Connectivity among semantic associates: an fMRI study of semantic priming

Semantic priming refers to a reduction in the reaction time to identify or make a judgment about a stimulus that has been immediately preceded by a semantically related word or picture and is thought to result from a partial overlap in the semantic associates of the two words. A semantic priming lexical decision task using spoken words was presented in event-related fMRI and behavioral paradigms. Word pairs varied in terms of semantic relatedness and the connectivity between associates. Thirteen right-handed subjects underwent fMRI imaging and 10 additional subjects were tested in a behavioral version of the semantic priming task. It was hypothesized priming would be greatest, reaction time fastest, and cortical activation reduced the most for related word pairs of high connectivity, followed by related word pairs of low connectivity, and then by unrelated word pairs. Behavioral and fMRI results confirmed these predictions. fMRI activity located primarily in bilateral posterior superior and middle temporal regions showed modulation by connectivity and relatedness. The results suggest that these regions are involved in semantic processing.     

The impact of retrieval suppression on conceptual implicit memory

ABSTRACT

When people suppress retrieval of episodic memories, it can induce forgetting on later direct tests of memory for those events. Recent reports indicate that suppressing retrieval affects less conscious, unintentional retrieval of unwanted memories as well, at least on perceptually-oriented indirect tests. In the current study we examined how suppressing retrieval affects conceptual implicit memory for the suppressed content, using a category verification task. Participants studied cue-target words pairs in which the targets were exemplars of 22 semantic categories, such as vegetables or occupations. They then repeatedly retrieved or suppressed the targets in response to the cues for some of those pairs. Afterwards, they were exposed to the targets intermixed with novel items, one at a time, and asked to verify the membership of each of the words in a semantic category, as quickly as possible. Judgment response times to studied words were faster than to unstudied exemplars, reflecting repetition priming, as has been previously observed. Strikingly, the beneficial effects of prior exposure on response time were eliminated for targets that had been suppressed. Follow-up explicit memory tests also demonstrated that retrieval suppression continued to disrupt episodic recall for the items that had been just been re-exposed on the category verification test. These findings support the contention that the effects of retrieval suppression are not limited to episodic memory, but also affect indirect expressions of those memories on conceptually oriented tests, raising the possibility that underlying semantic representations of suppressed content are affected.     

Selective impairment of masked priming in dual-task performance

This study investigated the impact of divided attention on masked priming. In a dual-task setting, two tasks had to be carried out in close temporal succession: a tone discrimination task and a masked priming task. The order of the tasks was varied between experiments, and attention was always allocated to the first task—that is, the first task was prioritized. The priming task was the second (nonprioritized) task in Experiment 1 and the first (prioritized) task in Experiment 2. In both experiments, “novel” prime stimuli associated with semantic processing were essentially ineffective. However, there was intact priming by another type of prime stimuli associated with response priming. Experiment 3 showed that all these prime stimuli can reveal significant priming effects during a task-switching paradigm in which both tasks were performed consecutively. We conclude that dual-task specific interference processes (e.g., the simultaneous coordination of multiple stimulus–response rules) selectively impair priming that is assumed to rely on semantic processing.     

Effects of the degree of meaning similarity on cross-language semantic priming in highly proficient bilinguals

This study aimed to determine if access to meaning can be directly achieved from the words in the two languages, examining the influence of the degree of semantic overlap between related words across languages in the pattern of priming effects. Nonassociative semantically related words (members of the same category) were used, avoiding explicitly associative relationships. Using a priming paradigm, highly proficient Catalan–Spanish bilinguals were visually presented with pairs of words that either were translations of each other, had a very close semantic relationship (in terms of shared features), a close semantic relationship, or no semantic relationship at all. Participants performed either a lexical decision task (Experiment 1) or a semantic decision task (Experiment 2). The main results of the study were the same in both language directions (Spanish–Catalan and Catalan–Spanish), showing that the degree of semantic overlap (in terms of shared features) between words in different languages can modulate priming effects, regardless of the language of the prime and the task used. These results demonstrate that there is cross-language activation of shared semantic representations and, thus, that highly proficient bilinguals can have direct access to word meaning from the two languages.     

Estructura morfológica y recuperación léxica

Resumen

El objetivo principal de esta investigación es el de contribuir a un mayor conocimiento del papel que desempeña la estructura morfológica de las palabras en la organización del léxico interno y, por consiguiente, en las estrategias que emplean los sujetos para acceder a la representación mental de las palabras. Más en concreto, se trata de ver cuál es la relación existente entre la representación de la forma base de una palabra (por ej., flor) y la de formas derivadas de la misma (por ej., florero, florecer, florido) de cara a una posible simplificación del inventario mental de entradas léxicas.

Se han realizado tres experimentos, basados en una tarea de decisión léxica y en la utilización de la técnica de «priming» o presentación previa de un supuesto elemento facilitador del reconocimiento de cada estímulo. Se midió la latencia de respuesta para clasificar los estímulos como palabras o no-palabras del idioma. Los dos primeros experimentos se efectuaron bajo la modalidad visual de reconocimiento y el tercero, bajo la modalidad auditiva. En todos los casos, las comparaciones relevantes se establecen entre los TRs correspondientes a una misma palabra en condiciones experimentales diferentes: según vaya precedida por sí misma, o por una relacionada morfológicamente, o cuando no vaya precedida ni por sí misma ni por otra relacionada (condición de control).

Los resultados obtenidos bajo las dos modalidades perceptivas son coincidentes y ponen de manifiesto que: 1) se da un efecto de facilitación en el reconocimiento, tanto al presentar una palabra precedida por sí misma (repetición) como al presentarla precedida por otra relacionada morfológicamente; 2) el efecto de facilitación por repetición es significativamente superior al de facilitación por relación morfológica; y 3) dentro de este último no aparecen diferencias significativas entre la facilitación de la forma base por la derivada y la de ésta por aquélla.

Estos resultados se interpretan a la luz de los distintos modelos propuestos acerca de la representación léxica. Sin que sean cruciales para decidirse por uno de ellos en contra de los otros, sí que parecen apoyar la existencia de un código de representación abstracto que aglutina familias de palabras relacionadas morfológicamente en torno a una misma entrada léxica. En cualquier caso, y aun suponiendo que hubiera entradas léxicas distintas para cada forma particular, sería preciso postular algún mecanismo adicional que diera cuenta del papel que desempeña la información morfológica en la organización general del léxico interno.     

Effects of speed of word processing on semantic access: the case of bilingualism

Bilingual speakers generally manifest slower word recognition than monolinguals. We investigated the consequences of the word processing speed on semantic access in bilinguals. The paradigm involved a stream of English words and pseudowords presented in succession at a constant rate. English-Welsh bilinguals and English monolinguals were asked to count the number of letters in pseudowords and actively disregard words. They were not explicitly told that pairs of words in immediate succession were embedded and could either be semantically related or not. We expected that slower word processing in bilinguals would result in semantic access indexed by semantic priming. As expected, bilinguals showed significant semantic priming, indexed by an N400 modulation, whilst monolinguals did not. Moreover, bilinguals were slower in performing the task. The results suggest that bilinguals cannot discriminate between pseudowords and words without accessing semantic information whereas monolinguals can dismiss English words on the basis of subsemantic information.     

Phonological priming and cohort effects in toddlers

Adult word recognition is influenced by prior exposure to phonologically or semantically related words (cup primes cat or plate) compared to unrelated words (door), suggesting that words are organised in the adult lexicon based on their phonological and semantic properties and that word recognition implicates not just the heard word, but also related words. We investigate the phonological organisation of the toddler lexicon with two experiments using a picture priming technique. Twenty-four month olds showed inhibition of target recognition in related primed trials compared to unrelated primed trials (Experiment 1) and also in related primed trials compared to unprimed trials (Experiment 2). Further analysis of children’s responding found that this inhibition effect was modulated by the cohort and neighbourhood size of the words tested. Overall, the results indicate a lexical basis for the reported effects and suggest that the phonological properties provide an organisational basis for words in the toddler lexicon.