Despite a century of research into visual word recognition, basic questions remain unresolved about the functional architecture of the process that maps visual inputs from orthographic analysis onto lexical form and meaning and about the units of analysis in terms of which these processes are conducted. Here we use magnetoencephalography, supported by a masked priming behavioral study, to address these questions using contrasting sets of simple ( walk ), complex ( swimmer ), and pseudo-complex ( corner ) forms. Early analyses of orthographic structure, detectable in bilateral posterior temporal regions within a 150–230 msec time frame, are shown to segment the visual input into linguistic substrings (words and morphemes) that trigger lexical access in left middle temporal locations from 300 msec. These are primarily feedforward processes and are not initially constrained by lexical-level variables. Lexical constraints become significant from 390 msec, in both simple and complex words, with increased processing of pseudowords and pseudo-complex forms. These results, consistent with morpho-orthographic models based on masked priming data, map out the real-time functional architecture of visual word recognition, establishing basic feedforward processing relationships between orthographic form, morphological structure, and lexical meaning.

An ongoing debate is whether and to what extent access to cortical representations is automatic or dependent on attentional processes. To address this, we modulated the level of attention on auditory input and recorded ERPs elicited by syllables completing acoustically matched words and pseudowords. Under nonattend conditions, the word-elicited response (peaking at ∼120 msec) was larger than that to pseudowords, confirming early activation of lexical memory traces. However, when attention was directed toward the auditory input, such word–pseudoword difference disappeared. Whereas responses to words seemed unchanged by attentional variation, early pseudoword responses were modulated significantly by attention. Later on, attention modulated a positive deflection at ∼230 msec and a second negativity at ∼370 msec for all stimuli. The data indicate that the earliest stages of word processing are not affected by attentional demands and may thus possess certain automaticity, with attention effects on lexical processing accumulating after 150–200 msec. We explain this by robustness of preexisting memory networks for words whose strong internal connections guarantee rapid full-scale activation irrespective of the attentional resources available. Conversely, the processing of pseudowords, which do not have such stimulus-specific cortical representations, appears to be strongly modulated by the availability of attentional resources, even at its earliest stages. Topography analysis and source reconstruction indicated that left peri-sylvian cortices mediate attention effects on memory trace activation.

There are two views about morphology, the aspect of language concerned with the internal structure of words. One view holds that morphology is a domain of knowledge with a specific type of neurocognitive representation supported by specific brain mechanisms lateralized to left fronto-temporal cortex. The alternate view characterizes morphological effects as being a by-product of the correlation between form and meaning and where no brain area is predicted to subserve morphological processing per se. Here we provided evidence from Arabic that morphemes do have specific memory traces, which differ as a function of their functional properties. In an MMN study, we showed that the abstract consonantal root, which conveys semantic meaning (similarly to monomorphemic content words in English), elicits an MMN starting from 160 msec after the deviation point, whereas the abstract vocalic word pattern, which plays a range of grammatical roles, elicits an MMN response starting from 250 msec after the deviation point. Topographically, the root MMN has a symmetric fronto-central distribution, whereas the word pattern MMN lateralizes significantly to the left, indicating stronger involvement of left peri-sylvian areas. In languages with rich morphologies, morphemic processing seems to be supported by distinct neural networks, thereby providing evidence for a specific neuronal basis for morphology as part of the cerebral language machinery.

Traditional views link semantic context integration to neurophysiological activity at 300–500 msec. To study possible early dynamics related to semantic context integration, we recorded, in passive oddball paradigm, magnetic evoked responses to spoken word pairs, the second word being either congruent or incongruent with the first one. The same experimental words were placed in orthogonally varied context, thus providing a strict control for any effects of acoustic, phonological, and psycholinguistic stimulus features. Responses to the same critical words were obtained also outside of semantic context. We found that regardless of their acoustic features, semantically incongruent stimuli elicited a brain response already at ∼115 msec after the critical word onset. The same words did not produce such deflection in semantically legal context. The responses were maximal at left temporal and inferior frontal cortical sites, which was also confirmed by distributed current source analysis. The left temporal activation preceded the frontal one by ∼16 msec. No late response dynamics (>350 msec) were found that would reflect the semantic modulation in this nonattend passive design, indicating the possible role of attention in generating the later responses. Our results suggest that the earliest brain processes of semantic context integration can occur at ∼100 msec after the onset of spoken words in the left inferior frontal and superior temporal cortex.

The brain basis of action words may be neuron ensembles binding language-and action-related information that are dispersed over both language-and action-related cortical areas. This predicts fast spreading of neuronal activity from language areas to specific sensorimotor areas when action words semantically related to different parts of the body are being perceived. To test this, fast neurophysiological imaging was applied to reveal spatiotemporal activity patterns elicited by words with different action-related meaning. Spoken words referring to actions involving the face or leg were presented while subjects engaged in a distraction task and their brain activity was recorded using high-density magnetoencephalography. Shortly after the words could be recognized as unique lexical items, objective source localization using minimum norm current estimates revealed activation in superior temporal (130 msec) and inferior frontocentral areas (142-146 msec). Face-word stimuli activated inferior frontocentral areas more strongly than leg words, whereas the reverse was found at superior central sites (170 msec), thus reflecting the cortical somatotopy of motor actions signified by the words. Significant correlations were found between local source strengths in the frontocentral cortex calculated for all participants and their semantic ratings of the stimulus words, thus further establishing a close relationship between word meaning access and neurophysiology. These results show that meaning access in action word recognition is an early automatic process reflected by spatiotemporal signatures of word-evoked activity. Word-related distributed neuronal assemblies with specific cortical topographies can explain the observed spatiotemporal dynamics reflecting word meaning access.

To address the cerebral processing of grammar, we used whole-head high-density magnetoencephalography to record the brain's magnetic fields elicited by grammatically correct and incorrect auditory stimuli in the absence of directed attention to the stimulation. The stimuli were minimal short phrases of the Finnish language differing only in one single phoneme (word-final inflectional affix), which rendered them as either grammatical or ungrammatical. Acoustic and lexical differences were controlled for by using an orthogonal design in which the phoneme's effect on grammaticality was inverted. We found that occasional syntactically incorrect stimuli elicited larger mismatch negativity (MMN) responses than correct phrases. The MMN was earlier proposed as an index of preattentive automatic speech processing. Therefore, its modulation by grammaticality under nonattend conditions suggests that early syntax processing in the human brain may take place outside the focus of attention. Source analysis (single—dipole models and minimum-norm current estimates) indicated grammaticality dependent differential activation of the left superior temporal cortex suggesting that this brain structure may play an important role in such automatic grammar processing.

A sound turned off for a short moment can be perceived as continuous if the silent gap is filled with noise. The neural mechanisms underlying this “continuity illusion” were investigated using the mismatch negativity (MMN), an eventrelated potential reflecting the perception of a sudden change in an otherwise regular stimulus sequence. The MMN was recorded in four conditions using an oddball paradigm. The standards consisted of 500-Hz, 120-msec tone pips that were either physically continuous (Condition 1) or were interrupted by a 40-msec silent gap (Condition 2). The deviants consisted of the interrupted tone, but with the silent gap filled by a burst of bandpass-filtered noise. The noise either occupied the same frequency region as the tone and elicited the continuity illusion (Conditions 1a and 2a), or occupied a remote frequency region and did not elicit the illusion (Conditions 1b and 2b). We predicted that, if the continuity illusion is determined before MMN generation, then, other things being equal, the MMN should be larger in conditions where the deviants are perceived as continuous and the standards as interrupted or vice versa, than when both were perceived as continuous or both interrupted. Consistent with this prediction, we observed an interaction between standard type and noise frequency region, with the MMN being larger in Condition 1a than in Condition 1b, but smaller in Condition 2a than in Condition 2b. Because the subjects were instructed to ignore the tones and watch a silent movie during the recordings, the results indicate that the continuity illusion can occur outside the focus of attention. Furthermore, the latency of the MMN (less than approximately 200 msec postdeviance onset) places an upper limit on the stage of neural processing responsible for the illusion.