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Mapping feature-sensitivity and attentional modulation in human auditory cortex with functional magnetic resonance imaging

Feature-specific enhancement refers to the process by which selectively attending to a particular stimulus feature specifically increases the response in the same region of the brain that codes that stimulus property. Whereas there are many demonstrations of this mechanism in the visual system, the evidence is less clear in the auditory system. The present functional magnetic resonance imaging (fMRI) study examined this process for two complex sound features, namely frequency modulation (FM) and spatial motion. The experimental design enabled us to investigate whether selectively attending to FM and spatial motion enhanced activity in those auditory cortical areas that were sensitive to the two features. To control for attentional effort, the difficulty of the target-detection tasks was matched as closely as possible within listeners. Locations of FM-related and motion-related activation were broadly compatible with previous research. The results also confirmed a general enhancement across the auditory cortex when either feature was being attended to, as compared with passive listening. The feature-specific effects of selective attention revealed the novel finding of enhancement for the nonspatial (FM) feature, but not for the spatial (motion) feature. However, attention to spatial features also recruited several areas outside the auditory cortex. Further analyses led us to conclude that feature-specific effects of selective attention are not statistically robust, and appear to be sensitive to the choice of fMRI experimental design and localizer contrast.

from the European Journal of Neuroscience

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Patterned Tone Sequences Reveal Non-Linear Interactions in Auditory Spectrotemporal Receptive Fields in the Inferior Colliculus

Linear measures of auditory receptive fields do not always fully account for a neuron’s response to spectrotemporally-complex signals such as frequency-modulated sweeps (FM) and communication sounds. A possible source of this discrepancy is cross-frequency interactions, common response properties which may be missed by linear receptive fields but captured using two-tone masking. Using a patterned tonal sequence that included a balanced set of all possible tone-to-tone transitions, we have here combined the spectrotemporal receptive field with two-tone masking to measure spectrotemporal response maps (STRM). Recording from single units in the mustached bat inferior colliculus, we found significant non-linear interactions between sequential tones in all sampled units. In particular, tone-pair STRMs revealed three common features not visible in linear single-tone STRMs: 1) two-tone facilitative interactions, 2) frequency-specific suppression, and 3) post-stimulatory suppression in the absence of spiking. We also found a correlative relationship between these nonlinear receptive field features and sensitivity for different rates and directions of FM sweeps, dynamic features found in many vocalizations, including speech. The overwhelming prevalence of cross-frequency interactions revealed by this technique provides further evidence of the central auditory system’s role as a pattern-detector, and underscores the need to include nonlinearity in measures of the receptive field.

from Hearing Research