Jakke Tamminen

Sleep Spindle Activity is Associated with the Integration of New Memories and Existing Knowledge

Sleep spindle activity has been associated with improvements in procedural and declarative memory. Here, for the first time, we looked at the role of spindles in the integration of newly learned information with existing knowledge, contrasting this with explicit recall of the new information. Two groups of participants learned novel spoken words (e.g., cathedruke) that overlapped phonologically with familiar words (e.g., cathedral). The sleep group was exposed to the novel words in the evening, followed by an initial test, a polysomnographically monitored night of sleep, and a second test in the morning. The wake group was exposed and initially tested in the morning and spent a retention interval of similar duration awake. Finally, both groups were tested a week later at the same circadian time to control for possible circadian effects. In the sleep group, participants recalled more words and recognized them faster after sleep, whereas in the wake group such changes were not observed until the final test 1 week later. Following acquisition of the novel words, recognition of the familiar words was slowed in both groups, but only after the retention interval, indicating that the novel words had been integrated into the mental lexicon following consolidation. Importantly, spindle activity was associated with overnight lexical integration in the sleep group, but not with gains in recall rate or recognition speed of the novel words themselves. Spindle activity appears to be particularly important for overnight integration of new memories with existing neocortical knowledge.

The role of sleep spindles and slow-wave activity in integrating new information in semantic memory.

Assimilating new information into existing knowledge is a fundamental part of consolidating new memories and allowing them to guide behavior optimally and is vital for conceptual knowledge (semantic memory), which is accrued over many years. Sleep is important for memory consolidation, but its impact upon assimilation of new information into existing semantic knowledge has received minimal examination. Here, we examined the integration process by training human participants on novel words with meanings that fell into densely or sparsely populated areas of semantic memory in two separate sessions. Overnight sleep was polysomnographically monitored after each training session and recall was tested immediately after training, after a night of sleep, and 1 week later. Results showed that participants learned equal numbers of both word types, thus equating amount and difficulty of learning across the conditions. Measures of word recognition speed showed a disadvantage for novel words in dense semantic neighborhoods, presumably due to interference from many semantically related concepts, suggesting that the novel words had been successfully integrated into semantic memory. Most critically, semantic neighborhood density influenced sleep architecture, with participants exhibiting more sleep spindles and slow-wave activity after learning the sparse compared with the dense neighborhood words. These findings provide the first evidence that spindles and slow-wave activity mediate integration of new information into existing semantic networks.

Newly learned spoken words show long-term lexical competition effects

Newly learned spoken words (e.g., “cathedruke”) become fully engaged in the mental lexicon, as measured via lexical competition with their pre-existing phonological neighbours (e.g., “cathedral”), over the course of several hours or days, and this lexical restructuring is associated with sleep (Dumay & Gaskell, 2007). Here, we investigated the longer-term effects of word learning for three sets of novel words learned at different times using phoneme monitoring and repetition tasks. The effects of these exposure sessions on lexical memory were assessed in a battery of tests. Lexical decision latencies to pre-existing neighbouring words showed that lexical competition effects for the novel words remained observable 8 months after initial exposure. Furthermore, the order-of-acquisition of the novel words affected their production speed (but not recognition speed), with an advantage for earlier acquired words. The results suggest that the consolidation of novel words results in a long-term and stable change in the lexical competition process.

Novel word integration in the mental lexicon: Evidence from unmasked and masked semantic priming

We sought to establish whether novel words can become integrated into existing semantic networks by teaching participants new meaningful words and then using these new words as primes in two semantic priming experiments, in which participants carried out a lexical decision task to familiar words. Importantly, at no point in training did the novel words co-occur with the familiar words that served as targets in the primed lexical decision task, allowing us to evaluate semantic priming in the absence of direct association. We found that familiar words were primed by the newly related novel words, both when the novel word prime was unmasked (Experiment 1) and when it was masked (Experiment 2), suggesting that the new words had been integrated into semantic memory. Furthermore, this integration was strongest after a 1-week delay and was independent of explicit recall of the novel word meanings: Forgetting of meanings did not attenuate priming. We argue that even after brief training, newly learned words become an integrated part of the adult mental lexicon rather than being episodically represented separately from the lexicon.

Frequency effects in spoken and visual word recognition: evidence from dual-task methodologies.

The authors report 3 dual-task experiments concerning the locus of frequency effects in word recognition. In all experiments, Task 1 entailed a simple perceptual choice and Task 2 involved lexical decision. In Experiment 1, an underadditive effect of word frequency arose for spoken words. Experiment 2 also showed underadditivity for visual lexical decision. It was concluded that word frequency exerts an influence prior to any dual-task bottleneck. A related finding in similar dual-task experiments is Task 2 response postponement at short stimulus onset asynchronies. This was explored in Experiment 3, and it was shown that response postponement was equivalent for both spoken and visual word recognition. These results imply that frequency-sensitive processes operate early and automatically.

The role of memory consolidation in generalisation of new linguistic information

Accounts of memory that postulate complementary learning systems (CLS) have become increasingly influential in the field of language learning. These accounts predict that generalisation of newly learnt linguistic information to untrained contexts requires offline memory consolidation. Such generalisation should not be observed immediately after training, as these accounts claim unconsolidated representations are context and hippocampus-dependent and gain contextual and hippocampal independence only after consolidation. We trained participants on new affixes (e.g., -nule) attached to familiar word stems (e.g., buildnule), testing them immediately or 2days later. Participants showed an immediate advantage for trained affixes in a speeded shadowing task as long as these affixes occurred in the stem contexts in which they were learnt (e.g., buildnule). This learning effect generalised to words with untrained stems (e.g., sailnule) only in the delayed test condition. By contrast, a non-speeded definition selection task showed immediate generalisation. We propose that generalisation can be supported by initial context-dependent memories given sufficient processing time, but that context-independent lexical representations emerge only following consolidation, as predicted by CLS accounts.

Age of acquisition modulates the amplitude of the P300 component in spoken word recognition

Words acquired earlier in life are easier to process in adulthood than words acquired later; this is known as the age of acquisition (AoA) effect. The goal of this study was to establish whether the P300 component of event-related potentials (ERPs) is sensitive to AoA. Early-acquired words (12.5%), late-acquired words (12.5%) and pseudo-words (75%) were presented in an auditory lexical decision task. The two sets of words were matched for length, word type, concreteness, imageability and, crucially, word frequency. Early-acquired words were recognised faster and more accurately than late-acquired words. In addition, AoA modulated ERP activity in centroparietal electrode sites, with early-acquired words eliciting a larger positivity (P300) than late-acquired words. This is the first study to demonstrate an ERP correlate of AoA effects. An important implication of our findings is that AoA may need to be controlled in ERP studies of lexical processing, especially in designs in which it is likely to be a confound (e.g., studies of lexical category effects).

The nature of phoneme representation in spoken word recognition.

Four experiments used the psychological refractory period logic to examine whether integration of multiple sources of phonemic information has a decisional locus. All experiments made use of a dual-task paradigm in which participants made forced-choice color categorization (Task 1) and phoneme categorization (Task 2) decisions at varying stimulus onset asynchronies. In Experiment 1, Task 2 difficulty was manipulated using words containing matching or mismatching coarticulatory cues to the final consonant. The results showed that difficulty and onset asynchrony combined in an underadditive way, suggesting that the phonemic mismatch was resolved prior to a central decisional bottleneck. Similar results were found in Experiment 2 using nonwords. In Experiment 3, the manipulation of task difficulty involved lexical status, which once again revealed an underadditive pattern of response times. Finally, Experiment 4 compared this prebottleneck variable with a decisional variable: response key bias. The latter showed an additive pattern of responses. The experiments show that resolution of phonemic ambiguity can take advantage of cognitive slack time at short asynchronies, indicating that phonemic integration takes place at a relatively early stage of spoken word recognition.

Targeted memory reactivation of newly learned words during sleep triggers REM-mediated integration of new memories and existing knowledge

HighlightsTargeted memory reactivation (TMR) during sleep known to enhance declarative memory.TMR during slow wave sleep (SWS) did not enhance memory integration in word learning.TMR did impact on the role of rapid eye movement (REM) sleep in this process.SWS and REM may have complementary roles in memory integration. ABSTRACT Recent memories are spontaneously reactivated during sleep, leading to their gradual strengthening. Whether reactivation also mediates the integration of new memories with existing knowledge is unknown. We used targeted memory reactivation (TMR) during slow‐wave sleep (SWS) to selectively cue reactivation of newly learned spoken words. While integration of new words into their phonological neighbourhood was observed in both cued and uncued words after sleep, TMR‐triggered integration was predicted by the time spent in rapid eye movement (REM) sleep. These data support complementary roles for SWS and REM in memory consolidation.

Spoken Word Processing Creates a Lexical Bottleneck.

We report 3 experiments that examined whether presentation of a spoken word creates an attentional bottleneck associated with lexical processing in the absence of a response to that word. A spoken word and a visual stimulus were presented in quick succession, but only the visual stimulus demanded a response. Response times to the visual stimulus increased as the lag between it and the spoken word decreased, suggesting a bottleneck in processing. This effect was modulated by the uniqueness point of the spoken word; bottleneck effects were strongest when the spoken word had a late uniqueness point (Experiment 1). The effect was also modulated by the nature of the second task, with the effect stronger when the visual stimulus was a word rather than a shape (Experiment 2) or face (Experiment 3). Word processing appears to create a transient lexical bottleneck that is driven by the magnitude of lexical activity.