Forgetting Can Be Helpful for Learning: How Wakeful,Offline Processing Influences Infant Language Learning
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Authors Ahmad, Neida Basheer
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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.
2
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
6
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.
7
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
8
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
9
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
12
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
13
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
14
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.
15
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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.