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At least 415 records · Page 23Linked to original sources
PubMed1985

Effects of frequency modulation on absolute, masked, and reflex thresholds.

Behavioral and acoustic reflex thresholds were determined for five normal-hearing subjects in response to carrier signals of 500 and 2000 Hz which were unmodulated or modulated sinusoidally at rates of 2, 20, and 200 times per second with frequency deviations (delta f) of 30, 100, and 300 Hz. Behavioral (absolute and masked) thresholds were determined using an adaptive two-alternative forced-choice procedure. Acoustic reflex thresholds were determined by visual inspection of stored reflex waveforms. Frequency modulation was not found to exert a systematic effect at absolute threshold. Frequency modulation did affect threshold estimates systematically, but differentially, at masked threshold and acoustic reflex threshold. Increasing the frequency deviation of the modulation was associated with an increase in masked threshold and with a decrease in acoustic reflex threshold at both test frequencies. The findings are discussed in terms of critical band phenomena.

Acoustic Impedance Tests↗
PubMed1995

Optimal temporal frequencies in oscillatory movement hyperacuity measurements of visual function in cataract patients.

Hyperacuity tasks have been suggested for the assessment of potential visual function in the presence of cataracts. To test this suggestion, hyperacuity thresholds for an oscillating bar were measured in 30 subjects with idiopathic cataract and in 24 age-matched normals over a range of oscillation frequencies. Each subject's cataract was categorized using the Oxford Clinical Cataract Classification and Grading System. Cataract was found to have a significant effect on thresholds, although a differential morphological effect on thresholds was equivocal. Thresholds at higher temporal frequencies were significantly raised when compared to the normal group. The main conclusion to be drawn from this study is that motion hyperacuity thresholds appear unaffected by cataract at low oscillation frequencies and should be used in preference to higher frequencies in the assessment of such patients.

Aged↗
PubMedDate not supplied

[The thresholds of discriminating the duration of frequency-modulated signals by cats behaving freely].

Threshold values of duration if frequency modulated signals (sweeps) were measured under the free behaviour conditions in cats. Modulation of the sweeps was carried out linearly in a diapason of 2-100 ms with both increasing and decreasing frequency and embedded in tone stimuli with central frequency of 2.5 kHz and total duration of 0.5 s. The sweeping rate was the same in all cases and equal to 1.2 kHz/s. While training, animals had to discriminate "short" (2 ms) signals (heard by a human as clicks) and "long" (100 ms) signals (with well expressed frequency change when hearing). Different durations being used in experiments, at the sweeping duration of 30 ms cats qualified signals as "short" and "long" ones with equal probabilities. The results are similar to those obtained for humans in spite of significant difference in frequency resolution ability for animals and humans.

Acoustic Stimulation↗
PubMed1993

Red-green color discrimination in peripheral vision.

Color discrimination thresholds were measured for four colors from the red-green portion of the visible spectrum. Thresholds were measured for a stimulus field 1.5 deg in diameter in the fovea and at three locations on the nasal retina (eccentricities of 5, 20 and 40 deg). Outside the fovea threshold increased exponentially with eccentricity and the slope of the function was similar for all four standard colors. Peripheral thresholds were adequately described by an equation developed for foveal red-green thresholds by Boynton and Kambe [(1980) Color Research and Applications, 5, 13-23] and also by a modified form of this equation containing a rod term. Differences between foveal and peripheral thresholds were characterized by changes in two coefficients in the equations. The CIELUV color difference equation also provided a reasonably good description of peripheral thresholds.

Adult↗
PubMed1981

[Latencies of reaction indicating disturbed behaviour during evaluation of pure tone threshold (author's transl)].

In a psychoacoustic experiment intervals between tonal stimuli and responses at different sound levels allow to differentiate real threshold functions from limited responding. The audiometric and time measuring procedure has to be applied in a designated manner. A range of about 20 dB and steps of sometimes as small as 1 dB must be employed. Disturbed behaviour during audiometry (resulting into pseudohypacusis) is then indicated by prolonged latencies, unsteady correlation ot time intervals and stimulus level, or fluctuating threshold of reaction. Limits of reaction intervals have been established.

Adult↗
PubMed1995

Glaucomatous visual fields. FASTPAC versus full threshold strategy of the Humphrey Field Analyzer.

PURPOSE: This study examined how FASTPAC, a fast strategy for the Humphrey Field Analyzer (HFA), compares to the standard 4/2-dB full threshold strategy in patients with glaucoma. METHOD: The author tested one eye each of 50 patients with glaucoma (23 with only relative defects, 27 with at least one absolute defect; age range, 25 to 79 years; median age, 61.5 years) with both strategies using program 30-2 of the HFA (stimulus size III). Global visual field indices as calculated by Statpac, unweighted mean sensitivity, and examination time were compared. In addition, a point by point analysis of the sensitivity values was performed. RESULTS: Between the two strategies, no significant differences were found for indices directly related to the sensitivity values (mean sensitivity [MS], mean deviation [MD]) or for the actual thresholds. For the entire population, FASTPAC showed higher mean short-term fluctuation (SF; P = 0.018), lower mean pattern standard deviation (PSD; P = 0.006), and mean corrected PSD (CPSD; P < 0.001) values and a time reduction of more than 30% (P < 0.001) compared to the standard strategy. These differences between the strategies were found to be independent of the amount of field loss, except for PSD (P = 0.001). No age influence was present. Statistically significant linear regression (r > 0.70, P < 0.001) was found between the FASTPAC values of MS, MD, PSD, CPSD, and the corresponding values determined with the standard strategy. No correlation exists for SF (r < 0.46, P > 0.030). CONCLUSIONS: FASTPAC provides a considerable time reduction at the cost of higher threshold fluctuation. This may lead to problems in detecting relative defects or changes in differential light threshold in follow-up examinations.

Adult↗