Grammar Learning by Rhesus Macaques ( Macaca mulatta ) : 1 Exploring the Role of Grammar Complexity and Sequence Length 2 3 4 5

25 Humans and nonhuman primates can learn about the organization of stimuli in the environment 26 using implicit sequential pattern learning capabilities. However, most previous artificial grammar 27 learning studies with nonhuman primates have involved relatively simple grammars and short input 28 sequences. The goal in the current experiments was to assess the learning capabilities of monkeys on an 29 artificial grammar-learning task that was more complex than most others previously used with 30 nonhumans. Three experiments were conducted using a joystick-based, symmetrical-response serial 31 reaction time (SR-SRT) task in which two monkeys were exposed to grammar-generated sequences at 32 sequence lengths of four in Experiment 1, six in Experiment 2, and eight in Experiment 3. Over time, the 33 monkeys came to respond faster to the sequences generated from the artificial grammar compared to 34 random versions. In a subsequent generalization phase, subjects generalized their knowledge to novel 35 sequences, responding significantly faster to novel instances of sequences produced using the familiar 36 grammar compared to those constructed using an unfamiliar grammar. These results reveal that rhesus 37 monkeys can learn and generalize the statistical structure inherent in an artificial grammar that is as 38 complex as some used with humans, for sequences up to eight items long. These findings are discussed 39 in relation to whether or not rhesus macaques and other primate species possess implicit sequence 40 learning abilities that are similar to those that humans draw upon to learn natural language grammar. 41 42