Browsing by Subject "valikoiva tarkkaavaisuus"
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(2018)The aim of this study is to examine the development of selective and divided attention in adolescence using functional magnetic resonance imaging (fMRI) and behavioral measures. Although the prefrontal cortex, a key area for attention and cognitive control, is thought to mature well into adulthood, few studies have examined the development of attention in adolescents and young adults. No fMRI studies have been conducted on the development of divided attention. In this study, development was examined both cross-sectionally and longitudinally to also assess the possible differences in the results they produced, as nearly all previous studies have been cross-sectional. Brain activity was measured from 103 participants aged 13–22 who were divided into three age cohorts. The youngest two cohorts were measured again after 1.5 years for the longitudinal study. While in the scanner, participants performed a sentence congruence task where they were instructed either to attend to only the speech or text stimulus or divide their attention between both modalities simultaneously. The cross-sectional results showed improvement in task performance between the youngest cohort (13– 14y.) and the older cohorts in both selective and divided attention tasks. No difference was found between the older two cohorts (16–17y. and 20–22y.) However, the longitudinal results did not indicate clear performance improvement with age in either task type. According to the longitudinal fMRI results from age 13–14 to 15–16, in the selective attention task brain activity decreased mainly in the medial prefrontal area and activity increased slightly in parietal regions. In the divided attention task, the decreased prefrontal activity was more lateral. From age 16–17 to 18– 19, increased activity in motor regions and precuneus was found in both tasks. In general, the effects were very subtle, possibly due to a short measurement interval and relatively small cohort sizes. The cross-sectional results indicated quite a different pattern of change in brain activity, concentrated on temporal areas. This difference in results emphasizes the importance of conducting longitudinal developmental studies in the future. Although the effects were not large, the longitudinal fMRI results were in line with some previous findings that prefrontal areas are recruited less with age, so that activity in more posterior task-related areas increases. The current results suggest that some fine-tuning of the attention and cognitive control-related network still occurs from adolescence to early adulthood, as the prefrontal cortex and its connections mature.
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(2019)The present study uses functional magnetic resonance imaging (fMRI) to study the neural basis of naturalistic audiovisual speech processing. The study focuses on how performing different speech-related tasks affects the neural activation observed in the brain. The neural basis of speech processing has been studied for long, but previous experiments have mainly employed paradigms with simple stimuli, such as single phonemes, syllables, and words, and unnatural tasks, such as discrimination and memory tasks. Moreover, current models of speech processing are mainly based on studies using auditory-only stimuli. In natural situations, however, the aim of speech processing is to understand the meaning of what is being said, speech is most often audiovisual, it is often selectively attended to, and the signal-to-noise ratio of the speech signal varies (due to, for example, background noise). The present study aims to study speech processing in a more naturalistic setting that takes into account the above-mentioned factors. Moreover, it compares a situation where speech is processed naturalistically to a situation where speech is processed sub-lexically, as is often done in studies of speech processing. The participants of the present study were 19 healthy adults. They were presented with audiovisual dialogues where two people discuss everyday matters. In the background of the videos, the voice of a third speaker was always present so that the participants had to selectively attend to the dialogues. The auditory and visual qualities of the dialogues were modulated on two different levels. The participants performed three different tasks: 1) A semantic task, during which the participants focused on the semantic content of the dialogues. 2) A phonological task, during which the participants focused on the phonological structure of the speech. 3) A visual task, during which the participants ignored the dialogues and focused on a fixation cross. Task-dependent effects in the neural activation were found in multiple regions of the brain. Selective attention to speech was found to activate regions in the temporal lobes and the left inferior frontal gyrus (LIFG), a result consistent with earlier research. The semantic task was found to activate areas associated with semantic and socio-cognitive processing more than either of the other tasks, while the phonological task activated the posterior portion of the LIFG as well as the ventral portion of the left premotor cortex. Interactions between the effects of task and audiovisual quality were also found in many brain areas. These results show that task-dependent effects in speech processing can be seen in widespread regions of the brain, and that audiovisual quality can modulate activation differentially during different tasks. These findings highlight the importance of using naturalistic stimuli and tasks in studies of speech processing.
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