The effect of age on discrimination learning and self-control in a marshmallow test for pigs

Annika Krause,Sandra Düpjan,Armin Tuchscherer,Birger Puppe,Maren Kreiser

doi:10.1038/s41598-021-97770-x

Abstract

Both humans and nonhuman animals need to show self-control and wait for a larger or better reward instead of a smaller or less preferred but instant reward on an everyday basis. We investigated whether this ability undergoes ontogenetic development in domestic pigs (similar to what is known in human infants) by testing if and for how long nine- and 16-week-old pigs wait for a larger amount of their preferred reward. In a delay-of-gratification task, animals first learned that a small reward was hidden under a white cup and a large reward under a black cup, and then the delay to deliver the large reward was gradually increased. The results show that older pigs could wait longer for a larger reward than younger pigs (10.6 ± 1.3 s vs. 5.2 ± 1.5 s), thereby confirming our hypothesis of ontogenetic development of self-control in pigs. This self-control is likely to be regulated by the behavioural inhibition system and associated systems. Self-control or, more specifically the lack of it may be involved in the development of abnormal behaviours, not only in humans but also in animals. Therefore, research on self-control in decision-making might provide a new perspective on abnormal behaviours in captive animals.

Highlights

Both humans and nonhuman animals need to show self-control and wait for a larger or better reward instead of a smaller or less preferred but instant reward on an everyday basis
Mischel and Metzner[8] hypothesized that younger children might not discriminate between different delays and only develop this ability until they are approximately 9 years old
In a proof of concept study, Zebunke and colleagues[20] found that domestic pigs can learn to wait for a larger or better reward and show self-control. We investigated whether this ability undergoes ontogenetic development

Summary

Introduction

Both humans and nonhuman animals need to show self-control and wait for a larger or better reward instead of a smaller or less preferred but instant reward on an everyday basis. The everyday life of both humans and nonhuman animals is filled with conflicting motivations, forcing the individual to choose between two or more options on a regular basis In his seminal study, Walter Mischel and colleagues[1] investigated preschool children in a so-called delay-of-gratification task, offering them either one marshmallow there and or two marshmallows after a waiting time. The question was whether the children could inhibit their initial impulse (i.e., to seek instant gratification and choose the immediate but less favourable reward) and wait for the second marshmallow (i.e., to accept the delay of gratification and choose the more favourable reward) This ability to suppress one motivation (e.g., for instant gratification) and withhold the associated behavioural response is called self-control (e.g. ref.[2]). They are usually weaned at 3 to 5 weeks of age, and they reach puberty at approximately 6 to 7 months of age, so the differences found between pre-schoolers and pre-pubertal children could be reflected by differences within only a few weeks of life in piglets

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