The effects of rhythmic presentation of stimuli on item and source memory

Previous research has shown that presenting stimuli in a temporally consistent manner (i.e. rhythmic or structured timing) during a study task can increase accuracy in a subsequent recognition test, compared to arrhythmic or unstructured presentation timing. However, no research has been done on whether this benefit extends to source memory (i.e., memory of contextual details). In this study, thirty-one participants (mean age = 27.39 years; SD = 4.92), were presented with a stream of images of everyday objects with either a cyan (blue) or magenta (pink) border during a study task. This was then followed by a recognition task where participants were instructed to respond for each item whether it was previously presented with a blue border, previously presented with a pink border, or was new. A blocked design was used, in which half the blocks the images were presented in a rhythmic temporal structure during encoding, and half the blocks were presented in an arrhythmic temporal structure during encoding. Electroencephalogram (EEG) was recorded throughout the experiment to measure the electrical activity in the brain during both the study (encoding) and recognition (retrieval) tasks. This was to understand the underlying neural processes involved in both the encoding and the retrieval of information. Specifically, we were interested in the effect of presentation timing during encoding on a number of memory-specific event related potential (ERP) components that have been observed in previous studies on recognition memory; namely the Dm effect (‘differential neural activity based on memory') at encoding, and the FN400 old/new effect, the late positive component (LPC) old/new effect and Late Frontal Effect (LFE) at retrieval.

Overall, there was no effect of temporal condition on item memory accuracy (i.e., the participants ability to discriminate between previously studied and new items). The two old/new effect ERPs that have been studied in relation to retrieval (the FN400 and LPC old/new effects) were replicated in this study for item memory, whereby items correctly identified as old elicit a more positive amplitude than items correctly identified as new. However, there was no effect of temporal condition on these ERPs. That is, the FN400 and LPC old/new effects were present in both the rhythmic and the arrhythmic conditions. No old/new effects were seen for the Late Frontal Effect (LFE) in either temporal condition. For source memory, no old/new effects were seen for the FN400, LPC or LFE when correct source and incorrect source responses were compared. However, source accuracy in the behavioural data was significantly greater in the arrhythmic than the rhythmic condition (i.e., the participants ability to identify the correct border colour for old items). This suggests that different processes may be used for retrieving source information compared to the processes required for item recognition only.