ERP Manifestations of Processing Printed Words at Different Psycholinguistic Levels: Time Course and Scalp Distribution

Abstract

The aim of the present study was to examine the time course and scalp distribution of electrophysiological manifestations of the visual word recognition mechanism. Event-related potentials (ERPs) elicited by visually presented lists of words were recorded while subjects were involved in a series of oddball tasks. The distinction between the designated target and nontarget stimuli was manipulated to induce a different level of processing in each session (visual, phonological/phonetic, phonological/lexical, and semantic). The ERPs of main interest in this study were those elicited by nontarget stimuli. In the visual task the targets were twice as big as the nontargets. Words, pseudowords, strings of consonants, strings of alphanumeric symbols, and strings of forms elicited a sharp negative peak at 170 msec (N170); their distribution was limited to the occipito-temporal sites. For the left hemisphere electrode sites, the N170 was larger for orthographic than for nonorthographic stimuli and vice versa for the right hemisphere. The ERPs elicited by all orthographic stimuli formed a clearly distinct cluster that was different from the ERPs elicited by nonorthographic stimuli. In the phonological/phonetic decision task the targets were words and pseudowords rhyming with the French word vitrail, whereas the nontargets were words, pseudowords, and strings of consonants that did not rhyme with vitrail. The most conspicuous potential was a negative peak at 320 msec, which was similarly elicited by pronounceable stimuli but not by nonpronounceable stimuli. The N320 was bilaterally distributed over the middle temporal lobe and was significantly larger over the left than over the right hemisphere. In the phonological/lexical processing task we compared the ERPs elicited by strings of consonants (among which words were selected), pseudowords (among which words were selected), and by words (among which pseudowords were selected). The most conspicuous potential in these tasks was a negative potential peaking at 350 msec (N350) elicited by phonologically legal but not by phonologically illegal stimuli. The distribution of the N350 was similar to that of the N320, but it was broader and including temporo-parietal areas that were not activated in the "rhyme" task. Finally, in the semantic task the targets were abstract words, and the nontargets were concrete words, pseudowords, and strings of consonants. The negative potential in this task peaked at 450 msec. Unlike the lexical decision, the negative peak in this task significantly distinguished not only between phonologically legal and illegal words but also between meaningful (words) and meaningless (pseudowords) phonologically legal structures. The distribution of the N450 included the areas activated in the lexical decision task but also areas in the fronto-central regions. The present data corroborated the functional neuroanatomy of word recognition systems suggested by other neuroimaging methods and described their timecourse, supporting a cascade-type process that involves di...

Does Binding of Synesthetic Color to the Evoking Grapheme Require Attention?

“…Stroop-like paradigms have been used to study synesthesia in the lab (e.g., Odgaard et al, 1999;Bergfeld-Mills et al, 1999;Dixon et al, 2000). Others have used variants of visual search paradigms in synesthetes to address the perceptual reality of color-grapheme synesthesia (Palmeri et al, 2002;Ramachandran and Hubbard, 2001a).…”

“…Synesthetes' typically report that synesthesia is experienced as soon as the inducer is seen. ERPs to orthographic and non-orthographic material diverge as soon as ~150ms post stimulus presentation (Bentin et al, 1999). Indeed preliminary ERP data from both AD and CP suggested that by 150-200ms the responses to congruently and incongruently colored letters differ (Sagiv, Knight, and Robertson, 2003).…”

“…Perhaps most striking of those is the case of RM, a Balint's Syndrome patient who nearly completely lost spatial information as a result of bilateral parietal lesions. Subsequently, RM experienced illusory conjunctions even under free viewing conditions (Bernstein & Robertson, 1998;Friedman-Hill, Robertson, & Treisman, 1995;Robertson, Treisman, Friedman-Hill, & Grabowecky, 1997, see Humphreys et al, 2000 for confirming evidence). Features such as color and form are initially encoded in different ventral visual areas, and the data from RM suggest that accurately integrating the signals in these areas requires spatial processing of the parietal lobe.…”

“…However, since the color is experienced as a surface feature (with well-defined spatial extent), it would be more parsimonious to take advantage of existing circuits subserving spatial attention. For example, subjects seeing two line fragments as eyes, engage brain mechanisms subserving face perception (Bentin et al, 2002). 3 Some of these data have been reviewed in Robertson (2003a) and in Sagiv & Robertson (2004). of the synesthetic features to their inducing stimuli required visual attention.…”

Impairments in generation of early-stage transient visual evoked potentials to magno- and parvocellular-selective stimuli in schizophrenia

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