Factors that loaded most strongly on g scores were most related to delay scores

In humans, delay of gratification appears to be related to general intelligence

For humans, there appears to be a clear link between general intelligence and self-control behavior, such as sustained delay of gratification []. Chimpanzees also delay gratification [] and can be given tests of general intelligence (g) [], but these two constructs have never been compared within the same sample of nonhuman animals. We presented 40 chimpanzees with the hybrid delay task (HDT) [], which measures inter-temporal choices and the capacity for sustained delay of gratification, and the primate cognitive test battery (PCTB), which measures g in chimpanzees []. Importantly, none of the sub-tasks in the PCTB directly assesses self-control or other forms of behavioral inhibition. Rather, they assess areas of physical cognition (e.g., quantity discrimination) or social cognition (e.g., gaze following). In three phases of testing, we consistently found that the strongest relation was between chimpanzee g scores and efficiency in the HDT. Chimpanzee g was not most closely related to the proportion of trials the chimpanzees chose to try to wait for delayed rewards, but rather most closely related to how good they were at waiting for those rewards when they chose to do so. We also found the same strong relation between HDT efficiency and those factors in the PCTB that loaded most strongly on chimpanzee g. These results highlight that, as with humans, there is a strong relation between chimpanzees’ self-control and overall intelligence—a relation that likely reflects the role of successful inhibitory control during cognitive processing of information and intelligent decision-making.

Chimpanzees (Pan troglodytes) can wait, when they choose to: a study with the hybrid delay task.

The hybrid delay task: can capuchin monkeys (Cebus apella) sustain a delay after an initial choice to do so?.

Maintenance of self-imposed delay of gratification by four chimpanzees (Pan troglodytes) and an orangutan (Pongo pygmaeus).

Preference for delayed reward as a function of age, intelligence, and length of delay interval.

What No Child Left Behind leaves behind: The roles of IQ and self-control in predicting standardized achievement test scores and report card grades.

Results

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Schaeffer J. Chimpanzee intelligence is heritable. Figure 1 Performance of Each Chimpanzee in the HDT Show full caption The bars show the proportion of trials on which each chimpanzee choose the LL option. The points indicate the mean number of items obtained on those LL trials (maximum = 12). Figure 1 presents the performance of each chimpanzee in each condition of the hybrid delay task (HDT) in terms of how often the delayed option was selected and how many items were accumulated on those trials. Of specific interest was whether performance on the HDT task was associated with domain general intelligence (g). g refers to a latent, general problem-solving skill [] that some have argued was selected for in primate evolution and accounts for the wide range of cognitive specializations observed in humans compared to more distantly related species []. There is debate as to whether the construct of a g factor more accurately reflects the nature of primate cognition versus a more modular conception of intelligence []. Our hypothesis, given past testing with chimpanzees that indicated evidence of a g factor for chimpanzee intelligence [], was that efficient engagement of delay of gratification should be associated with better overall cognitive performance, and we predicted that significant positive associations would be found between HDT performance and overall g scores derived from the primate cognitive test battery (PCTB) rather than specific subscale scores. Delay of gratification is a form of self-control, and in the HDT, it is reflected in the accumulation of larger quantities over time, where immediate consumption of available reward ended any additional accumulation.

Figure 2 Relationship between PCTB Scores and HDT Performance Show full caption This is shown in terms of the percentage of choice of the LL set (left), HDT mean number of items accumulated when the LL set had been selected (center), and HDT efficiency score (right). For all inter-item transfer rates (3 s, 10 s, and 20 s), the efficiency score best predicted PCTB performance in this sample of chimpanzees. Figure 2 presents the relation of composite PCTB g scores to three measures from the HDT in each of the three conditions. First, PCTB scores are shown in relation to the proportion of choices of the larger-later (LL) option in each condition ( Figures 2 A, 2D, and 2G). As a reminder, this measure reflects how often the chimpanzees pointed to 12 grapes rather than 4 grapes. Second, PCTB scores are shown in relation to the average number of items accumulated in the delay phase of trials where the 12-item set was selected ( Figures 2 B, 2E, and 2H). As a reminder, these panels would reflect the relation of g to how long chimpanzees could wait for accumulating rewards when they had chosen to wait for those rewards. Third, PCTB scores are shown in relation to a measure of overall task efficiency ( Figures 2 C, 2F, and 2I). This measure reflects the average number of grapes eaten across all trials, whether the smaller-sooner (SS) or LL option was selected. It is designated as a measure of efficiency because it allows for ranking chimpanzees in terms of how much food they obtained but is agnostic as to whether a given chimpanzee should have chosen the SS or LL option on a given trial. Rather, it indicates how the overall performance pattern of the chimpanzee in its choices and in its delay of gratification during LL trials produced reward. Thus, it could be viewed as a measure of cognitive monitoring of self-control resources rather than just the proportion of self-control choices that are made.

For the 3-s delay condition, there was a significant correlation of PCTB score and proportion of LL choices made (r(38) = 0.57, p < 0.001). There also was a significant correlation of PCTB score and the average accumulation performance on LL trials (r(38) = 0.42, p < 0.001). Additionally, there was a significant correlation of PCTB score and efficiency score (r(38) = 0.65, p < 0.001). Given that all of these HDT measures showed individual significant relations with PTCB performance, we conducted a multiple regression analysis with those three factors to determine which of them best predicted PCTB score. That analysis showed that the efficiency score best predicted PCTB score (t(38) = 5.30, p < 0.001), and it accounted for 42.4% of the variance. The other two factors, proportion choice LL and accumulation performance in LL trials, did not account for statistically significant additional levels of variance (proportion choice t(38) = 1.61, p = 0.11; accumulation t(38) = 1.61, p = 0.11).

Crucially, there also was not a significant relation between proportion choice of the LL response and accumulation performance on LL trials (r(38) = 0.11, p = 0.51). This indicates that those chimpanzees that waited longer when accumulating were not necessarily those who also chose most often the LL option.

For the 10-s delay, there was a significant correlation of PCTB score and proportion of LL choices made (r(38) = 0.60, p < 0.001). There also was a significant correlation of PCTB score and the average accumulation performance on LL trials (r(38) = 0.49, p < 0.001). Additionally, there was a significant correlation of PCTB score and efficiency score (r(38) = 0.63, p < 0.001). Given that all of these HDT measures showed individual significant relations with PTCB performance, we conducted a multiple regression analysis with those three factors to determine which of them best predicted PCTB score. That analysis showed that the efficiency score best predicted PCTB score (t(38) = 4.96, p < 0.001), and it accounted for 39.3% of the variance. The other two factors, proportion choice LL and accumulation performance in LL trials, did not account for statistically significant additional levels of variance (proportion choice, t(38) = 1.85, p = 0.06; accumulation t(38) = 1.88, p = 0.06).

For this condition, there was a significant relation between proportion choice of the LL response and accumulation performance on LL trials (r(38) = 0.42, p = 0.001).

For the 20-s delay, there was a significant correlation of PCTB score and proportion of LL choices made (r(18) = 0.59, p < 0.001). There also was a significant correlation of PCTB score and the average accumulation performance on LL trials (r(18) = 0.54, p < 0.001). Additionally, there was a significant correlation of PCTB score and efficiency score (r(18) = 0.71, p < 0.001). Again, we conducted a multiple regression analysis with those three factors to determine which of them best predicted PCTB score. That analysis showed that the best model included efficiency score (t(18) = 2.43, p < 0.001), which accounted for 49.7% of the variance, and accumulation performance (t(18) = 3.04, p < 0.001), which accounted for an additional 17.7% of the variance. Proportion choice of the LL set did not account for statistically significant additional levels of variance (t(18) = 0.82, p = 0.43).

As in condition 1, for condition 3 there was not a significant relation between proportion choice of the LL response and accumulation performance on LL trials (r(18) = 0.17, p = 0.49). This again highlights that those chimpanzees that waited longer when accumulating were not necessarily those who also chose most often the LL option.

Table 1 PCTB Tasks, Number of Trials Administered, PAF Score Weighting, and Pearson Product Moment Correlations between PCTB Tasks and HDT Performance at Each Delay Interval Task Trials PAF Weighting 3 s 10 s 20 s Physical Cognition Tasks Spatial Memory 6 .348 .211 .108 .225 Object Permanence 18 .671 .339∗ .420∗∗ .788∗ Rotation 18 .567 .406∗∗ .344∗ .602∗∗ Transposition 18 .540 .318∗ .388∗ .733∗ Quantity 24 .515 .564∗∗ .455∗ .504∗ Causality (Noise) 12 .181 .363 .018 .396 Causality (Visual) 12 .293 .210 .380∗ .357 Tool Use 12 .411 .520∗∗ .415∗∗ .423 Tool Properties 12 .178 .047 .098 .128 Social Cognition Tasks Gaze/Point Comprehension 12 .593 .533∗∗ .595∗∗ .517∗∗ Gesture Production 8 .631 .513∗∗ .561∗∗ .444∗ Attention State 18 .491 .386∗ .385∗ .239 Gaze Following 6 .113 .044 -.153 -.012 ∗p < 0.05, ∗∗ p < 0.01 Figure 3 The Relation of Weighted Score of each PCTB Task and HDT Performance Show full caption Weighted scores were computed from the PAF analysis and the correlation coefficient value found between each task and the HDT scores at 3-s, 10-s, and 20-s delays (see Table 1 ). Significant positive correlations were found between HDT performance and several PCTB tasks, including object permanence, rotation, transposition, numbers, tool use, gaze/point comprehension, gesture production, and attention-getting behaviors ( Table 1 ). Figure 3 shows that significant positive associations were found between PCTB task-loading weights and the correlation coefficients between each measure and the HDT measures at 3 s, 10 s, and 20 s. Thus, for PCTB tasks that more strongly loaded on the principal axis factor (PAF) analysis-derived g, these same measures also showed stronger associations with HDT performance across the three-delay intervals.

As with the PAF scores, the correlations of unit-weighted factor (UWF) scores and HDT scores were positive and significant for the 3-s delays (r(38) = 0.610, p < 0.001), the 10-s delays (r(38) = 0.562, p < 0.001), and the 20-s delays (r(18) = 0.643, p < 0.01). Thus, using a UWF instead of a PAF score to reflect g does not change the results.