A low cost, non-individualized surround sound system based upon head related transfer functions: an ergonomics study and prototype development.

This paper reports on the types and magnitudes of localization errors of simulated binaural direction cues generated using non-individualized, head-related transfer functions (HRTFs) with different levels of complexity. Four levels of complexity, as represented by the number of non-zero coefficients of the associated HRTF filters (128, 64, 32, 18 non-zero coefficients), were studied. Experiment 1 collected 1728 data runs that were exhaustive combinations of the four levels of complexity, nine simulated directions of sound (no direction (i.e., diotical-mono), 0 degrees , 45 degrees , 90 degrees , 135 degrees , 180 degrees , 225 degrees , 270 degrees , and 315 degrees azimuth angles at 0 degrees elevation), two repetitions, and 24 participants). Binaural cues generated from HRTFs of reduced complexity (from 128 to 18 non-zero coefficients) produced significantly higher localization errors for the directions of 45 degrees , 135 degrees , 225 degrees , and 315 degrees azimuth angles (p<0.01). From the directions of 0 degrees , 90 degrees , and 270 degrees azimuth angles, the cues produced by HRTFs with reduced complexity did not affect the localization error (p>0.2). Surprisingly, cues produced by HRTFs of 128 non-zero coefficients did not have the lowest number of errors. From 45 degrees , 135 degrees , 225 degrees , and 315 degrees , the lowest numbers of errors were obtained from cues produced by HRTFs of 64, 32, 32, and 64 non-zero coefficients, respectively. Based on these findings, a prototype virtual headphone-based surround-sound (VHSS) system was developed. A double-blind usability experiment with 32 participants indicated that the prototype VHSS system received significantly better surround-sound ratings than did a Dolby stereo system (p<0.02). This paper reports results from an original ergonomics study and the application of these results to the design of a consumer product.

Weight gain in epileptic patients during treatment with valproic acid: a retrospective study.

BACKGROUND: Weight gain has been recognized as a common adverse effect of valproic acid (VPA) that leads to discontinuation in some patients but its incidence and correlates have been rarely studied. METHODS: We have analyzed the records retrospectively and interviewed 70 adult patients attending an epilepsy clinic on VPA mono- or polytherapy followed over a median of 27 months (range 3-189), as well as 20 patients on carbamazepine (CBZ) monotherapy. Patients were divided into non-weight gainers (< 5% baseline body weight), mild-moderate weight gainers (5-10% body weight) and marked weight gainers (> 10% body weight). The following variables were statistically analyzed to determine their relationship to weight gain: gender, age, body mass index, drug dose, personal or family history of obesity and monotherapy versus polytherapy. RESULTS: Seventy-one percent of the VPA group were weight gainers versus 43% in the CBZ group. A weight gain of more than 4 kg in 70% of the VPA group was observed. The weight gain was often sustained and frequently socially significant to the patients. Patients below or within normal range body mass index prior to the start of VPA experienced the most severe percentage weight gain. From the structured patient interviews, patients with no personal history of weight problems experienced the greatest initial weight increase. CONCLUSION: Strategies should be devised to help patients avoid weight gain when starting on VPA, especially if they are not already overweight.

Successful long-term management of a gonadotroph adenoma with bromocriptine.

OBJECTIVE: To report the successful 10-year management of a gonadotroph macroadenoma with bromocriptine and review the management of gonadotroph adenomas with bromocriptine. METHODS: We present a case and review the pertinent literature. The effectiveness of bromocriptine in the management of gonadotroph adenomas is evaluated. RESULTS: A 62-year-old man was found to have a pituitary tumor after seeking medical assistance because of a 6-month history of headaches and blurred vision. He had decreased visual acuity and bitemporal field defects. Serum follicle-stimulating hormone (FSH) levels were increased, whereas serum luteinizing hormone and total testosterone levels were normal. Treatment with bromocriptine resulted in a decrease in serum FSH levels, complete resolution of his symptoms, and considerable improvement in his visual acuity and visual field defects. Treatment with only bromocriptine for 10 years resulted in maintenance of normal serum FSH levels and no recurrence of symptoms. CONCLUSION: In the management of a gonadotroph adenoma, we recommend consideration of a therapeutic trial of bromocriptine. In cases that are refractory to this therapy, surgical treatment or external pituitary irradiation could then be used.

Effects of spectral manipulation on nonindividualized head-related transfer functions (HRTFs).

BACKGROUND: Directional sounds simulated using nonindividualized head-related transfer functions (HRTFs) often result in front-back confusion. OBJECTIVE: This study was designed to examine how manipulating these nonindividualized HRTF spectra can reduce front-back confusion in headphone-simulated directional sounds. METHOD: HRTFs of six ear-level directions were studied (angles of 0 degrees, 45 degrees, 135 degrees, 180 degrees, 225 degrees, and 315 degrees). The HRTF gains in each of six frequency bands (200 to 690 Hz, 690 to 2400 Hz, 2400 to 6500 Hz, 6500 to 10000 Hz, 10000 to 14000 Hz, and 14000 to 22000 Hz) were amplified or attenuated by 0, 12, or 18 dB. Each manipulated HRTF generated a directional sound stimulus. For this study, 32 participants were invited to localize the randomly ordered stimuli. RESULTS: The results indicate that a 12- or 18-dB manipulation of five of the six frequency bands produced significantly better directional accuracy, with significantly less front-back confusion. A reduction of up to 70% in localization error was obtained, along with 66% less front-back confusion. Significant interactions were found between the manipulation level and frequency. CONCLUSION: A 12-dB spectral manipulation of selected HRTF frequency bands produces better directional accuracy. APPLICATION: The results of this research could be applied to the development of tunable nonindividualized HRTFs for audio products.