PubMed · 4714081
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J J Moore, D W Massaro. 1973. Attention and processing capacity in auditory recognition.. https://doi.org/10.1037/h0034735
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Cortical processing of change in direction of a perceived sound source was investigated in 12 human subjects using whole-head magnetoencephalography. The German word "da" was presented either with or without 0.7 msec interaural time delays to create the impression of right- or left-lateralized or midline sources, respectively. Midline stimuli served as standards, and lateralized stimuli served as deviants in a mismatch paradigm. Two symmetrically linked dipoles fitted to the mismatch fields showed stronger moments in the hemisphere contralateral to the side of the deviant. The right dipole displayed equal latencies to both left and right deviants, whereas left dipole latencies were longer for ipsilateral than contralateral deviants. Frequency analysis between 20-70 Hz and statistical probability mapping revealed increased induced gamma-band activity at 53+/-2.5 Hz to both types of deviants. Right deviants elicited spectral amplitude enhancements in this frequency range, peaking at latencies of 160 and 240 msec. These effects were localized bilaterally over the angular gyri and posterior temporal regions. Coherence analysis suggested the existence of two separate interhemispheric networks. For left-lateralized deviants, both spectral amplitude enhancements at 110 and 220 msec and coherence increases were restricted to the right hemisphere. In conclusion, both mismatch dipole latencies at the supratemporal plane and gamma-band activity in posterior parietotemporal areas suggested a right hemisphere engagement in the processing of bidirectional sound-source shifts. In contrast, left-hemisphere regions responded predominantly to contralateral events. These findings may help to elucidate phenomena such as unilateral auditory neglect.
Loud sounds damage the cochlea, the auditory receptor organ, reducing hearing sensitivity. Previous studies demonstrate that the centrifugal olivocochlear pathways can moderately reduce these temporary threshold shifts (TTSs), protecting the cochlea. This effect involves only the olivocochlear pathway component known as the crossed medial olivocochlear system pathway, originating from the contralateral brainstem and terminating on outer hair cells in the cochlea. Here I demonstrate that even moderate noise backgrounds can significantly exacerbate the cochlear TTSs induced by loud tones, but this is prevented because in such conditions there is additional activation of uncrossed olivocochlear pathways, enhancing protection of cochlear hearing sensitivity. Activation of the uncrossed pathways differs from that of the crossed pathway in that it is achieved only in noise backgrounds but can then be obtained under monaural conditions of loud tone and background noise. In contrast, activation of the crossed pathway is achieved only by binaural loud tones and is not further enhanced by background noise. Thus, conjoint activation of both crossed and uncrossed efferent pathways can occur in noise backgrounds to powerfully protect the cochlea under conditions similar to those encountered naturally by humans.
This study investigated how duration changes are processed in the human brain as indexed by the mismatch negativity (MMN), a component of the auditory event-related potential (ERP) reflecting sensory memory. Subjects were presented with sequences of repetitive 100-ms white noise bursts interspersed by occasional duration deviants which were 1, 10, or 50 ms (decrements) or 110, 150, or 200 ms (increments) in duration. In a separate task, subjects were asked to detect deviants within the sequence via a button-press. MMN was elicited by both stimulus decrements and increments and increased in amplitude as a function of the amount of deviation from the standard duration except for the shortest, 1-ms deviant. Behavioural detection paralleled the MMN responses, suggesting a link between the processes underlying MMN and behavioural measures.