EXAMINING FACE-SENSITIVE BRAIN POTENTIALS IN NATURAL ENVIRONMENTS USING MOBILE EEG

Abstract Faces are a unique type of stimulus for humans. As such, they are processed differently to other types of stimuli like houses or objects. In the past, laboratory based testing has been used to examine the neural correlates of human face processing. However, viewing faces in a laboratory differs considerably from how it occurs the real world. This thesis examines the neural mechanisms underlying the processing of face images in a naturalistic setting. A custom-design mobile brain and body imaging technique was used to explore the neural mechanisms governing naturalistic face processing. Simultaneous mobile electroencephalography (EEG) and eye-tracking data was recorded from participants while they freely viewed images presented in a mock art gallery. The synchronisation of both data streams allowed us to analyse the EEG signal by time-locking markers to naturally occurring visual events captured by the eye tracker. Using this methodology the effects of emotion, familiarity and body posture on the face-sensitive N170 ERP component were investigated. The findings demonstrated, for the first time, the possibility of detecting face-specific brain potentials in freely moving, unrestricted subjects during passive viewing of images, as well as during active interactions with another person. The results present the effects of emotional valence on the N170 amplitude and replicate previous lab-based findings. Furthermore, the effects of body posture on early visual ERPs, but not the face-sensitive N170 contribute new insights to the face processing literature. Finally, the N170 component produced during a dyadic social interaction is described in relation to previous laboratory based reports. The experimental chapters present a novel methodology for recording mobile EEG signals as well as an adaptable experimental design that can be used in a wide variety of fields. The thesis demonstrates that EEG activity associated to the viewing static faces in laboratory conditions resemble those produced in real world environments as well as during natural social interactions. Moreover, the effects of emotional content on face processing were represented in the N170 component particularly, when disgusted faces were viewed

Neural correlates of prospective memory: an EEG and ICA approach

Have you ever entered a room and wondered ‘What am I supposed to do here?’ or have you ever forgotten to turn off the oven, hang your clothes to dry or make a phone call. These examples illustrate the relevance of ‘prospective memory’ or ‘delayed intentions’ in our daily life activities. Prospective memory is the ability to remember to do something after a delay. This thesis addresses three questions relevant to understand maintenance and execution of intentions: Is attention required to retrieve delayed intentions? What does monitoring mean in the context of prospective memory? Is prospective memory a discrete memory system or it is based on already known attentional and memory mechanisms? To answer these questions, we used electroencephalography (EEG), in (traditional) non-movement and free-movement experimental paradigms. We explored the neural substrate of prospective memory across its different stages: (1) holding intentions during a delay, (2) detecting the right context to perform the delayed intention, and (3) retrieving the content of the intention (the action to be performed). Two types of prospective memory tasks were used: Event-based prospective memory (performing a delayed intention in response to an external cue) and time-based prospective memory (performing the intention at a particular time). Results indicate that: prospective memory always requires attention, at least in experimental contexts; monitoring involves different mechanisms depending on the particular features of the prospective memory task and; prospective memory is not a discrete memory system, but relies on well-established mechanisms for attention and executive control