Biomedical subjects

Werner Sommer

Publications and source records attributed to Werner Sommer.

At least 19 recordsLinked to original sources

PubMed2006

Memory systems for structural and semantic knowledge of faces and buildings.

It is an ongoing debate whether specific neurocognitive systems are involved in face and object recognition, particularly for analyses that require the access to stored structural and semantic knowledge. Here we compared the processing of familiar (at the exemplar level) and unfamiliar faces and buildings by recording event-related potentials in a repetition priming paradigm. We focused on the early repetition effect (ERE/N250r) which has been proposed to indicate the access to stored structural knowledge and the late repetition effect (LRE/N400), a possible indicator of semantic knowledge. An ERE/N250r was present for familiar buildings and smaller than for faces, but indistinguishable in terms of scalp topography. In contrast, the LRE/N400 was stimulus specific in topography. These findings suggest initial access to a common store of structural knowledge followed by the activation of category-specific cortical representations of person- and building-related semantic knowledge.

Adult↗

PubMed2006

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.

Adolescent↗

PubMed2005

Dissociating perceptual and representation-based contributions to priming of face recognition.

Repetition priming of object identification refers to the phenomenon whereby experience with an object induces systematic changes in subsequent processing of that same object. This data-driven form of priming is distinct from conceptually-driven priming. To date, considerable controversy exists about whether data-driven priming reflects facilitation in perceptual processing or mediation by preexisting object representations. The present study concerned priming of recognizing familiar and unfamiliar faces and how this priming is influenced by face inversion, which interferes with perceptual face processing. Perceptual and representation-based loci conjointly contributed to priming; the perceptual locus was operative similarly for familiar and unfamiliar faces, whereas the representation-based locus was only invoked for familiar faces and resulted in a response-time reduction triple the magnitude of that from the perceptual locus. The results constrain theoretical accounts of data-driven priming by indicating that improved identification can result from the combination of perceptual and representation-based facilitation.

Adult↗

PubMed2005

Semantic processing of unattended meaning is modulated by additional task load: evidence from electrophysiology.

Recently, we observed that the perception of word meaning, as measured with the N400 component of the event-related brain potential, is delayed but unimpaired by various additional tasks when the language task requires the processing of semantic properties of the word stimuli. In the present study, we assessed whether similar effects would be observed when the language task relates to acoustic rather than to semantic properties of the word stimuli. The N400 was elicited by synonymous and non-synonymous spoken noun pairs that were to be classified according to tone pitch. In a single task experiment, there was a small but clear synonymity effect in ERPs (N400), indicating the availability of word meaning to the semantic system. Additional processing load, imposed by an overlapping task, abolished N400 for all SOAs when stimulus-response assignments were incompatible. For compatible assignments, N400 amplitude was present but much attenuated at the longest SOA. We conclude that the availability of task-irrelevant meaning is modulated by additional task load and decay in short-term memory.

Adult↗

PubMed2005

ERP components reflecting stimulus identification: contrasting the recognition potential and the early repetition effect (N250r).

The recognition potential component (RP) in the event-related brain potential (ERP) appears during rapid stream stimulation and has been related to the activation of word form or word meaning. The early repetition effect (ERE/N250r) is observed in repetition priming designs and has been linked to the access to stored representations of the structure of familiar faces and names. Because of the apparent similarities in latency, topography and theoretical interpretation we compared the RP and ERE/N250r within the same rapid stream stimulation design and for the same type of stimulus material: names and faces of famous persons and names and pictures of common objects. Contrasting with RP, the ERE/N250r occurred later and differed in both scalp topography and amplitude patterns across stimulus conditions. Therefore, the ERE/N250r seems to reflect a separate and content-specific stage of information processing, following the RP, which appears to reflect domain-general processes of structural analyses.

Adolescent↗

PubMed2005

Correlates of implicit memory for words and faces in event-related brain potentials.

Prior research has suggested an ERP correlate of implicit memory for words consisting of a centro-parietal positivity around 400 ms. We attempted (1) to replicate this ERP modulation in a different task, involving only trials with correct responses, and (2) to compare the findings to the domain of faces. Two experiments were conducted with a modified Sternberg task, in which both targets and nontargets were presented repeatedly. In Experiment 1, positive ERP differences between repeated and new nontargets were observed, which were domain-specific in topography and, for words, replicated the previously reported findings. In Experiment 2, the amplitude of the modulation for words, but not for faces, was unaffected by a variation of the level of processing during encoding, supporting the implicitness of the processes underlying the ERP modulation to nontarget words.

Adult↗

PubMed2005

Priming emotional facial expressions as evidenced by event-related brain potentials.

As human faces are important social signals in everyday life, processing of facial affect has recently entered into the focus of neuroscientific research. In the present study, priming of faces showing the same emotional expression was measured with the help of event-related potentials (ERPs) in order to investigate the temporal characteristics of processing facial expressions. Participants classified portraits of unfamiliar persons according to their emotional expression (happy or angry). The portraits were either preceded by the face of a different person expressing the same affect (primed) or the opposite affect (unprimed). ERPs revealed both early and late priming effects, independent of stimulus valence. The early priming effect was characterized by attenuated frontal ERP amplitudes between 100 and 200 ms in response to primed targets. Its dipole sources were localised in the inferior occipitotemporal cortex, possibly related to the detection of expression-specific facial configurations, and in the insular cortex, considered to be involved in affective processes. The late priming effect, an enhancement of the late positive potential (LPP) following unprimed targets, may evidence greater relevance attributed to a change of emotional expressions. Our results (i) point to the view that a change of affect-related facial configuration can be detected very early during face perception and (ii) support previous findings on the amplitude of the late positive potential being rather related to arousal than to the specific valence of an emotional signal.

Adult↗

PubMed2004

Neural correlates of intentional and incidental recognition of famous faces.

Event-related potentials (ERPs) were used to study the relationship between intentional and incidental recognition of famous faces. Intentional and incidental recognition were operationally defined as repeated presentations of targets and nontargets within a modified Sternberg task. These repetitions elicited temporally and topographically distinct ERP modulations. A repetition effect around 300 ms (ERE/N250r) and a preceding modulation did not differ between intentional and incidental recognition, whereas a following repetition effect (LRE/N400) around 500 ms showed differences between incidental and intentional recognition. These results show that during the first few hundred milliseconds intentional and incidental face recognition relate to similar processing, indicating that familiar faces are recognized even when their identification is not required.

Adolescent↗

PubMed2004

Time pressure effects on information processing in overlapping tasks: evidence from the lateralized readiness potential.

Information processing is impaired when two tasks are performed concurrently. The interference between the tasks is commonly attributed to structural bottlenecks or strategic scheduling of information processing. The present experiment investigated the effects of time pressure for the second of two responses on information processing in overlapping tasks by recording the lateralized readiness potential (LRP). Time pressure shortened the latency of the second response by diminishing the time devoted to motoric processing. In addition, task interference decreased under time pressure, which is probably due to the relatively early availability of the central bottleneck stage rather than to increased overlap of central stages. The LRP also provided direct evidence for an additional bottleneck following response selection, possibly due to supramodal refractoriness of response initiation.

Acoustic Stimulation↗

PubMed2004

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.

Adult↗

PubMed2004

Face repetition effects in direct and indirect tasks: an event-related brain potentials study.

We investigated immediate repetition effects on event-related potentials (ERPs) during direct and indirect tasks for sequentially presented face pairs. The first face (F1) was presented masked or unmasked, and at different stimulus onset asynchronies (SOAs, 67 vs. 1000 ms) preceding the second face (F2). Experiment I (indirect task) required a semantic classification of F2, with F1 identity being irrelevant. Experiment II (direct task) used the same stimulus sequence but required a physical identity matching of F1 and F2. Whereas no masked repetition effects in behaviour or ERPs were seen, such effects were clearly shown for unmasked F1 faces. For short SOAs, an early-onset ( approximately 100 ms) occipital repetition effect, an inferior temporal N250r (200-300 ms) and a central-parietal N400 modulation (300-500 ms) were seen in both tasks, whereas a parietal P600 effect (500-800 ms) was only present in the indirect task. For long SOAs, the early occipital effect disappeared, suggesting that it reflects a fast decaying iconic memory trace. Clear task differences were seen for N250r, N400, and P600 modulations: P600 was larger for the indirect task, and may be a correlate of semantic analysis required by this task. By contrast, N250r and N400 were larger for the direct task, suggesting that these components are sensitive to task relevance and/or attentional focus to F1, and thus do not reflect purely automatic facilitation in processing. This suggests an influence of strategic processing on the activation of both perceptual representations of faces and semantic representations of people.

Adolescent↗

PubMed2004

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.

Adult↗

PubMed2004

I recognize your face, but I can't remember your name: a question of expertise?

In four experiments on the identification of familiar faces we reassessed a robust performance pattern--namely, the temporal advantage for retrieving biographical facts as compared to recalling proper names, which has been interpreted as reflecting a serial ordering of the access to semantic and name information. Evidence for recent parallel accounts had been provided by Scanlan and Johnston (1997) who reported an advantage for name retrieval in children. Here we replicated the findings of Scanlan and Johnston but also showed that the naming advantage disappears, and performance is very similar to that of adults when stimuli and tasks are used that are familiar to children. Conversely, we also demonstrated an advantage for name retrieval in adults when highly unfamiliar semantic facts were associated with the faces. Together these findings suggest that there is no fundamental difference in the cognitive architectures of children and adults. The experiments indicate that the relative speed of naming and semantic fact retrieval depends on the expertise with the semantic facts to be retrieved. Implications for models of face identification and naming are discussed.

Adult↗

PubMed2004

The functional locus of the lateralized readiness potential.

The lateralized readiness potential (LRP) is considered to reflect motor activation and has been used extensively as a tool in elucidating cognitive processes. In the present study, we attempted to more precisely determine the origins of the LRP within the cognitive system. The response selection and motor programming stages were selectively manipulated by varying symbolic stimulus response compatibility and the time to peak force of an isometric finger extension response. Stimulus response compatibility and time to peak force affected response latency, as measured in the electromyogram, in a strictly additive fashion. The effects of the experimental manipulations on stimulus- and response-synchronized LRPs indicate that the LRP starts after the completion of response-hand selection and at the beginning of motor programming. These results allow a more rigorous interpretation of LRP findings in basic and applied research.

Adult↗

PubMed2004

What's special about personally familiar faces? A multimodal approach.

Dual-route models of face recognition suggest separate cognitive and affective routes. The predictions of these models were assessed in recognition tasks with unfamiliar, famous, and personally familiar faces. Whereas larger autonomic responses were only triggered for personally familiar faces, priming effects in reaction times to these faces, presumably reflecting cognitive recognition processes, were equal to those of famous faces. Activation of stored structural representations of familiar faces (face recognition units) was assessed by recording the N250r component in event-related brain potentials. Face recognition unit activation increased from unfamiliar over famous to personally familiar faces, suggesting that there are stronger representations for personally familiar than for famous faces. Because the topographies of the N250r for personally and famous faces were indistinguishable, a similar network of face recognition units can be assumed for both types of faces.

Adult↗

PubMed2003

Does phonological encoding in speech production always follow the retrieval of semantic knowledge? Electrophysiological evidence for parallel processing.

In this article a new approach to the distinction between serial/contingent and parallel/independent processing in the human cognitive system is applied to semantic knowledge retrieval and phonological encoding of the word form in picture naming. In two-choice go/nogo tasks pictures of objects were manually classified on the basis of semantic and phonological information. An additional manipulation of the duration of the faster and presumably mediating process (semantic retrieval) allowed to derive differential predictions from the two alternative models. These predictions were tested with two event-related brain potentials (ERPs), the lateralized readiness potential (LRP) and the N200. The findings indicate that phonological encoding can proceed in parallel to the retrieval of semantic features. A suggestion is made how to accommodate these findings with models of speech production.

Adult↗

PubMed2003

Are fingers special? Evidence about movement preparation from event-related brain potentials.

Ulrich, Leuthold, and Sommer (1998) suggested that movement preparation at the level of the motor cortex, as indexed by the lateralized readiness potential (LRP), proceeds in a strongly hierarchical fashion, where parameters other than response hand are prepared only if all the movement parameters are known. These conclusions were based on an experiment where a precue provided information about response hand, direction of finger movement, and movement force. To assess the generality of these findings, we replaced the force parameter with response finger. LRP indicated that preparation of the required finger is possible even when preliminary information is incomplete. Therefore, movement preparation appears to follow different rules when anatomical relationships (hand and finger) are concerned as compared to functional parameters like movement direction. On the other hand, at a limb-unspecific level, as indicated by the contingent negative variation, we confirmed evidence for parallel programming of all movement parameters.

Adult↗

PubMed2002

The effect of intentional expectancy on mental processing: a chronopsychophysiological investigation.

Expected events are processed faster than unexpected ones. Previously, we have reported evidence that passive expectancies determined by the preceding event sequence mainly affected the duration of motoric processes. Here we examined the effects of instructed, intentional expectancies in a two-choice reaction time (RT) task. As predicted, RTs were shorter for expected than unexpected events. Onset of the lateralized readiness potential as an index of selective response activation, and the latency of the P300 component of the event-related potential, reflecting the duration of perceptual processing, indicated that intentional expectancy affected the time demands for central processing but did not influence the duration of early perceptual or motoric processes. Together the present and our previous results provide evidence that different kinds of expectancy can be distinguished by their locus of action within the information processing system.

Adult↗