Brain research
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We report first results of a multilevel, cross-modal study on the neuronal mechanisms underlying auditory sequential streaming, with the focus on the impact of visual sequences on perceptually ambiguous tone sequences which can either be perceived as two separate streams or one alternating stream. We combined two psychophysical experiments performed on humans and monkeys with two human brain imaging experiments which allow to obtain complementary information on brain activation with high spatial (fMRI) and high temporal (MEG) resolution. ⋯ Thus, comparable to an explicit instruction, this approach can be used to control the subject's perceptual organization of an ambiguous sound sequence without the need for the subject to directly report it. This finding is of particular importance for animal studies because it allows to compare electrophysiological responses of auditory cortex neurons to the same acoustic stimulus sequence eliciting either a segregated or integrated percept.
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Comparative Study
Timbre discrimination in normal-hearing and hearing-impaired listeners under different noise conditions.
In an attempt to quantify differences in object separation and timbre discrimination between normal-hearing and hearing-impaired listeners with a moderate sensorineural hearing loss of two different configurations, psychoacoustic measurements were performed with a total of 50 listeners. The experiments determined just noticeable differences (JND) of timbre in normal-hearing and hearing-impaired subjects along continua of "morphed" musical instruments and investigated the variance of JND in silence and different background noise conditions and on different sound levels. ⋯ In the condition testing, transferability from silence to noise (i.e., the ability to imagine how the stimulus heard in silence would sound in noise), no significant JND differences across listener groups were found. The results can be explained by primary factors involved in sensorineural hearing loss and contradict the hypothesis that hearing-impaired people generally have more problems in object discrimination than normal-hearing people.
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Auditory perception comprises bottom-up as well as top-down processes. While research in the past has revealed many neural correlates of bottom-up processes, less is known about top-down modulation. Memory processes have recently been associated with oscillations in the gamma-band of human EEG (30 Hz and above) which are enhanced when incoming information matches a stored memory template. ⋯ Analysis of evoked gamma-band responses yielded no significant task-dependent modulation, but we observed a stimulus dependency, which was also present in a control experiment: The amplitude of evoked gamma responses showed an inverted U-shape as a function of stimulus frequency. Investigation of total gamma activity revealed functionally relevant responses at high frequencies (90 Hz to 250 Hz), which showed significant modulations by matches with STM: Complete matches led to the strongest enhancements (starting around 100 ms after stimulus onset) and partial matches resulted in intermediate ones. The results support the conclusion that very high frequency oscillations (VHFOs) are markers of active stimulus discrimination in STM matching processes and are attributable to higher cognitive functions.
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An event-related potential (ERP) experiment was conducted to investigate the development of orthographic and phonological processing during Chinese sentence reading between school children and adult readers. Participants were visually presented with sentences, word-by-word, and were asked to judge whether the sentences were semantically acceptable. The crucial manipulation was on the sentence-final two-character compound words, which were either correct or incorrect. ⋯ Moreover, the offset of the N400 effects appeared earlier for adults than for children and for orthographic mismatch than for phonological mismatch. These findings suggest that both Chinese adult readers and school children rely more on orthographic information than on phonological information to access lexical semantics in reading Chinese sentences. However, the differential effects between orthography and phonology may have different ERP manifestations in adults and children.
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We investigated changes in pain behavior after injection of acetic acid in the hindpaws of rats with L5 spinal nerve ligation (SNL)-induced neuropathy. We also examined immunoreactivity for acid-sensing ion channel 3 (ASIC3) in the dorsal root ganglion (DRG) of rats with L5 SNL. Two weeks after SNL, the withdrawal threshold to a mechanical stimulus was significantly lower in the SNL group than in the sham-operated group (n=9 per group, P<0.01). ⋯ In the ipsilateral L5 DRG, the proportion of ASIC3-ir neurons was not significantly affected by treatment. However, L5 SNL significantly increased (P<0.01) the proportion of small (<1200 mm(2)) ASIC3-ir neurons and significantly decreased (P<0.01) the proportion of large ASIC3-ir neurons compared to proportions in sham-operated animals. These findings suggest that ASIC3 is associated with hyperalgesia in response to a chemical stimulus in the L5 SNL rat model.