Examining the neural basis of unitization: A review.

Associative memory refers to the ability to form and remember associations between individual pieces of information rather than memory for a single object or word. Encoding associations in memory tends to be a more difficult task than item (only) encoding, because associative memory requires encoding multiple items as well as the specific links amongst the items. Accordingly, researchers have worked to identify interventions and strategies to reduce the effort and neural resources required for successful associative memory processing. Unitization is one such strategy that has traditionally been defined as the process by which two or more discrete items are processed, or encoded, such that they are perceived as a single ensemble. The current review explores the neural research on unitization while considering the behavioral benefits that accompany the process.

Investigating the neural basis of schematic false memories by examining schematic and lure pattern similarity.

ABSTRACTSchemas allow us to make assumptions about the world based upon previous experiences and aid in memory organisation and retrieval. However, a reliance on schemas may also result in increased false memories to schematically related lures. Prior neuroimaging work has linked schematic processing in memory tasks to activity in prefrontal, visual, and temporal regions. Yet, it is unclear what type of processing in these regions underlies memory errors. The current study examined where schematic lures exhibit greater neural similarity to schematic targets, leading to this memory error, as compared to neural overlap with non-schematic lures, which, like schematic lures, are novel items at retrieval. Results showed that patterns of neural activity in ventromedial prefrontal cortex, medial frontal gyrus, middle temporal gyrus, hippocampus, and occipital cortices exhibited greater neural pattern similarity for schematic targets and schematic lures than between schematic lures and non-schematic lures. As such, results suggest that schematic membership, and not object history, may be more critical to the neural processes underlying memory retrieval in the context of a strong schema.

Does unitization really function like items? The role of interference on item and associative memory processes.

Associative memory declines as we age, while item memory remains relatively stable. Previous work has shown that, in both younger and older adults, while item recognition declines linearly across time and interference, associative recognition declines only with longer delays and more interference. Unitization is a memory process found to support associative memory by allowing pairs to presumably be processed like single items. Research has found that unitization can benefit memory in aging by boosting associative memory to be on par with that of younger adults. Yet it remains unclear exactly the mechanism responsible for this enhancement in memory. The current studies aimed to determine whether unitized pairs show similar memory to that of items or associations with increasing time and interference, and determine how physically similar unitized pairs must be to perform like items and examine the effect of age on unitization in a continuous recognition paradigm. The results show that while unitized pairs exhibit higher corrected recognition compared with associative pairs at all lags, unitized pairs are not remembered to the degree that items are. It is critical that unitization boosts accurate recognition of pairs in both age groups across all early and middle lags compared with associative pairs. The results suggest that unitization may promote a more efficient associative link than unrelated associations over increasing time and interference, but the benefit does not reach that of item memory. These results demonstrate that while unitization benefits corrected recognition with earlier interference, its effect may not hold with later interference.

Investigating the neural basis of schematic false memories by examining schematic and lure pattern similarity.

Schemas allow us to make assumptions about the world based upon previous experiences and aid in memory organization and retrieval. However, a reliance on schemas may also result in increased false memories to schematically related lures. Prior neuroimaging work has linked schematic processing in memory tasks to activity in prefrontal, visual, and temporal regions. Yet, it is unclear what type of processing in these regions underlies memory errors. The current study examined where schematic lures exhibit greater neural similarity to schematic targets, leading to this memory error, as compared to neural overlap with non-schematic lures, which, like schematic lures, are novel items at retrieval. Results showed that patterns of neural activity in ventromedial prefrontal cortex, medial frontal gyrus, middle temporal gyrus, hippocampus, and occipital cortices exhibited greater neural pattern similarity for schematic targets and schematic lures than between schematic lures and non-schematic lures. As such, results suggest that schematic membership, and not object history, may be more critical to the neural processes underlying memory retrieval in the context of a strong schema.

The effect of memory cue duration on performance in the directed forgetting task in healthy aging.

Although forgetting is usually considered a memory error, intentional forgetting can function as an adaptive mechanism. The current study examined the effect of increased processing time on directed forgetting in aging as a mechanism to compensate for age-related forgetting. Specifically, an item-method directed forgetting paradigm was used in conjunction with Remember/Know/New responding to examine the effect of cue duration (1, 3, 5 s) on directed forgetting and remembering in younger and older adults. Results indicated that increased processing time improved performance in both age groups. Critically, older adults exhibited a linear increase in directed remembering performance across all cue durations which was related to individual differences in cognitive reserve. Specifically, those older adults with the highest levels of cognitive functioning showed the greatest memory benefit in the longest cue duration condition. These findings indicate the importance of processing time in accounting for intentional memory performance in older adults.

Understanding associative false memories in aging using multivariate analyses.

Age-related declines in associative memory are ubiquitous, with decreases in behavioral discriminability largely arising from increases in false memories for recombined lures. Using representational similarity analyses to examine the neural basis of associative false memories in aging, the current study found that neural pattern similarity between Hits and FAs and Hits and CRs differed as a function of age in occipital ROIs, such that older adults exhibited a smaller difference between the two similarity metrics than did younger adults. Additionally, greater Hit-FA representational similarity correlated with increases in associative FAs across several ROIs. Results suggest that while neural representations underlying targets may not differ across ages, greater pattern similarity between the neural representation of targets and lures may reflect reduced distinctiveness of the information encoded in memory, such that old and new items are more difficult to discriminate, leading to more false alarms.