansink et al, 2006).…”

To Err Is (Not Only) Human: Fallibility as a Window Into Primate Cognition

“…Chimpanzees fall prey to the same bias. When given marshmallows or gelatin in small or large transparent cups, they preferred cups that looked more filled, even if those contained a smaller amount of food (Parrish & Beran, 2014a; Figure 3). Even aspects of food items that do not impact their quality or quantity, such as their wholeness, seem to affect chimpanzee choice behavior.…”

“…When humans look at food, their perception of portion sizes can be strongly affected by the context in which that food is presented. The size, the color, and the shape of containers holding food directly impact how people estimate the amount of food they are looking at (e.g., Wansink, Parrish and Beran (2014a). These arrangements were used to mimic the Delboeuf illusion in a food discrimination task.…”