Processing of parafoveally presented words. An fMRI study.

Abstract The present fMRI study investigated neural correlates of parafoveal preprocessing during reading and the type of information that is accessible from the upcoming - not yet fixated - word. Participants performed a lexical decision flanker task while the constraints imposed by the first three letters (the initial trigram) of parafoveally presented words were controlled. Behavioral results evidenced that the amount of information extracted from parafoveal stimuli, was affected by the difficulty of the foveal stimulus. Easy to process foveal stimuli (i.e., high frequency nouns) allowed parafoveal information to be extracted up to the lexical level. Conversely, when foveal stimuli were difficult to process (orthographically legal nonwords) only constraining trigrams modulated the task performance. Neuroimaging findings showed no effects of lexicality (i.e., difference between words and pseudowords) in the parafovea independently from the difficulty of the foveal stimulus. The constraints imposed by the initial trigrams, however, modulated the hemodynamic response in the left supramarginal gyrus. We interpreted the supramarginal activation as reflecting sublexical (phonological) processes. The missing parafoveal lexicality effect was discussed in relation to findings of experiments which observed effects of parafoveal semantic congruency on electrophysiological correlates

No Effect of cathodal tDCS of the posterior parietal cortex on parafoveal preprocessing of words

Abstract The present study investigated the functional role of the posterior parietal cortex during the processing of parafoveally presented letter strings. To this end, we simultaneously presented two letter strings (word or pseudoword) – one foveally and one parafoveally – and asked the participants to indicate the presence of a word (i.e., lexical decision flanker task). We applied cathodal transcranial direct current stimulation (tDCS) over the posterior parietal cortex in order to establish causal links between brain activity and lexical decision performance (accuracy and latency). The results indicated that foveal stimulus difficulty affected the amount of parafoveally processed information. Bayes factor analysis showed no effects of brain stimulation suggesting that posterior parietal cathodal tDCS does not modulate attention-related processes during parafoveal preprocessing. This result is discussed in the context of recent tDCS studies on attention and performance

Phonology is Fundamental in Skilled Reading

There is controversy about the importance of phonology in skilled reading. Event-related potential (ERP) evidence from the initial moments of visual word recognition indicates that processing sub-lexical phonology is fundamental to skilled reading. The early timecourse of this phonological activation explains the predictive power of phonological awareness for early reading development, affirms the importance of phonological processing in learning to read, and illuminates the persistent challenges of dyslexia

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

Event related potentials reveal that increasing perceptual load leads to increased responses for target stimuli and decreased responses for irrelevant stimuli

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Automatic Lexical Access in Visual Modality: Eye-Tracking Evidence

Language processing has been suggested to be partially automatic, with some studies suggesting full automaticity and attention independence of at least early neural stages of language comprehension, in particular, lexical access. Existing neurophysiological evidence has demonstrated early lexically specific brain responses (enhanced activation for real words) to orthographic stimuli presented parafoveally even under the condition of withdrawn attention. These studies, however, did not control participants’ eye movements leaving a possibility that they may have foveated the stimuli, leading to overt processing. To address this caveat, we recorded eye movements to words, pseudowords, and non-words presented parafoveally for a short duration while participants performed a dual non-linguistic feature detection task (color combination) foveally, in the focus of their visual attention. Our results revealed very few saccades to the orthographic stimuli or even to their previous locations. However, analysis of post-experimental recall and recognition performance showed above-chance memory performance for the linguistic stimuli. These results suggest that partial lexical access may indeed take place in the presence of an unrelated demanding task and in the absence of overt attention to the linguistic stimuli. As such, our data further inform automatic and largely attention-independent theories of lexical access

Parafoveal and foveal N400 effects in natural reading:A timeline of semantic processing from fixation-related potentials

The depth at which parafoveal words are processed during reading is an ongoing topic of debate. Recent studies using RSVP-with-flanker paradigms have shown that implausible words within sentences elicit N400 components while they are still in parafoveal vision, suggesting that the semantics of parafoveal words can be accessed to rapidly update the sentence representation. To study this effect in natural reading, we combined the co-registration of eye movements and EEG with the deconvolution modeling of fixation-related potentials (FRPs) to test whether semantic plausibility is processed parafoveally during Chinese sentence reading. For one target word per sentence, both its parafoveal and foveal plausibility were orthogonally manipulated using the boundary paradigm. Consistent with previous eye movement studies, we observed a delayed effect of parafoveal plausibility on fixation durations that only emerged on the foveal word. Crucially, in FRPs aligned to the pre-target fixation, a clear N400 effect emerged already based on parafoveal plausibility, with more negative voltages for implausible previews. Once participants fixated the target, we again observed an N400 effect of foveal plausibility. Interestingly, this foveal N400 was absent whenever the preview had been implausible, indicating that when a word’s (im)plausibility is already processed in parafoveal vision, this information is not revised anymore upon direct fixation. Implausible words also elicited a late positive complex (LPC), but exclusively in foveal vision. Our results provide convergent neural and behavioral evidence for the parafoveal uptake of semantic information, but also indicate different contributions of parafoveal versus foveal information towards higher-level sentence processing

Development of quality standards for multi-center, longitudinal magnetic resonance imaging studies in clinical neuroscience

Magnetic resonance imaging (MRI) data is generated by a complex procedure. Many possible sources of error exist which can lead to a worse signal. For example, hidden defective components of a MRI-scanner, changes in the static magnetic field caused by a person simply moving in the MRI scanner room as well as changes in the measurement sequences can negatively affect the signal-to-noise ratio (SNR). A comprehensive, reproducible, quality assurance (QA) procedure is necessary, to ensure reproducible results both from the MRI equipment and the human operator of the equipment. To examine the quality of the MRI data, there are two possibilities. On the one hand, water or gel-filled objects, so-called "phantoms", are regularly measured. Based on this signal, which in the best case should always be stable, the general performance of the MRI scanner can be tested. On the other hand, the actually interesting data, mostly human data, are checked directly for certain signal parameters (e.g., SNR, motion parameters). This thesis consists of two parts. In the first part a study-specific QA-protocol was developed for a large multicenter MRI-study, FOR2107. The aim of FOR2107 is to investigate the causes and course of affective disorders, unipolar depression and bipolar disorders, taking clinical and neurobiological effects into account. The main aspect of FOR2107 is the MRI-measurement of more than 2000 subjects in a longitudinal design (currently repeated measurements after 2 years, further measurements planned after 5 years). To bring MRI-data and disease history together, MRI-data must provide stable results over the course of the study. Ensuring this stability is dealt with in this part of the work. An extensive QA, based on phantom measurements, human data analysis, protocol compliance testing, etc., was set up. In addition to the development of parameters for the characterization of MRI-data, the used QA-protocols were improved during the study. The differences between sites and the impact of these differences on human data analysis were analyzed. The comprehensive quality assurance for the FOR2107 study showed significant differences in MRI-signal (for human and phantom data) between the centers. Occurring problems could easily be recognized in time and be corrected, and must be included for current and future analyses of human data. For the second part of this thesis, a QA-protocol (and the freely available associated software "LAB-QA2GO") has been developed and tested, and can be used for individual studies or to control the quality of an MRI-scanner. This routine was developed because at many sites and in many studies, no explicit QA is performed nevertheless suitable, freely available QA-software for MRI-measurements is available. With LAB-QA2GO, it is possible to set up a QA-protocol for an MRI-scanner or a study without much effort and IT knowledge. Both parts of the thesis deal with the implementation of QA-procedures. High quality data and study results can be achieved only by the usage of appropriate QA-procedures, as presented in this work. Therefore, QA-measures should be implemented at all levels of a project and should be implemented permanently in project and evaluation routines

The Contribution of the Magnocellular Visual Pathway to the Process of Visual Word Recognition

Previous research on visual word recognition has uncovered a variety of factors which influence how easily this process is achieved. Some factors are intrinsic to the word itself (e.g., length, frequency, regularity) and some are environmental factors (e.g., stimuli contrast or visual field position). Any proposed account of visual word recognition must consider not only the properties of the word itself, but also the properties of the visual system that processes the words. This thesis tested the hypothesis that the magnocellular visual pathway contributes to the processing of words and that this contribution is most evident when words are presented in parafoveal vision. Experiments 1 and 2 investigated the effect on the recognition of isolated words of limiting input to the visual system by occluding one eye. We looked at the effect of visual field presentation position and word length. Previous research using binocular viewing had shown a large length effect in the left visual field. We found that occluding the right eye reduced the left visual field length effect. Experiments 3, 4 and 5 looked at the impact of varying presentation position on competent readers and dyslexics. Numerous studies in sentence processing have shown that phonological information can be extracted during parafoveal preview. We asked whether dyslexics’ well attested phonological impairment will hinder their ability to extract phonological information in parafoveal vision. Experiments 3 and 4 demonstrated that only the dyslexic group showed an effect of word regularity. Experiment 5 used a rhyme-matching task to show that only dyslexic readers have a problem in extracting phonological information from word pairs presented to the right visual field. We relate this to magnocellular functioning. Experiments 6, 7 and 8 used isoluminant stimuli to directly test the consequences of inhibiting the magnocellular visual pathway on the recognition of words presented both foveally and parafoveally. The results of these experiments show that blocking the magnocellular pathway affects parafoveal areas of the visual field more than the foveal area and that words are affected by this whereas non-words are not. In conclusion, we demonstrated that the magnocellular pathway does contribute significantly to the recognition of words and that the parafoveal area of the retina is more heavily dependent on the magnocellular pathway compared to the foveal area of the retina. We go on to propose plans for future research looking at the role of the magnocellular pathway in parafoveal preview in sentence reading