Concurrent cognitive processes in rat serial pattern learning: Item memory, serial position, and pattern structure

Abstract

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. In the 1970s, Stewart H. Hulse and his students conducted research on rats' ability to learn to anticipate a series of different food quantities presented in a runway (Hulse, 1973;Hulse & Campbell, 1975;Hulse & Dorsky, 1977;. This seemingly simple paradigm belied a sophisticated approach to answering a central question in animal learning theory. The question Hulse posed was whether or not nonhuman animals such as rats could learn about the structure of a sequence, that is, the abstract organizational properties of the sequence.

Central cholinergic involvement in sequential behavior: Impairments of performance by atropine in a serial multiple choice task for rats

“…This view depends on past research which showed that when rats learn to anticipate chunk-boundary elements they encode compound cues, where the stimulus compound they learn is composed of both the temporal pause itself and the serial position of the pause in the chunk (Muller & Fountain, 2010). This view also depends on past research showing that when rats learn to anticipate the violation element they encode compound cues, where the stimulus compound they learn is composed of multiple pattern elements preceding the violation element that uniquely predict it (Muller & Fountain, 2010).…”

“…This view depends on past research which showed that when rats learn to anticipate chunk-boundary elements they encode compound cues, where the stimulus compound they learn is composed of both the temporal pause itself and the serial position of the pause in the chunk (Muller & Fountain, 2010). This view also depends on past research showing that when rats learn to anticipate the violation element they encode compound cues, where the stimulus compound they learn is composed of multiple pattern elements preceding the violation element that uniquely predict it (Muller & Fountain, 2010). Evidence indicates that learning to anticipate within-chunk elements, on the other hand, depends on learning a motor program or abstract rule that is independent of external stimuli, as shown by nearly perfect performance for within-chunk elements after transferring rats to a novel operant chamber (Muller & Fountain, 2010).…”

“…Digits indicate the clockwise position of correct levers in the circular 8-lever array on each trial, dashes indicate 3-second pauses that served as phrasing cues (Muller & Fountain, 2010; Stempowski, Carman, & Fountain, 1999), and all other intertrial intervals were 1 second. The first element of each 3-element chunk is termed the chunk-boundary element .…”

“…Learning to anticipate chunk-boundary elements in a phrased pattern (a pattern with phrasing cues) has been shown to depend on both associative S-R learning and serial-position learning concurrently (Muller & Fountain, 2010; Stempowski et al, 1999). Earlier work has also shown that both rats and mice find violation elements unusually difficult to learn and that they learn to anticipate violation elements by associative discrimination learning involving multiple item cues from several preceding trials that signal the impending violation trial (Kundey & Fountain, 2010), In contrast, learning to anticipate within-chunk elements depends on learning a motor program or an abstract rule that is independent of external stimuli (Muller & Fountain, 2010). …”

“…The studies examined the effects of atropine on elements controlled by rules, such as the elements within chunks, versus elements controlled by discriminative cues through S-R learning, such as violation elements and chunk-boundary elements with and without signaling phrasing cues (Kundey & Fountain, 2010; Muller & Fountain, 2010; Stempowski et al, 1999). In both experiments, rats were first trained to a high criterion before drug challenge.…”