Lucia Sweeney Abstracts

Lucia Sweeney
Ph.D. Candidate
Cognitive Science

Cognitive Development Society (CDS) Biennial

Louisville, KY
October 17-19, 2019

Previous research on sleep-dependent memory formation in infancy suggests that naps protect memories from greater loss than occurs during wakefulness but do not stabilize specific details of the memory. Here we investigate whether naps contribute to greater stabilization of a memory in older, more mature infants. In prior work, 15-month-olds heard phrases from an artificial grammar containing two nonadjacent dependencies (NADs), e.g. “vot-kicey-jic, pel-wadim-rud, pel-puser-rud,” where “vot-X-jic” forms NAD, and “pel-X-rud” forms the second (Gomez et al, 2006). In the 4 hours after training, infants either napped or remained awake then were tested using the HTP Procedure. On half of the test trials, infants heard familiar phrases from training (e.g. vot-X-jic, pel-X-rud). On the other half of the test trials, infants heard unfamiliar phrases from another grammar, violating the NADs from training (e.g. vot-X-rud, pel-X-jic). Infants in the No-nap groups discriminated familiar from unfamiliar strings after 4 hours (Gomez et al., 2006) but not 24-hours later (Hupbach et al., 2009). The nap groups showed generalization, looking longer to trials consistent with their first test trial versus trials from the other grammar 4 and 24-hours later, suggesting loss of the specific vocabulary making up the NADs from familiarization but not that there was a relationship between the 1st and 3rd words in phrases. To assess how retention of NADs develops, we tested older 18-month-olds using the same procedure. Now infants who nap discriminated familiar phrases (M = 7.75 sec) from unfamiliar ones (M = 6.58, p < .05) indicating that at 18 months, sleep stabilizes memory and prevents loss of detail. We also investigated whether infants could extend their knowledge of the learned NADs to completely novel vocabulary. Infants first listened to a NAD language with phrases such as guf-X-zam/miv-X-fop and napped in the four hours between learning and test. On half of the trials, infants heard phrases containing vot-X-jic/pel-X-rud NADs. The other half of test trials contained phrases from another grammar with opposite NADs (vot-X-rud/pel-X-jic). If infants could extend their knowledge of NADs to the grammar they hear in the first test trial, then they would learn the dependency in that trial and use it to guide their looking for the remaining trials. Indeed, 18-month-olds looked longer to trials consistent with the first test trial (M = 6.99s) versus trials inconsistent with that grammar (M = 5.85s p < .05). Thus, by 18 months, sleep stabilizes memory such that infants remember the specific NADs heard during training. Moreover, infants can recognize the same grammatical rule presented in completely novel vocabulary. Comparing these findings with our published data on 15 month-olds, we see a shift in sleep-dependent memory formation. At 15-months, sleep promotes generalization potentially due to loss of detail. At 18-months, sleep promotes a stable and specific representation, flexible enough to apply to new vocabulary.

Abstract for Lay Audience

The current study investigates how infants learn grammatical rules in language, along with whether there are developmental differences in the role of sleep in memory formation. Specifically, we focus on acquisition of non-adjacent dependency rules, or NADs, in 15- and 18-month old infants. In English, NADs appear in verb phrases like “he is jumping,” “she is singing,” and “the dog is barking,” where the verb is and the inflectional ending -ing remain constant, but the verb that occurs between these items can vary greatly. In English, is and –ing form an NAD. Previous studies examining acquisition of NADs used artificial languages to ensure the infants were not already familiar with the linguistic material presented during the experiment. We use artificial languages in the research presented here; these familiarization languages consisted of phrases like, “vot kicey jic, pel wadim rud, pel puser rud, vot coomoo jic” where “vot-X-jic” forms an NAD, and “pel-X-rud” forms the second NAD (Gomez, Bootzin, & Nadel, 2006). Four hours after familiarization, infants were tested on their memory for the NADs they heard. On half of the test trials, infants heard a familiar grammar consistent with the NADs during training (e.g. vot-X-jic, pel-X- rud). On the other half of the test trials, infants heard an unfamiliar grammar violating the NADs from training (e.g. vot-X-rud, pel-X-jic). After a 4-hour delay including only wakefulness, 15-month-olds listened longer to familiar trials versus unfamiliar trials. This difference indicates infants remembered the NADs they listened to during familiarization, and they could discriminate such phrases from those that violated the NAD. However, 24 hours after learning, they lose the ability to discriminate, indicating infants who stayed awake after learning forgot the rule during the daylong delay (Hupbach et al., 2009). On the other hand, 15-month-olds who napped soon after learning showed a generalization effect. These infants did not remember the specific vocabulary that made up the NADs from familiarization. Rather, with sleep they forgot the exact vocabulary but remembered that there is a relationship between the word in the 1st slot and the word in the 3rd slot of each phrase. During the first test trial they hear phrases that are similar to the language they heard previously, so they pick up on the 1st and 3rd words in the first test trial and form a dependency between these words. They remember these dependencies throughout the remainder of the test and use this information to guide their behavior (Gomez et al., 2006). To assess how retention of NADs develops, we tested 18-month-olds using the same procedure. Now infants who nap in the 4 hours between learning and test discriminate familiar phrases from unfamiliar ones. This suggests that at 18 months, sleep stabilizes memory and prevents loss of detail. We also investigated whether infants could extend their knowledge of the learned NADs to completely novel vocabulary. Infants first listened to an NAD language with phrases like guf- X-zam/miv-X-fop and napped in the 4 hours between learning and test. On half of the test trials, infants heard G1, containing vot-X-jic/pel-X-rud NADs. The other half of test trials contained G2, with opposite NADs (vot-X-rud/pel-X-jic). If infants could extend their knowledge of NADs to the grammar they hear in the first test trial, then they would learn the dependency in that trial and use it to guide their behavior for the remaining trials. Indeed, 18-month-olds looked longer to trials consistent with the first test trial versus inconsistent trials. Thus, by 18 months, sleep stabilizes memory so that infants remember the specific phrases heard during familiarization. Moreover, infants can recognize the same grammatical rule presented in completely novel vocabulary. Overall, we see a shift in sleep- dependent memory formation. To conclude, this research informs our understanding of how sleep benefits language learning at different stages in development. At 15-months, sleep promotes generalization potentially due to loss of detail. At 18-months, sleep promotes a stable and specific representation, flexible enough to apply to new vocabulary.