The processes of pattern separation and pattern completion are very important in the correct discrimination of similar memories. Much research has been conducted on these processes, but there are some gaps that need to be addressed. First, there is some debate as to whether false alarms to lure items come about because of a failure to accurately encode a memory or a failure to retrieve a memory. Second, much of the research on pattern separation and pattern completion in humans is done with visual stimuli and contributions of stimulus modality to these processes are not well understood as a result.Study 1 consisted of three experiments conducted using a combination of eye tracking and functional magnetic resonance imaging (fMRI) methods. Analyses of eye tracking data in the experiments examined the contribution of fixation counts at encoding and retrieval, as well as target-lure similarity level, to accuracy on lure trials. Task designs were altered across studies to attempt to replicate specific research previously conducted with a specific answer period, as well as generalize the findings to a broader body of research that allows participants to answer while the stimulus is presented. The three experiments showed mixed support for the contribution of fixation counts at encoding and retrieval to the accurate discrimination of similar lures. Target- lure similarity, however, was a robust predictor of accuracy for all three experiments.Prior research examining activity in the hippocampus demonstrates a reduction of fMRI activity to repetitions of a stimulus. Greater activity is also observed in the dentate gyrus/CA3 (DG/CA3) subregions for correct rejections of lure items compared to lure false alarms. There should be a greater reduction in the DG/CA3 as a function of encoding for lure false alarms than for lure correct rejections if memory encoding drives the activity differences between these outcomes. The fMRI data showed a marked reduction of activity in the left hippocampus to repetition trials as a function of encoding trial fixation count. There was no significant difference between activity as a function of encoding fixation count in the DG/CA3 for lure correct rejections and lure false alarms. There was also no difference in activity for the CA1 either. Overall, the results of the eye tracking and fMRI data give support for the contribution of pattern completion to false alarms to lure stimuli rather than poor encoding.Study 2 examined the contribution of sensory modality to accurate discriminations of lure stimuli. A behavioral task was developed to directly compare discrimination of similar lures on visual and auditory stimuli. Participants were significantly more accurate and more confident of their responses when discriminating visual stimuli as compared to discriminating auditory stimuli.



College and Department

Family, Home, and Social Sciences; Psychology



Date Submitted


Document Type



pattern separation, pattern completion, sensory modality, memory encoding, memory specificity