Number, but not rhythmicity, of temporal cues determines phrasing effects in rat serial-pattern learning

Recent work on experimental manipulations that affect chunking in sequentia l learning has shown that cues inserted into a sequence, termed "phrasing c ues," can facilitate learning by serving as discriminative cues that oversh adow associations between sequence items (Stempowski, Carman, & Fountain, 1 999). This experiment assessed whether rhythmicity is an important determin ant of temporal phrasing effects or, instead, that a discrimination learnin g view can adequately account for the results of manipulating the number an d sequential positioning of phrasing cues. Rats learned serial patterns in which the number and organization of phrasing cues were manipulated so that phrasing cues were positioned at the beginning of four or eight chunks in an eight-chunk serial pattern. Alternate Chunks phrasing, Aperiodic phrasin g (four cues always positioned before the first, third, fourth, and seventh chunks), and Random phrasing (four cues positioned at four chunks chosen r andomly for each new pattern presentation) produced equal facilitation of a cquisition for cued chunks relative to a No Phrasing condition, but not as much facilitation as Every Chunk phrasing. Cue removal produced deficits, w ith greater impairment observed for the eight- versus four-cue conditions. Thus, the effects of temporal phrasing cues were predicted less by their rh ythmicity than by the common discrimination learning notion that associativ e strength is a function of the number of stimulus-response pairings. (C) 2 000 Academic Press.