Sub-Optimal Choice in Dogs: Cheese or Cheese and Carrot?

Evidence suggests dogs do not always make the best choice. A new study finds that far as food choice is concerned, they use the same heuristic previously demonstrated in humans and monkeys.

A white dog nibbles on a carrot that it holds between the paws
Photo: Igor Sokolov (breeze) / Shutterstock

By Zazie Todd, PhD

Earlier research has found that if people are asked to estimate the value of a set of 24 good condition dishes vs a set of 40 dishes (of which 31 are in good condition), they tend to think the former is more valuable. The broken dishes seem to detract from the fact the second set has more dishes in good condition. This is known as the ‘less is more’ effect.

This effect has been demonstrated in monkeys, too. Monkeys like grapes and they also like slices of cucumber, although not as much. If given a choice between a grape vs a grape and a slice of cucumber, they tend to choose the grape.

Does the same hold true for dogs? Kristina Pattison and Thomas Zentall (University of Kentucky) set out to investigate.

The experiment took place in a plain room at the University. Since some dogs can be nervous in a new environment, dogs were given 5 minutes to investigate the room, and then offered a piece of cheese, a piece of carrot, followed by a piece of cheese with a piece of carrot. Dogs had to eat all of these items in order to qualify to participate. 

In the experiment, dogs were given a choice between a slice of cheese or a slice of cheese and a slice of carrot. After demonstrating that she had both items, the experimenter held her hands out with the items in the palm, and the handler released the dog. As soon as the dog touched one of her hands, the experimenter closed the other hand so the dog only had access to the hand it had chosen. The dog was allowed to eat the item(s), then went back to the handler to repeat the experience.

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Ten pet dogs took part, including five mixed breeds, a Cavalier King Charles Spaniel, a Siberian Husky, a Belgian Tervuren and a Golden Retriever (the researchers don’t say what the other dog was). 

The dogs showed a significant preference for a single piece of cheese rather than a piece of cheese and a piece of carrot. On average across all the dogs, cheese plus carrot was chosen only 27% of the time. 

One of the ten dogs actually showed a consistent preference for cheese plus carrot. Interestingly, this was a dog that was adopted as an adult rescue, having previously been a stray. The authors hypothesized that he may have had a greater motivation for choosing two items of food over one.  In fact, they point out that the dogs in this study and the monkeys in the monkey study all had relatively little motivation, since they are well-fed and not starving.

Some dogs have a preference for going to the left or right hand, and these dogs were weeded out in pre-tests. In addition, since it was theoretically possible that dogs have a preference for a single item rather than two items, there was another test in which dogs were given a choice between one slice of cheese and two slices of cheese. They picked two slices of cheese 95% of the time.

Why would people and dogs make this kind of choice? The authors say,
“The less is more effect, first demonstrated in humans, is an affect heuristic that results in a preference for the qualitative over the quantitative evaluation of options. Its function appears to have been the rapid evaluation of alternatives. It is likely that in many cases it is relatively easy to judge the qualitative value of alternatives but perhaps more difficult to judge their quantitative value, and when rapid decisions are necessary, such heuristics may be quite functional. For example, within-species competition may favour rapid decisions because hesitation may result in losing food to a faster competitor.”
Given the small sample size, further research is needed to see if this fascinating result applies widely.

The nice thing about this experiment is that it is relatively easy to replicate at home. Why not give your dog this choice a few times, and report back?

Zazie Todd, PhD, is the author of Wag: The Science of Making Your Dog Happy. She is the founder of the popular blog Companion Animal Psychology, where she writes about everything from training methods to the human-canine relationship. She also writes a column for Psychology Today and has received the prestigious Captain Haggerty Award for Best Training Article in 2017. Todd lives in Maple Ridge, BC, with her husband and two cats.

Useful links:
Pattison, K., & Zentall, T. (2014). Suboptimal choice by dogs: when less is better than more Animal Cognition, 17 (4), 1019-1022 DOI: 10.1007/s10071-014-0735-2
P.S. Will work for hot dog and now where's my treat?

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  1. This is very interesting, about the dogs but also humans! I'll try with my dogs someday soon, although I think I have two that have a side bias.

    You got me thinking about numbers. Are those the actual numbers of dishes they used in the human study? And did people see the actual dishes or just get informed of the numbers? If the latter, I think there may have even other factors besides the "shadow" cast by the 9 broken ones in the larger group. Valuing something can include considering resale. 24 is a great number of dishes. Could be a place setting of 3 for 8 people, or 4 for 6 people. But 31 dishes sounds like a burden to unload unless there were a heck of a lot of serving pieces!

    Hard to know what one would actually do, but I suspect I would be a cheese only person and would have to admit to being a suboptimal chooser. Definitely I'd go for the 24 dishes as they are described, but would take a little convincing that that was a suboptimal choice.

    Although maybe I'm just revealing my own strong bias against odd numbers, and prime numbers in particular. Thanks for a great (and practical!) thought problem.

  2. Thanks for your thoughtful comment! Thinking about it is almost like a game. What would you prefer, a bar of chocolate, or a bar of chocolate and a slice of ham? A bunch of six perfect red roses, or a bunch of eight perfect red roses with three wilted gladioli?

    I hear you on the china! It does make a difference if you’ve got a nice size set or some extra pieces that you’ll never use.

    That’s just an example though. One of the interesting things about this heuristic is that it applies to all sorts of things. For example, Slovic had a study in which people were asked about the purchase of airport security equipment. One group were told it would save 150 lives, and the other group told it would save 98% of 150 lives. The latter case had greater support. (Perhaps it’s easier to judge a percentage than an absolute number that you don’t know how to relate to in terms of risk). Other studies have looked at things like the absolute number of people dead from a disease vs a percentage of them, or whether or not you would insure an item in shipping, or games of pick-the-jellybean.

    I hadn’t thought about the type of numbers but I can see how that would come into play.

    With dogs, of course, we can’t get into these abstractions! Better to focus on what they prefer to eat. Let me know if you do try it with your dogs, but some dogs do have a side preference. One of mine doesn’t, but he is on a diet right now so I haven’t tried it yet.


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