Publications

Abstract

Studies of perception have long shown that the brain adds information to its sensory analysis of the physical environment. A touchstone example for humans is language use: to comprehend a physical signal like speech, the brain must add linguistic knowledge, including syntax. Yet, syntactic rules and representations are widely assumed to be atemporal (i.e., abstract and not bound by time), so they must be translated into time-varying signals for speech comprehension and production. Here, we test 3 different models of the temporal spell-out of syntactic structure against brain activity of people listening to Dutch stories: an integratory bottom-up parser, a predictive top-down parser, and a mildly predictive left-corner parser. These models build exactly the same structure but differ in when syntactic information is added by the brain—this difference is captured in the (temporal distribution of the) complexity metric “incremental node count.” Using temporal response function models with both acoustic and information-theoretic control predictors, node counts were regressed against source-reconstructed delta-band activity acquired with magnetoencephalography. Neural dynamics in left frontal and temporal regions most strongly reflect node counts derived by the top-down method, which postulates syntax early in time, suggesting that predictive structure building is an important component of Dutch sentence comprehension. The absence of strong effects of the left-corner model further suggests that its mildly predictive strategy does not represent Dutch language comprehension well, in contrast to what has been found for English. Understanding when the brain projects its knowledge of syntax onto speech, and whether this is done in language-specific ways, will inform and constrain the development of mechanistic models of syntactic structure building in the brain.

Abstract

Face-to-face communication is not only about ‘what’ is said but also ‘how’ it is said, both in speech and bodily signals. Beat gestures are rhythmic hand movements that typically accompany prosodic prominence in con-versation. Yet, it is still unclear how beat gestures influence language comprehension. On the one hand, beat gestures may share the same functional role of focus markers as prosodic prominence. Accordingly, they would drive attention towards the concurrent speech and highlight its content. On the other hand, beat gestures may trigger inferences of high speaker confidence, generate the expectation that the sentence content is correct and thereby elicit the commitment to the truth of the statement. This study directly disentangled the two hypotheses by evaluating additive and interactive effects of prosodic prominence and beat gestures on language comprehension. Participants watched videos of a speaker uttering sentences and judged whether each sentence was true or false. Sentences sometimes contained a world knowledge violation that may go unnoticed (‘semantic illusion’). Combining beat gestures with prosodic prominence led to a higher degree of semantic illusion, making more world knowledge violations go unnoticed during language comprehension. These results challenge current theories proposing that beat gestures are visual focus markers. To the contrary, they suggest that beat gestures automatically trigger inferences of high speaker confidence and thereby elicit the commitment to the truth of the statement, in line with Grice’s cooperative principle in conversation. More broadly, our findings also highlight the influence of metacognition on language comprehension in face-to-face ommunication.

Abstract

The increased interest in developing next-gen social robots has raised questions about the factors affecting the perception of robot emotions. This study investigates the impact of robot appearances (human-like, mechanical) and face regions (full-face, eye-region) on human perception of robot emotions. A between-subjects user study (N = 305) was conducted where participants were asked to identify the emotions being displayed in videos of robot faces, as well as a human baseline. Our findings reveal three important insights for effective social robot face design in Human-Robot Interaction (HRI): Firstly, robots equipped with a back-projected, fully animated face – regardless of whether they are more human-like or more mechanical-looking – demonstrate a capacity for emotional expression comparable to that of humans. Secondly, the recognition accuracy of emotional expressions in both humans and robots declines when only the eye region is visible. Lastly, within the constraint of only the eye region being visible, robots with more human-like features significantly enhance emotion recognition.

Abstract

To date, research has reliably shown that language can engage and modify perceptual processes in a top-down manner. However, our understanding of the cognitive and neural mechanisms underlying such top-down influences is still under debate. In this review, we provide an overview of findings from literature investigating the organization of semantic networks in the brain (spontaneous engagement of the visual system while processing linguistic information), and linguistic cueing studies (looking at the immediate effects of language on the perception of a visual target), in an effort to isolate such mechanisms. Additionally, we connect the findings from linguistic cueing studies to those reported in (nonlinguistic) literature on priors in perception, in order to find commonalities in neural processes allowing for top-down influences on perception. In doing so, we discuss the effects of language on perception in the context of broader, general cognitive and neural principles. Finally, we propose a way forward in the study of linguistic influences on perception.

Abstract

Prosody underpins various linguistic domains ranging from semantics and syntax to discourse. For instance, prosodic information in the form of lexical stress modifies meanings and, as such, syntactic contexts of words as in Turkish kaz-má "pickaxe" (noun) versus káz-ma "do not dig" (imperative). Likewise, prosody indicates the focused constituent of an utterance as the noun phrase filling the wh-spot in a dialogue like What did you eat? I ate----. In the present study, we investigated the relevance of such prosodic variations for discourse comprehension in Turkish. We aimed at answering how lexical stress and prosodic focus mismatches on critical noun phrases-resulting in grammatical anomalies involving both semantics and syntax and discourse-level anomalies, respectively-affect the perceived correctness of an answer to a question in a given context. To that end, 80 native speakers of Turkish, 40 participating in a psychometric experiment and 40 participating in an EEG experiment, were asked to judge the acceptability of prosodic mismatches that occur either separately or concurrently. Psychometric results indicated that lexical stress mismatch led to a lower correctness score than prosodic focus mismatch, and combined mismatch received the lowest score. Consistent with the psychometric data, EEG results revealed an N400 effect to combined mismatch, and this effect was followed by a P600 response to lexical stress mismatch. Conjointly, these results suggest that every source of prosodic information is immediately available and codetermines the interpretation of an utterance; however, semantically and syntactically relevant lexical stress information is assigned more significance by the language comprehension system compared with prosodic focus information.

Abstract

The N400 is an endogenous event-related brain potential (ERP) that is sensitive to semantic processes during language comprehension. The general question we address in this paper is which aspects of the comprehension process are manifest in the N400. The focus is on the sensitivity of the N400 to the automatic process of lexical access, or to the controlled process of lexical integration. The former process is the reflex-like and effortless behavior of computing a form representation of the linguistic signal, and of mapping this representation onto corresponding entries in the mental lexicon. The latter process concerns the integration of a spoken or written word into a higher-order meaning representation of the context within which it occurs. ERPs and reaction times (RTs) were acquired to target words preceded by semantically related and unrelated prime words. The semantic relationship between a prime and its target has been shown to modulate the amplitude of the N400 to the target. This modulation can arise from lexical access processes, reflecting the automatic spread of activation between words related in meaning in the mental lexicon. Alternatively, the N400 effect can arise from lexical integration processes, reflecting the relative ease of meaning integration between the prime and the target. To assess the impact of automatic lexical access processes on the N400, we compared the effect of masked and unmasked presentations of a prime on the N400 to a following target. Masking prevents perceptual identification, and as such it is claimed to rule out effects from controlled processes. It therefore enables a stringent test of the possible impact of automatic lexical access processes on the N400. The RT study showed a significant semantic priming effect under both unmasked and masked presentations of the prime. The result for masked priming reflects the effect of automatic spreading of activation during the lexical access process. The ERP study showed a significant N400 effect for the unmasked presentation condition, but no such effect for the masked presentation condition. This indicates that the N400 is not a manifestation of lexical access processes, but reflects aspects of semantic integration processes.

Abstract

Broca′s and Wernicke′s aphasics performed speeded lexical decisions on the third member of auditorily presented triplets consisting of two word primes followed by either a word or a nonword. In three of the four priming conditions, the second prime was a homonym with two unrelated meanings. The relation of the first prime and the target with the two meanings of the homonym was manipulated in the different priming conditions. The two readings of the ambiguous words either shared their grammatical form class (noun-noun ambiguities) or not (noun-verb ambiguities). The silent intervals between the members of the triplets were varied between 100, 500, and 1250 msec. Priming at the shortest interval is mainly attributed to automatic lexical processing, and priming at the longest interval is mainly due to forms of controlled lexical processing. For both Broca′s and Wernicke′s aphasics overall priming effects were obtained at ISIs of 100 and 500 msec, but not at an ISI of 1250 msec. This pattern of results is consistent with the view that both types of aphasics can automatically access the semantic lexicon, but might be impaired in integrating lexical-semantic information into the context. Broca′s aphasics showed a specific impairment in selecting the contextually appropriate reading of noun-verb ambiguities, which is suggested to result from a failure either in the on-line morphological parsing of complex word forms into a stem and an inflection or in the on-line exploitation of the syntactic implications of the inflectional suffix. In a final experiment patients were asked to explicitly judge the semantic relations between a subset of the primes that were used in the lexical decision study. Wernicke′s aphasics performed worse than both Broca′s aphasics and normal controls, indicating a specific impairment for these patients in consciously operating on automatically accessed lexical-semantic information.

Abstract

This paper presents event-related brain potential (ERP) data from an experiment on syntactic processing. Subjects read individual sentences containing one of three different kinds of violations of the syntactic constraints of Dutch. The ERP results provide evidence for M electrophysiological response to syntactic processing that is qualitatively different from established ERP responses to semantic processing. We refer to this electro-physiological manifestation of parsing as the Syntactic Positive Shift (SPS). The SPS was observed in an experiment in which no task demands, other than to read the input, were imposed on the subjects. The pattern of responses to the different kinds of syntactic violations suggests that the SPS indicates the impossibility for the parser to assign the preferred structure to an incoming string of words, irrespective of the specific syntactic nature of this preferred structure. The implications of these findings for further research on parsing are discussed.