Humans may not have a uniquely enhanced sequence memory: sequence discrimination is facilitated by causal-logical framing in humans and chimpanzees

Humans have been suggested to possess uniquely enhanced memory for sequences, based on sequence discrimination learning (SDL) tasks involving arbitrarily ordered sequences with no functional connection to outcomes. Such tasks underestimate animals' SDL as they lack affordances of real-world situations. We tested whether stimuli causally connected to outcomes facilitate SDL. A total of 13 chimpanzees, 24 capuchin monkeys, 23 squirrel monkeys, 77 adult and 239 juvenile humans completed an AB versus BA, BB and AA task. Humans discriminated causal sequences better than arbitrary ones and one chimpanzee succeeded in the causal frame condition after 324 trials, suggesting that performance gaps in previous studies are partly due to the arbitrariness of sequences (monkeys mostly failed the training). Without causal framing, children found the task difficult until 10-11 years of age. The sequence memory hypothesis needs to be evaluated with a broader set of tasks and account for cultural scaffolding of participants' understanding of task requirements.