Abstract
Functional neuroimaging studies have highlighted the roles of three networks in processing language, all of which are typically left-lateralized: a ventral stream involved in semantics, a dorsal stream involved in phonology and speech production, and a more dorsal “multiple demand” network involved in many effortful tasks. As lateralization in all networks may be affected by life factors such as age, literacy, education, and brain pathology, we sought to develop a task paradigm with which to investigate the engagement of these networks, including manipulations to selectively emphasize semantic and phonological processing within a single task performable by almost anyone regardless of literacy status. In young healthy participants, we administered an auditory word monitoring task, in which participants had to note the occurrence of a target word within a continuous story presented in either their native language, Portuguese, or the unknown language, Japanese. Native language task performance activated ventral stream language networks, left lateralized but bilateral in the anterior temporal lobe. Unfamiliar language performance, being more difficult, activated left hemisphere dorsal stream structures and the multiple demand network bilaterally, but predominantly in the right hemisphere. These findings suggest that increased demands on phonological processing to accomplish word monitoring in the absence of semantic support may result in the bilateral recruitment of networks involved in speech perception under more challenging conditions.
Highlights
All three appear to be somewhat lateralized, with the left hemisphere playing a larger role in supporting language function, the homologous networks in the right hemisphere may be involved in special circumstances [5], with variability across individuals related to such factors as age [6], multilingualism [7], education [8], and response to brain damage [9]
Behavioral Assessment in the Auditory Attention Task ison to the other conditions, results reveal that the accuracy score was evenly distributed each ofConsequently, the three conditions, of for thethe behavioral results were overFor all blocks
Without comprehension of the speech signal, few experimental manipulations are available within the context of the task, but comparing it with monitoring in the native language offers a straightforward way to examine the relative engagement of distinct networks for semantic and phonological aspects of the task, with the unknown language expected to place increased demands on phonological processing, shortterm memory, and auditory attention
Summary
Neuroimaging investigations into human language processing have confirmed the importance of the two “classic” brain regions in which lesions are associated with language deficits: the Broca’s and Wernicke’s areas. They have demonstrated that both of these regions are part of larger connected networks. All three appear to be somewhat lateralized, with the left hemisphere playing a larger role in supporting language function, the homologous networks in the right hemisphere may be involved in special circumstances [5], with variability across individuals related to such factors as age [6], multilingualism [7], education [8], and response to brain damage [9]
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