Rhesus monkeys lack a consistent peak-end effect.

Area of Science:

• Cognitive Neuroscience
• Primate Behavior
• Decision Science

Background:

• Sequential reward order influences human subjective utility, a phenomenon known as the peak-end effect.
• Understanding order effects in primates can reveal the generality of these decision-making processes.

Purpose of the Study:

• To investigate the influence of reward-quality order on decision-making in rhesus macaque monkeys.
• To compare primate reward order effects with human peak-end effect findings.

Main Methods:

• Three rhesus macaques (Macaca mulatta) were presented with choices between high-low and low-high reward sequences.
• Follow-up experiments controlled for delay discounting to isolate the effect of reward order.

Main Results:

• All three monkeys preferred sequences where the high-value reward was received first.
• For two of the three monkeys, choices were solely dependent on reward-quality order, not delay.
• Rhesus monkeys did not display the peak-end effect observed in humans, where choices are discounted when a low-value reward follows a high-value one.

Conclusions:

• Reward-quality order significantly influences decision-making in rhesus monkeys.
• Rhesus monkeys' decision-making regarding sequential rewards differs from humans, specifically lacking the peak-end effect.
• These findings highlight species-specific variations in how sequential outcomes are evaluated.