Real-Time Dynamics of Language Acquisition in Two-Year-Old Children and Connectionist Models Jessica S. Horst Larissa K. Samuelson Bob McMurray Dept. of Psychology University of Iowa

Word Learning Children are amazing word learners: By 5 th birthday know 60,000 words Estimated to learn 9 words/day from 18mo (Carey, 1978) Big Question: What it takes to turn a novel name into a known name? “Puppy” “Kitty” “Doll” “Teddy” “?” “Bunny”

Fast Mapping Linking a novel name to a novel referent with minimal exposure (Carey & Bartlett, 1978) Literature associates amazing word learning with fast mapping: Children can fast map several names in a single session (Golinkoff et al., 1992) Children can determine the referent of a novel name in less than 3 seconds (Halberda, submitted) Big Picture: Understanding the processes of word learning, by determining exactly what children are learning about name-object mappings taught with minimal exposure

Two Times Scales in Language Acquisition Fast Mapping and Word Learning represent two time scales of learning: Fast Mapping: quick process emerging in the moment Based on the Principle of Lexical Contrast (Clark, 1987) Rabbit “Rabbit”? “Kitty” ≠ “Rabbit” “Puppy” ≠ “Rabbit” This must be “Rabbit”

Word Learning: gradual process over the course of development Evidenced by production or identification of the referent after a delay Next week, we’re going to see Sally’s Rabbit. She might let you pet the Rabbit. The Rabbit is very soft, but you must be very gentle with the Rabbit…. My Picture Book Rabbit !

Question: Is Lexical Contrast enough to truly learn a word, i.e., to show evidence of learning after a delay?

General Methods Fast mapping trials: 2 familiar objects 1 novel object 3 warm-up trials with 3 familiar objects are presented before the FM trials. 1 additional warm-up trial is presented before the retention trials. Cow (familiar)Block (familiar)Yok (novel) Retention trials: 1 target 1 prev. named novel 1 prev. unnamed novel Child is asked for both familiar (cow) and novel (fode) objects across trials Five-minute delay period Yok (target) Tannin (named foil) unnamed foil (previously seen)

24-month-old children (N = 16) 2 familiar & 1 novel objects 8 familiar and 8 novel trials (e.g., “get the cow!” or “get the yok!”) Experiment 1: Children were excellent at fast mapping (finding the referent of novel and familiar words in the moment). Children were unable to show evidence of retention* after a five-minute delay. *Note: only tested correctly fast mapped names for retention Familiar NamesNovel NamesRetention Proportion of Correct Choices Chance *** *** p <.001

Did Children Learn Individual Words? What if children may retain 1, but not as many as 8 names? names were analyzed by order of presentation during fast mapping none of the positions above chance levels Children unable to retain mappings after a 5-minute delay Names 1 & 2 Proportion of Correct Choices Names 3 & 4Names 5 & 6Names 7 & 8 Chance Retention Data

Initial findings replicated with simpler tasks: effect of number of names or trials? Children’s difficulty in retaining newly fast-mapped names is not related to the number of names or trials Experiments 2 and 3 Fast MappingRetention 10/16 * 4/10 Fast MappingRetention 8/16 † 3/8 * Binomial, p <.05, † Binomial, p =.12 Replication #1 (E2) (N = 16) Replication #2 (E3) (N = 16) 1 Novel Name 8 Familiar Names 7 Preference Trials 1 Novel Name 2 Familiar Names Expected by chance: 3.33Expected by chance: 2.67Expected by chance: 5.33

The Model End State Post Learning Intermediate State During Learning 15 Auditory & 15 Visual units: Activate according to what child sees and hears 90 Decision units Names presented singly with a variable number of objects Name-Decision & Object-Decision associations strengthened via learning After 4000 training trials network forms localist representations Learns name-object links and to ignore visual competitors Decision Units Auditory Units Visual Units

Activation feeds from input layers to decision layers. Decision units compete via inhibition. Activation feeds back to input layers. Cycle continues until system settles. Processing In The Model (McMurray & Spivey, 2000) Unsupervised Hebbian learning occurs on every cycle. Decision Units (Hidden) Layer Auditory Inputs Visual Inputs “fork” “spoon” “cup” “plate” “knife” “napkin”

Online decision dynamics reflect auditory and visual competitors.

Auditory Input Decision Units Connection Strength

20 networks initialized with random weights 15 word lexicon (names & objects): Familiarization with Initial Vocabulary: Familiarized with 5 familiar items for 5000 epochs Items presented in random order Fast Mapping Experiment: 5 familiar names 5 novel names 5 held out 5 retention trials 10 fast mapping trials familiar novel held out cup “Fode” ball fode “Yok”yok fode ???

Fast Mapping In The Model Model succeeded on both types of fast-mapping trials Model behavior patterned with empirical results Learning was not turned of during fast mapping Familiar NameNovel Name Proportion of Correct Choices *** Chance

The model fails to “retain” the newly learned words after a “delay” Learning was not turned of during retention Chance Familiar NameNovel NameRetention Proportion of Correct Choices *** Retention In The Model

Why Didn’t The Simulations Retain? Analyses of weight matrices revealed that relatively little learning occurred during fast mapping trials. End Familiar Words Familiar Words Novel Words Control Words After Learning After Test Squared Deviations Change (RMS) in portions of weight matrix Familiar WordsNovel WordsControl Words After Test Squared Deviations Temporal dynamics of processing

Prior to Experiment After Experiment Connection Strength

Implications Making the name-object mapping in the moment is not enough to form a long-term memory representation of the novel name Lexical Contrast provided in 1 fast mapping trial not sufficient to turn a novel name into a known name Goal for Experiment 4: Add more support to the task to facilitate word learning: Increase the number of naming instances (see Merriman & Marazita,1995) Provide reinforcement Provide ostensive naming (see Mervis & Bertrand, 1994)

Methods Two conditions: reinforced and ostensive definition All children heard the names 5 times before each trial: “Can you get the yok? Help me find the yok! Are you ready to find the yok? Can you help me get the yok? Let’s get the yok!” Reinforced Condition: “Yes, that is the yok” (Child holding) Ostensive Naming: “Look, this is the yok” (Exptr holding Target & pointing) Correct choice: Incorrect choice: Reinforced Condition: “That is the cow.” (Child holding) Ostensive Naming: “Look, this is the yok” (Exptr holding Target & pointing)

Experiment 4: Again, children were excellent at fast mapping Overall, however, they were very poor at retaining* No effects of Condition were found for fast mapping * Note: only tested correctly fast mapped names for retention Familiar NamesNovel NamesRetention Proportion of Correct Choices Retention Ostensive Definition *** *** p <.001 chance

When analyzed by block, it is clear that children retained names in the Ostensive Definition Condition Data suggests children can learn up to 4 names in this task Analysis of looking indicated that children attended to novel object twice as much in OD condition Block 1Block 2Block 3Block 4 Proportion of Correct Choices Retention Ostensive Definition * * * p <.05

Overall, children were excellent at finding the referent in the moment, but unable to retain the names over a five- minute delay (E1) Follow-up experiments indicate poor retention not due to The number of names introduced (E2) or The number of trials in the session (E3) The Connectionist Network captured the data and Showed the same pattern of results: excellent Fast Mapping, poor Retention Learning was occurring during fast mapping, but not enough learning to support later evidence of retention Conclusions

Together, Experiments and Simulations suggest that Lexical Contrast alone is not enough to allow children to form a strong enough representation of a novel name to show evidence of word learning after five minutes Children are able to retain words taught in a Fast Mapping Task if: Provided with multiple naming instances And ostensive definitions (E4) But only able to learn up to 4 words Future research will explore the role of attention in helping children turn novel names into known names

Take Home Message: Fast Mapping is a quick, online mechanism that can produce smart online behavior but not actual word learning.

Carey, S. (1978). The child as word learner. In M. Halle, J. Bresnan & A. Miller (Eds.), Linguistic Theory and Psychological Reality (pp ). Cambridge, MA: MIT Press. Carey, S., & Bartlett, E. (1978). Acquiring a single new word. Proceedings of the Stanford Child Language Conference, 15(17-29). Clark, E. (1987). The Principle of Contrast: A Constraint on Language Acquisition. In B. McWhinney (Ed.), Mechanisms of Language Acquisition (pp. 1-33). Hillsdale, NJ: Lawrence Erlbaum Associates Inc. Golinkoff, R. M., Hirshpasek, K., Bailey, L. M., & Wenger, N. R. (1992). Young-Children and Adults Use Lexical Principles to Learn New Nouns. Developmental Psychology, 28(1), Halberda, J. & Goldman, J. (submitted). One Trial Learning in 2-Year-Olds: Children Learn New Nouns in 3 Seconds Flat. Mervis, C. B., & Bertrand, J. (1994). Acquisition of the Novel Name Nameless Category (N3c) Principle. Child Development, 65(6), Merriman, W. E. & Marazita, J. M. (1995). The Effect of Hearing Similar Sounding Words on Young 2- Year-Olds’ Disambiguation of Novel Reference. Developmental Psychology, 31(6), McMurray, B., & Spivey, M. (2000). The Categorical Perception of Consonants: The Interaction of Learning and Processing, The Proceedings of the Chicago Linguistics Society, 34(2), References Acknowledgements The authors would like to thank Joseph Toscano for programming assistance and support. This work was supported by NICHD Grant R01-HD to LKS.