Computational Bases of Two Types of Developmental Dyslexia

The bases of developmental dyslexia were explored using connectionist models. The behavioral literature suggests that there are two dyslexic subtypes: "phonological" dyslexia involves impairments in phonological knowledge whereas in "surface " dyslexia phonological knowledge is apparently intact and the deficit may instead reflect a more general developmental delay. We examined possible computational bases for these impairments within connectionist models of the mapping from spelling to sound. Phonological dyslexia was simulated by reducing the capacity of the models to represent this type of information. The surface pattern was simulated by reducing the number of hidden units. Performance of the models captured the major behavioral phenomena that distinguish the two subtypes. Phonological impairment has a greater impact on generalization (reading nonwords such as NUST); the hidden unit limitation has a greater impact on learning exception words such as PINT. More severe impairments produce mixed cases in which both nonwords and exceptions are impaired. Thus, the simulations capture the effects of different types and degrees of impairment within a major component of the reading system

Using Connectionist Networks to Examine thue Role of Prior Constraints in Human Learning

This research investigated the effects of prior knowledge on learning in psychologically-plausible connectionist networks. This issue was examined with respect to the benchmark orthography-to-phonology mapping task (Sejnowski & Rosenberg, 1986; Seidenberg & McClelland, 1989). Learning about the correspondences between orthography and phonology is a critical step in learning to read. Children (unlike the networks mentioned above) bring to this task extensive knowledge about the sound-structure of their language. We first describe a simple neural network that acquired some of this phonological knowledge. W e then summarize simulations showing that having this knowledge in place facilitates the acquisition of orthographicphonological correspondences, producing a higher level of asymptotic performance with fewer implausible errors and better nonword generalization. The results suggest that connectionist networks may provide closer approximations to human performance if they incorporate more realistic assumptions about relevant sorts of background knowledge

Functional Bases of Phonological Universals: A Connectionist Approach

Proceedings of the Twenty-Fourth Annual Meeting of the Berkeley Linguistics Society: General Session and Parasession on Phonetics and Phonological Universals (1998

Toddlers Activate Lexical Semantic Knowledge in the Absence of Visual Referents: Evidence from Auditory Priming

Language learners rapidly acquire extensive semantic knowledge, but the development of this knowledge is difficult to study, in part because it is difficult to assess young children\u27s lexical semantic representations. In our studies, we solved this problem by investigating lexical semantic knowledge in 24-month-olds using the Head-turn Preference Procedure. In Experiment 1, looking times to a repeating spoken word stimulus (e.g., kitty-kitty-kitty) were shorter for trials preceded by a semantically related word (e.g., dog-dog-dog) than trials preceded by an unrelated word (e.g., juice-juice-juice). Experiment 2 yielded similar results using a method in which pairs of words were presented on the same trial. The studies provide evidence that young children activate of lexical semantic knowledge, and critically, that they do so in the absence of visual referents or sentence contexts. Auditory lexical priming is a promising technique for studying the development and structure of semantic knowledge in young children

Modeling the Use of Frequency and Contextual Biases in Sentence Processing

MacDonald, Pearlmutter, and Seidenberg (1993) propose an alternative to the dominant view in sentence processing that syntactic ambiguities are resolved by heuristics based on structural simplicity. MacDonald et al. argue that such ambiguities can be defined in terms of alternatives associated with information in individual lexical items, and thus that syntactic ambiguities can be resolved by lexical disambiguation mechanisms relying on access to the relative frequencies of alternatives and to biases created by contextual constraints. We present evidence from a computer simulation of the use of frequency-based and contextual constraints in the processing of the main verb/reduced relative syntactic ambiguity, showing that frequency and relatively limited contextual information from a sample of natural language can interact sufficiently to model basic results in the literature

Acquisition and Representation of Grammatical Categories: Grammatical Gender in a Connectionist Network

In traditional models of language production grammatical categories are represented as abstract features independent of semantics and phonology. An alternative view is proposed where syntactic categories emerge as a higher-order regularity from semantic and phonological properties of words. The proposal was tested using grammatical gender in Serbian, a south Slavic language with rich morphology. Semantic and phonological correlates of gender are described using a corpus of 1221 Serbian nouns. A PDP network was trained to produce the same words based on distributed semantic representation as input and distributed phonological representation as output, and with no explicit representation of grammatical gender. Upon successful learning of the training corpus, generalization was explored using test corpora designed to capture semantic and phonological properties of different genders. The findings suggest that grammatical gender, as other syntactic categories, may be viewed as emerging through coherent co-variation of semantic and phonological properties of words during learning

Multiple code activation in word recognition: Evidence from rhyme monitoring

Seidenberg and Tanenhaus (1979) reported that orthographically similar rhymes were detected more rapidly than dissimilar rhymes in a rhyme monitoring task with auditory stimulus presentation. The present experiments investigated the hypothesis that these results were due to a rhyme production-frequency bias in favor of similar rhymes that was present in their materials. In three experiments, subjects monitored short word lists for the word that rhymed with a cue presented prior to each list. All stimuli were presented auditorily. Cue-target rhyme production frequency was equated for orthographically similar and dissimilar rhymes. Similar rhymes were detected more rapidly in all three experiments, indicating that orthographic information was accessed in auditory word recognition. The results suggest that multiple codes are automatically accessed in word recognition. This entails a reinterpretation of phonological "recoding" in visual word recognition