Study Results-Old – Language Acquisition Lab

When do infants start segmenting English verbs and morphemes? (6-14-months)

In this set of studies, we ask whether monolingual English-learning 6-month-olds are able to pull out conjugated verbs (i.e., ‘smile’ in ‘Mommy smiles’) in stories where they follow the familiar word “mommy/mama”. Our results show that not only can 6-month-olds pull out these verbs, they can also relate them to the bare form of the verb ‘smile’. Our results show that infants can segment verbs and decompose the root of the verb (‘smile’) and the grammatical morpheme (-s) at a very young age (6 months). These results have implications on verb acquisition and morpheme learning. We also tested if infants can relate any part word to a word, e.g. the word bab to the nonsense sequence babsh but they do not. Therefore, English-learning 6-month-olds know that word final –s is special, and used as a grammatical marker in English.

Currently we are also testing the endings –ing, -ed, and plural -s, and we are trying to determine whether they know that–s, –ing, and -ed go after verbs by testing them on babs, babbing, and babbed, and whether they know that possessive ‘s goes after nouns by testing them on ‘Mommy’s babs’. We are testing 6mo, 8mos, 12mos, and 14mos to determine the timing of acquisition of those morphemes. So far we have found that infants before 14mos treat 3^rd person singular –s like plural –s, i.e., they can’t tell them apart yet by looking at the linguistic context. But they start to become sensitive to this difference by 14mos. We are currently developing stimuli to test other potential inflections in English.

How do monolingual and bilingual infants segment words from continuous speech? (7-9-months)

In this study, we investigate whether monolingual English, monolingual Spanish and bilingual English-Spanish infants can find words in Spanish and English. We found that even monolingual English 8-month-olds succeed at finding Spanish words like SALsa that start with a stressed syllable. This replicates results from English-acquiring infants segmenting English words (they succeed with DOCtor). However, in Spanish, they do so when we familiarize them with Spanish stories for 60s (not the typical 45s). Additionally, we have found they also succeed at segmenting words like coRRAL, that end in a stressed syllable given 60s of familiarization time as well. Contrastively, they fail to segment similar words in French. We believe this is due to the fact that French does not have variable stress (it’s always final) while both English and Spanish have lexical stress (PREsent and present have different meanings). English-acquiring infants can therefore segment words from fluent speech by aligning stress to word onsets of offsets so long as the language has lexical stress.

We have also found that bilingual 8mo-olds exposed to both English (>50%) and Spanish (<50%) successfully segment English iambs (guiTAR) and with only 45s of familiarization. This is striking because monolingual English-learning infants fail at segmenting English stress-final words with 45s of familiarization time. We believe bilinguals learn from Spanish to segment words that end with a stressed syllable (40% of Spanish disyllabic words have final stress), and then transfer that knowledge to English, a language in which stress falls 90% on the first syllable. We are currently still testing bilingual English-Spanish infants as well as monolingual Spanish infants.

How do infants distinguish different intonations? (4-8-months)

Languages differ in whether they use pitch to signal differences in meaning. In languages like Mandarin, words with identical consonant and vowel sequences, when produced with a difference in pitch can signal a difference in meaning. In other languages like English or Portuguese, identical consonant and vowel sequences, when produced with a difference in pitch on the last syllable can signal the difference between a question (raising intonation) and a statement (falling intonation). We found that 4mo-olds learning English, a language that does not use pitch contrastively, failed to group words based only on pitch, even when the consonants and vowels were kept constant. Given the reported success of Portuguese learning 4-month-olds, we can be sure that language experience affects infants’ ability to distinguish pitch contrasts, i.e., in English, questions are also different in terms of the word order and morphology, in Portuguese they are only different in terms of intonation, so infants *must* pay attention to this cue. Currently we want to test tone-language-acquiring infants aged 4-8mo to learn more about tone and pitch discrimination. We are still testing this group.

How do monolingual and bilingual English and Spanish learning infants distinguish vowels?(4-20-months)

Research on monolingual infants shows that speech perception abilities of infants are affected by their language experience. Although there are no exact statistics available, it has been suggested that there are as many, if not more, children growing up bilingual than monolingual (Tucker, 1998). Despite the growing bilingual population, as researchers, we have few answers concerning the speech and language development of the sizeable, bilingual part of the population.

In this study we ask if bilingual infants learning Spanish and English are able to distinguish between English vowels at the same age as their monolingual peers. We are particularly interested in vowels that are present only in English not Spanish. We have tested 4-month-old monolingual English, monolingual Spanish, and bilingual English and Spanish learning infants on their ability to distinguish the vowels in the words “take” and “tic” (note Spanish only has the first type of /e/ sound, but not the second). Infants in all three groups are able to distinguish the contrast. This replicated previous findings that very young infants are “citizens of the world”.

We have also tested 8-month-olds and 12-month-olds in all 3 groups, however, and all three groups fail, including the monolingual English-learning infants fail. We believe this is because English-acquiring infants have not yet encountered enough examples in their input that allow them to conclude these two vowels are different phonological categories in English. We are currently testing 18-20mo infants to verify that English-acquiring infants go through a U-shaped learning path to vowel acquisition, and hope to find a similar pattern in the bilingual group.

When do American-English infants learn that /d/ and /t/ alternate with a tap? (8-12-months)

In English, some sounds change depending on the context. The verb ‘pat’ ends in a “hard” [t], but when used in the word ‘patting’, the [t] becomes a ‘ tap’. We’ve tested 8 and 12mo olds on their ability to associate ‘pat’ to ‘patting’, as well as ‘pad’ (ending in a softer consonant) to ‘padding’. While they succeed with ‘pad’, 8mos fail with ‘pat’. However, by 12mo, they succeed with both. We suspect that the more different the features of the consonant are, the longer it takes for them to create that consonantal alternation. We are currently developing stimuli to test other possible alternating phonemes that are not present in English (e.g., take – taging) to investigate whether infants have learned those alternations based on their input or based on their phonetic similarity.

Do infants show a preference for looking at faces talking in their native language? (4 & 8-months)

Infants have been known to be able to distinguish between two languages using just the visual cues to speech – the movement of the mouth and rest of the face. In this study, we ask whether infants show a preference for their native language when they just have access to the visual cues to speech. 4- and 8-month-old infants were presented with side-by-side videos of a bilingual speaker producing English and Spanish and we measured how long they looked to each video. Infants learning only-English and bilingual English-Spanish-learning infants were tested. Results show that English-learning infants looked longer and more often to the English stimuli, demonstrating a native language preference. Bilingual infants, with exposure to both English and Spanish, looked equally often at both languages.

English-learning 4- and 8-month-olds were also tested to see if they still showed a preference for their native language when they could only hear speech, but not see anyone talking. Interim results suggest that 4-month-olds showed no preference, but 8-month-olds do, confirming previous research.

English-learning 4-month-olds were also tested on their preference between Dutch and Spanish. Dutch is a language that is closely related to English and shares many features. For example, they have similar speech rhythms. Spanish, on the other hand, is considered to be rhythmically distinct from English/Dutch. If infants prefered English over Spanish – that is, if infants were able to identify English as their native language and Spanish as a non-native langauge – using rhythm properties, then they should treat Dutch like their native language and prefer it over Spanish, as well. On the other hand, if they identify English by language-specific movements of the mouth and face, they should show no preference between Spanish and Dutch, since both will be non-native. According to interim results, when presented with side-by-side videos of a bilingual speaker producing Dutch and Spanish, 4-month-old English-learning infants show a preference for Dutch over Spanish.

Do infants have a preference for voiceless or voiced sounds? (4, 6, & 9-months)

Fricatives are a set of sounds distinguished by their noisiness. They include sounds such as /s/, /z/, /f/, /v/, /sh/, and /th/, giving examples from English. Fricatives can be divided into two subsets – voiceless fricatives and voiced fricatives. A fricative is considered to be voiced if the vocal folds are vibrating, or producing sound, when pronounced, and include /z/ and /v/. Fricatives without any vocal fold vibration are voiceless, and include /s/, /f/ and /sh/.

Fricatives are common across the world’s languages – and voiceless fricatives are far more common than voiced fricatives. Not only do more languages have voiceless fricatives than languages with voiced fricatives, but in many languages, voiceless fricatives are more frequent than voiced fricatives. This experiment examines whether there is any innate bias for voiceless fricatives that might explain this typological pattern. That is, are infants born with a preference for voiceless fricatives over voiced fricatives? Or do they develop a preference because they appear more frequently in their native language?

We have shown that 4- to 6-month-old English-learning infants show no preference for voiceless fricatives over voiced fricatives. 8- to 10-month-olds, on the other hand, do prefer voiceless fricatives over voiced. However, interim results indicate this preference is only observed when the innate bias and the statistical bias align. For example, infants show no preference between voiced and voiceless /th/ – the one voiced fricative that is statistically more common than its voiceless counterpart.

Follow up experiments comparing the possibility of an innate preference over a statistically-based preference showed that the voiceless preference only exists when both the innate bias and the statistical bias align.

What information do babies use to distinguish between languages? (5, 7, & 9-months)

Previous research shows that infants are born with the ability to distinguish between different languages, as long as those languages are prosodically distinct – that is, as long as they have very different rhythms and intonation patterns. Infants cannot distinguish between prosodically similar languages – for example, English and German – until a later age, and even then, they can only distinguish between their native language and a non-native language. It is unclear what infants are listening to in their native language that allows them to distinguish it from a non-native language. The first part of this study tried to determine when American English-learning infants learned to distinguish their native language from German, and from Australian English. The second part tried to determine what infants were listening to that allowed them to distinguish between the languages.

We found that 5-month-olds were not able to discriminate between American English and German, but 7-month-olds were, indicating this ability develops between those two ages. Neither 5, nor 7-month-olds were able to distinguish between American English and Australian English, but interim results suggest that 9-month-olds might, indicated this ability develops around that age.

We then tested 7-mo-olds to determine what information they were using to discriminate between English and German – segmental, pitch (or intonation) or rhythmic cues. To do this, we tested infants using low-pass filtered speech (removing segmental information), speech resynthesized with an artificial pitch contour and speech with a monotone pitch contour (both removing pitch information). We found that 7-mo-olds could still discriminate between English and German after the stimuli had been low-pass filtered, but not when the pitch contours of the stimuli were replaced. These results indicate that infants strongly attend to pitch information when discriminating languages.

What are the cues that infants use to segment vowel-initial words? (11-months)

In this experiment, babies listened for a minute or two to a passage. Then, we played them words that were present in the passage and words that were not. If babies correctly segment the words, they are expected to listen longer to words present in the passage. We asked if 11-month-olds who have a hard time segmenting words that begin with vowels (e.g. ash), can do so when these words follow a highly frequent function word, such as “the.”

The results of this study demonstrate that 11-month-olds, but not 8-month-olds, are able to use the frequently occurring function word “the” to segment vowel-initial words. This suggests that function words are known words for infants, and 11-month-olds are able to use this “known word” to find other words in a passage.

Can infants learn a specific sound change? Are they biased towards one type of change over another?(12-13 months)

Previous research has shown that infants are sensitive to phonetic similarity when learning phonological patterns (Steriade, 2001/2008; White, 2014). Our goal for this study was to see if infants’ willingness to generalize newly learned phonological alternations depend on the phonetic similiarity of the sounds involved. We exposed 12-13-month-olds to words from an artificial language whose distributions provided evidence for a phonological alternation between two relatively dissimilar sounds ([p ~ v] or [t ~ z]) and two relatively similar sounds ([b ~ v] or [d ~ z]). The infants favored and generalized to the pair of sounds that were more similar. The results indicate a learning bias favoring alternations between similar sounds.

Is infant babbling altered by short term exposure to a second language? (12-months)

In this study, we analyze the babbling of monolingual infants who have been exposed to Spanish in experimental settings for 30 minutes – 5 hours. Preliminary results show that with just 5 hours of exposure to Spanish, monolingual English learning infants are able to systematically alter their babbling when interacting with a Spanish versus an English interlocutor. In follow up studies, monolingual infants are being tested to determine if this result is an affect of direct imitation or learning, and bilingual infants are being tested to see if the trends in the data from infants with short term exposure mirror the babbling patterns of bilingual infants.

When does the transition from mere associative understanding to referential understanding of nouns emerge? (14 & 17-months)

Infants’ ability to recognize and reference the meaning of familiar words gradually increases over the 2^nd year of life. Initially, infants’ understanding of familiar words is restricted to certain contexts containing cues to aid recognition. Although at the beginning of word learning these cues are essential to highlighting novel word-object relationships, eventually the infant must be able to reference a word’s meaning when presented with speech devoid of these cues. Interim results suggest that 14-month-olds can reference the meaning of familiar words (ball, car, shoe, dog) without the most salient cues to word recognition: joint attention, visual referrent, and frequently-used sentence frame. Follow up studies are being conducted to determine if infants’ word-object referencing abilities can be generalized to different types of exemplars.

When are English-learning infants sensitive to the distribution of sound sequences in their native language?

In this experiment, we presented English-learning 5-month-olds with two sets of lists of monosyllables – one had English sounds that are common (e.g. boir, koof) and the other had English sounds that are uncommon (e.g., choiz, shuth). Infants were tested using the Headturn Preference Procedure[MS1] . English-learning 5-month-olds listened longer to lists with the more common English sounds, indicating that they are already familiar with the distribution of permissible sound sequences in English.

Study results