Self-control is defined as forgoing immediate gratification to obtain a greater rewards…These results indicate that capuchins are capable of delaying gratification when a higher quality reinforcer is present and that tool experience can influence levels of control in this task.
Self-control and Tool Use in Tufted Capuchin Monkeys (Cebus Apella) Introduction Self-control can be operationally defined as choosing to forgo immediate gratification in order to obtain a more valuable, but delayed reward (Mischel, 1974)…The goal of our study was to test for a relationship between self-control and tool use in a tool-using species, the tufted capuchin monkeys.
Self-control has been evaluated in some common laboratory species, including rats (Rattus), and pigeons (Columbia), and non-human primates (NHPs; Macaca, Pan, Pongo, Saguinus, and Saimiri)…These findings suggest that self-control may be limited to Old World NHPs (apes and Old World monkeys).
Tool use, however, is a behavior seen frequently in both Old World and New World NHPs…Therefore, this New World primate species may exhibit a level of self-control comparable to that seen in Old World monkeys and apes, if tested in a deliberate investigation of self-control behavior.
In the self-control paradigm, a number of methodological variables have been established as predictors of self-control and impulsive behaviors (for full list, see Tobin & Logue, 1994…Additionally, reinforcer quality (e.g., flavor or quantity) has been shown to influence choice in the self-control paradigm. Subjects’ self-control can be strengthened or diminished by increasing the reinforcer quality associated with the self-control or impulse response, respectively (King & Logue, 1990; Logue & King, 1991).
Although it has never been tested before, experience with long lasting complex tasks, such as tool use tasks, may also relate to an individual’s level of self-control…An alternative explanation for such relationship is that animals with inherently higher levels of self-control are the only ones to attempt complex tool tasks.
In the present study, we tested tufted capuchin monkey in a self-control paradigm…Consistent with the latter hypothesis, we also predicted that more experienced tool users should be less affected by the methodological variables of distance and reinforcer quality than less experienced tool users because of the possession of greater self-control. Method
Participants Twenty tufted capuchin monkeys (Cellus Apella) were tested: 5 adults males, 12 adult females, and 3 juvenile males…Five monkeys were moderately experienced in probing or other tool use tasks (I.e., participated in one previous investigation of probing tool behavior or exhibited the tendency to manipulate objects outside of experimental conditions), and 10 had little tool experience (I.e., had exhibited little or no manipulative behavior in experimental or natural conditions). Materials
The test apparatus was a PVC cylinder with a circular cap and mountable base…When given the choice between celery and pretzel, the monkeys reached for the pretzel first in a mean of 75% of trials (five trials for each monkey). Procedure
Before each trial, the apparatus was mounted in a corner of the monkey’s outdoor enclosure…Each subject was tested only once per day. Analysis The monkeys’ responses was converted to a bivariate dummy code (1 = use of the item as a tool = self-control response; 0 = consumption of the item = impulsive response)…An alpha level of p < .05 was used to determine statistical significance for all analysis.
Results The distribution of monkeys’ self-control responses differed significantly from a chance distribution across experimental conditions (Figure 1), x2(2, N = 20) = 18.00, p <.001…Although the self-control response occurred more frequently in the baited-near condition (18 responses) than in the baited-far condition (11 responses), the distribution of responses was not significantly influenced by distance: baited near vs. baited far, x2(1, N = 20) = 3.00, p > .05.
The distribution of self-control responses was not influenced by reinforcer quality: pretzel vs. celery, x2(1, N = 20) = 0.33, p >.05…Subjects from all three experience groups approached the apparatus either before or after they consumed their tool item despite the presence of the entire social group during testing.
Further, tool experience interacted with distance and reinforcer quality to influence the distribution of self-control responses…Also, inexperienced and highly experienced monkeys used celery sticks as tool objects somewhat more frequently than pretzel rods, whereas moderately experienced monkeys used each item as a tool in an equal number of trials, x2(6, N = 20) = 32.56, p < .001 (see Figure 1). Discussion
Several monkeys exhibited self-control (tool use) responses in both baited conditions…This study suggests that some New World primates, like Old Worth primates, exhibit self-control. The number of self control responses displayed by the monkeys varied by a combination of different factors…It is possible that, if tested in a self-control paradigm not involving tools, inexperienced tools users may still exhibit self-control.
Second, the distance from the tool site at which monkeys were given a tool did not influence the distribution of self-control responses…A possible explanation for this result is that the difference in delay period between the two conditions (between 5 and 15 s) was not dramatic enough to produce a statistical significant difference in self-control responses in these monkeys.
Third, we found that reinforcer quality also did not influence self-control…A possible explanation for this result is that the monkeys’ greater preference for pretzel rods than for celery sticks was not strong enough to produce a significant difference in self-control responses.
Although distance and reinforcer quality did not influence self-control acting alone, each interacted with tool experience to influence self-control…This result suggests that tool experience does not allow monkeys additional self-control in the face of more tempting food items.
Our monkeys demonstrated their ability to delay gratification in order to obtain a higher quality reinforcer by means of tool use…Further manipulation of methodological variables, including delay period, reinforcer quality, and additional untested variables (see Tobin & Logue, 1994), will be necessary to compare accurately the self-control of these monkeys with previously investigated species.