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Hierarchical organization of speech perception in human auditory cortex
Colin Humphries1, Merav Sabri1, Kimberly Lewis1
1Department of Neurology, Medical College of Wisconsin Milwaukee, WI, USA.
Frontiers in Neuroscience
|January 8, 2015
Summary
This study used fMRI to explore how the brain processes speech sounds. Distinct areas in the superior temporal cortex respond differently to speech sound features, revealing a hierarchical processing stream for auditory perception.
Area of Science:
- Neuroscience
- Auditory Perception
- Speech Processing
Background:
- Human speech involves complex, dynamic spectral changes.
- Understanding the neural basis of speech perception is crucial for deciphering auditory processing.
Purpose of the Study:
- To investigate neural activity in the superior temporal cortex during the perception of speech sound segments.
- To differentiate brain responses to spectral transitions versus steady-state vowel segments.
- To examine the effects of adaptation on neural responses to phonemic and non-phonemic sounds.
Main Methods:
- Functional magnetic resonance imaging (fMRI) was employed.
- Subjects listened to synthesized consonant-vowel syllables and control sounds.
- Adaptation paradigms manipulated transition and steady-state sound features.
Main Results:
- Two distinct areas in the superior temporal cortex showed differential sensitivity to sound features and adaptation.
- The dorsal superior temporal gyrus (STG) responded to adaptation type irrespective of phonemic content.
- The ventral STG showed increased activity for phonemic stimuli, without adaptation effects.
- A third area in the medial superior temporal plane responded more to non-phonemic sounds.
Conclusions:
- A hierarchical processing stream for speech sounds exists in the superior temporal cortex, extending from the temporal plane to the sulcus.
- Neural representations become more complex and abstract at successive processing stages.
- This hierarchy supports the brain's ability to decode intricate spectrotemporal features of speech.
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