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Imitation paradigms are used in various domains of developmental psychological research to assess various cognitive processes such as memory (deferred imitation), action perception and action understanding (mainly direct imitation), as well as categorization and learning about objects (deferred imitation with a change in target objects and generalized imitation). Although these processes are most likely not independent from each other, their relations are still largely unclear. On the one hand, deferred imitation studies have shown that infants' performance improves with increasing age, resulting in the reproduction of more target actions after longer delay intervals. On the other hand, imitation studies focusing on infants' action understanding have found that infants do not necessarily imitate the model's exact actions – actions or action steps that seem to be irrational or irrelevant are omitted by infants under certain circumstances (selective imitation). Additionally, findings of imitation studies that require a transfer of the target actions to novel objects have demonstrated that infants do not only learn about actions, but also about objects, when they engage in imitation.
The present dissertation aims at integrating different perspectives of imitation research by testing 12- and 18-month-old infants in deferred imitation tests consisting of functional vs. arbitrary target actions, and by combining deferred imitation with eye tracking in half of the experiments. A deferred imitation paradigm was chosen to assess memory performance. Systematic variation of target action characteristics enabled the assessment of infants' imitation pattern, i.e., if they would imitate one kind of target actions more frequently than the other. Functionality was chosen as the action characteristic in focus because function is an object's most important property, thus this variation might shed some light on infants' learning about objects in the context of an imitation test. The main goal of the eye tracking experiments was to tackle the relations between infants' visual attention to, and deferred imitation of, different kinds of target actions.
The behavioral experiments revealed that both 12- and 18-month-olds imitated significantly more functional than arbitrary target actions after a delay of 30 minutes. In addition, while 12-month-olds showed a memory effect only for functional actions, 18-month-olds showed a memory effect for both kinds of actions. Thus, 12-month-olds imitated strictly selectively, and 18-month-olds imitated more exactly. This shows that the well established memory effect is modulated by target action functionality, which affects 12- and 18-month-olds' imitation differently. Furthermore, when retested after a two weeks delay, 18-month-olds' performance rates of functional and arbitrary target actions decreased parallel. This suggests that selective imitation is not affected by the duration of the retention interval, and that selection of target actions takes place at an earlier stage of action perception and memory processes.
In the eye tracking experiments, both 12- and 18-month-olds' imitation patterns replicated the findings of the behavioral experiments, showing consistently higher imitation rates of functional than arbitrary target actions. Contrary to this, infants' fixation times to the target actions were not affected by target action functionality. This contrast was supported by statistical analyses that found no clear correspondence between visual attention to and deferred imitation of target actions. This suggests that selective imitation cannot be explained by selective visual attention. Nevertheless, finer-grained analyses of gaze and imitation data in the 18 months old group suggested that infants' increased attention to the social-communicative context of the imitation task was related to more exact imitation, i.e. imitation of not only functional, but also arbitrary target actions.
The findings are discussed against the background of imitation theories, with regard to the relations between different cognitive processes underlying infants' imitation, such as memory, action perception and learning about objects.
Eye-Tracking bezeichnet das Messen und Aufzeichnen der Blickbewegungen einer Person. Historisch gesehen basiert Eye-Tracking auf Beobachtungen des Testleiters, der das Blickverhalten der Probanden während des Versuchsablaufes oder die Videoaufzeichnung des Blickverhaltens eines Probanden in einer Testsituation kodierte. Dabei konnte allerdings nur die Blickrichtung des Probanden erhoben werden. Heutzutage ist es jedoch möglich, aufgrund neuerer, automatisierter Eye-Tracking-Techniken detailliertere Blickbewegungen, wie z.B. Fixationen und Sakkaden, zu messen. Diese Verbesserung der Eye-Tracking-Technik ermöglicht nicht nur passives Eye-Tracking, sondern auch aktives Blickkontingenz-Eye-Tracking. Passives Eye-Tracking bezeichnet das Messen und Aufzeichnen des Blickverhaltens, um herauszufinden, wo der Proband hinschaut. Im Gegensatz dazu erhebt das aktive Blickkontingenz-Eye-Tracking nicht nur, wo ein Proband hinschaut, sondern ermöglicht dem Probanden auch, die Stimuli, die auf einem Bildschirm präsentiert werden, aktiv zu verändern oder zu kontrollieren. Dabei wird das Blickverhalten online kodiert, und spezifisches Blickverhalten ist an eine kontingente Veränderung der Stimuli auf dem Bildschirm gekoppelt. Deshalb kann das aktive Blickkontingenz-Eye-Tracking eingesetzt werden, um den Probanden aktive Kontrolle über ihre visuelle Umwelt zu ermöglichen.
In der psychologischen Forschung ist Eye-Tracking ein wichtiges Forschungs-instrument, da das Blickverhalten in spezifischen Eye-Tracking-Aufgaben genutzt werden kann, um Aufschluss über kognitive Prozesse, wie z.B. Aufmerksamkeit, Lernen und Gedächtnis, zu gewinnen. Unterschiedliche passive und aktiv-blickkontingente Eye-Tracking- Aufgaben wurden entwickelt, um eine Vielzahl an kognitiven Prozessen im Erwachsenen- und Säuglingsalter zu untersuchen. Diese Aufgaben sind besonders wichtig in der Säuglingsforschung, da es in diesem Alter schwierig ist, kognitive Prozesse zu untersuchen. Dies hängt damit zusammen, dass es sich um eine präverbale Stichprobe, die nur über ein limitiertes motorisches Repertoire verfügt, handelt. Obwohl kognitive Prozesse von Erwachsenen anhand verbaler oder anderer motorischer Aufgaben untersucht werden können, werden passive und aktiv-blickkontingente Eye-Tracking-Aufgaben regelmäßig in dieser Altersgruppe eingesetzt, da sie zusätzliche Informationen über kognitive Prozesse liefern können. Neben der Möglichkeit zur Untersuchung von kognitiven Prozessen bieten aktiv-blickkontingente Eye-Tracking-Aufgaben den Probanden auch die Gelegenheit, ihre visuelle Umwelt aktiv zu kontrollieren. Dennoch werden aktiv-blickkontingente Eye-Tracking- Aufgaben nur selten eingesetzt, um Probanden visuelle Kontrolle über ihre Umwelt zu verschaffen.
Bis jetzt wurden aktiv-blickkontingente Eye-Tracking-Aufgaben zur Kontrolle der visuellen Umwelt nur bei Erwachsenen, aber noch nicht bei Säuglingen eingesetzt. Da diese Aufgaben jedoch auch für Säuglinge und Kleinkinder geeignet sind, besteht die Möglichkeit, diese Methode über die gesamte Lebenspanne hinweg anzuwenden. Somit kann das Erlernen des Kontrollierens der Umwelt durch Blickverhalten über die gesamte Lebensspanne untersucht werden.
Die vorliegende Dissertation hat sich genau dies zum Ziel gesetzt. Um dieses Ziel zu erreichen, wurde eine neue aktiv-blickkontingente Eye-Tracking-Aufgabe entwickelt, die sogenannte gaze-contingent learning task (GCLT). Im Wesentlichen ist die GCLT eine operante Konditionierungsaufgabe, bei der sich Probanden Kontrolle über ihre visuelle Umwelt aneignen, indem sie eine bestimmte blickkontingente Assoziation zwischen ihrem Blickverhalten und einem visuellen Effekt erlernen. Die in dieser Dissertation verwendete GCLT umfasst zwei Hauptversionen: zum einen die sog. one disc GCLT, und zum anderen die two discs GCLT. In der one disc GCLT wird ein Kreis auf der rechten Bildschirmseite gezeigt. Jedes Mal, wenn der Proband auf diesen Kreis schaut, erscheint ein Stimulus auf der linken Bildschirmseite. Somit kommt dem Kreis eine Schalterfunktion zu. In der two discs GCLT ist sowohl am rechten als auch am linken Bildschirmrand ein Kreis zu sehen. Hier kommt nur jeweils einem der beiden Kreise die Schalterfunktion zu. Um ihre visuelle Umwelt zu kontrollieren, müssen Probanden innerhalb der one disc GCLT die blickkontingente Assoziation zwischen ihren Blicken auf den Kreis und dem Erscheinen eines Stimulus erlernen, während sie in der two discs GCLT außerdem noch lernen müssen, zwischen dem Kreis mit und dem Kreis ohne Schalterfunktion zu unterscheiden.
In our daily life, we carry out lots of tasks like typing, playing tennis, and playing the piano, without even noticing there is sequence learning involved. No matter how simple or complex they are, these tasks require the sequential planning and execution of a series of movements. As an ability of primary importance in one’s life, and an ability that everyone manages to learn, action-sequence learning has been studied by researchers from different fields: psychologists, neurophysiologists as well as roboticists. In the concept of sequence learning, perceptual learning and motor learning, implicit and explicit learning have been studied and discussed independently.
We are interested in infancy research, because infants, with underdeveloped brain functions and with limited motor ability, have little experience with the world and not yet built internal models as presumption of how to interpret the world. A series of infant experiments in the 1980s provided evidence that infants can rapidly develop anticipatory eye movements for visual events. Even when infants have no control of those spatial-temporal patterns, they can respond actually prior to the onset of the visual event, referred as "Anticipation".
In this work, we applied a gaze-contingent paradigm using real-time eye tracking to put 6- and 8-month-old infants in direct control of their visual surroundings. This paradigm allows the infant to change an image on a screen by looking at a peripheral red disc, which functions as a switch. We found that infants quickly learn to perform eye movements to trigger the appearance of new stimuli and that they anticipate the consequences of their actions in an early stage of the experiment.
Attention-shift from learning one stimulus to the next novel stimulus is important in sequence learning. In the test phase of infant visual habituation with two objects, we propose a new theory of explaining the familiarity-to-novelty shift. In our opinion an infant’s interest in a stimulus is related to its learning progress, the improvement of performance. As a consequence, infants prefer the stimulus which their current learning progress is maximal for, naturally giving rise to a familiarity-to-novelty shift in certain situations. Our network model predicts that the familiarity-to-novelty-shift only emerges for complex stimuli that produce bell-shaped learning curves after brief familiarization, but does not emerge for simple stimuli that produce exponentially decreasing learning curves or for long familiarization time, which is consistent with experimental results. This research suggests the infant's interest in a stimulus may be related to its current learning progress. This can give rise to a dynamic familiarity-to-novelty shift depending on both the infant's learning efficiency and the task complexity.
We know that for both infants and adults, the performance on certain motor-sequence tasks can be improved through practice. However, adults usually have to perform complex tasks in complicated environments; for example, learning multiple tasks is unavoidable in our daily life. In existing research, learning multiple tasks showed puzzling and seemingly contradictory results. On the one hand, a wide variety of proactive and retroactive interference effects have been observed when multiple tasks have to be learned. On the other hand, some studies have reported facilitation and transfer of learning between different tasks.
In order to find out the interaction between multiple-task learning, and to find an optimal training schedule, we use a recurrent neural network to model a series of experiments on movement sequence learning. The network model learns to carry out the correct movement sequences through training and reproduces differences between training schedules such as blocked training vs. random training in psychophysics experiments. The network model also shows striking similarity to human performance, and makes prediction for tasks similarity and different training schedules.
In conclusion, the thesis presents learning sequences of actions in infants and recurrent neural networks. We carried out a gaze-contingent experiment to study infants’ rapid anticipation of their own action outcomes, and we also constructed two recurrent neural network models, with one model explaining infant attention shift in visual habituation, and the other model directing to task similarity and training schedule in motor sequence control in adults.
Current theories of schizophrenia suggest that the pathophysiology of the disorder may be the result of a deficit in the coordination of neural activity within and between areas of the brain, which may lead to impairments in basic cognitive functions such as contextual disambiguation and dynamic grouping (Phillips and Silverstein, 2003). This notion has been supported by recent studies showing that patients with schizophrenia are characterized by reduced synchronous, oscillatory activity in the gamma-frequency band during sensory processing (Spencer et al. 2003, Green et al. 2003, Wynn et al. 2005). However, it is currently unclear to what extent high-frequency gamma-band oscillations (> 60 Hz) contribute to impaired neural synchronization as research has so far focussed on gamma-band oscillations between 30 and 60 Hz. In addition, it is not known whether deficits in high-frequency oscillations are already present at the onset of the disorder and to what extent reductions may be related to the confounding influence of antipsychotic medication. Finally, the neural generators underlying impairments in synchronous oscillatory activity in schizophrenia have not been investigated yet. To address these questions, we recorded MEG activity during a visual closure task (Mooney faces task) in medicated chronic schizophrenia patients, drug-naive first-episode schizophrenia patients and healthy controls. MEG data were analysed for spectral power between 25 and 150 Hz, and beamforming techniques were used to localize the sources of oscillatory gamma-band activity. In healthy controls, we observed that the processing of Mooney faces was associated with sustained high-frequency gamma-band activity (> 60 Hz). A time-resolved analysis of the neural generators underlying perceptual closure revealed a network of distributed sources in occipito-temporal, parietal and frontal regions, which were differentially activated during specific time intervals. In chronic schizophrenia patients, we found a pronounced reduction of high-frequency gamma-band oscillatory activity that was accompanied by an impairment in perceptual organization and involved reduced source power in various brain regions associated with perceptual closure. First-episode patients were also characterized by a deficit in high-frequency gamma-band activity and reductions of source power in multiple areas; these impairments, however, were less pronounced than in chronic patients. Regarding behavioral performance, first-episode patients were not impaired in their ability to detect Mooney faces, but exhibited a loss in specificity of face detection. In conclusion, our results suggest that schizophrenia is associated with a widespread reduction in high-frequency oscillations that indicate local network abnormalities. These dysfunctions are independent of medication status and already present at illness onset, suggesting a possible progressive deficit during the course of the disorder.
Gedächtnisaspekte, die auch mit zunehmendem Alter stabil und zuverlässig bleiben, sind in heutiger Forschung von besonderem Interesse. Studien im Bereich des Gedächtnisses für einfache Handlungen konnten zeigen, dass dieses Itemmaterial besser erinnert wird, wenn es während der Einprägephase motorisch ausgeführt wird (vgl. z.B. Knopf, 1995) im Gegensatz zum rein verbalen Einprägen vergleichbaren Materials. Dieser Gedächtnisvorteil des handelnden Enkodierens, der so genannte Handlungseffekt, ist auch bei älteren Probanden zu beobachten. Da der Handlungseffekt altersübergreifend vergleichbar groß ist, erreichen Ältere auch bei handelndem Enkodieren nicht das Leistungsniveau Jüngerer (Alterseffekt, z.B. Knopf, 2005).
Die vorliegende Arbeit beschäftigte sich vor allen Dingen mit der Frage, ob die Gedächtnisleistung nach handelndem und verbalem Enkodieren bei einer Wiederholung der Lernaufgabe mit jeweils neuem Lernmaterial noch gesteigert werden kann. Dabei wurden mögliche enkodiertypabhängige sowie altersabhängige Leistungsunterschiede untersucht. Weiterhin wurde geprüft, ob eine beobachtete Leistungssteigerung nach wiederholtem Lernen mit jeweils neuem Lernmaterial auch nach einem halben Jahr noch zu beobachten ist. In zwei zusätzlichen Fragestellungen wurde theoretischen Erklärungen des Handlungseffektes nachgegangen, indem die seriellen Positionskurven sowie der zeitliche Verlauf des Abrufes untersucht wurden.
Zur Untersuchung der Fragestellungen wurden verschiedene Studien mit Jüngeren und Älteren durchgeführt. Das Lernmaterial bestand aus Serien von einfachen Handlungsphrasen, welche entweder durch Ausführen oder verbal enkodiert und in unmittelbaren freien Erinnerungstests reproduziert wurden. Zur Untersuchung einer möglichen Leistungssteigerung nach Wiederholung der Lernaufgabe mit jeweils unterschiedlichem Material wurden vier Termine in wöchentlichem Abstand angesetzt. Um die Stabilität der Leistung nach einem halben Jahr zu untersuchen, wurde ein fünfter Messzeitpunkt realisiert.
Die Ergebnisse zeigen eine Replikation von Handlungs- und Alterseffekt (Knopf, 2005). Eine Wiederholung der Aufgabe mit jeweils neuem Lernmaterial führt unabhängig vom Alter der Teilnehmer oder der Enkodierbedingung zu einer ähnlichen Steigerung der Gedächtnisleistung, die auch nach einem halben Jahr noch nachweisbar ist. Die Untersuchungen der seriellen Positionskurven des Abrufes zeigen, dass nach handelndem Enkodieren vor allen Dingen die letzten Items der zu lernenden Itemserie eine erhöhte Erinnerungswahrscheinlichkeit haben. Auch der Alterseffekt scheint eher in den letzteren seriellen Positionen einer Itemserie begründet zu sein, wobei diese Positionen bei verbalem und handelndem Enkodieren unterschiedlich sind. Die Leistungssteigerung zeigt sich bei beiden Enkodierbedingungen in einer signifikanten Steigerung der mittleren Positionen der seriellen Positionskurven, beim verbalen Enkodieren zusätzlich in einer Steigerung der letzen Positionen. Demnach führen bei den beiden Enkodierbedingungen unterschiedliche Veränderungen zum Leistungsanstieg. Bei der Betrachtung des zeitlichen Verlaufes des Abrufes kann zudem gezeigt werden, dass der Abruf nach handelndem Enkodieren schneller abzulaufen scheint.
Faces are thought to be processed primarily according to their configurations which is in-ferred from comparisons with non-facial stimuli. While the whole (face) seems to be more than the sum of its parts, the same does not apply to objects which are processed analytically according to their featural information. A recent recognition model stresses the importance of certain visual information within facial stimuli. By applying a specific filtering technique, stimuli can be generated that are restricted to contain information of only a certain orienta-tion. Dakin and Watt (2009) reported greatest recognition performance with faces that only contained horizontally aligned information with accuracy continuously declining at vertical. Furthermore, they showed that, compared with images of natural scenes, horizontal contours within faces have an unusual tendency to fall into vertically co-aligned clusters which were labelled biological ‘bar code’ referring to a highly constrained one-dimensional code. Con-secutive research tested for face-specific processing by comparing faces and objects that displayed information of different orientations. Results suggested configural processing only for faces that contained horizontal information (Goffaux & Dakin, 2010). The findings con-tribute important insight on a still unanswered question in face processing research: what information is extracted from faces for recognizing them. Despite the importance of remembering human faces on a daily basis, this ability seems to develop disadvantageously over lifetime. Decreased accuracy cannot be attributed to de-creased general cognitive ability (Hildebrandt, Wilhelm, Schmiedek, Herzmann, & Sommer, 2011) and slower reactions times are assumed to be a product of decision making rather than sensory speed (Habak, Wilkinson, & Wilson, 2008). Considering the amount of published work on face recognition, there is a lack of studies available assessing this important ability at a higher age. New theoretical concepts are rarely examined with older participants, appar-ently assuming their general validity. The current dissertation tries to help fill this gap by assessing the importance of horizontal information from a developmental perspective com-paring younger and older adults under different experimental variations. The first study showed, that presenting older participants with horizontally filtered faces has a dispropor-tional negative impact on recognizing younger unfamiliar faces suggesting differential pro-cessing mechanisms, since recognizing stimuli that only contained vertical information did not differ between age groups. On this basis, the following study manipulated the presented stimulus material, since some evidence suggests that own-age faces are more easily recog-nized compared to faces of other ages, which is referred to as “own-age bias”. Therefore, the second study systematically assessed the impact of stimulus age on recognition sensitivity. Moreover, encoding modalities were varied by providing increased exposure duration to the stimuli. The results of the first study were replicated, as older participants’ performance was still poor at recognizing younger faces, independent from encoding modalities. However, similar face recognition sensitivity compared to younger adults was observable when filtered faces of the older adults’ own age had to be recognized. Interestingly, correlations between recognizing filtered and unfiltered faces were obtained for younger adults but not for older adults suggesting age variant processing of horizontal information. The last study assessed the importance of horizontal information with stimulus material familiar to the observer. Although research highlights differences between recognizing unfamiliar and familiar stimu-lus material, this factor is often not considered by contemporary research. By presenting par-ticipants with their own faces, a stimulus of greatest individual familiarity was chosen. The superiority of own face recognition over other familiar material is referred to as “self-face advantage” and has been shown in comparison with personally familiar faces (Keyes & Brady, 2010) and famous faces (Caharel et al., 2002). While younger adults indeed recog-nized their self-faces better compared to famous faces independent from stimuli being fil-tered or unfiltered, older participants displayed a completely different pattern including the inability to recognize their filtered self-faces. Again, significant associations were obtained between filtered and unfiltered recognition conditions suggesting convergent processing mechanisms for younger adults but not for the older age group. This dissertation provides a first insight in the divergence of response behavior in older adults with a recent face processing model. While the obtained data undermine the im-portance of horizontal information in younger adults by replicating and extending previously published work, a profoundly different type of processing is suggested at a higher age which largely relies on low-level pictorial information due to the inability to process horizontally filtered faces configurally. Specifically, it is suggested that with age, focusing on aging-salient features with configural processing disrupted may function as a critical source of di-agnostic information which can ultimately result in performance similar to younger adults.
Deferred imitations assess declarative memory in infants. Many cross-sectional and a few longitudinal studies revealed that, with development, infants learn faster,and retain more target actions over longer retention intervals. Longitudinal stabilities are modest and increase through the second year. To date, there are only few multivariate deferred imitation studies pointing to interactions between declarative memory, language and self-development. However, as these studies applied variable-centered data analysis approaches, the individual stance was not taken into account.Therefore, the present dissertation focuses on the explanation of inter-individual differences of deferred imitation through the second year. In the multivariate, longitudinal Frankfurt Memory Study (FRAMES), declarative memory (deferred imitation), non-declarative memory (train task), as well as cognitive, language, motor, social, emotional and body self-awareness development (Developmental Test for 6-month- to 6-year-olds, ET6-6) were assessed on three measurement occasions (12-, 18- and 24-month-olds). From a psychometric perspective, sound tests for the assessment of deferred imitation in the respective age groups were developed (Paper 1 & 2). Reliability analyses (Paper 3) indicated relatively high short-term-stability for the deferred imitation test (12-month-olds). The co-development of declarative and nondeclarative memory in 12- and 18-month-olds provided evidence for discriminative validity (Paper 4). Longitudinally, deferred imitation performance tremendously increased throughout the second year, and performance was moderately stable between 12 and 18 months and stability increased between 18 and 24 months. Using a person-centered analysis approach (relative difference scores; cluster analysis), developmental subgroups were extracted out of the total sample. These groups differed in terms of mean growth and stability. However, between the first and second measurement occasion, the groups did not differ with respect to motor, cognitive and language development (Paper 5). Using the data of three measurement occasions, subgroups were extracted showing significant differences with respect to language, motor and body self-awareness development (Paper 6). The results are discussed against the background of infancy development theories.
Stress influences health not only directly, but also indirectly through changes in health-related behaviours, such as diet. Research has shown that stress influences individuals’ eating behaviour in different ways: Some increase, some decrease food intake, while others show no change. Identifying individuals at risk for stress-induced eating is essential for the development of tailored strategies for the prevention and treatment of overweight and obesity. The individual-difference model of stress-induced eating suggests that individual differences in the dietary response to stress are determined by differences in learning history, attitudes, or biology. Even though many studies have tried to identify person-characteristics that explain individual differences in the dietary response to stress, evidence remains inconclusive. Considering that eating is a repeated-occurrence health behaviour which is performed multiple times a day, Ecological Momentary Assessment (EMA) seems particularly promising to study the complex relationship between stress and food intake when and where it naturally occurs. Despite its potential, the number of studies applying EMA to assess the stress and eating relationship is limited. Furthermore, previous EMA studies show two limitations: (1) Actual food intake is not assessed and (2) inappropriate data analysis approaches are applied to semicontinuous outcomes. Therefore, the first aim of the present dissertation was to address the lack of an EMA tool that allows the assessment of stress and actual food intake by developing and evaluating the APPetite-mobile-app. Feasibility and usability of the APPetite-mobile-app as well as validity of the incorporated food record were empirically examined (Paper 1). Given the lack of an appropriate data analysis procedure, the second aim of the present dissertation was the introduction of a sophisticated statistical approach for semicontinuous data (Paper 2): Multilevel two-part modelling allows studying the influence of stress on the occurrence (i.e., whether individuals eat) as well as the amount of food intake (i.e., how much individuals eat) while accounting for the potential dependency between the two. Lastly, the novel EMA tool and the advanced data analysis procedure were integrated in order to gain novel insights into individual differences in the dietary response to stress and thereby identify individuals at risk for stress-induced eating in daily life (Paper 3). Results of Paper 1 showed good feasibility and acceptable usability of the APPetite-mobile-app as well as validity of the incorporated food record. Findings of Paper 2 highlight that multilevel two-part models offer novel and distinct insights in terms of the occurrence and the amount of food intake and are therefore not only methodologically but also conceptually promising. Paper 3 provides first evidence that the dietary response to stress might not be as stable as yet assumed. Time-varying factors might moderate the relationship between stress and actual food intake. Therefore, an expansion of the individual-difference model is proposed which accounts for time-varying factors. Further EMA studies are needed to verify the expanded model and identify time-varying factors which influence the dietary response to stress. Beyond that, improvements in the dietary assessment are required in order to allow prolonged EMA periods as well as larger samples. The present dissertation contributes to the research on the stress and eating relationship as it overcomes limitations of previous EMA studies and yields novel insights into the relationship between stress and actual food intake in daily life. Not only identifying individuals at risk for stress-induced eating, but also the identification of situations with an increased risk for stress-induced eating appears to be important for the development of targeted strategies for the prevention and treatment of overweight and obesity.
