Orthographic neighborhood density modulates the size of transposed-letter priming effects.

We used transposed-letter (TL) priming to test the lexical tuning hypothesis, which states that words from high-density orthographic neighborhoods have more precise orthographic codes than words from low-density neighborhoods. Replicating standard TL priming effects, target words elicited faster lexical decision responses and smaller amplitude N250s and N400s when preceded by TL primes (e.g., leomn-LEMON) compared with substitution primes (e.g., leuzn-LEMON) overall. We expected that if high-density words have more precise orthographic representations (i.e., with each letter assigned to a specific position), then they should be relatively less activated by TL primes and should give rise to smaller TL priming effects. In line with our prediction, N250 (but not N400 or behavioral) TL priming was significantly smaller for high-density words compared with low-density words over posterior sites. Such an interaction was not observed for pseudoword targets. Consistent with the lexical tuning hypothesis then, this pattern suggests that the nature of the orthographic code used to access lexical representations differs depending on the number of neighboring words in the lexicon. We conclude by discussing how lexical tuning could be implemented in current models of orthographic processing.

Pre-output Language Monitoring in Sign Production.

A domain-general monitoring mechanism is proposed to be involved in overt speech monitoring. This mechanism is reflected in a medial frontal component, the error negativity (Ne), present in both errors and correct trials (Ne-like wave) but larger in errors than correct trials. In overt speech production, this negativity starts to rise before speech onset and is therefore associated with inner speech monitoring. Here, we investigate whether the same monitoring mechanism is involved in sign language production. Twenty deaf signers (American Sign Language [ASL] dominant) and 16 hearing signers (English dominant) participated in a picture-word interference paradigm in ASL. As in previous studies, ASL naming latencies were measured using the keyboard release time. EEG results revealed a medial frontal negativity peaking within 15 msec after keyboard release in the deaf signers. This negativity was larger in errors than correct trials, as previously observed in spoken language production. No clear negativity was present in the hearing signers. In addition, the slope of the Ne was correlated with ASL proficiency (measured by the ASL Sentence Repetition Task) across signers. Our results indicate that a similar medial frontal mechanism is engaged in preoutput language monitoring in sign and spoken language production. These results suggest that the monitoring mechanism reflected by the Ne/Ne-like wave is independent of output modality (i.e., spoken or signed) and likely monitors prearticulatory representations of language. Differences between groups may be linked to several factors including differences in language proficiency or more variable lexical access to motor programming latencies for hearing than deaf signers.

Cross-language Neighborhood Effects in Learners Indicative of an Integrated Lexicon.

This study examined how acquisition of novel words from an unknown language (L2) is influenced by their orthographic similarity with existing native language (L1) words in beginning adult learners. Participants were tested in a two-alternative forced-choice recognition task and a typing production task as they learned to associate 80 L2 (pseudo)words with pictures depicting their meanings. There was no effect of L1 orthographic neighborhood density on accuracy in the two-alternative forced-choice task, but typing accuracy was higher for L2 words with many L1 neighbors in the earliest stages of learning. ERPs recorded during a language decision task before and after learning also showed differences as a function of L1 neighborhood density. Across sessions, L2 words with many L1 neighbors elicited slower responses and larger N400s than words with fewer L1 neighbors, suggesting that L1 neighbors continued to influence processing of the L2 words after learning (though to a lesser extent). Finally, ERPs recorded during a typing task after learning also revealed an effect of L1 neighborhood that began about 700 msec after picture onset, suggesting that the cross-language neighborhood effects cannot solely be attributed to bottom-up activation of L1 neighbors. Together, these results demonstrate that strategic associations between novel L2 words and existing L1 neighbors scaffold learning and result in interactions among cross-language neighbors, suggestive of an integrated L1-L2 lexicon.

Interactions in the neighborhood: Effects of orthographic and phonological neighbors on N400 amplitude.

The present study investigated effects of phonological and orthographic neighborhood density on event-related potentials, with an aim to better specify the factors that determine N400 amplitude in single word reading paradigms. We orthogonally manipulated the number of orthographic and phonological neighbors of words using the Levenshtein Distance metric (OLD20 and PLD20, respectively). The results showed opposite effects of phonological neighborhood density (PND) as a function of orthographic neighborhood density (OND). Larger N400 amplitudes were elicited by words with high PND compared with low PND when OND was high, and smaller N400 amplitudes were observed with high PND compared with low PND words when OND was low. We interpret these findings using the notion of cross-code consistency, according to which the compatibility of orthographic and phonological representations activated by a given word influences the process of recognizing that word. Words with similar numbers of orthographic and phonological neighbors have more consistent spellings and pronunciations across the neighborhood, and generate larger N400 amplitudes.

One of the most well-established age-related changes in neural activity disappears after controlling for visual acuity.

Numerous studies using a variety of imaging techniques have reported age-related differences in neural activity while subjects carry out cognitive tasks. Surprisingly little attention has been paid to the potential impact of age-associated changes in sensory acuity on these findings. Studies in the visual modality frequently report that their subjects had "normal or corrected- to-normal vision." However, in most cases, there is no indication that visual acuity was actually measured, and it is likely that the investigators relied largely on self-reported visual status of subjects, which is often inaccurate. We investigated whether differences in visual acuity influence one of the most commonly observed findings in the event-related potentials literature on cognitive aging, a reduction in posterior P3b amplitude, which is an index of cognitive decision-making/updating. Well-matched young (n=26) and old adults (n=29) participated in a visual oddball task. Measured visual acuity with corrective lenses was worse in old than young adults. Results demonstrated that the robust age-related decline in P3b amplitude to visual targets disappeared after controlling for visual acuity, but was unaffected by accounting for auditory acuity. Path analysis confirmed that the relationship between age and diminished P3b to visual targets was mediated by visual acuity, suggesting that conveyance of suboptimal sensory data due to peripheral, rather than central, deficits may undermine subsequent neural processing. We conclude that until the relationship between age-associated differences in visual acuity and neural activity during experimental tasks is clearly established, investigators should exercise caution attributing results to differences in cognitive processing.

Rapid modulation of spoken word recognition by visual primes.

In a masked cross-modal priming experiment with ERP recordings, spoken Japanese words were primed with words written in one of the two syllabary scripts of Japanese. An early priming effect, peaking at around 200ms after onset of the spoken word target, was seen in left lateral electrode sites for Katakana primes, and later effects were seen for both Hiragana and Katakana primes on the N400 ERP component. The early effect is thought to reflect the efficiency with which words in Katakana script make contact with sublexical phonological representations involved in spoken language comprehension, due to the particular way this script is used by Japanese readers. This demonstrates fast-acting influences of visual primes on the processing of auditory target words, and suggests that briefly presented visual primes can influence sublexical processing of auditory target words. The later N400 priming effects, on the other hand, most likely reflect cross-modal influences on activity at the level of whole-word phonology and semantics.

Neural changes underlying early stages of L2 vocabulary acquisition.

Research has shown neural changes following second language (L2) acquisition after weeks or months of instruction. But are such changes detectable even earlier than previously shown? The present study examines the electrophysiological changes underlying the earliest stages of second language vocabulary acquisition by recording event-related potentials (ERPs) within the first week of learning. Adult native English speakers with no previous Spanish experience completed less than four hours of Spanish vocabulary training, with pre- and post-training ERPs recorded to a backward translation task. Results indicate that beginning L2 learners show rapid neural changes following learning, manifested in changes to the N400 - an ERP component sensitive to lexicosemantic processing and degree of L2 proficiency. Specifically, learners in early stages of L2 acquisition show growth in N400 amplitude to L2 words following learning as well as a backward translation N400 priming effect that was absent pre-training. These results were shown within days of minimal L2 training, suggesting that the neural changes captured during adult second language acquisition are more rapid than previously shown. Such findings are consistent with models of early stages of bilingualism in adult learners of L2 (e.g. Kroll and Stewart's RHM) and reinforce the use of ERP measures to assess L2 learning.

A Thousand Words Are Worth a Picture: Snapshots of Printed-Word Processing in an Event-Related Potential Megastudy.

In the experiment reported here, approximately 1,000 words were presented to 75 participants in a go/no-go lexical decision task while event-related potentials (ERPs) were recorded. Partial correlations were computed for variables selected to reflect orthographic, lexical, and semantic processing, as well as for a novel measure of the visual complexity of written words. Correlations were based on the item-level ERPs at each electrode site and time slice while a false-discovery-rate correction was applied. Early effects of visual complexity were seen around 50 ms after word onset, followed by the earliest sustained orthographic effects around 100 to 150 ms, with the bulk of orthographic and lexical influences arising after 200 ms. Effects of a semantic variable (concreteness) emerged later, at around 300 ms. The overall time course of these ERP effects is in line with hierarchical, cascaded, interactive accounts of word recognition, in which fast feed-forward influences are consolidated by top-down feedback via recurrent processing loops.

Investigating age-related changes in anterior and posterior neural activity throughout the information processing stream.

Event-related potential (ERP) and other functional imaging studies often demonstrate age-related increases in anterior neural activity and decreases in posterior activity while subjects carry out task demands. It remains unclear whether this "anterior shift" is limited to late cognitive operations like those indexed by the P3 component, or is evident during other stages of information processing. The temporal resolution of ERPs provided an opportunity to address this issue. Temporospatial principal component analysis (PCA) was used to identify underlying components that may be obscured by overlapping ERP waveforms. ERPs were measured during a visual oddball task in 26 young, 26 middle-aged, and 29 old subjects who were well-matched for IQ, executive function, education, and task performance. PCA identified six anterior factors peaking between ∼140 ms and 810 ms, and four posterior factors peaking between ∼300 ms and 810 ms. There was an age-related increase in the amplitude of anterior factors between ∼200 and 500 ms, and an age-associated decrease in amplitude of posterior factors after ∼500 ms. The increase in anterior processing began as early as middle-age, was sustained throughout old age, and appeared to be linear in nature. These results suggest that age-associated increases in anterior activity occur after early sensory processing has taken place, and are most prominent during a period in which attention is being marshaled to evaluate a stimulus. In contrast, age-related decreases in posterior activity manifest during operations involved in stimulus categorization, post-decision monitoring, and preparation for an upcoming event.

Orthographic and Phonological Code Activation in Deaf and Hearing Readers.

Grainger et al. (2006) were the first to use ERP masked priming to explore the differing contributions of phonological and orthographic representations to visual word processing. Here we adapted their paradigm to examine word processing in deaf readers. We investigated whether reading-matched deaf and hearing readers (n = 36) exhibit different ERP effects associated with the activation of orthographic and phonological codes during word processing. In a visual masked priming paradigm, participants performed a go/no-go categorization task (detect an occasional animal word). Critical target words were preceded by orthographically-related (transposed letter - TL) or phonologically-related (pseudohomophone - PH) masked non-word primes were contrasted with the same target words preceded by letter substitution (control) non-words primes. Hearing readers exhibited typical N250 and N400 priming effects (greater negativity for control compared to TL or PH primed targets), and the TL and PH priming effects did not differ. For deaf readers, the N250 PH priming effect was later (250-350 ms), and they showed a reversed N250 priming effect for TL primes in this time window. The N400 TL and PH priming effects did not differ between groups. For hearing readers, those with better phonological and spelling skills showed larger early N250 PH and TL priming effects (150-250 ms). For deaf readers, those with better phonological skills showed a larger reversed TL priming effect in the late N250 window. We speculate that phonological knowledge modulates how strongly deaf readers rely on whole-word orthographic representations and/or the mapping from sublexical to lexical representations.

Sentence superiority in the reading brain.

When a sequence of written words is briefly presented and participants are asked to identify just one word at a post-cued location, then word identification accuracy is higher when the word is presented in a grammatically correct sequence compared with an ungrammatical sequence. This sentence superiority effect has been reported in several behavioral studies and two EEG investigations. Taken together, the results of these studies support the hypothesis that the sentence superiority effect is primarily driven by rapid access to a sentence-level representation via partial word identification processes that operate in parallel over several words. Here we used MEG to examine the neural structures involved in this early stage of written sentence processing, and to further specify the timing of the different processes involved. Source activities over time showed grammatical vs. ungrammatical differences first in the left inferior frontal gyrus (IFG: 321-406 ms), then the left anterior temporal lobe (ATL: 466-531 ms), and finally in both left IFG (549-602 ms) and left posterior superior temporal gyrus (pSTG: 553-622 ms). We interpret the early IFG activity as reflecting the rapid bottom-up activation of sentence-level representations, including syntax, enabled by partly parallel word processing. Subsequent activity in ATL and pSTG is thought to reflect the constraints imposed by such sentence-level representations on on-going word-based semantic activation (ATL), and the subsequent development of a more detailed sentence-level representation (pSTG). These results provide further support for a cascaded interactive-activation account of sentence reading.

Different language control mechanisms in comprehension and production: Evidence from paragraph reading.

Chinese-English bilinguals read paragraphs with language switches using a rapid serial visual presentation paradigm silently while ERPs were measured (Experiment 1) or read them aloud (Experiment 2). Each paragraph was written in either Chinese or English with several function or content words switched to the other language. In Experiment 1, language switches elicited an early, long-lasting positivity when switching from the dominant language to the nondominant language, but when switching to the dominant language, the positivity started later, and was never larger than when switching to the nondominant language. In addition, switch effects on function words were not significantly larger than those on content words in any analyses. In Experiment 2, participants produced more cross-language intrusion errors when switching to the dominant than to the nondominant language, and more errors on function than content words. These results implicate different control mechanisms in bilingual language selection across comprehension and production.

Dissociating N400 effects of prediction from association in single-word contexts.

When a word is preceded by a supportive context such as a semantically associated word or a strongly constraining sentence frame, the N400 component of the ERP is reduced in amplitude. An ongoing debate is the degree to which this reduction reflects a passive spread of activation across long-term semantic memory representations as opposed to specific predictions about upcoming input. We addressed this question by embedding semantically associated prime-target pairs within an experimental context that encouraged prediction to a greater or lesser degree. The proportion of related items was used to manipulate the predictive validity of the prime for the target while holding semantic association constant. A semantic category probe detection task was used to encourage semantic processing and to preclude the need for a motor response on the trials of interest. A larger N400 reduction to associated targets was observed in the high than the low relatedness proportion condition, consistent with the hypothesis that predictions about upcoming stimuli make a substantial contribution to the N400 effect. We also observed an earlier priming effect (205-240 msec) in the high-proportion condition, which may reflect facilitation because of form-based prediction. In summary, the results suggest that predictability modulates N400 amplitude to a greater degree than the semantic content of the context.

The dissociation between early and late selection in older adults.

Older adults exhibit a reduced ability to ignore task-irrelevant stimuli; however, it remains to be determined where along the information processing stream the most salient age-associated changes occur. In the current study, ERPs provided an opportunity to determine whether age-related differences in processing task-irrelevant stimuli were uniform across information processing stages or disproportionately affected either early or late selection. ERPs were measured in young and old adults during a color-selective attention task in which participants responded to target letters in a specified color (attend condition) while ignoring letters in a different color (ignore condition). Old participants were matched to two groups of young participants on the basis of neuropsychological test performance: one using age-appropriate norms and the other using test scores not adjusted for age. There were no age-associated differences in the magnitude of early selection (attend-ignore), as indexed by the size of the anterior selection positivity and posterior selection negativity. During late selection, as indexed by P3b amplitude, both groups of young participants generated neural responses to target letters under the attend versus ignore conditions that were highly differentiated. In striking contrast, old participants generated a P3b to target letters with no reliable differences between conditions. Individuals who were slow to initiate early selection appeared to be less successful at executing late selection. Despite relative preservation of the operations of early selection, processing delays may lead older participants to allocate excessive resources to task-irrelevant stimuli during late selection.

The impact of visual acuity on age-related differences in neural markers of early visual processing.

The extent to which age-related differences in neural markers of visual processing are influenced by changes in visual acuity has not been systematically investigated. Studies often indicate that their subjects had normal or corrected-to-normal vision, but the assessment of visual acuity seems to most frequently be based only on self-report. Consistent with prior research, to be included in the current study, subjects had to report normal or corrected-to-normal vision. Additionally, visual acuity was formally tested using a Snellen eye chart. Event-related potentials (ERPs) were studied in young adults (18-32years old), young-old adults (65-79years old), and old-old adults (80+ years old) while they performed a visual processing task involving selective attention to color. Age-related differences in the latency and amplitude of ERP markers of early visual processing, the posterior P1 and N1 components, were examined. All results were then re-analyzed after controlling for visual acuity. We found that visual acuity declined as a function of age. Accounting for visual acuity had an impact on whether older and younger adults differed significantly in the size and latency of the posterior P1 and N1 components. After controlling for visual acuity, age-related increases in P1 and N1 latency did not remain significant, and older adults were found to have a larger P1 amplitude than young adults. Our results suggest that until the relationship between age-associated differences in visual acuity and early ERPs is clearly established, investigators should be cautious when interpreting the meaning of their findings. Self-reports about visual acuity may be inaccurate, necessitating formal measures. Additional investigation is needed to help establish guidelines for future research, especially of very old adults.

An ERP investigation of visual word recognition in syllabary scripts.

The bimodal interactive-activation model has been successfully applied to understanding the neurocognitive processes involved in reading words in alphabetic scripts, as reflected in the modulation of ERP components in masked repetition priming. In order to test the generalizability of this approach, in the present study we examined word recognition in a different writing system, the Japanese syllabary scripts hiragana and katakana. Native Japanese participants were presented with repeated or unrelated pairs of Japanese words in which the prime and target words were both in the same script (within-script priming, Exp. 1) or were in the opposite script (cross-script priming, Exp. 2). As in previous studies with alphabetic scripts, in both experiments the N250 (sublexical processing) and N400 (lexical-semantic processing) components were modulated by priming, although the time course was somewhat delayed. The earlier N/P150 effect (visual feature processing) was present only in "Experiment 1: Within-script priming", in which the prime and target words shared visual features. Overall, the results provide support for the hypothesis that visual word recognition involves a generalizable set of neurocognitive processes that operate in similar manners across different writing systems and languages, as well as pointing to the viability of the bimodal interactive-activation framework for modeling such processes.

ERPs Reveal How Semantic and Syntactic Processing Unfold across Parafoveal and Foveal Vision during Sentence Comprehension.

We examined how readers process content and function words in sentence comprehension with ERPs. Participants read simple declarative sentences using a rapid serial visual presentation (RSVP) with flankers paradigm. Sentences contained either an unexpected semantically anomalous content word, an unexpected syntactically anomalous function word or were well formed with no anomalies. ERPs were examined when target words were in the parafoveal or foveal vision. Unexpected content words elicited a typically distributed N400 when displayed in the parafovea, followed by a longer-lasting, widely distributed positivity starting around 300 ms once foveated. Unexpected function words elicited a left lateralized LAN-like component when presented in the parafovea, followed by a left lateralized, posteriorly distributed P600 when foveated. These results suggested that both semantic and syntactic processing involve two stages-the initial, fast process that can be completed in parafovea, followed by a more in depth attentionally mediated assessment that occurs with direct attention.

Electrophysiological patterns of visual word recognition in deaf and hearing readers: An ERP mega-study.

Deaf and hearing readers have different access to spoken phonology which may affect the representation and recognition of written words. We used ERPs to investigate how a matched sample of deaf and hearing adults (total n = 90) responded to lexical characteristics of 480 English words in a go/no-go lexical decision task. Results from mixed effect regression models showed a) visual complexity produced small effects in opposing directions for deaf and hearing readers, b) similar frequency effects, but shifted earlier for deaf readers, c) more pronounced effects of orthographic neighborhood density for hearing readers, and d) more pronounced effects of concreteness for deaf readers. We suggest hearing readers have visual word representations that are more integrated with phonological representations, leading to larger lexically-mediated effects of neighborhood density. Conversely, deaf readers weight other sources of information more heavily, leading to larger semantically-mediated effects and altered responses to low-level visual variables.

How (and why) does iconicity effect lexical access: An electrophysiological study of American sign language.

Prior research has found that iconicity facilitates sign production in picture-naming paradigms and has effects on ERP components. These findings may be explained by two separate hypotheses: (1) a task-specific hypothesis that suggests these effects occur because visual features of the iconic sign form can map onto the visual features of the pictures, and (2) a semantic feature hypothesis that suggests that the retrieval of iconic signs results in greater semantic activation due to the robust representation of sensory-motor semantic features compared to non-iconic signs. To test these two hypotheses, iconic and non-iconic American Sign Language (ASL) signs were elicited from deaf native/early signers using a picture-naming task and an English-to-ASL translation task, while electrophysiological recordings were made. Behavioral facilitation (faster response times) and reduced negativities were observed for iconic signs (both prior to and within the N400 time window), but only in the picture-naming task. No ERP or behavioral differences were found between iconic and non-iconic signs in the translation task. This pattern of results supports the task-specific hypothesis and provides evidence that iconicity only facilitates sign production when the eliciting stimulus and the form of the sign can visually overlap (a picture-sign alignment effect).

Asymetric Event-Related Potential Priming Effects Between English Letters and American Sign Language Fingerspelling Fonts.

Letter recognition plays an important role in reading and follows different phases of processing, from early visual feature detection to the access of abstract letter representations. Deaf ASL-English bilinguals experience orthography in two forms: English letters and fingerspelling. However, the neurobiological nature of fingerspelling representations, and the relationship between the two orthographies, remains unexplored. We examined the temporal dynamics of single English letter and ASL fingerspelling font processing in an unmasked priming paradigm with centrally presented targets for 200 ms preceded by 100 ms primes. Event-related brain potentials were recorded while participants performed a probe detection task. Experiment 1 examined English letter-to-letter priming in deaf signers and hearing non-signers. We found that English letter recognition is similar for deaf and hearing readers, extending previous findings with hearing readers to unmasked presentations. Experiment 2 examined priming effects between English letters and ASL fingerspelling fonts in deaf signers only. We found that fingerspelling fonts primed both fingerspelling fonts and English letters, but English letters did not prime fingerspelling fonts, indicating a priming asymmetry between letters and fingerspelling fonts. We also found an N400-like priming effect when the primes were fingerspelling fonts which might reflect strategic access to the lexical names of letters. The studies suggest that deaf ASL-English bilinguals process English letters and ASL fingerspelling differently and that the two systems may have distinct neural representations. However, the fact that fingerspelling fonts can prime English letters suggests that the two orthographies may share abstract representations to some extent.