Annette Hohlfeld

Semantics prevalence over syntax during sentence processing: A brain potential study of noun–adjective agreement in Spanish

A review of the literature about the interplay of syntax and semantics, using event-related brain potentials (ERPs), revealed that the results are highly heterogeneous, owing to several possible variables. An experiment was conducted with Spanish sentences that factorially combined syntactic and semantic violations in the same sentence-intermediate adjective and controlled for working memory demands, variables that in previous studies have rarely been taken into consideration. Violations consisted in noun-adjective number or gender disagreements (syntactic violation), noun-adjective semantic incompatibility (semantic violation), or both (combined violation). The N400 to semantic violations was unaffected by additional syntactic violations. The P600/SPS component, considered to reflect syntactic processes, was elicited by both single syntactic and semantic violations but seemed to be diminished in combined violations relative to single syntactic violations. These results suggest that under the conditions of the present experiment semantic information may have a prevailing role over syntactic information.

Effects of additional tasks on language perception: an event-related brain potential investigation.

The authors investigated effects of task and overlapping processing load on semantic processing. In 3 experiments the brain potential component N400 was elicited by synonymous and nonsynonymous spoken noun pairs that were to be classified according to semantic relatedness. The time course of the N400 component to the nouns was delayed, and its amplitude was reduced when additional tasks had to be performed. The delay increased with temporal overlap and was more pronounced for language-related than for spatial additional tasks. Delays of N400 were also caused by a compatibility manipulation in the additional tasks. Theoretical accounts of the observed interference of overlapping tasks with language perception in terms of attentional shifts were discarded. Explanations in terms of resource sharing and single channel processing are discussed.

Does the semantic content of verbal categories influence categorical perception? An ERP study

Accumulating evidence suggests that visual perception and, in particular, visual discrimination, can be influenced by verbal category boundaries. One issue that still awaits systematic investigation is the specific influence of semantic contents of verbal categories on categorical perception (CP). We tackled this issue with a learning paradigm in which initially unfamiliar, yet realistic objects were associated with either bare labels lacking explicit semantic content or labels that were accompanied by enriched semantic information about the specific meaning of the label. Two to three days after learning, the EEG was recorded while participants performed a lateralized oddball task. Newly acquired verbal category boundaries modulated low-level aspects of visual perception as early as 100-150 ms after stimulus onset, suggesting a genuine influence of language on perception. Importantly, this effect was not further influenced by enriched semantic category information, suggesting that bare labels and the associated minimal and predominantly perceptual information are sufficient for CP. Distinct effects of semantic knowledge independent of category boundaries were found subsequently, starting at about 200 ms, possibly reflecting selective attention to semantically meaningful visual features.

Rules and heuristics during sentence comprehension: Evidence from a dual-task brain potential study

Whether syntactic and semantic processes during sentence comprehension follow strict sets of rules or succumb to context-dependent heuristics was studied by recording event-related potentials in a dual-task design. In one condition, sentence-extraneous acoustic material was either semantically congruent or incongruent relative to an adjective in the visually presented sentence, the latter being either semantically correct or incorrect within the sentence context. Homologous syntactic (gender) manipulations were performed in another condition. Syntactic processing within the sentence appeared to be blind to the syntactic content of the second task. In contrast, semantically incongruous material of the second task induced fluctuations typically associated with the detection of within-sentence semantic anomalies (N400) even in semantically correct sentences. Subtle but extant differences in topography between this N400 and that obtained with within-sentence semantic violations add to recent proposals of separate semantic subsystems differing in their specificity for sentence structure and computational procedures. Semantically incongruous material of the second task also influenced later stages of the processing of semantically incorrect adjectives (P600 component), which are traditionally assumed to pertain to the syntactic domain. This result is discussed in the light of current proposals of a third combinatorial stream in sentence comprehension.

Is word perception in a second language more vulnerable than in one's native language? Evidence from brain potentials in a dual task setting.

We assessed the effect of additional tasks on language perception in second-language and native speakers. The N400 component of the event-related potential was recorded to spoken nouns that had to be judged for synonymity with a preceding word, while additional choice responses were required to visual stimuli. In both participant groups N400 was delayed as a function of temporal overlap with the additional task. In second-language speakers there was a global delay of N400 independent of additional task load and a decrease of accuracy at highest overlap. These findings are interpreted within a single channel account of language perception.

Overlapping Tasks Methodology as a Tool for Investigating Language Perception

A series of studies is reviewed that investigated the effects of additional tasks on the N400 component of the event-related brain potential (ERP) within the framework of an overlapping tasks paradigm. In all studies the N400 component was elicited by words that could be either synonymous or nonsynonymous to a preceding word and by subtracting the ERP to synonymous from those to non-synonymous words. Additional task stimuli were visual and could be presented at high to low temporal overlap with the words. The N400 was delayed in time when there was high temporal overlap with the additional task stimulus. The delay was more pronounced when the additional task was more difficult and more language-like. Second-language speakers showed very similar interference effects albeit at a globally slower level. Somewhat different interference effects were obtained when the meaning of the eliciting words were irrelevant to the task. In contrast, eye movements and visuo-spatial attention shifts had no effects on N400 latency. Together, the results indicate that the N400-eliciting processes – presumably the access to semantic knowledge – belong to a group of central processes that form a bottleneck in the cognitive system because they can handle only one process at a time. On the basis of these findings dual-task methodology is suggested to be a valuable tool not only for investigating the processes supporting language perception and, more generally, the retrieval of semantic knowledge but also for other language perception processes.

Is Semantic Processing During Sentence Reading Autonomous or Controlled? Evidence from the N400 Component in a Dual Task Paradigm.

The present study contributes to the discussion on the automaticity of semantic processing. Whereas most previous research investigated semantic processing at word level, the present study addressed semantic processing during sentence reading. A dual task paradigm was combined with the recording of event-related brain potentials. Previous research at word level processing reported different patterns of interference with the N400 by additional tasks: attenuation of amplitude or delay of latency. In the present study, we presented Spanish sentences that were semantically correct or contained a semantic violation in a critical word. At different intervals preceding the critical word a tone was presented that required a high-priority choice response. At short intervals/high temporal overlap between the tasks mean amplitude of the N400 was reduced relative to long intervals/low temporal overlap, but there were no shifts of peak latency. We propose that processing at sentence level exerts a protective effect against the additional task. This is in accord with the attentional sensitization model (Kiefer & Martens, 2010), which suggests that semantic processing is an automatic process that can be enhanced by the currently activated task set. The present experimental sentences also induced a P600, which is taken as an index of integrative processing. Additional task effects are comparable to those in the N400 time window and are briefly discussed.