Phonological aspects of word recognition as revealed by high-resolution spatio-temporal brain mapping

Abstract

We describe, for the first time, the use of high-resolution event-related brain potentials (hrERP) to identify the spatio-temporal characteristics of neural systems involved in phonological analysis. Subjects studied a visual word/non-word that was followed by the brief presentation of a prime letter (e.g. House, M) with the instruction to anticipate the word/non-word formed by replacing the word's first letter with the prime letter. After the prime letter, an auditory target word/non-word was presented that either matched/mismatched expectations (e.g., Mouse/Barn). ERPs were recorded to the onset of the auditory targets and scalp topographical maps were derived for the phonological mismatch negativity (PMN). The PMN reflected phonological analysis and examination of the peak topography revealed that the response was characterized by a prominent frontal, right-asymmetrical distribution. Spatial de-blurring (using current source density maps) indicated that the PMN scalp topography resulted primarily from an active left anterior source. The current results provide the initial evidence for the localization of the intra-cranial generator(s) involved in phonological analysis.

Activation in the anterior left auditory cortex associated with phonological analysis of speech input: localization of the phonological mismatch negativity response with MEG

“…When the sentence-ending words were both phonologically and semantically unexpected, both PMN and N400 responses were elicited, and, in the opposite case, neither the PMN nor N400 responses were obtained. In agreement with this study, a PMN response, independent of the N400, has been obtained whenever a violation against the expected auditory phonemic features has been introduced [5,6,8,22,24,31].…”

“…However, this process appears to be insensitive to semantic top-down effects since words not embedded in a sentence [5,6] and non-words [6] also elicit the PMN. A non-semantic paradigm in which participants were instructed to expect a word/non-word that rhymed with a presented word/non-word and began with a certain sound produced enhanced PMNs to mismatches in both word and non-word conditions [6].…”

“…It has been suggested that the PMN relates to the phonological processing of the speech input, possibly reflecting, in the perception of natural spoken language, the stage when lexical candidates are set up, searched or phonologically evaluated [6]. However, this process appears to be insensitive to semantic top-down effects since words not embedded in a sentence [5,6] and non-words [6] also elicit the PMN.…”

Electrophysiological differentiation of phonological and semantic integration in word and sentence contexts

“…Because the amplitude of this early negative shift varied as a function of the congruence of the word initial phoneme(s) with the contextually most expected word, Connolly and Phillips (1994) labeled this the phonological mismatch negativity or PMN. In a more recent study, they combined high density EEG and MEG to model the possible sources of the PMN and they concluded that it may have a left anterior source (Connolly et al, 2001). This finding was further bolstered with the results of an fMRI study (D'Arcy et al, 2004).…”

“…However, in their 1994 study, the ERPs were obtained from 5 electrodes, and the authors were therefore not able to identify if the topographic distribution of the early negative shift was different from that of the N400, something that was clearly established in the present study. More recent studies of Connolly and colleagues (Connolly et al, 2001;D'Arcy et al, 2004) with high density ERP/MEG and fMRI have modeled a possible left anterior source of the PMN. However, in these studies, word priming paradigms were used instead of sentence contexts, and as has been shown in the present study, these two types of contexts may have differential effects on processing.…”