Efthymia C. Kapnoula

Evaluating cognitive models of visual word recognition using fMRI: Effects of lexical and sublexical variables

In this study predictions of the dual-route cascaded (DRC) model of word reading were tested using fMRI. Specifically, patterns of co-localization were investigated: (a) between pseudoword length effects and a pseudowords vs. fixation contrast, to reveal the sublexical grapho-phonemic conversion (GPC) system; and (b) between word frequency effects and a words vs. pseudowords contrast, to reveal the orthographic and phonological lexicon. Forty four native speakers of Greek were scanned at 3T in an event-related lexical decision task with three event types: (a) 150 words in which frequency, length, bigram and syllable frequency, neighborhood, and orthographic consistency were decorrelated; (b) 150 matched pseudowords; and (c) fixation. Whole-brain analysis failed to reveal the predicted co-localizations. Further analysis with participant-specific regions of interest defined within masks from the group contrasts revealed length effects in left inferior parietal cortex and frequency effects in the left middle temporal gyrus. These findings could be interpreted as partially consistent with the existence of the GPC system and phonological lexicon of the model, respectively. However, there was no evidence in support of an orthographic lexicon, weakening overall support for the model. The results are discussed with respect to the prospect of using neuroimaging in cognitive model evaluation.

Newly learned word forms are abstract and integrated immediately after acquisition

A hotly debated question in word learning concerns the conditions under which newly learned words compete or interfere with familiar words during spoken word recognition. This has recently been described as a key marker of the integration of a new word into the lexicon and was thought to require consolidation Dumay & Gaskell, (Psychological Science, 18, 35–39, 2007; Gaskell & Dumay, Cognition, 89, 105–132, 2003). Recently, however, Kapnoula, Packard, Gupta, and McMurray, (Cognition, 134, 85–99, 2015) showed that interference can be observed immediately after a word is first learned, implying very rapid integration of new words into the lexicon. It is an open question whether these kinds of effects derive from episodic traces of novel words or from more abstract and lexicalized representations. Here we addressed this question by testing inhibition for newly learned words using training and test stimuli presented in different talker voices. During training, participants were exposed to a set of nonwords spoken by a female speaker. Immediately after training, we assessed the ability of the novel word forms to inhibit familiar words, using a variant of the visual world paradigm. Crucially, the test items were produced by a male speaker. An analysis of fixations showed that even with a change in voice, newly learned words interfered with the recognition of similar known words. These findings show that lexical competition effects from newly learned words spread across different talker voices, which suggests that newly learned words can be sufficiently lexicalized, and abstract with respect to talker voice, without consolidation.

Training Alters the Resolution of Lexical Interference: Evidence for Plasticity of Competition and Inhibition

Language learning is generally described as a problem of acquiring new information (e.g., new words). However, equally important are changes in how the system processes known information. For example, a wealth of studies has suggested dramatic changes over development in how efficiently children recognize familiar words, but it is unknown what kind of experience-dependent mechanisms of plasticity give rise to such changes in real-time processing. We examined the plasticity of the language processing system by testing whether a fundamental aspect of spoken word recognition, lexical interference, can be altered by experience. Adult participants were trained on a set of familiar words over a series of 4 tasks. In the high-competition (HC) condition, tasks were designed to encourage coactivation of similar words (e.g., net and neck) and to require listeners to resolve this competition. Tasks were similar in the low-competition (LC) condition, but did not enhance this competition. Immediately after training, interlexical interference was tested using a visual world paradigm task. Participants in the HC group resolved interference to a fuller degree than those in the LC group, demonstrating that experience can shape the way competition between words is resolved. TRACE simulations showed that the observed late differences in the pattern of interference resolution can be attributed to differences in the strength of lexical inhibition. These findings inform cognitive models in many domains that involve competition/interference processes, and suggest an experience-dependent mechanism of plasticity that may underlie longer term changes in processing efficiency associated with both typical and atypical development.

Short-Term and Long-Term Effects on Visual Word Recognition.

Effects of lexical and sublexical variables on visual word recognition are often treated as homogeneous across participants and stable over time. In this study, we examine the modulation of frequency, length, syllable and bigram frequency, orthographic neighborhood, and graphophonemic consistency effects by (a) individual differences, and (b) item repetition. A group of 129 participants performed lexical decision and naming, in counterbalanced order, using a set of 150 Greek words in which these variables were decorrelated. Frequency, length, and syllable frequency effects were reduced by a preceding task. Length effects were inversely related to years of education. Neighborhood effects depended on the metric used. There were no significant effects or interactions of bigram frequency or consistency. The results suggest that exposure to a word causes transient effects that may cumulatively develop into permanent individual differences. Models of word recognition must incorporate item-specific learning to account for these findings.

Evaluating the sources and functions of gradiency in phoneme categorization: An individual differences approach.

During spoken language comprehension listeners transform continuous acoustic cues into categories (e.g., /b/ and /p/). While long-standing research suggests that phonetic categories are activated in a gradient way, there are also clear individual differences in that more gradient categorization has been linked to various communication impairments such as dyslexia and specific language impairments (Joanisse, Manis, Keating, & Seidenberg, 2000; López-Zamora, Luque, Álvarez, & Cobos, 2012; Serniclaes, Van Heghe, Mousty, Carré, & Sprenger-Charolles, 2004; Werker & Tees, 1987). Crucially, most studies have used 2-alternative forced choice (2AFC) tasks to measure the sharpness of between-category boundaries. Here we propose an alternative paradigm that allows us to measure categorization gradiency in a more direct way. Furthermore, we follow an individual differences approach to (a) link this measure of gradiency to multiple cue integration, (b) explore its relationship to a set of other cognitive processes, and (c) evaluate its role in individuals’ ability to perceive speech in noise. Our results provide validation for this new method of assessing phoneme categorization gradiency and offer preliminary insights into how different aspects of speech perception may be linked to each other and to more general cognitive processes.

Lexical and sublexical effects on visual word recognition in Greek: comparing human behavior to the dual route cascaded model

ABSTRACT We evaluated the dual route cascaded (DRC) model of visual word recognition using Greek behavioural data on word and nonword naming and lexical decision, focusing on the effects of syllable and bigram frequency. DRC was modified to process polysyllabic Greek words and nonwords. The Greek DRC and native speakers of Greek were presented with the same sets of word and nonword stimuli, spanning a wide range on several psycholinguistic variables, and the sensitivity of the model to lexical and sublexical variables was compared to the effects of these factors on the behavioural data. DRC pronounced correctly all the stimuli and successfully simulated the effects of frequency in words, and of length and bigram frequency in nonwords. However, unlike native speakers of Greek, DRC failed to demonstrate sensitivity to word length and syllabic frequency. We discuss the significance of these findings in constraining models of visual word recognition.

The young and the meaningless: Novel-word learning without meaning or sleep

Existing work suggests that sleep-based consolidation (Gaskell & Dumay, 2003) is required for newly learned words to interact with other words and phonology. Some studies report that meaning may also be needed (Leach and Samuel, 2007), making it unclear whether meaningful representations are required for such interactions. We addressed these issues by examining lexical competition between novel and known words during online word recognition. After a brief training on novel word-forms (without referents), we evaluated whether the newly learned items could compete with known words. During testing, participants heard word stimuli that were made by cross-splicing novel with known word-forms (NEP+NET=NEpT) and the activation of the target-word was quantified using the visual world paradigm. Results showed that the freshly learned word-forms engaged in competition with known words with only 15 minutes of training. These results are important for two reasons: First, lexical integration is initiated very early in learning and does not require associations with semantic representations or sleep-based consolidation. Second, given studies showing that lexical competition plays a critical role in resolving acoustic ambiguity (McMurray, Tanenhaus & Aslin, 2008; McMurray et al, 2009), our results imply that this competition does not have to be between semantically integrated lexical units.