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Richard J Baker

Publications and source records attributed to Richard J Baker.

5 recordsLinked to original sources
PubMed2006

Auditory filter nonlinearity across frequency using simultaneous notched-noise masking.

Psychoacoustic masking experiments have been widely used to investigate cochlear function in human listeners. Here we use simultaneous notched-noise masking experiments in normal hearing listeners to characterize the changes in auditory filter shape with stimulus level over the frequency range 0.25-6 kHz. At each frequency a range of fixed signal levels (30-70 dB SPL) and fixed masker levels (20-50 dB SPL spectrum level) are used in order to obtain accurate descriptions of the filter shapes in individual listeners. The notched-noise data for individual listeners are fitted with two filter shape models: a rounded exponential (roex) shape in which the filter skirt changes as a linear function of probe-tone level and the other, in which the gain of the tip filter relative to the filter tail changes as a function of signal level [Glasberg and Moore, J. Acoust. Soc. Am. 108, 2318-2328 (2000)]. The parameters for these fitted models are then described with a simple set of equations that quantify the changes in auditory filter shape across level and frequency. Both these models fitted the data equally well and both demonstrated increasing tip-tail gain as frequency increased.

Adult↗
PubMed2003

Empirical aminoglycosides for peritonitis do not affect residual renal function.

BACKGROUND: Aminoglycosides have been proven to be an efficacious treatment for peritonitis in peritoneal dialysis patients for many years. Consequently, they have been recommended in previous guidelines for the empirical treatment of peritonitis. However, with the increasing emphasis on preserving residual renal function (RRF), there has been concern about the nephrotoxic potential of these compounds. The 2000 International Society of Peritoneal Dialysis (ISPD) guidelines recommended that aminoglycosides not be used in patients with RRF, and that ceftazidime be used instead. In 1997, in response to the 1996 ISPD guidelines, we changed our peritonitis regimen from vancomycin and ciprofloxacin to cefazolin and gentamicin. The aim of this study is to compare the change in renal function occurring after treatment of peritonitis with and without gentamicin. METHODS: Using 6-monthly urine and dialysis clearance measurements, preperitonitis and postperitonitis RRF (mean of 24-hour urea and creatinine clearance) were determined for 70 peritonitis episodes treated with the aminoglycoside-based regimen (group A), 61 episodes treated without aminoglycosides (group B), and 74 control patients without peritonitis (group C). RESULTS: Group A had mean declines in estimated glomerular filtration rate and urine output of -0.08 +/- 0.50 mL/min/mon and -8.82 +/- 88.09 mL/24 h/mon compared with -0.17 +/- 0.27 mL/min/mon and -34.68 +/- 69.58 mL/24 h/mon in group B and -0.20 +/- 0.39 mL/min/mon and -14.61 +/- 77.33 mL/24 h/mon in group C, respectively. There were no significant differences between groups. CONCLUSION: In our patients, there was no evidence of an accelerated decline in RRF when using an empirical regimen containing aminoglycosides for peritonitis. Because there are few data to contradict this finding, we recommend the continued use of these drugs in peritonitis regimens, even in patients with significant RRF.

Administration, Oral↗
PubMed2002

Auditory filter nonlinearity in mild/moderate hearing impairment.

Sensorineural hearing loss has frequently been shown to result in a loss of frequency selectivity. Less is known about its effects on the level dependence of selectivity that is so prominent a feature of normal hearing. The aim of the present study is to characterize such changes in nonlinearity as manifested in the auditory filter shapes of listeners with mild/moderate hearing impairment. Notched-noise masked thresholds at 2 kHz were measured over a range of stimulus levels in hearing-impaired listeners with losses of 20-50 dB. Growth-of-masking functions for different notch widths are more parallel for hearing-impaired than for normal-hearing listeners, indicating a more linear filter. Level-dependent filter shapes estimated from the data show relatively little change in shape across level. The loss of nonlinearity is also evident in the input/output functions derived from the fitted filter shapes. Reductions in nonlinearity are clearly evident even in a listener with only 20-dB hearing loss.

Acoustic Stimulation↗