Abstract
Recent models on speech perception propose a dual-stream processing network, with a dorsal stream, extending from the posterior temporal lobe of the left hemisphere through inferior parietal areas into the left inferior frontal gyrus, and a ventral stream that is assumed to originate in the primary auditory cortex in the upper posterior part of the temporal lobe and to extend toward the anterior part of the temporal lobe, where it may connect to the ventral part of the inferior frontal gyrus. This article describes and reviews the results from a series of complementary functional magnetic resonance imaging studies that aimed to trace the hierarchical processing network for speech comprehension within the left and right hemisphere with a particular focus on the temporal lobe and the ventral stream. As hypothesized, the results demonstrate a bilateral involvement of the temporal lobes in the processing of speech signals. However, an increasing leftward asymmetry was detected from auditory–phonetic to lexico-semantic processing and along the posterior–anterior axis, thus forming a “lateralization” gradient. This increasing leftward lateralization was particularly evident for the left superior temporal sulcus and more anterior parts of the temporal lobe.
Highlights
The research on speech perception, language, and human communication behavior has a long history in science and reveals to be an actual topic through centuries and, with the venue of neuroimaging methods, became an even broader research field over the last two decades (Price, 2012)
Broca was the first to describe an association between language deficit and the damage of a specific frontal brain area, which is referred to as “Broca’s area” (Dronkers et al, 2007), while Carl Wernicke noticed that lesions of the posterior part of the left superior temporal gyrus (STG) could cause language disorders, even though these disorders substantially differed from those deficits caused by frontal lesions (Wernicke, 1874)
Auditory speech perception is, as illustrated in this summary, a complex interaction of different brain areas that are integrated into a hierarchical network structure
Summary
The research on speech perception, language, and human communication behavior has a long history in science and reveals to be an actual topic through centuries and, with the venue of neuroimaging methods, became an even broader research field over the last two decades (Price, 2012). This article describes and reviews the results from a series of complementary functional magnetic resonance imaging studies that aimed to trace the hierarchical processing network for speech comprehension within the left and right hemisphere with a particular focus on the temporal lobe and the ventral stream.
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