On this page you can find a brief overview of selected results from my research (both reference and synopsis). Please click onto a publication's title to display more information.
Timing-Mechanismen im Gehirn / Neural timing mechanisms
From early on, infants learn to detect, predict, and adjust to internal and external events through interaction with their environment. Research shows that aspects of timing inherent in these events seem to modulate and facilitate infants’ perceptual and cognitive processing... (learn more)
Research has shown that infants are able to track a moving target efficiently - even if it is transiently occluded from sight. This basic ability allows prediction of when and where events happen in everyday life. Yet, it is unclear whether, and how, infants internally represent the time course of ongoing movements to derive predictions.
In this study, 10-month-old crawlers observed the video of a same-aged crawling baby that was transiently occluded and reappeared in either a temporally continuous or non-continuous manner (i.e., delayed by 500 ms vs. forwarded by 500 ms relative to the real-time movement). Eye movement and rhythmic neural brain activity (EEG) were measured simultaneously. Eye movement analyses showed that infants were sensitive to slight temporal shifts in movement continuation after occlusion. Furthermore, brain activity associated with sensorimotor processing differed between observation of continuous and non-continuous movements.
Early sensitivity to an action's timing may hence be explained within the internal real-time simulation account of action observation. Overall, the results support the hypothesis that 10-month-old infants are well prepared for internal representation of the time course of observed movements that are within the infants' current motor repertoire.
Infants possess the remarkable capacity to perceive occluded movements as ongoing and coherent. Little is known about the neural mechanisms that enable internal representation of conspecifics' and inanimate objects' movements during visual occlusion.
In this study, 10-month-old infants watched briefly occluded human and object movements. Prior to occlusion, continuous and distorted versions of the movement were shown. EEG recordings were used to assess neural activity assumed to relate to processes of attention (occipital alpha), memory (frontal theta), and sensorimotor simulation (central alpha) before, during, and after occlusion. Oscillatory activity was analyzed using an individualized data approach taking idiosyncrasies into account.
Results for occipital alpha were consistent with infants' preference for attending to social stimuli. Furthermore, frontal theta activity was more pronounced when tracking distorted as opposed to continuous movement, and when maintaining object as opposed to human movement. Central alpha did not discriminate between experimental conditions. In sum, we conclude that observing occluded movements recruits processes of attention and memory which are modulated by stimulus and movement properties.
The aim of this study was to investigate neural dynamics of audiovisual temporal fusion processes in 6-month-old infants using event-related brain potentials (ERPs). In a habituation-test paradigm, infants did not show any behavioral signs of discrimination of an audiovisual asynchrony of 200 ms, indicating perceptual fusion. In a subsequent EEG experiment, audiovisual synchronous stimuli and stimuli with a visual delay of 200 ms were presented in random order.
In contrast to the behavioral data, brain activity differed significantly between the two conditions. Critically, N1 and P2 latency delays were not observed between synchronous and fused items, contrary to previously observed N1 and P2 latency delays between synchrony and perceived asynchrony. Hence, temporal interaction processes in the infant brain between the two sensory modalities varied as a function of perceptual fusion versus asynchrony perception.
The visual recognition components Pb and Nc were modulated prior to sound onset, emphasizing the importance of anticipatory visual events for the prediction of auditory signals. Results suggest mechanisms by which young infants predictively adjust their ongoing neural activity to the temporal synchrony relations to be expected between vision and audition.
Young infants are sensitive to multisensory temporal synchrony relations, but the neural dynamics of temporal interactions between vision and audition in infancy are not well understood. We investigated audiovisual synchrony and asynchrony perception in 6-month-old infants using event-related potentials (ERP).
In a prior behavioral experiment (n = 45) infants were habituated to an audiovisual synchronous stimulus and tested for recovery of interest by presenting an asynchronous test stimulus in which the visual stream was delayed with respect to the auditory stream by 400 ms. Infants who behaviorally discriminated the change in temporal alignment were included in further analyses. In the EEG experiment (final sample: n = 15), synchronous and asynchronous stimuli (visual delay of 400 ms) were presented in random order.
Results show latency shifts in the auditory ERP components N1 and P2 as well as the infant ERP component Nc. Latencies in the asynchronous condition were significantly longer than in the synchronous condition. After video onset but preceding the auditory onset, amplitude modulations propagating from posterior to anterior sites and related to the Pb component of infants’ ERP were observed.
Results suggest temporal interactions between the two modalities. Specifically, they point to the significance of anticipatory visual motion for auditory processing, and indicate young infants’ predictive capacities for audiovisual temporal synchrony relations.
Soziales Lernen und Gedächtnis / Social Learning and Memory
Available evidence suggests that infants use adults’ social cues for learning by the second half of the first year of life. However, little is known about the short-term or long-term effects of joint attention interactions on learning and memory in younger infants. In the present study, 4-month-old infants were familiarized with visually presented objects in either of two conditions that differed in the degree of joint attention (high vs. low).
Brain activity in response to familiar and novel objects was assessed immediately after the familiarization phase (immediate recognition), and following a 1-week delay (delayed recognition). The latency of the Nc component differentiated between recognition of old versus new objects. Pb amplitude and latency were affected by joint attention in delayed recognition.
Moreover, the frequency of infant gaze to the experimenter during familiarization differed between the two experimental groups and modulated the Pb response. Results show that joint attention affects the mechanisms of long-term retention in 4-month-old infants.
We conclude that joint attention helps children at this young age to recognize the relevance of learned items.
Joint attention develops during the first year of life but little is known about its effects on long-term memory. We investigated whether joint attention modulates long-term memory in 9-month-old infants. Infants were familiarized with visually presented objects in either of two conditions that differed in the degree of joint attention (high versus low).
EEG indicators in response to old and novel objects were probed directly after the familiarization phase (immediate recognition), and following a 1-week delay (delayed recognition). In immediate recognition, the amplitude of positive slow-wave activity was modulated by joint attention. In the delayed recognition, the amplitude of the Pb component differentiated between high and low joint attention. In addition, the positive slow-wave amplitude during immediate and delayed recognition correlated with the frequency of infants’ looks to the experimenter during familiarization.
Under both high- and low-joint-attention conditions, the processing of unfamiliar objects was associated with an enhanced Nc component. Our results show that the degree of joint attention modulates EEG during immediate and delayed recognition.
We conclude that joint attention affects long-term memory processing in 9-month-old infants by enhancing the relevance of attended items.
Eye gaze is a fundamental component of human communication. During the first post-natal year, infants rapidly learn that the gaze of others provides socially significant information. In addition, infants are sensitive to several emotional expressions. However, little is known regarding how eye contact influences the way the infant brain processes emotional expressions.
We measured 4-month-old infants’ brain electric activity to assess neural processing of faces displaying neutral, happy and angry emotional expressions when accompanied by direct and averted eye gaze. The results show that processing of angry facial expressions was influenced by eye gaze. In particular, infants showed enhanced neural processing of angry expressions when these expressions were accompanied by direct eye gaze.
These results show that by 4 months of age, the infant detects angry emotional expressions, and the infant brain processes their relevance to the self.
Arbeitsgedächtnis / Working Memory
EEG coherence as a measure of synchronization of brain activity was used to investigate effects of irrelevant speech. In a delayed serial recall paradigm 21 healthy participants retained verbal items over a 10-s delay with and without interfering irrelevant speech. Recall after the delay was varied in two modes (spoken vs. written).
Behavioral data showed the classic irrelevant speech effect and a superiority of written over spoken recall mode. Coherence, however, was more sensitive to processing characteristics and showed interactions between the irrelevant speech effect and recall mode during the rehearsal delay in theta (4–7.5 Hz), alpha (8–12 Hz), beta (13–20 Hz), and gamma (35–47 Hz) frequency bands. For gamma, a rehearsal-related decrease of the duration of high coherence due to presentation of irrelevant speech was found in a left-lateralized fronto-central and centro-temporal network only in spoken but not in written recall.
In theta, coherence at predominantly fronto-parietal electrode combinations was indicative for memory demands and varied with individual working memory capacity assessed by digit span. Alpha coherence revealed similar results and patterns as theta coherence. In beta, a left-hemispheric network showed longer high synchronizations due to irrelevant speech only in written recall mode. EEG results suggest that mode of recall is critical for processing already during the retention period of a delayed serial recall task. Moreover, the finding that different networks are engaged with different recall modes shows that the disrupting effect of irrelevant speech is not a unitary mechanism.
Rehearsal mechanisms in human short-term memory are increasingly understood in the light of both behavioural and neuroanatomical findings. However, little is known about the cooperation of participating brain structures and how such cooperations are affected when memory performance is disrupted. In this paper we use EEG coherence as a measure of synchronization to investigate rehearsal processes and their disruption by irrelevant speech in a delayed serial recall paradigm.
Fronto-central and fronto-parietal theta (4–7.5 Hz), beta (13–20 Hz), and gamma (35–47 Hz) synchronizations are shown to be involved in our short-term memory task. Moreover, the impairment in serial recall due to irrelevant speech was preceded by a reduction of gamma band coherence. Results suggest that the irrelevant speech effect has its neural basis in the disruption of left-lateralized fronto-central networks. This stresses the importance of gamma band activity for short-term memory operations.
Working memory (WM) carries out control processes involved in the temporary maintenance and manipulation of information. The aim of our investigations is to dissociate such control processes from visual and motor processes.
For this purpose a high WM load condition (based of an ordered memory set of geometrical patterns) was compared with non-WM conditions (a simple, a selective and a choice reaction time condition based on the elements of the memory set). EEG coherence within the frequency band 13-20 Hz was used to assess synchronization .
The results show that the interregional coherence of the electrode pairs Fz-P4, Fz-Pz, F4-Pz and F4-P4 was larger in the high WM load condition than in the non-WM load conditions. These findings support the hypothesis that mental effort for control processes in WM can be dissociated from mental effort for visual and motor processes on the basis of the synchronization of specific fronto-parietal brain regions.
Soziale Interaktionsprozesse / Social Interaction
The concept of maternal affect attunement has evoked considerable theoretical interest, but attempts at empirical validation have been scarce. The aim of this study was to refine the coding scheme for assessment of maternal affect attunement and to establish the internal validity of the measure. Forty dyads with seven-month-old infants and their mothers were recorded in two face-to-face play situations. Mother-child interactions were coded by four raters on the dimensions of Maintaining Attention and Warm Sensitivity, the latter comprising the subscales of Positive Affect, Social Responsiveness, and Warm Concern.
Inter-rater agreements for all scales and subscales were high. Scale reliabilities and construct stabilities as estimated by test-retest correlations were satisfactory. We conclude that the Maternal Affect Attunement Scale (MAAS) reliably captures individual differences in Maintaining Attention and Warm Sensitivity.