Can infants distinguish between two types of /l/? (6-months)
How do monolingual and bilingual English and Spanish learning infants distinguish vowels?(4 & 8-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.
We are currently testing 4- and 8-month-old monolingual English and Bilingual English and Spanish learning infants on their ability to distinguish the English /e/ (e.g. the vowel in “bayed”) – /E/ (“bed”) vowels. Note that Spanish has only one vowel /e/ (e.g. in “perro”) Preliminary findings indicate that, when the two languages being learned are rhythmically dissimilar like Spanish and English, bilingual infants are able to discriminate vowel contrasts that are present in one, but not the other language, at an earlier age.
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.
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.
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.
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.
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 2nd 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.