Colin Phillips

A cortical network for semantics: (de)constructing the N400.

Measuring event-related potentials (ERPs) has been fundamental to our understanding of how language is encoded in the brain. One particular ERP response, the N400 response, has been especially influential as an index of lexical and semantic processing. However, there remains a lack of consensus on the interpretation of this component. Resolving this issue has important consequences for neural models of language comprehension. Here we show that evidence bearing on where the N400 response is generated provides key insights into what it reflects. A neuroanatomical model of semantic processing is used as a guide to interpret the pattern of activated regions in functional MRI, magnetoencephalography and intracranial recordings that are associated with contextual semantic manipulations that lead to N400 effects.

Auditory Cortex Accesses Phonological Categories: An MEG Mismatch Study

The studies presented here use an adapted oddball paradigm to show evidence that representations of discrete phonological categories are available to the human auditory cortex. Brain activity was recorded using a 37-channel biomagnetometer while eight subjects listened passively to synthetic speech sounds. In the phonological condition, which contrasted stimuli from an acoustic /d/-/t/ continuum, a magnetic mismatch field (MMF) was elicited in a sequence of stimuli in which phonological categories occurred in a many-to-one ratio, but no acoustic many-to-one ratio was present. In order to isolate the contribution of phonological categories to the MMF responses, the acoustic parameter of voice onset time, which distinguished standard and deviant stimuli, was also varied within the standard and deviant categories. No MMF was elicited in the acoustic condition, in which the acoustic distribution of stimuli was identical to the first experiment, but the many-to-one distribution of phonological categories was removed. The design of these studies makes it possible to demonstrate the all-or-nothing property of phonological category membership. This approach contrasts with a number of previous studies of phonetic perception using the mismatch paradigm, which have demonstrated the graded property of enhanced acoustic discrimination at or near phonetic category boundaries.

Linear Order and Constituency

This article presents a series of arguments that syntactic structures are built incrementally, in a strict left-to-right order. By assuming incremental structure building it becomes possible to explain the differences in the range of constituents available to different diagnostics of constituency, including movement, ellipsis, coordination, scope, and binding. In an incremental derivation structure building creates new constituents, and in doing so it may destroy existing constituents. The article presents detailed evidence for the prediction of incremental grammar that a syntactic process may refer only to those constituents that are present at the point in the derivation when the process applies.

The role of structural prediction in rapid syntactic analysis

A number of recent electrophysiological studies of sentence processing have shown that a subclass of syntactic violations elicits very rapid ERP responses, occurring within around 200 ms of the onset of the violation. Such findings raise the question of how it is possible to diagnose violations so quickly. This paper suggests that very rapid diagnosis of errors is possible specifically in situations where the diagnosis problem is tightly constrained by specific expectations generated before the critical word is presented. In an event-related potentials (ERP) study of visual sentence reading participants encountered violations of a word order constraint (...Maxs of...) that has elicited early ERP responses in previous studies. Across conditions the illicit sequence was held constant, while sentence context was used to manipulate the expectation for a noun following the possessor Maxs, by manipulating the possibility of ellipsis of the head noun. Results showed that the anterior negativity elicited by the word category violation was attenuated when the availability of ellipsis reduced the expectation for a noun in the position of the offending preposition of, with divergence between conditions starting around 200 ms after the onset of the violation. This suggests a role for structural expectations in accounting for very fast syntactic diagnosis processes.

The linguistic processes underlying the P600

The P600 is an event-related brain potential (ERP) typically associated with the processing of grammatical anomalies or incongruities. A similar response has also been observed in fully acceptable long-distance wh-dependencies. Such findings raise the question of whether these ERP responses reflect common underlying processes, and what might be the specific mechanisms that are shared between successful processing of well-formed sentences and the detection and repair of syntactic anomalies. The current study presents a comparison of the ERP responses elicited by syntactic violations, garden path sentences, and long-distance wh-dependencies, using maximally similar materials in a within-subjects design. Results showed that a P600 component was elicited by syntactic violations and garden path sentences, but was less robustly elicited in the long-distance wh-dependency condition. Differences in the scalp topography, onset and duration of the P600 effects are characterised in terms of the syntactic operations involved in building complex syntactic structures, with particular attention to retrieval processes, which control the latency of the P600, and structure building processes, which control its duration and amplitude.

Task-induced asymmetry of the auditory evoked M100 neuromagnetic field elicited by speech sounds

The auditory evoked neuromagnetic fields elicited by synthesized speech sounds (consonant-vowel syllables) were recorded in six subjects over the left and right temporal cortices using a 37-channel SQUID-based magnetometer. The latencies and amplitudes of the peaks of the M100 evoked responses were bilaterally symmetric for passively presented stimuli. In contrast, when subjects were asked to discriminate among the same syllabic stimuli, the amplitude of the M100 increased in the left and decreased in the right temporal cortices. Single equivalent current dipole modeling of the activity elicited by all stimulus-types localized to a well-circumscribed area in supratemporal auditory cortex. The results suggest that attentional modulation affects the two supratemporal cortices in a differential manner. Task-conditioned attention to speech sounds is reflected in lateralized supratemporal cortical responses possibly concordant with hemispheric language dominance.

Illusory Licensing Effects across Dependency Types: ERP Evidence.

A number of recent studies have argued that grammatical illusions can arise in the process of completing linguistic dependencies, such that unlicensed material is temporarily treated as licensed due to the presence of a potential licensor that is semantically appropriate but in a syntactically inappropriate position. A frequently studied case involves illusory licensing of negative polarity items (NPIs) like ever and any, which must appear in the scope (i.e., c-command domain) of a negative element. Speakers often show intrusive licensing effects in sentences where an NPI is preceded but not c-commanded by a negative element, as in ( *)The restaurants that no newspapers have recommended in their reviews have ever gone out of business. Existing accounts of intrusive licensing have focused on the role of general memory retrieval processes. In contrast, we propose that intrusive licensing of NPIs reflects semantic/pragmatic processes that are more specific to NPI licensing. As a test of this claim, we present results from an ERP study that presents a structurally matched comparison of intrusive licensing in two types of linguistic dependencies, namely NPI licensing and the binding of reflexive anaphors like himself, and herself. In the absence of a potential licensor, both NPIs and reflexives elicit a P600 response, but whereas there is an immediate ERP analog of the intrusion effect for NPI licensing, no such effect is found for reflexive binding. This suggests that the NPI intrusion effect does not reflect general-purpose retrieval mechanisms.

Syntax at Age Two: Cross-Linguistic Differences 1

The 1990s witnessed a major expansion in research on childrens morphosyntactic development, due largely to the availability of computer-searchable corpora of spontaneous speech in the CHILDES database. This led to a rapid emergence of parallel findings in different languages, with much attention devoted to the widely attested difficulties in inflectional morphology in the speech of two-year-olds. First written in 1995, and framed within the terms of contemporary syntactic theories, this article argues that cross-linguistic differences in the distribution of childrens morphosyntactic errors provide important clues to the source of the errors, in particular whether they are morphological or syntactic in origin. The article takes as its starting point some striking previous findings that childrens verb inflection errors are systematically correlated, on a sentence-by-sentence basis, with errors in the use of overt subjects, and with the use of syntactically complex constructions such as wh-questions. The article shows that these correlations are found in some languages but not in others, and argues that these differences are predictable, based on the verb movement and case licensing properties of individual languages. The article argues that childrens errors reflect a combination of grammatical and speech production deficits.

The Role of Feature-Number and Feature-Type in Processing Hindi Verb Agreement Violations

This article presents studies of Hindi that investigate whether responses to syntactic agreement violations vary as a function of the type and number of incorrect agreement features, using both electrophysiological (ERP) and behavioral measures. Hindi is well suited to investigation of this issue, since verbs in Hindi mark agreement with the person, number, and gender features of the nominative subject noun phrase. In an ERP study evoked responses were recorded for visually presented verbs appearing at the end of a sentence-initial adverbial clause, comparing responses in a grammatically correct condition with four grammatically incorrect conditions that mismatched the correct agreement on different dimensions (Gender, Number, Gender/Number, Person/Gender). A P600 response was elicited in all grammatically incorrect conditions. No amplitude differences were found among the Gender, Number, and combined Gender/Number violations. This suggests that the feature distance between observed and expected word forms at the morphosyntactic level does not impact ERP responses, contrasting with findings on semantic and auditory processing, and suggests that the P600 response to agreement violations is not additive based on the number of mismatching features and does not reflect top-down, predictive mechanisms. A significantly larger P600 response was elicited by the combined Person/Gender violation, and two different violations involving the Person feature were judged as more severe and recognized more quickly in the behavioral studies. This effect is attributed to the greater salience of the Person feature at multiple levels of representation.

Processing of vowels in supratemporal auditory cortex

The auditory evoked neuromagnetic fields elicited by synthesized vowels of two different fundamental frequencies F0 were recorded in six subjects over the left and right temporal cortices using a 37-channel biomagnetometer. Single equivalent current dipole modeling of the fields elicited by all vowel types localized activity to a well-circumscribed area in supratemporal auditory cortex in both hemispheres. There were hemisphere asymmetries in the amplitude and latency of the M100 response. We also observed changes in M100 latency related to vowel type, but not to F0. There was no clear effect of vowel type or F0 on dipole localization for the M100, but a possible vowel type by latency interaction. These M100 data provide further evidence that vowels are processed independently of their pitch.