How task format affects cognitive performance: a memory test with two species of New World monkeys

Abstract

In cognitive tests, animals are often given a choice between two options and obtain a reward if they choose correctly. We investigated whether task format affects subjects' performance in a physical cognition test. In experiment 1, a two-choice memory test, 15 marmosets, Callithrix jacchus, had to remember the location of a food reward over time delays of increasing duration. We predicted that their performance would decline with increasing delay, but this was not found. One possible explanation was that the subjects were not sufficiently motivated to choose correctly when presented with only two options because in each trial they had a 50% chance of being rewarded. In experiment 2, we explored this possibility by testing eight naïve marmosets and seven squirrel monkeys, Saimiri sciureus, with both the traditional two-choice and a new nine-choice version of the memory test that increased the cost of a wrong choice. We found that task format affected the monkeys' performance. When choosing between nine options, both species performed better and their performance declined as delays became longer. Our results suggest that the two-choice format compromises the assessment of physical cognition, at least in memory tests with these New World monkeys, whereas providing more options, which decreases the probability of obtaining a reward when making a random guess, improves both performance and measurement validity of memory. Our findings suggest that two-choice tasks should be used with caution in comparisons within and across species because they are prone to motivational biases.When the cognitive abilities of animals are assessed with cognitive tests, subjects are often presented with two options to choose from and rewarded with a food item if they choose the correct option. This two-choice task format has been used to test, in a range of animal species, a variety of cognitive abilities such as memory (e.g. delayed response tasks in ). One test that has extensively used the two-choice format in particular with a wide range of animal species is the object choice task. This task tests for sociocognitive abilities by assessing a subject's ability to use an experimenter's gestural cues (e.g. gaze, point, touch) in order to locate a reward that is hidden under one of usually two containers. The tested species include primates (all four great apes and some Old and New

Impact of stimulus format and reward value on quantity discrimination in capuchin and squirrel monkeys

“…Monkeys perform better and faster on cognitive tasks when they are more highly motivated (Gossette & Feldman, 1968;Minamimoto, La Camera, & Richmond, 2009;Schrier & Harlow, 1956;Schubiger, Kissling, & Burkart, 2016). Motivation levels are related to the subjective value of the reward, which can be based on a combination of objective features, such as reinforcement rates (Schubiger et al, 2016) or the quantity and visual availability of food (Minamimoto et al, 2009;Schrier & Harlow, 1956;Veling & Bijleveld, 2015), and subjective features, such as internal drive state or preference for food type (Gossette & Feldman, 1968;McKenzie et al, 2004;Minamimoto et al, 2009). Visual access to food rewards in the case of edible choice stimuli may therefore increase the subjective value of the reward, resulting in increased Note.…”

“…These findings are consistent with results of the present experiments that suggest New World monkeys assign a higher subjective reward value to preferred food items. Delay to reinforcement may also influence subjective reward value (Beran et al, 2009;Sanchez-Amaro et al, 2016;Schubiger et al, 2016), although recent findings are mixed. Some studies find a significant impact of delay on choice behavior (Beran et al, 2009), others find no effect (Sanchez-Amaro et al, 2016), and still others find that effects vary based on task parameters (Schubiger et al, 2016).…”

What animals do not do or fail to find: A novel observational approach for studying cognition in the wild

“…Other studies indicated how important it is to challenge study subjects and to provide many options when trying to test for cognitive skills . When Schubiger et al provided common marmosets ( Callithrix jacchus ) and squirrel monkeys ( Saimiri sciureus ) with the option to indicate where food was hidden in a two‐choice task, for which the chance of success is 50%, both species performed dramatically worse than when they were challenged to remember one location out of nine .…”

“…Other studies indicated how important it is to challenge study subjects and to provide many options when trying to test for cognitive skills . When Schubiger et al provided common marmosets ( Callithrix jacchus ) and squirrel monkeys ( Saimiri sciureus ) with the option to indicate where food was hidden in a two‐choice task, for which the chance of success is 50%, both species performed dramatically worse than when they were challenged to remember one location out of nine . Similarly, when Girndt et al found that when apes were offered a choice between pulling two prepositioned rakes to obtain food, where one of the rakes would push the food into a trap, they failed to choose the correct rake above chance .…”

“…83,84 When Schubiger et al 84 provided common marmosets (Callithrix jacchus) and squirrel monkeys (Saimiri sciureus) with the option to indicate where food was hidden in a two-choice task, for which the chance of success is 50%, both species performed dramatically worse than when they were challenged to remember one location out of nine. 84 Similarly, when Girndt et al 83 found that when apes were offered a choice between pulling two prepositioned rakes to obtain food, where one of the rakes would push the food into a trap, they failed to choose the correct rake above chance. 83 However, when they were challenged to use only one rake where they had to choose to move the rake to either side (the side with the trap or the side without) to eventually pull the food toward them, 80% of the apes made the correct choice in the first trial.…”