The ratio between frontal resting state EEG power in the theta and beta frequency bands (theta/beta ratio, TBR) was first associated with attention deficit hyperactivity disorder (ADHD) and later... Show moreThe ratio between frontal resting state EEG power in the theta and beta frequency bands (theta/beta ratio, TBR) was first associated with attention deficit hyperactivity disorder (ADHD) and later linked to various psychological functions and cognitive/emotional processes that rely on executive cognitive control. The aim of this thesis was to further investigate TBR as a potentially useful marker for executive/attentional control, particularly when studying threat selective attention and uncontrolled thoughts. It was found that high TBR was associated with more attention to mild than high threat and low threat-interference in visual-spatial tasks containing emotional information. TBR was also negatively related to self-reported attentional control. Frontal TBR was moreover significantly higher during uncontrolled thought compared to controlled thought and this effect was also found for functional connectivity of the ‘executive control network’, which was also correlated to the controlled versus uncontrolled thought effect on TBR. However, no evidence was found to suggest that TBR can be manipulated using Neurofeedback training. These findings provide clear indications of the neuropsychological functional nature of TBR and further support the notion that TBR reflects connectivity in brain networks involved in executive control processes. Show less
Tonal bilinguals of two closely related Chinese dialects handle two tonal systems in their mind; their two vocabularies are from closely related dialects; and they write translation equivalents... Show moreTonal bilinguals of two closely related Chinese dialects handle two tonal systems in their mind; their two vocabularies are from closely related dialects; and they write translation equivalents with common Chinese characters. Their unique language situation makes their mind special. This thesis investigates these tonal bilinguals’ lexical processing mechanism, studying how they produce and understand words. Their situation provides a valuable test case for a few important theories on bilingual lexical access. Bilingual lexical processing is flexible, influenced by the task and language mode. Moreover, compared with tonal monolinguals, these tonal bilinguals not only showed classical advantages in executive control, but sometimes even perform faster with lexical tasks. The structure of the bilingual lexicon can cause important differences in bilingual lexical processing and the corresponding functions of executive control. Show less
After experiencing distraction or temptation, people tend to be better able to cope with future conflict. In cognitive psychology, this is often shown by using sequential conflict tasks, such as... Show moreAfter experiencing distraction or temptation, people tend to be better able to cope with future conflict. In cognitive psychology, this is often shown by using sequential conflict tasks, such as the Stroop task, in which people are required to name the colour of the ink of a word, and ignore the word itself. After presentation of the word “red” in a green colour, for example, people show a smaller conflict effect if later shown the word “green” in a red colour. According to established theory, this is related to the working of executive control: initial conflict triggers increased attention (towards the colour instead of the word) or inhibition (of the word), thus making it easier to cope with repeated conflict. In this dissertation, I argue for a revision of this prominent theory towards a more memory based explanation of executive control. Instead of initial conflict working forward in time to affect the later task, the behavioural and psychophysiological experiments reported here show that the previous task is remembered due to the similarity with the current task, triggering similar modes of behaviour. Show less
