Biomedical subjects

Christian Dobel

Publications and source records attributed to Christian Dobel.

6 recordsLinked to original sources

PubMed2006

Describing scenes hardly seen.

Knowledge about scene categories, the so-called gist, can be extracted very rapidly, while recognition and naming of individual scene objects is a more effortful process. We investigate this phenomenon by presenting action scenes involving two actors for durations varying between 100 and 300 ms. Incoherence was created by mirroring individual scene actors. Upon masked presentation participants had to report content, actors and objects and to indicate whether the scene was meaningful or not. Scene coherence was judged correctly at all presentation durations. Actors were correctly identified in about one-third of the cases even with presentation durations of 100 ms, and identification rate increased up to 80% with longer durations. Identification depended on scene coherence, on the position of agents in the scene, and on the position of actors relative to the fixation cross. These interdependencies of scene and object perception indicate that the visual system seems to be very sensitive to meaningful interactions of living entities. A series of fixations is not necessary to identify actors of a scene.

Attention↗

PubMed2006

Effects of personal familiarity on early neuromagnetic correlates of face perception.

This study investigated effects of familiarity and orientation on face processing by means of magnetoencephalography. Participants were presented with photographs of personally familiar, famous and unfamiliar faces in both upright and inverted orientation. They had to decide whether faces were familiar by means of manual yes/no responses. Independent of orientation, we observed a clear modulation of the M170 by familiarity, with personally familiar faces evoking larger amplitudes than unknown faces. The M170 was also sensitive to orientation, with larger amplitudes for inverted than upright faces. Moreover, the M170 exhibited larger amplitudes over the right than over the left hemisphere, but this asymmetry was present for upright faces only. The present data suggest that at least for personally familiar faces, neural correlates of identification start no later than approximately 170 ms, and underline a special role of the right hemisphere for faces in their typical upright orientation.

Adult↗

PubMed2005

Lexically-driven syntactic priming.

Syntactic priming studies demonstrate that exposure to a particular syntactic structure leads speakers to reproduce the same structure in subsequent utterances. Explanations for this phenomenon rely on either the retrieval of morphosyntactic features associated with the verb in the prime sentence or the preservation of the mapping between message and word sequences in the prime sentence. Two experiments test the featural account of syntactic priming. We used single word primes to investigate the dative alternation in German (Experiment 1) and Dutch (Experiment 2). Native speakers read ditransitive verbs that are restricted either to the prepositional (dative) or double object construction, followed by pictures that can be described with either structure. We find that a single verb in isolation is sufficient to bias speakers' production preferences supporting lexically-driven accounts of syntactic priming.

Child↗

PubMed2005

Pre-attentive detection of syntactic and semantic errors.

This magnetoencephalographic study tested whether magnetic fields evoked by syntactic and semantic errors differ in their time course and magnitude from fields evoked by phonemic differences. An oddball design, using German sentences with embedded critical words was applied: The error condition (with the standard word RASEN, lawn, in 70% of the trials, and the syntactic and semantic errors ROSEN, roses and RIESEN, giant as deviants) was compared with a neutral, correct phonemic condition. Mismatch responses were significantly larger for syntactic and semantic errors as compared to mere phonemic deviations. The semantic error elicited higher mismatch responses than the syntactic error. This error-sensitive component is interpreted as a very early detector for semantic and syntactic errors.

Attention↗

PubMed2005

Structured perceptual input imposes an egocentric frame of reference-pointing, imagery, and spatial self-consciousness.

Perceptual input imposes and maintains an egocentric frame of reference, which enables orientation. When blindfolded, people tended to mistake the assumed intrinsic axes of symmetry of their immediate environment (a room) for their own egocentric relation to features of the room. When asked to point to the door and window, known to be at mid-points of facing (or adjacent) walls, they pointed with their arms at 180 degrees (or 90 degrees) angles, irrespective of where they thought they were in the room. People did the same when requested to imagine the situation. They justified their responses (inappropriately) by logical necessity or a structural description of the room rather than (appropriately) by relative location of themselves and the reference points. In eight experiments, we explored the effect on this in perception and imagery of: perceptual input (without perceptibility of the target reference points); imaging oneself versus another person; aids to explicit spatial self-consciousness; order of questions about self-location; and the relation of targets to the axes of symmetry of the room. The results indicate that, if one is deprived of structured perceptual input, as well as losing one's bearings, (a) one is likely to lose one's egocentric frame of reference itself, and (b) instead of pointing to reference points, one demonstrates their structural relation by adopting the intrinsic axes of the environment as one's own. This is prevented by providing noninformative perceptual input or by inducing subjects to imagine themselves from the outside, which makes explicit the fact of their being located relative to the world. The role of perceptual contact with a structured world is discussed in relation to sensory deprivation and imagery, appeal is made to Gibson's theory of joint egoreception and exteroception, and the data are related to recent theories of spatial memory and navigation.

Adult↗

PubMed2002

Slow event-related brain activity of aphasic patients and controls in word comprehension and rhyming tasks.

Slow event-related potentials (ERP) were examined in healthy and aphasic subjects in two-stimulus designs comprising a word comprehension and a rhyming task. Aphasics, though selected to perform above chance level, made significantly more errors and responded more slowly than controls, although canonical correlations did not indicate a statistical relationship between performance measures and ERP amplitudes. A discriminant analysis of ERP amplitudes distinguished the groups for the slow wave (SW; 0.5-1.0 s post-S1 onset) in the word comprehension, for the SW and the initial contingent negative variation (iCNV; 1.0-2.0 s post-S1 onset) in the rhyming task. Similarly for both tasks, ERP topography showed left-anterior predominance of the negative SW and iCNV in controls, whereas participants with aphasia showed smaller anterior and larger left-posterior amplitudes. The centroparietal terminal CNV (tCNV; 1 s pre-S2) was smaller in participants with aphasia than in controls, but similar in topography. Results suggest left-anterior activation for those language processes that were presumably provoked in the present tasks, like lexical access, or phonological encoding. The pattern of participants with aphasia may indicate effects of language impairment and recovery, but also consequences of the brain damage.

Adult↗