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Evidence from serial pattern learning research has been used to support the controversial claim that rats detect, encode, and use abstract rules. To understand why the evidence indicates that rats’ “rules”are abstract, we examine the basis of “pattern structure” in sequential tasks, how rats respond to pattern structure in highly-organized sequences, the role of “rules” in rats’ representation of patterned sequences, and the notion that rats’ “rules” differ from generalization. We show that “pattern structure” reflects systematic abstractions from stimuli that can be described by abstract relationships,that rats are flexible in representing sequential patterns, that rats use “rules” along with other forms of representation concurrently in serial pattern learning, and that associative/generalization models do not always predict rats’ “rule-governed” behavior. Both behavioral and neurobiological evidence suggest that “rules” are not simply emergent properties of associative networks, that instead rule abstraction and associative processes are mediated by separate concurrently active systems in serial pattern learning. It is not known how “rules” are instantiated in the nervous system, and a key problem at a more molar level of analysis is what determines the output of multiple concurrently active cognitive systems in serial pattern learning.

Rats, like humans, appear sensitive to the structure of the elements of sequences. In the present study, we examined the effects of phrasing a structurally ambiguous pattern as either a series of “runs” or “trills.” A pattern phrased as runs was easier to learn than when it was phrased as trills, a result that resembles a similar “runs bias” reported in the human sequential learning literature. Whereas rats learning the runs-phrased pattern showed rapid learning and little tendency to make trills errors, rats learning the trills-phrased version of the pattern produced inflated rates of both trills and runs errors. The results show that rats represented the runs- and trills-phrased versions of the pattern differently. These results add to the evidence that, in addition to serving as discriminative cues, phrasing cues can bias pattern perception in rat serial pattern learning resulting in memorial representations characterized by multiple interpretations of the same pattern. The results also fit well with recent behavioral and neurobehavioral studies implicating multiple concurrent psychological and neural processes in rat serial pattern learning.

Three experiments examined the processes mediating rat serial pattern learning for rule-consistent versus rule-violating pattern elements ("violation elements"). In all three experiments, rats were trained to press retractable levers in a circular array in a specific sequence for brain-stimulation reward (BSR). Experiment 1 examined the role of lever location (L) and element serial position (SP) cues in rats' ability to learn to anticipate a violation element positioned at the end of a 24-element serial pattern. Rats with L cues either alone or in combination with SP cues learned to anticipate the violation element, whereas those with SP cues alone did not. Rats in groups L and L + SP underwent a series of transfers designed to remove various cues that might have controlled their performance on the violation element. Results indicated that intra-chamber lever location cues mediated performance on the violation element whereas performance on rule-consistent elements within pattern chunks was mediated by an internal mnemonic representation that was insensitive to changes in lever location cues. Experiment 2 examined whether rats could learn to use SP cues alone to anticipate a violation element if it was positioned earlier in a serial pattern. Rats learned to anticipate the violation element based on SP cues alone when it was located in SP6 in a 24-element pattern, but not when it was in SP12. Experiment 3 examined whether or not rats spontaneously encode information about chunk length and the serial position of phrasing cues in serial patterns. Rats were trained to a high criterion on the serial pattern used in Experiment 1, then were challenged with three probe patterns that manipulated both chunk length and overall pattern length. Results indicated that rats spontaneously encoded information regarding the serial position of phrasing cues in relation to chunk length. Thus, rats appear to use at least three cognitive processes concurrently in serial pattern learning tasks, namely, item memory involving external discriminative cues, counting- or timing-like processes for encoding serial position, and rule abstraction for encoding an internal representation of pattern structure. (Contains 6 figures.)

Nonhuman animals, like humans, appear sensitive to the structure of the elements of sequences, perhaps even when the structure relates nonadjacent elements. In the present study, we examined the contribution of chunking, rule learning, and item memory when rats learned serial patterns composed of two interleaved subpatterns. In one group, the first interleaved subpattern was a formally simple sequence, whereas in two other groups the first subpattern was formally more complex, containing 2 or 4 violation elements, respectively. In all groups, the second interleaved subpattern encountered was formally simple. Evidence from the study suggests that rats chunked their interleaved patterns into component subpatterns, that is, they cognitively sorted pattern elements to form chunks based on nonadjacent structural relationships that can be characterized as rules. They also learned interitem associations via traditional discrimination learning to use adjacent elements as compound or configural cues for later events in the sequence. Thus, the evidence suggests that rats used chunking, rule learning, and interitem association learning concurrently to master these complex patterns.

Both associative and rule-learning theories have been proposed to account for rat serial pattern learning, but individually they are unable to account for a variety of recent behavioral and psychobiological phenomena. The present study examined the role of rule learning versus discriminative learning in rat pattern learning using a classic associative phenomenon: blocking. Rats learned to press levers in an 8-lever circular array according to a rule-based serial pattern, 123-234-345-456-567-678-781-812, where digits indicate the correct lever in the array for each trial. Each pattern presentation contained a chunk with a final element violation, such as 454 instead of 456. Rats learned in a first phase that a noise signaled the violation chunk; then, a concurrent spatial cue was added in a second phase. A test with spatial cues alone showed that blocking occurred. The results suggest that associative learning mediated cuing of violation elements. Taken together with other behavioral and psychobiological evidence already reported in the literature implicating rule learning when rats learn this pattern in this paradigm, these results implicate multiple concurrent learning processes in rat serial pattern learning. Keywords: sequential learning, discrimination learning, rule learning, serial position, rat DOI: 10.1037/a0016523

Hypotheses ranging from subsymbolic to symbolic have been proposed to account for rat sequential behaviour, and in the subsymbolic domain alone there are multiple proposed subsymbolic processes or factors thought to affect serial behaviour. A behavioural study and computer simulations were conducted to evaluate these hypotheses, and a new computational associative model based on pairwise associations and generalization was evaluated. Seven 3-element sequences were selected for study that systematically (1) varied sequence discriminability, (2) varied reward magnitude, and (3) manipulated the order of food quantities. Neither element discriminability nor response enhancement subsymbolic processes in isolation were able to account for the behavioural data; however, simulations from the computational model known as the sequential pairwise associative memory (SPAM) model with a log-linear mapping of stimulus dimension items to food quantities correlated well with the behavioural data. SPAM accounts for differential element anticipation in different sequences by appealing to pairwise association of sequence events and generalization between cues as the principal factors mediating pattern tracking in three-element sequences.

A computational model of sequence learning is described that is based on pairwise associations and generalization. Simulations by the model predicted that rats should learn a long monotonic pattern of food quantities better than a nonmonotonic pattern, as predicted by rule-learning theory, and that they should learn a short nonmonotonic pattern with highly discriminable elements better than 1 with less discriminable elements, as predicted by interitem association theory. In 2 other studies, the model also simulated behavioral 'rule generalization,' 'extrapolation,' and associative transfer data motivated by both rule-learning and associative perspectives. Although these simulations do not rule out the possibility that rats can use rule induction to learn serial patterns, they show that a simple associative model can account for the classical behavioral studies implicating rule learning in reward magnitude serial-pattern learning.

Research in sequential learning has shown temporal phasing cues are predicted largely by the common discrimmination learning concept that associative strength is produced by the number of stimulus-response pairings. The sequence of phasing cues do not appear to be significant as discriminative cues.

Serial learning research has identified factors which might affect how animals code sequences of events. Long and short intervals used as phrasing cues facilitated acquisition compared to subjects given no cues. This suggests that animals learn sequentially by dividing information into 'chunks' similar to those used in human learning.

In 3 experiments, rats and humans learned serial patterns composed of 24, 30, or 36 items. Patterns had a 2-, 3-, or 4-level hierarchical rule structure. In Experiments 1 and 2, patterns had either perfect hierarchical structure or 2 modified chunks that violated hierarchical structure, thus producing linear structure (i.e., nonhierarchical structure). For both rats and humans, pattern structure predicted pattern learning difficulty and also the nature and relative frequency of errors. Both treated chunks that were inconsistent with hierarchical structure as violation chunks, that is, they made errors that reflected their 'tendency to regularize the perception of an irregular pattern' (F. Restle & B. L. Burnside, 1972). The results support the view that rats can abstract and encode a representation of multilevel hierarchical structure in serial patterns in much the same way as humans do in analogous tasks.

Rats learned serial patterns composed of either 'run' chunks (e.g., 123 234 ...) or 'trill' chunks (e.g., 121 232 ...). For each type of pattern, 1 group of rats encountered an element at the end of the pattern that violated the run or trill structure. In both run and trill patterns, violations were unusually difficult for rats to learn, whereas corresponding elements in 'perfect' patterns that did not violate pattern structure were easy. Additionally, rats' errors on violation elements conformed to the structure of the patterns in which they were embedded. Thus, rats were sensitive to the run or trill organization of their patterns and mastered the rules governing the pattern before learning 'exceptions to the rule.'