Greater neural pattern dissimilarity in retrieval stage of spaced learning is associated with higher meaningfulness and better memory

Spaced learning research aims to find the best learning interval to improve people's learning efficiency. Although it has been studied for many years, people do not know the physiological mechanism behind it clearly. Some neural representation studies have found that under the condition of spaced learning, the representation similarity of two encoding increases, and believe that this conflicts with the classical encoding variability theory. In this experiment, we used a new experimental paradigm and a longer lag to let the Chinese university students to learn English-Chinese word pairs, and we introduced the idea of meaningful learning into the learning stage to improve the traditional keyword method experiment task. Finally, by comparing the difference (spaced learning - one-time learning) vs. difference (massed learning - one-time learning) in the final test (retrieval) stage, we get different results: there is no significant difference in ERP, At the same time, the neural spatial pattern dissimilarity (STPDS) had significant results in the parietal lobe of 400ms and the right frontal lobe of 600ms. However, we believe that there is no direct contradiction between the two experimental evidence. On the contrary, they reflect different aspects of the process of spaced learning. Based on the evidence of different neural representation evidence of encoding and retrieval, this paper presents an idea of reintegrating three classical theories, eliminates the opposition between encoding variability and defective processing, and summarizes and classifies the experimental paradigm of spaced learning.

Distributed Practice or Spacing Effect

The spacing effect (also known as distributed practice) refers to the finding that two or more learning opportunities that are spaced apart, or distributed, in time produce better learning than the same opportunities that occur in close succession. A number of theories have been proposed to account for the spacing effect. These include deficient processing, encoding variability, study-phase retrieval, and consolidation. According to the deficient processing account, learning opportunities that are spaced apart in time, compared to non-spaced or “massed” learning opportunities, are more likely to receive a learner’s full attention, ultimately leading to better quality learning. The encoding variability account proposes that spaced learning opportunities, because they are separated in time, are more likely to be associated with a number of different contextual cues that can benefit later memory for the information learned. Study-phase retrieval is based on the premise that retrieval benefits learning, and spaced learning opportunities are more likely than massed learning opportunities to involve retrieval of the previous learning experience. More recent evidence suggests that spacing learning opportunities across different days may benefit memory due to sleep-dependent neural consolidation processes. Research in authentic educational contexts shows that spacing benefits learning of a wide variety of materials, from basic facts to complex scientific concepts and skills. Regarding the practical question of when spaced learning opportunities should occur, the ideal scheduling of these opportunities depends upon how long the information needs to be remembered in the future, such that retention over longer intervals of time benefits most by longer spacing between repeated learning opportunities. Despite its promise for enhancing student learning, spacing can be challenging to implement in authentic educational contexts due to the intuitive notion that immediate repetition is better for learning, and the difficulties involved in setting a spaced study schedule in advance and adhering to it. To realize the full potential of spacing to enhance educational practices, future studies are needed that can measure implementation of spacing by students and teachers in real educational environments.

The unequal variance signal-detection model of recognition memory: Investigating the encoding variability hypothesis

Despite the unequal variance signal-detection (UVSD) model’s prominence as a model of recognition memory, a psychological explanation for the unequal variance assumption has yet to be verified. According to the encoding variability hypothesis, old item memory strength variance (σo) is greater than that of new items because items are incremented by variable, rather than fixed, amounts of strength at encoding. Conditions that increase encoding variability should therefore result in greater estimates of σo. We conducted three experiments to test this prediction. In Experiment 1, encoding variability was manipulated by presenting items for a fixed or variable (normally distributed) duration at study. In Experiment 2, we used an attentional manipulation whereby participants studied items while performing an auditory one-back task in which distractors were presented at fixed or variable intervals. In Experiment 3, participants studied stimuli with either high or low variance in word frequency. Across experiments, estimates of σo were unaffected by our attempts to manipulate encoding variability, even though the manipulations weakly affected subsequent recognition. Instead, estimates of σo tended to be positively correlated with estimates of the mean difference in strength between new and studied items ( d), as might be expected if σo generally scales with d. Our results show that it is surprisingly hard to successfully manipulate encoding variability, and they provide a signpost for others seeking to test the encoding variability hypothesis.

Encoding Variability: When Pattern Reactivation Does Not Benefit Context Memory

A growing body of evidence suggests that neural pattern reactivation supports successful memory formation across multiple study episodes. Previous studies investigating the beneficial effects of repeated encoding typically presented the same stimuli repeatedly under the same encoding task instructions. In contrast, repeating stimuli in different contexts is associated with superior item memory, but poorer memory for contextual features varying across repetitions. In the present functional magnetic-resonance imaging (fMRI) study, we predicted dissociable mechanisms to underlie the successful formation of context memory when the context in which stimuli are repeated is either held constant or varies at each stimulus presentation. Twenty participants studied names of famous people four times, either in the same task repeatedly, or in four different encoding tasks. This was followed by a surprise recognition memory test, including a source judgement about the encoding task. Behaviourally, different task encoding compared to same task encoding was associated with fewer correct context memory judgements but also better item memory, as reflected in fewer misses. Searchlight representational similarity analysis revealed fMRI pattern reactivation in the posterior cingulate cortex to be higher for correct compared to incorrect source memory judgements in the same task condition, with the opposite pattern being observed in the different task condition. It was concluded that higher levels of pattern reactivation in the posterior cingulate cortex index generalisation across context information, which in turn may improve item memory performance during encoding variability but at the cost of contextual features.

Predicting memory formation over multiple study episodes

Repeated study typically improves episodic memory performance. Two different types of explanations of this phenomenon have been put forward: 1) reactivating the same representations strengthens and stabilizes memories, or, in contrast, 2) greater encoding variability - through changes in context - benefits memory by promoting richer traces and a larger variety of retrieval cues. The present experiment was designed to directly compare these predictions in a design with multiple repeated study episodes, allowing to dissociate memory for studied items and their context of study. Participants repeatedly encoded names of famous people four times, either in the same task (optimal encoding for a reactivation view), or in different tasks (optimal encoding for an encoding variability view). During the test phase, an old/new judgement task was used to assess item memory, followed by a source memory judgement about the encoding task. Consistent with predictions from the encoding variability view, encoding stimulus in different contexts resulted in higher item memory and lower rates of forgetting. In contrast, consistent with the reactivation view, source memory performance was higher when participants encoded stimuli in the same task repeatedly. Taken together, our findings indicate that encoding variability benefits episodic memory, by increasing the number of items that are recalled and by decreasing forgetting. These benefits are however at the expenses of source recollection and memory for details, which are decreased, likely due to interference and generalisation across contexts.