Temporal Pitch Sensitivity in an Animal Model: Psychophysics and Scalp Recordings

Journal of the Association for Research in Otolaryngology - Cochlear implant (CI) users show limited sensitivity to the temporal pitch conveyed by electric stimulation, contributing to impaired...     

Determination of the antioxidant capacity in blood.

BACKGROUND: A vast amount of scientific research is directed towards the beneficial effects of antioxidants on health. For this reason, several assays have been developed to determine the total antioxidant capacity of blood. METHODS: In this study two procedures based on the use of the green-blue 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radical (ABTS(*+)) were compared. In the first (commercially available) procedure, ABTS(*+) was generated in the presence of the blood sample. In the second procedure, referred to as the decolorization assay, antioxidants react with preformed ABTS(*+). RESULTS: It was found that the first procedure leads to greater underestimation of the actual antioxidant capacity and is more prone to artifacts than the second procedure. Therefore, only the latter procedure was evaluated in detail and it appeared that (i) plasma is preferred over serum, (ii) the high background produced by albumin can be circumvented by deproteination, (iii) samples can be stored at -80 degrees C for 12 months, and (iv) the assay has high precision. Due to poor linearity, the procedure has to be standardized to allow sample comparison. CONCLUSIONS: The decolorization assay is a reliable and robust assay that can be applied routinely to predict the antioxidant capacity of blood.     

Tonotopic Selectivity in Cats and Humans: Electrophysiology and Psychophysics

Journal of the Association for Research in Otolaryngology - We describe a scalp-recorded measure of tonotopic selectivity, the “cortical onset response” (COR) and compare the results...     

Electrophysiological and Psychophysical Measures of Temporal Pitch Sensitivity in Normal-hearing Listeners

To obtain combined behavioural and electrophysiological measures of pitch perception, we presented harmonic complexes, bandpass filtered to contain only high-numbered harmonics, to normal-hearing listeners. These stimuli resemble bandlimited pulse trains and convey pitch using a purely temporal code. A core set of conditions consisted of six stimuli with baseline pulse rates of 94, 188 and 280 pps, filtered into a HIGH (3365–4755 Hz) or VHIGH (7800–10,800 Hz) region, alternating with a 36% higher pulse rate. Brainstem and cortical processing were measured using the frequency following response (FFR) and auditory change complex (ACC), respectively. Behavioural rate change difference limens (DLs) were measured by requiring participants to discriminate between a stimulus that changed rate twice (up-down or down-up) during its 750-ms presentation from a constant-rate pulse train. FFRs revealed robust brainstem phase locking whose amplitude decreased with increasing rate. Moderate-sized but reliable ACCs were obtained in response to changes in purely temporal pitch and, like the psychophysical DLs, did not depend consistently on the direction of rate change or on the pulse rate for baseline rates between 94 and 280 pps. ACCs were larger and DLs lower for stimuli in the HIGH than in the VHGH region. We argue that the ACC may be a useful surrogate for behavioural measures of rate discrimination, both for normal-hearing listeners and for cochlear-implant users. We also showed that rate DLs increased markedly when the baseline rate was reduced to 48 pps, and compared the behavioural and electrophysiological findings to recent cat data obtained with similar stimuli and methods.