Why computational models are better than verbal theories: the case of nonword repetition

Tests of nonword repetition (NWR) have often been used to examine children’s phonological knowledge and word learning abilities. However, theories of NWR primarily explain performance either in terms of phonological working memory or long-term knowledge, with little consideration of how these processes interact. One theoretical account that focuses specifically on the interaction between short-term and long-term memory is the chunking hypothesis. Chunking occurs because of repeated exposure to meaningful stimulus items, resulting in the items becoming grouped (or chunked); once chunked, the items can be represented in short-term memory using one chunk rather than one chunk per item. We tested several predictions of the chunking hypothesis by presenting 5-6 year-old children with three tests of NWR that were either high, medium, or low in wordlikeness. The results did not show strong support for the chunking hypothesis, suggesting that chunking fails to fully explain children’s NWR behavior. However, simulations using a computational implementation of chunking (namely CLASSIC, or Chunking Lexical And Sublexical Sequences In Children) show that, when the linguistic input to 5-6 year old children is estimated in a reasonable way, the children’s data is matched across all three NWR tests. These results have three implications for the field: (a) a chunking account can explain key NWR phenomena in 5-6 year old children; (b) tests of chunking accounts require a detailed specification both of the chunking mechanism itself and of the input on which the chunking mechanism operates; and (c) verbal theories emphasizing the role of long-term knowledge (such as chunking) are not precise enough to make detailed predictions about experimental data, but computational implementations of the theories can bridge the gap

Lexical and sub-lexical knowledge influences the encoding, storage, and articulation of nonwords

Nonword repetition (NWR) has been used extensively in the study of child language. Although lexical and sub-lexical knowledge is known to influence NWR performance, there has been little examination of the NWR processes (e.g., encoding, storage, articulation) that may be affected by lexical and sub-lexical knowledge. We administered 2- and 3-syllable spoken nonword recognition and nonword repetition tests on two independent groups of 31 children (M=5;07). Spoken nonword recognition primarily involves encoding and storage, whereas NWR involves an additional articulation process. The influence of lexical and sub-lexical knowledge was determined by examining the amount of lexical errors produced. There was a clear involvement of long-term lexical and sub-lexical knowledge in both spoken nonword recognition and NWR. In spoken nonword recognition, twice as many errors involved selecting a foil that contained a lexical item (e.g., yashukup) over a foil that contained only nonsense syllables (e.g., yashunup). In repetition, over 30% of errors changed a nonsense syllable to a lexical item. Our results show that long-term lexical and sub-lexical knowledge is pervasive in NWR – any explanation of NWR performance must therefore consider the influence of lexical and sub-lexical knowledge throughout the whole repetition process, from the encoding of nonwords to the articulation of them

Reasoning with Pseudowords: How Properties of Novel Verbal Stimuli Influence Item Difficulty and Linguistic-Group Score Differences on Cognitive Ability Assessments

Pseudowords (words that are not real but resemble real words in a language) have been used increasingly as a technique to reduce contamination due to construct-irrelevant variance in assessments of verbal fluid reasoning (Gf). However, despite pseudowords being researched heavily in other psychology sub-disciplines, they have received little attention in cognitive ability testing contexts. Thus, there has been an assumption that all pseudowords work equally and work equally well for all test-takers. The current research examined three objectives with the first being whether changes to the pseudoword properties of length and wordlikeness (how much a pseudoword resembles a typical or common word in English) led to changes in item difficulty on verbal Gf items. The second objective was whether boundary conditions existed such that changes to pseudoword properties would differentially impact two linguistic sub-groups of participants – those who have English as their dominant language and those who do not have English as their dominant language. The last objective was to index and explore performance on these verbal Gf items when pseudowords were replaced with real words. Hypotheses predicting how pseudoword properties influenced item difficulty, how stimulie type – pseudoword or real word, impacted performance across linguistic sub-groups, and how linguistic sub-group status interacted with pseudoword properties were tested. Four sets of pseudowords were developed – short and wordlike, long and wordlike, short and un-wordlike, and long and un-wordlike, as well as two sets of real words – short and wordlike, and long and un-wordlike. Sixteen verbal Gf items, adapted from the LSAT, were developed to accommodate the pseudowords or real words and explore these three objectives. While none of the hypotheses were statistically significant, the results did indicate further areas of exploration. Specifically, verbal Gf items were easier when they featured longer pseudowords and more difficult when they featured un-wordlike pseudowords. Additionally, while performance of English-non-dominant participants was fairly balanced across real and pseudoword sets, English-dominant participants performed better on items featuring real words. Similarly, linguistic status interacted with wordlikeness such that English-dominant participants featured a decrease in performance as pseudowords moved from wordlike to un-wordlike. A full discussion of the findings, their implications, limitations of the current study, and directions for future research are included

Learning novel sound patterns

The acquisition of vocabulary represents a key phenomenon in language acquisition, yet it is still poorly understood. Gathercole and colleagues have recently provided a rigorous test of vocabulary knowledge (the nonword repetition test, Gathercole, Willis, Baddeley, & Emslie, 1994) and have adapted the phonological loop part of the working memory model (Baddeley & Hitch, 1974) to explain the nonword repetition findings (e.g. Gathercole & Baddeley, 1989). However, there are two major failings in their explanation: there is no description of how words are learned, and no definition of how the phonological loop interacts with long-term memory. We present an EPAM based computational model which overcomes these problems by combining the phonological loop approach with the EPAM/chunking approach (Feigenbaum & Simon, 1984). Trained on naturalistic phonemically coded speech (from mother’s utterances to 2-3 year old children), the model provides a good match to the nonword repetition data from 2-3 year old children. The model is also able to show the effect on nonword repetition when the model is trained using different sets of input. Implementing the phonological loop within EPAM represents a parsimonious approach to learning novel sound patterns and provides a more precise definition of how vocabulary acquisition may occur

Percepcija tipičnosti u leksikonu: tipičnost oblika riječi, leksička gustoća i morfonotaktička ograničenja

The extent to which a symbolic time–series (a sequence of sounds or letters) is a typical word of a language, referred to as WORDLIKENESS, has been shown to have effects in speech perception and production, reading proficiency, lexical development and lexical access, short–term and long–term verbal memory. Two quantitative models have been suggested to account for these effects: serial phonotactic probabilities (the likelihood for a given symbolic sequence to appear in the lexicon) and lexical density (the extent to which other words can be obtained from a target word by changing, deleting or inserting one or more symbols in the target). The two measures are highly correlated and thus easy to be confounded in measuring their effects in lexical tasks. In this paper, we propose a computational model of lexical organisation, based on Self–Organising Maps with Hebbian connections defined over a temporal layer (TSOMs), providing a principled algorithmic account of effects of lexical acquisition, processing and access, to further investigate these issues. In particular, we show that (morpho–)phonotactic probabilities and lexical density, though correlated in lexical organisation, can be taken to focus on different aspects of speakers’ word processing behaviour and thus provide independent cognitive contributions to our understanding of the principles of perception of typicality that govern lexical organisation.Pokazano je da stupanj do kojeg je određeni simbolički vremenski slijed (slijed zvukova ili slova) tipična riječ u jeziku, odnosno TIPIčNOST OBLIKA RIJEčI, ima učinaka u proizvodnji i percepciji govora, uspješnosti čitanja, leksičkom razvoju i pristupu leksemima te kratkotrajnoj i dugotrajnoj verbalnoj memoriji. Predložena su dva kvantitativna modela kako bi se objasnili navedeni učinci: serijalne fonotaktičke vjerojatnosti (vjerojatnost pojavljivanja određenog simboličkog slijeda u leksikonu) i leksička gustoća (mjera do koje se druge riječi mogu proizvesti zamjenom, brisanjem ili umetanjem jednog ili više simbola u ciljnu riječ). Te dvije mjere visoko koreliraju, zbog čega su teško razdvojive pri mjerenju njihovih učinaka u leksičkim zadacima. U ovom radu predlažemo računalni model leksičke organizacije koji pruža sustavan algoritamski prikaz učinaka leksičkog usvajanja, obrade i pristupa kako bi se dodatno istražila ova pitanja. Taj se model temelji na samoorganizirajućim mapama s hebijanskim vezama definiranim preko vremenske razine (engl. TSOMs). Posebice pokazujemo da se (morfo-)fonotaktičke vjerojatnosti i leksička gustoća, iako korelirani u leksičkoj organizaciji, mogu shvatiti kao načini usredotočavanja na različite aspekte govornikova ponašanja pri obradi riječi i tako pružiti nezavisne kognitivne doprinose našem razumijevanju principa percepcije i tipičnosti koji upravljaju leksičkom organizacijom

Percepcija tipičnosti u leksikonu: tipičnost oblika riječi, leksička gustoća i morfonotaktička ograničenja

The extent to which a symbolic time–series (a sequence of sounds or letters) is a typical word of a language, referred to as WORDLIKENESS, has been shown to have effects in speech perception and production, reading proficiency, lexical development and lexical access, short–term and long–term verbal memory. Two quantitative models have been suggested to account for these effects: serial phonotactic probabilities (the likelihood for a given symbolic sequence to appear in the lexicon) and lexical density (the extent to which other words can be obtained from a target word by changing, deleting or inserting one or more symbols in the target). The two measures are highly correlated and thus easy to be confounded in measuring their effects in lexical tasks. In this paper, we propose a computational model of lexical organisation, based on Self–Organising Maps with Hebbian connections defined over a temporal layer (TSOMs), providing a principled algorithmic account of effects of lexical acquisition, processing and access, to further investigate these issues. In particular, we show that (morpho–)phonotactic probabilities and lexical density, though correlated in lexical organisation, can be taken to focus on different aspects of speakers’ word processing behaviour and thus provide independent cognitive contributions to our understanding of the principles of perception of typicality that govern lexical organisation.Pokazano je da stupanj do kojeg je određeni simbolički vremenski slijed (slijed zvukova ili slova) tipična riječ u jeziku, odnosno TIPIčNOST OBLIKA RIJEčI, ima učinaka u proizvodnji i percepciji govora, uspješnosti čitanja, leksičkom razvoju i pristupu leksemima te kratkotrajnoj i dugotrajnoj verbalnoj memoriji. Predložena su dva kvantitativna modela kako bi se objasnili navedeni učinci: serijalne fonotaktičke vjerojatnosti (vjerojatnost pojavljivanja određenog simboličkog slijeda u leksikonu) i leksička gustoća (mjera do koje se druge riječi mogu proizvesti zamjenom, brisanjem ili umetanjem jednog ili više simbola u ciljnu riječ). Te dvije mjere visoko koreliraju, zbog čega su teško razdvojive pri mjerenju njihovih učinaka u leksičkim zadacima. U ovom radu predlažemo računalni model leksičke organizacije koji pruža sustavan algoritamski prikaz učinaka leksičkog usvajanja, obrade i pristupa kako bi se dodatno istražila ova pitanja. Taj se model temelji na samoorganizirajućim mapama s hebijanskim vezama definiranim preko vremenske razine (engl. TSOMs). Posebice pokazujemo da se (morfo-)fonotaktičke vjerojatnosti i leksička gustoća, iako korelirani u leksičkoj organizaciji, mogu shvatiti kao načini usredotočavanja na različite aspekte govornikova ponašanja pri obradi riječi i tako pružiti nezavisne kognitivne doprinose našem razumijevanju principa percepcije i tipičnosti koji upravljaju leksičkom organizacijom

Perception of typicality in the lexicon: wordlikeness, lexical density and morphonotactic constraints

The extent to which a symbolic time–series (a sequence of sounds or letters) is a typical word of a language, referred to as WORDLIKENESS, has been shown to have effects in speech perception and production, reading proficiency, lexical development and lexical access, short–term and long–term verbal memory. Two quantitative models have been suggested to account for these effects: serial phonotactic probabilities (the likelihood for a given symbolic sequence to appear in the lexicon) and lexical density (the extent to which other words can be obtained from a target word by changing, deleting or inserting one or more symbols in the target). The two measures are highly correlated and thus easy to be confounded in measuring their effects in lexical tasks. In this paper, we propose a computational model of lexical organisation, based on Self–Organising Maps with Hebbian connections defined over a temporal layer (TSOMs), providing a principled algorithmic account of effects of lexical acquisition, processing and access, to further investigate these issues. In particular, we show that (morpho–)phonotactic probabilities and lexical density, though correlated in lexical organisation, can be taken to focus on different aspects of speakers’ word processing behaviour and thus provide independent cognitive contributions to our understanding of the principles of perception of typicality that govern lexical organisation

Nonword repetition depends on the frequency of sublexical representations at different grain sizes: evidence from a multi-factorial analysis

The nonword repetition task (NWR) has been widely used in basic cognitive and clinical research, as well as in clinical assessment, and has been proposed as a clinical marker for Specific Language Impairment (SLI). Yet the mechanisms underlying performance on this task are not clear. This study offers insights into these mechanisms through a comprehensive examination of item-related variables identified in previous research as possibly contributing to NWR scores and through testing the predictive power of each in relation to the others. A unique feature of the study is that all factors are considered simultaneously. Fifty-seven typically developing children were tested with a NWR task containing 150 nonwords differing in length, phonotactic probability, lexical neighbourhood and phonological complexity. The results indicate that phonological processing of novel words draws on sublexical representations at all grain sizes and that these representations are phonological, unstructured and insensitive to morphemehood. We propose a novel index – mean ngram frequency of all phonemes – that best captures the extent to which a nonword draws on sublexical representations. The study demonstrates the primacy of sublexical representations in NWR performance with implications for the nature of the deficit in SLI

A computational simulation of children's performance across three nonword repetition tests

The nonword repetition test has been regularly used to examine children’s vocabulary acquisition, and yet there is no clear explanation of all of the effects seen in nonword repetition. This paper presents a study of 5-6 year-old children’s repetition performance on three nonword repetition tests that vary in the degree of their lexicality. EPAM-VOC, a model of children’s vocabulary acquisition, is then presented that captures the children’s performance in all three repetition tests. The model represents a clear explanation of how working memory and long-term lexical and sub-lexical knowledge interact in a way that is able to simulate repetition performance across three nonword tests within the same model and without the need for test specific parameter settings