Forgetting Can Be Helpful for Learning: How Wakeful,Offline Processing Influences Infant Language Learning

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FORGETTING CAN BE HELPFUL FOR LEARNING: HOW WAKEFUL,

OFFLINE PROCESSING INFLUENCES INFANT LANGUAGE LEARNING

By

NEIDA BASHEER AHMAD

____________________

A Thesis Submitted to The Honors College

In Partial Fulfillment of the Bachelors degree

With Honors in

Psychology

THE UNIVERSITY OF ARIZONA

M A Y 2 0 1 7

Approved by: ____________________________ Dr. LouAnn Gerken Department of Psychology

Abstract

In previous work, 11-month-old infants were unable to learn rules about the relation of the

consonants in CVCV words when the stimuli were randomly ordered. By chance, the random-

ordering of the stimuli promoted local spurious generalizations that impeded infants’ learning of

the phonotactic rules. This experiment asked whether a 30-second delay after exposure to a list

of 24 randomly ordered words promotes learning. The 30-second delay did promote learning,

though not until the third block of testing, suggesting that a longer delay might have shown a

more robust effect. The interaction between conformity and block did not approach significance.

However, t-tests performed on each of the three blocks revealed that in the third block, infants

displayed a novelty preference, wherein they listened longer to stimuli that did not conform to

their familiarization rule than the stimuli that conformed to their familiarization rule.

Additionally, there is a trend toward an interaction between the previous experiment (no delay)

and the current experiment (30-sec delay), suggesting that the 30-second delay may have made a

difference in infants’ behavior.

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Introduction

A growing body of research has demonstrated that infants are able to learn a variety of

language-like rules in laboratory settings in a very short amount of time, including rules that

involve the possible relations among speech sounds in a word (e.g. Gómez & Gerken, 1999;

Gómez, 2002; Chambers, Onishi, & Fisher, 2003; Saffran & Thiessen, 2003; Gerken, 2006). In a

recently published study, our laboratory demonstrated that 11-month-olds are able to learn

phonotactic rules about the relation of two consonants in consonant-vowel-consonant-vowel

(CVCV) non-words from just four input words (Gerken & Knight, 2015). Infants learned one of

two phonotactic rules- in the Voicing Rule, C1 and C2 had the same voicing (they were both

either voiced or voiceless), and in the Place of Articulation (POA) Rule, C1 and C2 had the same

POA (both were labial or coronal).

Exp. Condition Rule: Pre-test Words Possible competing generalization(s)

Non-Conflicting

All words support feature-based

Voicing rule pota, tapa, biza, deva

Consonants share voicing

rules Place rule

poba, taza, bipa, desa Consonants share POA

Partially Conflicting

All words support feature-

Voicing rule dova, pota, pata, dava

Consonants share voicing vs.

Consonants are d/v; p/t

based rules and some words

support consonant-based rules

Place rule poba, dosa, dasa, paba

Consonants share POA vs.

consonants are p/b; d/s

Completely Conflicting

All words support both feature-

Voicing rule pota, pata, pita, peta

Consonants share voicing vs.

consonants are p/t

based and consonant-based

rules

Place rule peba, paba, poba, piba

Consonants share POA vs.

consonants are p/b

Table 1. Pre-test words for Voicing and Place of Articulation (POA) rules in Gerken & Knight (2015).

This study demonstrated that 11-month old infants can generalize from only 4 input

words, but an interesting finding from this study was that the subset of input that infants heard

during the familiarization phase (pretest) affected their responses at test. Gerken & Knight

designed different sets of stimuli to provide different degrees of support for an alternate

phonotactic rule: no support (Non-Conflicting condition), partial support (Partially Conflicting

3

Condition), or full support (Completely Conflicting Condition). In the Non-Conflicting

Condition, infants heard four words in which the primary rule was the only linguistically relevant

rule present. In the Partially Conflicting Condition, they heard four words that all obeyed the

relevant rule, but within the four words, pairs of words shared the same C1’s and C2’s and the

same vowels. In the Completely Conflicting Condition, all four words obeyed the relevant rule,

but all C1’s and C2’s were the same, making it so that an alternate rule was also fully supported.

These conditions and the pre-test words in these conditions are shown in Table 1. Infants in the

Non-Conflicting Condition showed a novelty preference, those in the Partially Conflicting

Condition showed a familiarity preference, and those in the Completely Conflicting Condition

showed no learning at test.

This pattern of behavior was taken to indicate that learning in the Non-Conflicting

Condition was most robust, because infants displayed a novelty preference in that they attended

longer to the non-conforming test items (test items that did not contain the same rule as pre-test

items) than to the conforming test items. This indicates that infants had learned the relevant rule

and were essentially getting bored of it, causing them to attend more to non-conforming test

items (Aslin, 2007; Gerken, Dawson, Chatila, & Tenenbaum, 2014). Learning in the Partially

Conflicting Condition was less robust, and it was suggested that in the Completely Conflicting

Condition, infants learned a rule about the particular consonants present within the stimuli (a

surface property) instead of the relevant rule. Gerken & Knight suggested that the presence of

“local spurious generalizations” (generalizations based on surface properties of the words – such

as shared consonants) in the Completely Conflicting Condition competed with the relevant

generalization, making it so that infants did not learn anything. They suggested that although it is

4

the standard procedure to randomly order stimuli, it is possible that random ordering with a

larger number of pretest stimuli may lead to more local spurious generalizations.

In order to determine how many spurious generalizations may arise from randomly

ordering stimuli, Gerken & Quam (2016) randomly ordered a set of 24 words, which resulted in

eight adjacent pairs of words for each rule; many of which shared surface properties (Table 2).

Experiment 1 found no evidence of learning, but after re-ordering the words to avoid adjacent

vowel- and consonant-sharing, infants were able to generalize in Experiment 2. This suggested

that infants make generalizations based on small adjacent subsets of data, and if local subsets

support a generalization that does not correspond to the generalization for the entire set, infants

may not be able to recover and will not learn the target rule.

Although infants did not learn in Experiment 1 of Gerken & Quam (2016) when they

were tested immediately after initial exposure to the stimuli of the 24 randomly-ordered words,

we wanted to see whether infants would show evidence of learning if tested after a 30-second

delay. A large body of work has demonstrated the importance of time and offline periods– with

an emphasis on sleep – in the improvement of memory. For instance, several studies have

demonstrated that time delays (including sleep) after training may promote higher-order relations

and the ability to generalize across motor-memory representations (Spencer, Sunm, & Ivry,

2006; Cohen et al., 2005). Much of this work, however, focuses on committing knowledge to

long-term memory (Ellenbogen et al., 2007; Rasch & Born, 2013; Fenn, Nusbaum, &

Margoliash, 2003), and little attention has been paid to how short increments of time between

exposure to stimuli and test play a role in short-term memory.

Though a majority of the research on memory and offline processing has looked at sleep

and prolonged increments of offline processing, Nestor, Tarr, & Creswell (2016) recently

5

demonstrated that a brief, two-minute offline processing period can enhance associative learning.

When (adult) participants were tested for memory after a two-minute distractor period, they were

able to recall more fictitious animal names than when they were tested immediately after

presentation of these animal names. While this is a clear demonstration of the way that wakeful

offline processing can enhance memory, the purpose of our research was to look specifically at

infant memory in relation to language learning. Though there has been much research on infant

memory, much of this research has looked at visual stimuli (Stinson & Brown, 1973; Kwon,

Luck, & Oates, 2014; Ross-Sheehy, Oakes, & Luck, 2003, 2011; Bertin, 2004; Rose, Feldmen,

& Jankowski, 2001), and while there has been some research on auditory stimuli, it focused on

non-linguistic sounds (Ross-Sheehy & Newman, 2015). Additionally, of the research that has

looked at offline processing’s role in the facilitation of learning linguistic sounds, there has been

a focus on the role of sleep in memory consolidation of linguistic patterns (Fenn, Nusbaum, &

Margoliash, 2003; Gómez et al., 2006; Hupback et al., 2009), but little investigation into short,

wakeful delays between exposure to stimuli and test. Our aim was to determine how short-term

memory relates to how infants learn phonotactic rules.

We used the headturn-preference procedure, as is the norm for language-research of this

kind, to determine if infants were able to generalize a language rule given exposure to 24

randomly ordered words, followed by a 30-second, music-filled delay. We chose a 30-second

delay because while we wanted a length of time that might allow infants to forget the local

spurious generalizations, we did not want this time to be so long that they would start to be fussy

and drop out of the experiment before we tested them. While infants were not able to generalize

in the previous experiment conducted by Gerken & Quam (2016), it was possible that a 30-

second delay may allow infants to forget the order of the items (allowing them to forget the local

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spurious generalizations that previously prevented learning), or they may simply forget the

words that were causing the confusion. We predicted that infants would be able to learn the rules

after a 30-second delay, and that the generalization would be robust, as would be indicated by a

novelty preference.

Methods

Participants

Participants were 24 infants (10 females, 14 males) from English-speaking homes,

ranging in age from 10.5 to 11.5 months. All infants were at least 37 weeks to term, at least 5lbs

8oz at birth, had no history of language or speech problems in their nuclear family, and were not

given medication for an ear infection within the week before testing. Four additional infants were

tested but not included because they either fussed during pre-test or test (N=2), or had mean

listening times more than 2SD above the group mean (N=2).

Study Design and Procedures

This study used a 2 test-item-conformity (conforming vs. non-conforming with pre-test

words) between-subjects design.

Participants were bought in for a single session. The headturn preference procedure

(Kemler Nelson et al., 1995; Figure 1) was used, taking place in a sound-proof booth. Infants

were seated on their parent’s lap in a small room in a chair in the center of the room. Parents

were instructed to keep the infant in their lap at all times and to avoid directing the infant’s

attention at any point during the study. They were also told that if any point during the study they

wanted to stop, they simply needed to raise their hand and the study would stop immediately.

Parents had headphones on and listened to pop music to mask the stimuli that the infants heard

and to prevent any unintentional influence on the infant.

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Figure 1. Schematicization of the Headturn Preference Procedure

The pre-test phase began with the flashing of a light in the center of the room, directly in

front of the infant, while the auditory stimuli was playing from one of the speakers on one side of

the room. The center light flashed until the observer (who is blind to the condition and cannot

hear the stimuli) judged that the infant was looking at it, at which point the center light was

turned off and a light on either the left or the right side of the room began to flash. When the

infant looked at the side light and then away for two consecutive seconds, that light was turned

off and the center light began to flash once again. This cycle continued for the duration of the

pre-test stimulus, which was played without interruption. During this stage there was no

correlation between the stimuli and infants’ looking behavior. The 24 pre-test words played for

about 28 seconds, were preceded by 1.5 minutes of Andean instrumental music and were

followed by 30 seconds of the same music. The 30 seconds of music after the pre-test words

constitute the delay between familiarization and test.

After the familiarization period and the 30-second delay, the test phase began

immediately. The test phase began the same way as the familiarization phase, with the center

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light flashing, except during this phase, the start of the stimuli was dependent on the infant

turning toward and looking at a side light. Every time one of the side lights began to flash and

the infant looked at it, one of the four test trials played, continuing for as long as the infant was

oriented toward the light or until the test trial reached its conclusion (23.5 seconds). Once the

infant looked away for two consecutive seconds or the test trial reached conclusion, the center

light began to flash again and the cycle continued through 12 test trials. To keep with the normal

practice in our lab, test trials that were shorter than 2 seconds were excluded from analysis and

two test trials shorter than 2 seconds qualified the infant as a “discard” because it was unlikely

that infants were able to encode the information on such short trials.

Stimuli and Measures

Stimuli were adapted from Gerken & Quam (2016). For Exp. 1, there were 24 pre-test

words generated by the POA Rule for one group of infants and 24 words generated by the

Voicing Rule for the other. Both sets of 24 words were randomly ordered following the usual

procedure used in our lab for creating a random sequence of pre-test words. Each word was

assigned a random number with the RAND function of Microsoft Excel and the same random

order was used for the list of words for each rule. Then, we re-ordered the words from both rules

in ascending order according to their random number to get the order for the pre-test stimulus.

Table 2 shows the ordered stimuli for the POA rule. The test words were the same 16 words as

used by Gerken and Knight (2015). Voicing Rule Test items were dɛba, tæfa, bida, posa, tifa,

bɛda, pæsa, doba; POA Test items were: dɛta, tæda, bifa, pova, tida, bɛfa, pæva, dota. All

infants heard all of the test items on different trials. For each rule, we created two different

orders of the test words, yielding four test trials that were repeated across three blocks, for a total

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of 12 test trials. The primary dependent measure was look-times; the length of time the infant

looked at the flashing light during the test phase.

Data Analytic Strategy

Because we were interested in how memory over time affected infants’ interest in the

conforming vs. non-conforming test stimuli, infants’ mean listening times (in seconds) of the test

trials were subjected to a 2 test-item-conformity (conforming vs. nonconforming with rule of

pre-test words) X 3 Block ANOVA. A main effect of conformity would indicate that infants

listened longer to one test item type or the other. A listening bias test stimuli that did not

conform to the familiarization stimuli would be a novelty preference, and a bias for test stimuli

that did conform to the familiarization stimuli would be a familiarity preference. A main effect of

block would suggest that infant listening times either increased or decreased as the experiment

proceeded. Lastly, an interaction effect of test-item-conformity and block, would suggest that

infant listening times changed over the blocks, but this change depended on whether they were

listening to conforming or non-conforming test items.

Additionally, the combined data from the two experiments was compared utilizing a 2

Experiment (no delay vs. 30-sec delay) X 2 test-item-conformity ANOVA to determine if there

were any main effects or interactions. A main effect of experiment would indicate that infants in

one experiment listened longer to test stimuli in one experiment over the other, and an interaction

between experiment and conformity would indicate that infants in the two experiments displayed

opposite or different sized biases.

Results

We predicted that though infants did not learn the voicing and place rules in Experiment

1 of Gerken & Knight (2016) when they were tested immediately after familiarization, they

10

would learn the rules when tested after a 30-second delay. Although either a significant novelty

or familiarity preference would indicate learning in the new experiment, we predicted a novelty

preference if infants forgot the local spurious generalizations during the 30-second delay.

Additionally, we predicted that there would be an interaction between experiment and

conformity, wherein infants in the experiment when tested with no delay did not demonstrate

learning, but infants in the 30-second delay experiment demonstrated learning.

Two infants had trials that were longer than 2SD above the group mean for that trial and

thus were excluded from the analysis. The means were subjected to a 2 test-item-conformity

(conforming vs. nonconforming with rule of pre-test words) X 3 Block ANOVA. The main

effect of conformity approached statistical significance (F(1, 18) = 3.19, p < 0.10), such that

infants listened numerically longer to the nonconforming (mean = 8.68) than the conforming

(mean = 7.70) test items. Because infants showed a marginal novelty preference, it appears that

the 30-second delay promoted robust learning. The main effect of block was statistically

significant (F(1,18) = 6.70, p < 0.02), such that listening times decreased from the beginning of

testing to the end. The interaction between conformity and block did not approach statistical

significance (F < 1), however, given the marginal effect of conformity and the strong effect of

block, t-tests were performed for each of the three blocks. They revealed that, in the third test

block, infants listened significantly longer to the nonconforming (mean = 8.48, SE = .67) stimuli

than to the conforming stimuli (mean = 6.60, SE = .67; t(18) = 2.29, p < 0.05). Thus, although

the effect of conformity wasn’t particularly robust, there were distinct hints of the predicted

effect in the data.

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Figure 2. Mean differences in listening times to test stimuli that conform vs. fail to

conform to pre-test items in Experiment 1 (no delay between familiarization and

test) and Experiment 2 (30-second delay between familiarization and test).

Lastly, given that this experiment was a follow-up of Experiment 1 in Gerken & Quam

(2016) which utilized the same stimuli without a 30-second delay between familiarization and

test and resulted in no significant effects, it was prudent to compare the results of the previous

experiment with this one (see Figure 1). In order to compare the two experiments, a 2

Experiment (no delay vs. 30-sec delay) X 2 test-item-conformity ANOVA was performed on the

combined data. The main effect of conformity was not significant (F < 1), but there was a main

effect of experiment such that infants in the no delay condition (mean = 6.26, SE = .32) had

significantly shorter listening times than infants in the delay condition (mean = 8.49 SE = .45;

F(1,18) = 20.73, p < 0.001). The expected interaction between experiment and conformity was

not significant (F(1, 36) = 4.52, p < 0.15). However, infants did show overall opposite effects in

the two experiments, such that in the previous experiment (no delay), infants showed a small

listening bias toward the test items that were consistent with their familiarization rule (familiarity

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preference), but in this experiment (30-second delay), infants showed a bias toward the test items

that were inconsistent with their familiarization rule (novelty preference). Additionally, given

that infants in this experiment showed the predicted effect in the last block of test, when only the

third block of test was compared across both experiments, the interaction between experiment

and conformity was significant (F(1,34) = 7.87, p < 0.01). This revealed that in the third block of

test in the previous experiment (no delay), infants showed a slight novelty preference, and in the

third block of test in this experiment (30-sec delay), infants showed a large novelty preference.

Discussion

Overall, the manipulation was effective, though as strong as we had hoped – infants

showed a learning effect in the experiment, but they did not show this effect until the last block

of the test phase. Given that in Experiment 1 of Gerken & Quam (2016), infants failed to

generalize from a set of randomly-ordered input words when tested immediately after exposure

to the stimuli, and that this experiment utilized the same 24 words, this result indicates a change

in the way the two sets of participants processed the stimuli. While in the previous experiment,

infants failed to generalize because of local spurious generalizations, wherein infants were

focusing on surface properties of adjacent words instead of the overall rule (voicing or POA)

used to generate the words – insertion of the 30-second delay between familiarization and test

may have allowed the infants’ focus to shift from local properties to the overall rule.

It is interesting to note that the infants did not demonstrate the predicted effect until the

very last block of testing. This may indicate that though the 30-second delay did allow for some

offline processing that aided in learning the rules of the stimuli, in reality, actually learning these

phonotactic rules and being able to apply them required a longer period of offline processing

than was provided by the delay. This would indicate that though infants are typically able to

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learn language-like rules, including phonotactic rules, in a very short period of time (Chambers,

Onishi, & Fisher, 2003), when randomly-ordered stimuli contain adjacent words that share

characteristics that lead to local spurious generalizations, learning the relevant rule is more

difficult (Gerken & Quam, 2016), and may require a longer period of offline processing in order

to induce the relevant rule. This is supported by the revelation that in the third block of test of the

previous experiment, infants had begun to show a bias toward non-conforming test items, and by

the third block of test in this experiment (30-sec delay), infants were displaying a robust novelty

preference. Additionally, the body of work looking at the effect of naps and how they aid in the

learning of complex grammatical rules of artificial languages (Gómez, Bootzin, & Nadel, 2006)

further supports the conclusion that longer periods of offline processing facilitate the learning of

more complex rules.

In order to test the theory that infants require a longer interval of offline processing to

learn the relevant rules, we plan to increase the time between familiarization and test in a

following experiment. Given that infants showed the predicted effect after the 30-second interval

and the first two blocks of testing, we averaged the time of the first two blocks (63 seconds), and

added this average to the 30-second delay, for a total delay of 93 seconds. If we were to utilize

this longer delay time between familiarization and test, this may allow for a more robust effect of

learning, given that infants will have a longer period of offline processing to a) forget the order

of the stimuli and therefore forget the local spurious generalizations, and b) to learn the relevant

rule. Furthermore, Ellenbogen et al., (2007) demonstrated that increases in offline-processing

time contribute to higher performance in relational memory, and though these researchers

utilized much longer periods of time between exposure and test than we intend to use, the finding

that longer periods of offline processing contributed to more robust learning given the

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complexity of the task provides foundation on which we can test our theory and expand on this

experiment.

This study sheds light on the importance of offline processing for language learning and

short-term memory, as well as the importance of the right amount of offline processing time.

This experiment was one of the first investigations into short periods of wakeful offline

processing in relation to the learning of language-like rules. Though not all results were

statistically significant, they approached significance, and given the trend of the data, with a few

more infants, the experiment would likely yield statistically significant results. This experiment

can serve as a pilot study for future investigations looking at how delays between familiarization

and test account for more robust learning of rules. Furthermore, this experiment illustrated the

importance of tailoring the amount of offline processing time to the complexity of the task.

Given that the local spurious generalizations in this stimuli made it difficult for infants to learn

the rule(s) after a 30-second delay, and that they did not learn the rule(s) at all when tested

immediately after familiarization (Gerken & Quam, 2016), it is clear that offline processing

plays a large and important role in learning, even if the aim is to simply commit information to

short-term memory and not long-term memory.

Acknowledgements

I would like to thank Dr. LouAnn Gerken for her guidance and support on my thesis

project and for the past three years. I would not have been able to do any of this without your

constant support. I would also like to thank everyone in the Tweety Language Development Lab

for being a constant source of encouragement and friendship over the years.

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Random Order Words N & N-1

shared C1’s

Words N & N-1

Shared V1’s

Words N & N-1

shared C2’s

piva

bofa

dɛsa

pɛba ɛ

bæpa

toza

pɛva

toda

tɛda t d

pæba

dita

poba

bæfa

bopa b

piba

tiza i

bipa i

dosa

tɛza

bɛpa ɛ

disa

dæsa d s

dæta d æ

tæza æ

Table 2. Randomly-ordered stimuli for the Place of Articulation (POA) rule. Adjacent pairs of word share rule-

irrelevant (spurious) properties.