Hilary Gomes

The mismatch negativity of event-related potentials as a probe of transient auditory memory: a review

The use of the mismatch negativity as a probe to study the memory upon which it depends is reviewed. Topics about the memory include its duration, its capacity, the kind of information that can be stored in the memory, how the information is stored, whether the memory is accessed in parallel or in series, whether it is hard-wired or can be modified by experience, and its relationship to sensory memory.

The Development of Multisensory Integration in High-Functioning Autism: High-Density Electrical Mapping and Psychophysical Measures Reveal Impairments in the Processing of Audiovisual Inputs

Successful integration of auditory and visual inputs is crucial for both basic perceptual functions and for higher-order processes related to social cognition. Autism spectrum disorders (ASD) are characterized by impairments in social cognition and are associated with abnormalities in sensory and perceptual processes. Several groups have reported that individuals with ASD are impaired in their ability to integrate socially relevant audiovisual (AV) information, and it has been suggested that this contributes to the higher-order social and cognitive deficits observed in ASD. However, successful integration of auditory and visual inputs also influences detection and perception of nonsocial stimuli, and integration deficits may impair earlier stages of information processing, with cascading downstream effects. To assess the integrity of basic AV integration, we recorded high-density electrophysiology from a cohort of high-functioning children with ASD (7-16 years) while they performed a simple AV reaction time task. Children with ASD showed considerably less behavioral facilitation to multisensory inputs, deficits that were paralleled by less effective neural integration. Evidence for processing differences relative to typically developing children was seen as early as 100 ms poststimulation, and topographic analysis suggested that children with ASD relied on different cortical networks during this early multisensory processing stage.

Multisensory processing in children with autism: high-density electrical mapping of auditory–somatosensory integration

Successful integration of signals from the various sensory systems is crucial for normal sensory–perceptual functioning, allowing for the perception of coherent objects rather than a disconnected cluster of fragmented features. Several prominent theories of autism suggest that automatic integration is impaired in this population, but there have been few empirical tests of this thesis. A standard electrophysiological metric of multisensory integration (MSI) was used to test the integrity of auditory–somatosensory integration in children with autism (N=17, aged 6–16 years), compared to age‐ and IQ‐matched typically developing (TD) children. High‐density electrophysiology was recorded while participants were presented with either auditory or somatosensory stimuli alone (unisensory conditions), or as a combined auditory–somatosensory stimulus (multisensory condition), in randomized order. Participants watched a silent movie during testing, ignoring concurrent stimulation. Significant differences between neural responses to the multisensory auditory–somatosensory stimulus and the unisensory stimuli (the sum of the responses to the auditory and somatosensory stimuli when presented alone) served as the dependent measure. The data revealed group differences in the integration of auditory and somatosensory information that appeared at around 175 ms, and were characterized by the presence of MSI for the TD but not the autism spectrum disorder (ASD) children. Overall, MSI was less extensive in the ASD group. These findings are discussed within the framework of current knowledge of MSI in typical development as well as in relation to theories of ASD.

Novel metaphors appear anomalous at least momentarily: evidence from N400.

This study addresses a central question in perception of novel figurative language: whether it is interpreted intelligently and figuratively immediately, or only after a literal interpretation fails. Eighty sentence frames that could plausibly end with a literal, truly anomalous, or figurative word were created. After validation for meaningfulness and figurativeness, the 240 sentences were presented to 11 subjects for event related potential (ERP) recording. ERPs first 200 ms is believed to reflect the structuring of the input; the prominence of a dip at around 400 ms (N400) is said to relate inversely to how expected a word is. Results showed no difference between anomalous and metaphoric ERPs in the early window, metaphoric and literal ERPs converging 300-500 ms after the ending, and significant N400s only for anomalous endings. A follow-up study showed that the metaphoric endings were less frequent (in standardized word norms) than were the anomalous and literal endings and that there were significant differences in cloze probabilities (determined from 24 new subjects) among the three ending types: literal > metaphoric > anomalous. It is possible that the low frequency of the metaphoric element and lower cloze probability of the anomalous one contributed to the processes reflected in the early window, while the incongruity and near-zero cloze probability of the anomalous endings produced an N400 effect in them alone. The structure or parse derived for metaphor during the early window appears to yield a preliminary interpretation suggesting anomaly, while semantic analysis reflected in the later window renders a plausible figurative interpretation.

The Development of Audiovisual Multisensory Integration Across Childhood and Early Adolescence: A High-Density Electrical Mapping Study

The integration of multisensory information is essential to forming meaningful representations of the environment. Adults benefit from related multisensory stimuli but the extent to which the ability to optimally integrate multisensory inputs for functional purposes is present in children has not been extensively examined. Using a cross-sectional approach, high-density electrical mapping of event-related potentials (ERPs) was combined with behavioral measures to characterize neurodevelopmental changes in basic audiovisual (AV) integration from middle childhood through early adulthood. The data indicated a gradual fine-tuning of multisensory facilitation of performance on an AV simple reaction time task (as indexed by race model violation), which reaches mature levels by about 14 years of age. They also revealed a systematic relationship between age and the brain processes underlying multisensory integration (MSI) in the time frame of the auditory N1 ERP component (∼ 120 ms). A significant positive correlation between behavioral and neurophysiological measures of MSI suggested that the underlying brain processes contributed to the fine-tuning of multisensory facilitation of behavior that was observed over middle childhood. These findings are consistent with protracted plasticity in a dynamic system and provide a starting point from which future studies can begin to examine the developmental course of multisensory processing in clinical populations.

Prototypicality of responses of autistic, language disordered, and normal children in a word fluency task

Abstract High-functioning autistic, specifically language-impaired, and normal children were administered word fluency tasks in which they were required to provide the names of animals and the names of vehicles. The exemplars provided by each subject for each category were assigned prototypicality ratings according to the norms of Uyeda and Mandler (1980). The autistic children provided less prototypic exemplars than did the language-impaired children or language-matched normals. The results support the notion that autistic children have a semantic processing impairment and that part of the basis for this impairment may lie at the level of organization within lexical categories.

Mismatch negativity in children and adults, and effects of an attended task

Attention has been shown to modulate the amplitude of the mismatch negativity (MMN) elicited by a small deviation in auditory stimuli in adults. The present study examined the effects of attention and deviant size on MMN amplitude in children. Children and adults were presented with sequences of tones containing standards (1000 Hz) and three deviants varying in degree of deviance from the standard (1050, 1200, and 1500 Hz). Tones were presented in three conditions: (1) while participants ignored them; (2) while participants listened to them and responded to all three deviants; and (3) while participants again ignored them. We found that the MMNs elicited by the hard deviant (1050 Hz) were larger when the children were actively discriminating the stimuli than when they were ignoring them. However, the MMNs elicited by the easy and medium deviants (1500 and 1200 Hz, respectively) in the children and by all three deviants in the adults were not affected by attention.

Lexical processing of visually and auditorily presented nouns and verbs: evidence from reaction time and N400 priming data

We investigated two aspects of lexical organization in normal adults employing behavioral and electrophysiological indices of semantic priming, namely: (1) Is there evidence for differential processing of nouns and verbs? (2) Is there evidence for separate systems for processing of orthographic and phonologic representations of words? Reaction time (RT), N400 amplitude and latency were used to examine the effect of semantic priming on lexical access of auditorily and visually presented nouns and verbs. We found that the temporal patterns of primed RTs and N400 latencies differed for nouns and verbs, indicating a functional difference in processing. However, the absence of topographic differences in N400 between nouns and verbs did not support anatomically distinct representations of these word classes. By contrast, a modality-specific topography at N400, in addition to RT and N400 amplitude differences between auditory and visual conditions, supported the proposed separation of the orthographic and phonologic representations of words. The implications of the findings for general theories of lexical organization are discussed.

The nature of preattentive storage in the auditory system

Event-related potentials were recorded to tones that subjects ignored while reading a book of their choosing. In all conditions, 90% of the tones were 100 msec in duration and 10% of the tones were 170 msec in duration. In a control condition, a customary oddball paradigm was used in which all of the tones were identical except for the longer duration tones. In two conditions, the tones varied over a wide range of tonal frequencies from 700 to 2050 Hz in 10 steps of 150 Hz. In another condition, the tones varied over the same frequencies but also varied in intensity from about 60 to 87 dB in steps of 3 dB. Thus, there was no standard tone in the sense of a frequently presented tone that had identical stimulus features. A mismatch negativity (MMN) was elicited in all conditions. The data are discussed in terms of the storage of information in the memory upon which the MMN is based.

Feature conjunctions and auditory sensory memory

This study sought to obtain additional evidence that transient auditory memory stores information about conjunctions of features on an automatic basis. The mismatch negativity of event-related potentials was employed because its operations are based on information that is stored in transient auditory memory. The mismatch negativity was found to be elicited by a tone that differed from standard tones in a combination of its perceived location and frequency. The result lends further support to the hypothesis that the system upon which the mismatch negativity relies processes stimuli in an holistic manner.