Neural localization of semantic context effects in electromagnetic and hemodynamic studies

Measures of electrical brain activity (event-related potentials, ERPs) have been useful in understanding language processing for several decades. Extant data suggest that the amplitude of the N400 component of the ERP is a general index of the ease or difficulty of retrieving stored conceptual knowledge associated with a word, which is dependent on both the stored representation itself, and the retrieval cues provided by the preceding context. Recordings from patients with brain damage, intracranial recordings, and magnetoencephalographic data implicate a (probably large portion of) the left temporal lobe as the largest source of the N400 semantic context effect, with a substantial but lesser contribution from the right temporal lobe. Event-related functional magnetic resonance (fMRI) studies using semantic context manipulations are dominated by observations of greater hemodynamic activity for incongruent sentence completions or semantically unrelated words than congruent or related words, consistent with the direction of the ERP effect. The locations of the hemodynamic effects show some variability across studies, but one commonly identified region is the left superior temporal gyrus, which is compatible with the electrophysiological results. A second commonly identified region in the fMRI studies is the left inferior frontal gyrus, which does not appear to make a substantial contribution to the N400 effect.     

Semantic weight and verb retrieval in aphasia

Individuals with agrammatic aphasia may have difficulty with verb production in comparison to nouns. Additionally, they may have greater difficulty producing verbs that have fewer semantic components (i.e., are semantically "light") compared to verbs that have greater semantic weight. A connectionist verb-production model proposed by Gordon and Dell (2003) learns through error correction to "divide the labor" between syntax and semantics. Verbs that are semantically heavier come to depend less on syntax and more on semantics. For lighter verbs, the reverse is true. We performed this study to clarify the role of semantic weight in aphasic verb production and to test the prediction from Gordon and Dell that a brain lesion that impairs the syntactic input to verb retrieval will impair lighter verbs more than heavier ones. Consistent with this prediction, we found that the decrement for lighter verbs was present in a group with agrammatic aphasia but not in a matched group without agrammatism.     

Implicit and explicit processing in deep dyslexia: Semantic blocking as a test for failure of inhibition in the phonological output lexicon

The failure of inhibition hypothesis posits a theoretical distinction between implicit and explicit access in deep dyslexia. Specifically, the effects of failure of inhibition are assumed only in conditions that have an explicit selection requirement in the context of production (i.e., aloud reading). In contrast, the failure of inhibition hypothesis proposes that implicit processing and explicit access to semantic information without production demands are intact in deep dyslexia. Evidence for intact implicit and explicit access requires that performance in deep dyslexia parallels that observed in neurologically intact participants on tasks based on implicit and explicit processes. In other words, deep dyslexics should produce normal effects in conditions with implicit task demands (i.e., lexical decision) and on tasks based on explicit access without production (i.e., forced choice semantic decisions) because failure of inhibition does not impact the availability of lexical information, only explicit retrieval in the context of production. This research examined the distinction between implicit and explicit processes in deep dyslexia using semantic blocking in lexical decision and forced choice semantic decisions as a test for the failure of inhibition hypothesis. The results of the semantic blocking paradigm support the distinction between implicit and explicit processing and provide evidence for failure of inhibition as an explanation for semantic errors in deep dyslexia.     

When phonology fails: orthographic neighbourhood effects in dyslexia

Both cerebral hemispheres contain phonological, orthographic and semantic representations of words, however there are between-hemisphere differences in the relative engagement and specialization of the different representations. Taking orthographic processing for example, previous studies suggest that orthographic neighbourhood size (N) has facilitatory effects in the right but not the left hemispheres. To pursue the nature of this asymmetric N effect, in particular whether there are individual differences in such specialisation, we examined N in a case of developmental dyslexia, FM. We first describe the nature of his difficulties, which are mainly severe phonological deficits. Employing the divided visual field paradigm with FM revealed a greater sensitivity in the right than in the left hemisphere to orthographic variables, with a significant inhibitory N effect in the left, but not right hemisphere. Such inhibition, to a lesser degree, was found among a group of adults with dyslexia but not among age-matched normal readers. We argue that enhanced sensitivity to orthographic cues is developed in some cases of dyslexia when a normal, phonology-based left hemisphere word recognition processing is not achieved. The interpretation presented here is cast in terms of differences between people with dyslexia and typical readers that originate in the atypical way in which orthographic representations are initially set up.     

The use theory of meaning and semantic stipulation

According to Horwich’s use theory of meaning, the meaning of a word W is engendered by the underived acceptance of certain sentences containing W. Horwich applies this theory to provide an account of semantic stipulation: Semantic stipulation proceeds by deciding to accept sentences containing an as yet meaningless word W. Thereby one brings it about that W gets an underived acceptance property. Since a word’s meaning is constituted by its (basic) underived acceptance property, this decision endows the word with a meaning. The use-theoretic account of semantic stipulation contrasts with the standard view that semantic stipulation proceeds by assigning the meaning (reference) to W that makes a certain set of sentences express true propositions. In this paper I will argue that the use-theoretic account does not work. I take Frege to have already made the crucial point: "a definition does not assert anything but lays down something ["etwas festsetzt"]” (Frege 1899, 36). A semantic stipulation for W cannot be the decision to accept a sentence containing W or be explained in terms of such an acceptance. Semantic stipulation constitutes a problem for Horwich's use theory of meaning, especially his basic notion of acceptance.

Context,content, and relativism

This paper argues against relativism, focusing on relativism based on the semantics of predicates of personal taste. It presents and defends a contextualist semantics for these predicates, derived from current work on gradable adjectives. It then considers metasemantic questions about the kinds of contextual parameters this semantics requires. It argues they are not metasemantically different from those in other gradable adjectives, and that contextual parameters of this sort are widespread in natural language. Furthermore, this paper shows that if such parameters are rejected, it leads to an unacceptably rampant form of relativism, that relativizes truth to an open-ended list of parameters.

Conceptual Hierarchies in a Flat Attractor Network: Dynamics of Learning and Computations

The structure of people's conceptual knowledge of concrete nouns has traditionally been viewed as hierarchical ( Collins & Quillian, 1969 ). For example, superordinate concepts ( vegetable ) are assumed to reside at a higher level than basic-level concepts ( carrot ). A feature-based attractor network with a single layer of semantic features developed representations of both basic-level and superordinate concepts. No hierarchical structure was built into the network. In Experiment and Simulation 1, the graded structure of categories (typicality ratings) is accounted for by the flat attractor network. Experiment and Simulation 2 show that, as with basic-level concepts, such a network predicts feature verification latencies for superordinate concepts ( vegetable ). In Experiment and Simulation 3, counterintuitive results regarding the temporal dynamics of similarity in semantic priming are explained by the model. By treating both types of concepts the same in terms of representation, learning, and computations, the model provides new insights into semantic memory.     

Social priming of dyslexia and reduction of the Stroop effect: What component of the Stroop effect is actually reduced?

Recently, Goldfarb, Aisenberg, and Henik (2011) showed that in a manual format of the Stroop task, dyslexia priming eliminates the normal magnitude of the interference-based Stroop-like findings otherwise exhibited by individuals participating in such research. Goldfarb et al. (2011) consequently concluded that the effect of word reading in a Stroop task (i.e., one automatic behavior) can be effectively controlled through an automatic instruction “do not read” (i.e., another automatic behavior). The present study further investigated these ideas by examining when and how dyslexia priming controls different processes involved in a Stroop task. To this end, the original finding was first replicated (Experiment 1) and subsequently extended to the vocal (instead of manual) response modality to examine whether previously reported eliminations of the Stroop effect persist with this response format (i.e., format producing larger Stroop effects). Since past work (e.g., Augustinova & Ferrand, 2012a; Brown, Joneleit et al., 2002; Ferrand & Augustinova, 2013) had suggested that various interventions were likely to reduce (rather than eliminate) the interference-based Stroop-like findings with vocal responses, a further aim of these experiments was to identify the component of these findings that dyslexia priming actually reduces. To this end, the effects of this intervention were examined in a more fine-grained variant of the Stroop task that distinguished between interference resulting from task-irrelevant processes involved in computing the lexical and semantic representations of the word (i.e., a written distractor to ignore) and task-relevant processes involved in the selection of a response (i.e., a color target to name) that are both involved in this task. In line with our past work (e.g., Augustinova & Ferrand, 2012a; Ferrand & Augustinova, 2013), the results of two experiments (Experiments 2 and 3) showed that in the vocal format, dyslexia priming reduces but does not eliminate the normal magnitude of the interference-based Stroop-like findings and that this reduction is solely due to the control of processes involved in the selection of a response (i.e., a color target to name) – processes that are known to be controllable in this format (Ferrand & Augustinova, 2013). Given that in this format, dyslexia priming had no effect on task-irrelevant processes involved in computing the lexical and semantic representations of a written distractor to be ignored – processes that are known to be automatic – further implications for the control of automatic processes via dyslexia priming are considered and an interpretation in terms of a unitary control mechanism for both the manual and vocal formats is proposed.     

Integrating the Automatic and the Controlled: Strategies in Semantic Priming in an Attractor Network With Latching Dynamics

Semantic priming has long been recognized to reflect, along with automatic semantic mechanisms, the contribution of controlled strategies. However, previous theories of controlled priming were mostly qualitative, lacking common grounds with modern mathematical models of automatic priming based on neural networks. Recently, we introduced a novel attractor network model of automatic semantic priming with latching dynamics. Here, we extend this work to show how the same model can also account for important findings regarding controlled processes. Assuming the rate of semantic transitions in the network can be adapted using simple reinforcement learning, we show how basic findings attributed to controlled processes in priming can be achieved, including their dependency on stimulus onset asynchrony and relatedness proportion and their unique effect on associative, category‐exemplar, mediated and backward prime‐target relations. We discuss how our mechanism relates to the classic expectancy theory and how it can be further extended in future developments of the model.     

Rethinking parafoveal processing in reading: Serial-attention models can explain semantic preview benefit and N+2 preview effects

During reading, some information about the word to the right of fixation in the parafovea is typically acquired prior to that word being fixated. Although some degree parafoveal processing is uncontroversial, its precise nature and extent are unclear. For example, can it advance up to the level of semantic processing? Additionally, can it extend across more than two spatially adjacent words? Affirmative answers to either of these questions would seemingly be problematic for serial-attention models of eye-movement control in reading, which maintain that attention is allocated to only one word at a time (see Reichle, 2011). However, in this paper we report simulation results using one such model, E-Z Reader (Reichle, Pollatsek, Fisher, & Rayner, 1998), to examine the two preceding questions. These results suggest the existence of both semantic preview and N+2 preview effects, indicating that they are not incompatible with serial-attention models. We discuss the implications of these findings for models of eye-movement control in reading and provide a new theoretical framework for conceptualizing parafoveal processing during reading and its influence on eye movement behaviour.