A visual M170 effect of morphological complexity

Recent masked priming studies on visual word recognition have suggested that morphological decomposition is performed prelexically, purely on the basis of the orthographic properties of the word form. Given this, one might expect morphological complexity to modulate early visual evoked activity in electromagnetic measures. We investigated the neural bases of morphological decomposition with magnetoencephalography (MEG). In two experiments, we manipulated morphological complexity in single word lexical decision without priming, once using suffixed words and once using prefixed words. We found that morphologically complex forms display larger amplitudes in the M170, the same component that has been implicated for letterstring and face effects in previous MEG studies. Although letterstring effects have been reported to be left-lateral, we found a right-lateral effect of morphological complexity, suggesting that both hemispheres may be involved in early analysis of word forms

MEG masked priming evidence for form-based decomposition of irregular verbs

To what extent does morphological structure play a role in early processing of visually presented English past tense verbs? Previous masked priming studies have demonstrated effects of obligatory form-based decomposition for genuinely affixed words (teacher-TEACH) and pseudo-affixed words (corner-CORN), but not for orthographic controls (brothel-BROTH). Additionally, MEG single word reading studies have demonstrated that the transition probability from stem to affix (in genuinely affixed words) modulates an early evoked response known as the M170; parallel findings have been shown for the transition probability from stem to pseudo-affix (in pseudo-affixed words). Here, utilizing the M170 as a neural index of visual form-based morphological decomposition, we ask whether the M170 demonstrates masked morphological priming effects for irregular past tense verbs (following a previous study which obtained behavioral masked priming effects for irregulars). Dual mechanism theories of the English past tense predict a rule-based decomposition for regulars but not for irregulars, while certain single mechanism theories predict rule-based decomposition even for irregulars. MEG data was recorded for 16 subjects performing a visual masked priming lexical decision task. Using a functional region of interest (fROI) defined on the basis of repetition priming and regular morphological priming effects within the left fusiform and inferior temporal regions, we found that activity in this fROI was modulated by the masked priming manipulation for irregular verbs, during the time window of the M170. We also found effects of the scores generated by the learning model of Albright & Hayes (2003) on the degree of priming for irregular verbs. The results favor a single mechanism account of the English past tense, in which even irregulars are decomposed into stems and affixes prior to lexical access, as opposed to a dual mechanism model, in which irregulars are recognized as whole forms

Early Form Based Morphological Decomposition in Tagalog: MEG Evidence from Reduplication, Infixation and Circumfixation

Neuro-and psycholinguistic experimentation supports the early decomposition of morphologically complex words within the ventral processing stream, which MEG has localized to the M170 response in the (left) visual word form area ( VWFA). Decomposition into an exhaustive parse of visual morpheme forms extends beyond words like farmer to those imitating complexity (e.g., brother; Lewis et al., 2011), and to “unique” stems occurring in only one word but following the syntax and semantics of their affix (e.g., vulnerable; Gwilliams & Marantz, 2018). Evidence comes primarily from suffixation; other morphological processes have been under-investigated. This study explores circumfixation, infixation, and reduplication in Tagalog. In addition to investigating whether these are parsed like suffixation, we address an outstanding question concerning semantically empty morphemes. Some words in Tagalog resemble English winter as decomposition is not supported (wint-er); these apparently reduplicated pseudoreduplicates lack the syntactic and semantic features of reduplicated forms. However, unlike winter, these words exhibit phonological behavior predicted only if they involve a reduplicating morpheme. If these are decomposed, this provides evidence that words are analyzed as complex, like English vulnerable, when the grammar demands it. In a lexical decision task with MEG, we find that VWFA activity correlates with stem:word transition probability for circumfixed, infixed, and reduplicated words. Furthermore, a Bayesian analysis suggests that pseudoreduplicates with reduplicate-like phonology are also decomposed; other pseudoreduplicates are not. These findings are consistent with an interpretation that decomposition is modulated by phonology in addition to syntax and semantics

The Effects of Aging on Lexical Access

As the U.S. population ages, the need to understand how language changes with age becomes more important. Difficulty with word retrieval is one of the most notable changes as individuals age (Burke & Shafto, 2004); however, theoretical models of aging disagree on the cause. Two prominent theories are the impaired lexical access hypothesis and the general slowing theory. The present study aimed to explore these two ideas using magnetoencephalography (MEG). A young adult group (N=17, mean age 20.6 years) and an older adult group (N=9, mean age =64.6 years) participated in a lexical decision task using verbs. MEG latency data corresponding to lexical access found no between-group difference. Behavioral response times were significantly slower in the older group. Results point either to the idea that linguistic difficulties experienced by older individuals are the result of reduced abilities in phonological or motor processing, or that while lexical representations remain intact, the connections between them become less efficient with age

The form of morphemes:MEG evidence from masked priming of two Hebrew templates

Studies of lexical access have benefited from comparisons between languages like English, which shows concatenative morphology, and Semitic languages showing non-concatenative morphology of roots and patterns. Morphological decomposition in Semitic has previously been probed using masked priming, originally developed to investigate concatenative morphology. However, studies conducted on Semitic languages have often targeted Semitic-specific questions, such as whether the root and the verbal template prime lexical access. The overall consequence of these studies for our understanding of lexical access remains unclear. In two experiments on Hebrew using MEG, we demonstrate that a verbal form which is orthographically and phonologically indistinguishable from non-verbal forms is primed by other verbs in the same template but not by similar nouns and adjectives. These results suggest that masked priming taps into more than just visual forms but reflects morphological content, even if this content is abstract, showing no distinct orthographic or phonological marking

Sensitivity to syntax in visual cortex

One of the most intriguing findings on language comprehension is that violations of syntactic predictions can affect event-related potentials as early as 120 ms, in the same time-window as early sensory processing. This effect, the so-called early left-anterior negativity (ELAN), has been argued to reflect word category access and initial syntactic structure building (Friederici, 2002). In two experiments, we used magnetoencephalography to investigate whether (a) rapid word category identification relies on overt category-marking closed-class morphemes and (b) whether violations of word category predictions affect modality-specific sensory responses. Participants read sentences containing violations of word category predictions. Unexpected items varied in whether or not their word category was marked by an overt function morpheme. In Experiment 1, the amplitude of the visual evoked M100 component was increased for unexpected items, but only when word category was overtly marked by a function morpheme. Dipole modeling localized the generator of this effect to the occipital cortex. Experiment 2 replicated the main results of Experiment 1 and eliminated two non-morphology-related explanations of the M100 contrast we observed between targets containing overt category-marking and targets that lacked such morphology. Our results show that during reading, syntactically relevant cues in the input can affect activity in occipital regions at around 125 ms, a finding that may shed new light on the remarkable rapidity of language processing

Modeling Morphological Processing in Human Magnetoencephalography

In this paper, we conduct a magnetoencephalography (MEG) lexical decision experiment and computationally model morphological processing in the human brain, especially the Visual Word Form Area (VWFA) in the visual ventral stream. Five neurocomputational models of morphological processing are constructed and evaluated against human neural activities: Character Markov Model and Syllable Markov Model as amorphous models without morpheme units, and Morpheme Markov Model, Hidden Markov Model (HMM), and Probabilistic Context-Free Grammar (PCFG) as morphous models with morpheme units structured linearly or hierarchically. Our MEG experiment and computational modeling demonstrate that morphous models outperformed amorphous models, PCFG was most neurologically accurate among morphous models, and PCFG better explained nested words with non-local dependencies between prefixes and suffixes. These results strongly suggest that morphemes are represented in the human brain and parsed into hierarchical morphological structures

How does iReadMore therapy change the reading network of patients with central alexia?

Central alexia (CA) is an acquired reading disorder co-occurring with a generalised language deficit (aphasia). The roles of perilesional and ipsilesional tissue in recovery from post-stroke aphasia are unclear. We investigated the impact of reading training (using iReadMore, a therapy app) on the connections within and between the right and left hemisphere of the reading network of patients with CA. In patients with pure alexia, iReadMore increased feedback from left inferior frontal region (IFG) to the left occipital (OCC) region. We aimed to identify if iReadMore therapy was effective through a similar mechanism in CA patients.Participants with chronic post-stroke CA (n=23) completed 35 hours of iReadMore training over four weeks. Reading accuracy for trained and untrained words was assessed before and after therapy. The neural response to reading trained and untrained words in the left and right OCC, ventral occipitotemporal (vOT) and IFG was examined using event-related magnetoencephalography.The training-related modulation in effective connectivity between regions was modelled at the group level with Dynamic Causal Modelling.iReadMore training improved participants' reading accuracy by an average of 8.4% (range: -2.77 to 31.66) while accuracy for untrained words was stable. Training increased regional sensitivity in bilateral frontal and occipital regions, and strengthened feedforward connections within the left hemisphere. Our data suggests that iReadMore training in these patients modulates lower-order visual representations, as opposed to higher-order, more abstract ones, in order to improve word reading accuracy.SIGNIFICANCE STATEMENTThis is the first study to conduct a network-level analyses of therapy effects in participants with post-stroke central alexia. When patients trained with iReadMore (a multimodal, behavioural, mass practice, computer-based therapy), reading accuracy improved by an average 8.4% on trained items. A network analysis of the magnetoencephalography data associated with this improvement revealed an increase in regional sensitivity in bilateral frontal and occipital regions and strengthening of feedforward connections within the left hemisphere. This indicates that in CA patients iReadMore engages lower-order, intact resources within the left hemisphere (posterior to their lesion locations) to improve word reading. This provides a foundation for future research to investigate reading network modulation in different CA subtypes, or for sentence level therapy

a mismatch negativity study

Complex words can be seen as combinations of elementary units, decomposable into stems and affixes according to morphological rules. Alternatively, complex forms may be stored as single lexical entries and accessed as whole forms. This study uses an event-related potential brain response capable of indexing both whole-form retrieval and combinatorial processing, the Mismatch Negativity (MMN), to investigate early brain activity elicited by morphologically complex derived words in German. We presented complex words consisting of stems “sicher” (secure), or “sauber” (clean) combined with abstract nominalising derivational affixes –heit or –keit, to form either congruent derived words: “Sicherheit” (security) and “Sauberkeit” (cleanliness), or incongruent derived pseudowords: *”Sicherkeit”, and *”Sauberheit”. Using this orthogonal design, it was possible to record brain responses for –heit and –keit in both congruent and incongruent contexts, therefore balancing acoustic variance. Previous research has shown that incongruent combinations of symbols elicit a stronger MMN than congruent combinations, but that single words or constructions stored as whole forms elicit a stronger MMN than pseudowords or non-existent constructions. We found that congruent derived words elicited a stronger MMN than incongruent derived words, about 150 milliseconds after perception of the critical morpheme. This pattern of results is consistent with whole-form storage of morphologically complex derived words as lexical units, or mini-constructions. Using distributed source localisation methods, the MMN enhancement for well-formed derivationally complex words appeared to be most prominent in the left inferior anterior-temporal, bilateral superior parietal and bilateral post- central, supra-marginal areas. In addition, neurophysiological results reflected the frequency of derived forms, thus providing further converging evidence for whole form storage and against a combinatorial mechanism