Final Report Summary - BRAININNATURALSOUND (The anatomy and dynamics of the cortical processing of naturalistic sounds)
The neuroimaging experiments carried out during this project significantly advanced our knowledge in the field:
1. We discovered that the spatial pattern of cortical activation contain information about low-level structure and sound category, and assessed the presence of regions in the auditory cortex that represent sound categories in an abstract fashion, i.e. independently of reliable between-category differences in low-level acoustical structure.
2. We discovered that the phase rather than power of time-varying cortical responses to sound: [a] tracks several time-varying acoustical features; [b] contains information for differentiating reliably between natural sounds, and between natural sounds on the one hand, and silence on the other; [c] contains information about the perceptual dissimilarity of natural sounds. Importantly, all of these encoding effects emerged for the phase of low-frequency oscillatory responses of the time-varying cortical response to sound.
3. We discovered that a region in the left prefrontal cortex is involved in the automatic, i.e. task-independent processing of the identity of a wide variety of sound sources: speakers, musical instruments and non-speech non-music sound sources (e.g. vacuum cleaners). We observed that this region tracks the identity of sound sources based on objective, measurable properties of the low-level structure of the sounds.
4. We discovered that the same cortical regions that respond selectively to one category of natural sounds (e.g. human voices) also represent a large deal of information about the same sound category in the spatial pattern of cortical activity: [a] differentiation of activating category from non-activating categories (e.g. human action); [b] differentiation of within-category exemplars (e.g. speech vs. physiological vocalizations such as sneezes); [c] perceptual dissimilarity of within-category exemplars.