Temporal integration in visual word recognition

When two displays are presented in close temporal succession at the same location, how does the brain assign them to one versus two conscious percepts? We investigate this issue using a novel reading paradigm in which the odd and even letters of a string are presented alternatively at a variable rate. The results reveal a window of temporal integration during reading, with a nonlinear boundary around approximately 80 msec of presentation duration. Below this limit, the oscillating stimulus is easily fused into a single percept, with all characteristics of normal reading. Above this limit, reading times are severely slowed and suffer from a word-length effect. ERPs indicate that, even at the fastest frequency, the oscillating stimulus elicits synchronous oscillations in posterior visual cortices, while late ERP components sensitive to lexical status vanish beyond the fusion threshold. Thus, the fusion/segregation dilemma is not resolved by retinal or subcortical filtering, but at cortical level by at most 300 msec. The results argue against theories of visual word recognition and letter binding that rely on temporal synchrony or other fine temporal codes

Dynamic causal modeling of spatiotemporal integration of phonological and semantic processes: an electroencephalographic study.: DCM of phonology and semantics

International audienceIntegration of phonological and lexicosemantic processes is essential for visual word recognition. Here we used dynamic causal modeling of event-related potentials, combined with group source reconstruction, to estimate how those processes translate into context-dependent modulation of effective connectivity within the temporal-frontal language network. Fifteen healthy human subjects performed a phoneme detection task in pseudo-words and a semantic categorization task in words. Cortical current densities revealed the sequential activation of temporal regions, from the occipital-temporal junction toward the anterior temporal lobe, before reaching the inferior frontal gyrus. A difference of activation between phonology and semantics was identified in the anterior temporal lobe within the 240-300 ms peristimulus time window. Dynamic causal modeling indicated this increase of activation of the anterior temporal lobe in the semantic condition as a consequence of an increase of forward connectivity from the posterior inferior temporal lobe to the anterior temporal lobe. In addition, fast activation of the inferior frontal region, which allowed a feedback control of frontal regions on the superior temporal and posterior inferior temporal cortices, was found to be likely. Our results precisely describe spatiotemporal network mechanisms occurring during integration of phonological and semantic processes. In particular, they support the hypothesis of multiple pathways within the temporal lobe for language processing, where frontal regions would exert a top-down control on temporal regions in the recruitment of the anterior temporal lobe for semantic processing

Brain asymmetry and visual word recognition: do we have a split fovea?

In this chapter we discuss how the anatomical divide between the left and the right brain half has implications for visual word recognition. In particular, it introduces the need for massive interhemispheric communication. Unlike what was believed in the traditional view, it looks increasingly likely that interhemispheric integration is already needed from the very first stages of word processing, when the letter information is combined to activate stored word representations. Taking into account these insights not only improves our understanding of the neurophysiological and cognitive mechanisms of reading, it also gives us new ideas to look at individual differences in reading

The functional locus of emotion effects in visual word processing

Die emotionale Valenz von Wörtern beeinflusst deren kognitive Verarbeitung. Ungeklärt ist, obwohl von zentraler Bedeutung für die Disziplinen der Psycholinguistik und der Neurowissenschaften, die Frage nach dem funktionellen Lokus von Emotionseffekten in der visuellen Wortverarbeitung. In der vorliegenden Dissertation wurde mit Hilfe von Ereignis-korrelierten Potentialen (EKPs) untersucht, ob emotionale Valenz auf lexikalischen oder auf semantischen Wortverarbeitungsstufen wirksam wird. Vorausgegangene Studien weisen auf einen post-lexikalischen Lokus von Emotionseffekten hin, wobei einige wenige heterogene Befunde von sehr frühen Emotionseffekten auch einen lexikalischen Lokus vermuten lassen. In der vorliegenden Arbeit wurden drei emotions-sensitive EKP Komponenten beobachtet, die distinkte zeitliche und räumliche Verteilungen aufwiesen, und daher verschiedene Wortverarbeitungsstufen zu reflektieren scheinen. Die Ergebnisse wurden im Rahmen von allgemeinen Annahmen aktueller Wortverarbeitungs- und semantischer Repräsentationsmodelle diskutiert. Als zentrales Ergebnis kann benannt werden, dass Emotion am stärksten semantische Wortverarbeitungsstufen beeinflusste. Hieraus wurde geschlussfolgert, dass emotionale Valenz einen Teil der Wortbedeutung darstellt. Eine Interaktion mit einem lexikalischen Faktor sowie sehr frühe Emotionseffekte deuten auf einen zusätzlichen Lokus auf lexikalischen oder sogar perzeptuellen Wortverarbeitungsstufen hin. Dies bedeutet, Emotion veränderte die visuelle Wortverarbeitung auf multiplen Stufen, dabei konnten separate emotions-sensitive EKP Komponenten, die unterschiedlichen Randbedingungen unterliegen, mit jeweils einem frühen (pre-)lexikalischen und einem späten semantischen Lokus in der Wortverarbeitung in Verbindung gesetzt werden. Die Befunde stützen Wortverarbeitungsmodelle, die zeitlich flexible und interaktive Wortverarbeitungsstufen annehmen.Emotional valence of words influences their cognitive processing. The functional locus of emotion effects in the stream of visual word processing is still elusive, although it is an issue of great importance for the disciplines of psycholinguistics and neuroscience. In the present dissertation event-related potentials (ERPs) were applied to examine whether emotional valence influences visual word processing on either lexical or semantic processing stages. Previous studies argued for a post-lexical locus of emotion effects, whereas a lexical locus has been indicated by a few heterogeneous findings of very early emotion effects. Three emotion-related ERP components were observed that showed distinct temporal and topographic distributions, and thus seem to reflect different processing stages in word recognition. Results are discussed within a framework of common assumptions from word recognition and semantic representation models. As a main finding, emotion impacted most strongly semantic processing stages. Thus, emotional valence can be considered to be a part of the meaning of words. However, an interaction of emotion with a lexical factor and very early emotion effects argued for an additional functional locus on lexical, or even on perceptual processing stages in word recognition. In conclusion, emotion impacted visual word processing on multiple stages, whereas distinct emotion-related ERP components, that are subject to different boundary conditions, were associated each with an early (pre-)lexical locus or a late semantic locus. The findings are in line with models of visual word processing that assume time-flexible and interactive processing stages, and point out the need for integration of word recognition models with models of semantic representation