Risk for speech disorder associated with early recurrent otitis media with effusion: two retrospective studies.

The goals of this two-part series on children with histories of early recurrent otitis media with effusion (OME) were to assess the risk for speech disorder with and without hearing loss and to develop a preliminary descriptive-explanatory model for the findings. Recently available speech analysis programs, lifespan reference data, and statistical techniques were implemented with three cohorts of children with OME and their controls originally assessed in the 1980s: 35 typically developing 3-year-old children followed since infancy in a university-affiliated pediatrics clinic, 50 typically developing children of Native American background followed since infancy in a tribal health clinic, and (in the second paper) 70 children followed prospectively from 2 months of age to 3 years of age and older. Dependent variables included information from a suite of 10 metrics of speech production (Shriberg, Austin, Lewis, McSweeny, & Wilson, 1997a, 1 997b). Constraints on available sociodemographic and hearing status information limit generalizations from the comparative findings for each database, particularly data from the two retrospective studies. The present paper reports findings from risk analysis of conversational speech data from the first two cohorts, each of which included retrospective study of children for whom data on hearing loss were not available. Early recurrent OME was not associated with increased risk for speech disorder in the pediatrics sample but was associated with approximately 4.6 (CI = 1.10-20.20) increased risk for subclinical or clinical speech disorder in the children of Native American background. Discussion underscores the appropriateness of multifactorial risk models for this subtype of child speech disorder.

Yellow lens effects upon visual acquisition performance.

Twenty subjects made a total of 400 threshold visual acquisitions of T-38 aircraft approaching from 9 miles out. Half of the acquisitions were made with the subjects wearing yellow ophthalmic filters, and the other half without filters. No overall statistically significant difference in acquisition performance due to the use of yellow filters was found.

Loudness judgment procedures for evaluating hearing aid preselection decisions for severely and profoundly hearing-impaired listeners.

Hearing aid fitting involves a two-phase process of preselection and evaluation (Seewald RC and Ross M. Amplification for the Hearing Impaired 1988:213-271). The purpose of the present study was to examine alternative procedures that clinicians might use in the evaluation phase to verify the adequacy of hearing aid preselection decisions for severely and profoundly hearing-impaired listeners. Bekesy tracking, loudness rating, and conventional bracketing procedures were used to determine threshold, most comfortable listening level, and uncomfortable listening level for 10 hearing-impaired young adults. Stimuli were pulsed pure tones of 500, 1000, and 2000 Hz and filtered words. Means and standard deviations of most comfortable listening levels and uncomfortable listening levels derived from loudness judgments of the 10 subjects showed only nominal differences across procedures. However, correlation analysis (Pearson r) indicated that individuals responded to the three procedures in varying ways, producing different loudness judgments and overall dynamic ranges. Thus, test procedure may influence the clinician's final evaluation of a preselected hearing aid. Initial work suggests that closed-set response categories such as loudness rating can limit measurement variability and potentially guide the clinician's evaluation of hearing aid preselection decisions.

Matrix methods for the evaluation of lens systems with radial gradient-index elements.

Matrix methods have been used to examine the paraxial performance of homogeneous systems. This method has been extended to include the presence of gradient lens elements in the optical array. To accomplish this, an inhomogeneous rotation-translation matrix is developed to describe the path of a ray through the lens elements with quadratic radial index gradients. The system matrix elements are then used to predict the paraxial properties of the array. Three examples are examined: the Wood lens, two thin lenses coupled to a radial gradient index rod, and a model of the human eye which contains a radial gradient index crystalline lens.

Insertion gain measured with three probe tube systems.

The study consisted of two experiments on the insertion gain measured with probe tube microphones. In experiment I, the insertion gain of the same mild gain hearing aid was measured twice on 12 subjects using three commercially available probe tube systems. Test-retest measurements were made by two different examiners. Mean test-retest differences were all less than 4 dB with 95% critical differences for these measures varying from approximately 3 to 8 dB depending upon the test system used. In experiment II, the three sets of probe tube measures of insertion gain were compared to behaviorally measured functional gain in 7 hearing-impaired subjects at several frequencies. There were no significant differences among the probe tube measures of insertion gain or between these measures and functional gain. Functional gain was significantly correlated with probe tube insertion gain for each device at frequencies from 500 through 4000 Hz.

Soft contact lens wear at altitude: effects of hypoxia.

In the U.S. Air Force, aircraft can be divided into two categories--those with cabin pressures equivalent to high altitudes and aircraft with cabin pressures equivalent to lower altitudes, with longer duration exposures. The purpose of this study was to determine the effects of soft contact lens wear under atmospheric pressures simulating these two types of aircraft environments. Ten subjects were tested to 7620 m (25,000 ft) in hypobaric chamber flights of 75 min and eight subjects were tested in hypobaric chamber flights at 3048 m (10,000 ft) for 4 h. Four subjects were also tested in dry air to further simulate cabin conditions. Vision and physiologic response were monitored by measurements of visual acuity, contrast sensitivity, and slit-lamp biomicroscopy examinations. The results of this study indicate that the physiologic responses of the cornea to soft contact lens wear at altitude are subject to higher levels of manifested stresses, but these occurred without measurable degradation in vision and did not preclude normal wear of soft contact lenses.

Contact lens wear at altitude: subcontact lens bubble formation.

A concern in the past regarding contact lens wear in aviation has been the fear of subcontact lens bubble formation. Previous reports have documented the occurrence of bubbles with hard (PMMA) lenses. Reported here are the results of contact lens bubble studies with soft hydrophilic and rigid gas-permeable lenses. Testing was accomplished in hypobaric chambers and onboard USAF transport aircraft. Hypobaric chamber flights were of three types: high-altitude flights up to 7,620 m (25,000 ft); explosive rapid decompressions from 2,438.4 m (8,000 ft) to 7,620 m (25,000 ft); and 4-h flights at 3,048 m (10,000 ft). Flights aboard transport aircraft typically had cabin pressures equivalent to 1,524-2,438.4 m (5,000-8,000 ft), and ranged in duration from 3 to 10 h. For subjects wearing rigid gas-permeable lenses, central bubbles were detected in 2 of 10 eyes and occurred at altitudes greater than 6,096 m (20,000 ft). With soft contact lenses, bubble formation was detected in approximately 24% (22 of 92 eyes) of the eyes tested, sometimes occurring at altitudes as low as 1,828.8 m (6,000 ft). Soft lens bubbles were always located at the limbus and were without sequela to vision or corneal epithelial integrity. Bubbles under the rigid lenses were primarily central, with potential adverse effects on vision and the corneal epithelium.

Effect of positive acceleration (+Gz) on soft contact lens wear.

The effects of positive acceleration on soft contact lens wear were tested on a human centrifuge to +8 Gz. There were 11 subjects who participated in this study; 5 were myopic subjects fit with low-, medium-, and high-water-content spherical soft lenses; 3 were astigmatic subjects fit with various designs of toric soft lenses and 3 were emmetropic control subjects. As an additional control, the contact lens subjects were tested with spectacles for comparison. Video photography was used to monitor lens position during the centrifuge rides and visual acuity was checked at +1, +2, +4, +6, and +8 Gz with a reduced Snellen eye chart. Each lens type and control run was evaluated in straight-ahead, lateral, and vertical gaze. No visually significant decentration was noted for any of the lens types tested up to the maximum level of +8 Gz. Visual acuity was reduced at the higher +Gz levels for contact lenses, and spectacle trials, and with the emmetropic controls--all to similar levels. Contact lens wear did not produce any corneal insult due to the +Gz exposure.

Acoustic-immittance measures in normal ears.

A data base of acoustic-immittance measures in normal adults is presented. The subject pool consisted of 127 adults with normal hearing and a negative otologic history. Norms are presented for hearing thresholds, ipsilateral and contralateral acoustic-reflex thresholds, tympanometry, static acoustic-admittance measures, and middle-ear (tympanogram peak) pressure.

Tympanometric measures of eustachian tube function.

The purpose of this study was to develop instructions and procedures and to establish a normal data base for four tympanometric tests of Eustachian tube function: Valsalva, Toynbee, Inflation, and Deflation. Data were obtained for 24 young adults (48 ears) with normal hearing and normal middle-ear function. The tympanograms were analyzed for differences between baseline and experimental (postmaneuver) and baseline and posttest tracings for seven measures: tympanogram peak pressure, peak acoustic admittance, static acoustic admittance, negative gradient, positive gradient, and negative and positive acoustic-admittance values at +/- 400 daPa. The results indicated a statistically significant difference only in peak pressure for baseline and experimental tympanograms. Peak-pressure shifts were most pronounced for the Valsalva and Toynbee procedures. The small pressure shifts characteristic of the Inflation and Deflation procedures coupled with the potential for instrumental error severely limit the use of these procedures as means of obtaining reliable indices of tubal function.

Acoustic-reflex growth for multitone complexes.

The effects of activator spectral density on the growth characteristics of the acoustic reflex were evaluated in normal-hearing subjects. Reflex-growth dynamics were evaluated for computer-synthesized activators composed of 2 to 50 components and bandwidths wider and more narrow than the reported critical band for loudness summation. Although acoustic-reflex characteristics varied with activator bandwidth, there were no significant differences in reflex-growth patterns as a function of activator density (number of components). The findings suggest that, like loudness summation, growth or magnitude characteristics of the acoustic reflex are unaffected by the spectral density of the signal.

Acoustic-reflex dynamics and the loudness-discomfort level.

Acoustic-reflex growth functions and Loudness-Discomfort Level (LDL) measures were obtained for 15 normal-hearing subjects. The hypothesis that signals considered uncomfortably loud occur at intensity levels that produce proportionately equal acoustic-reflex magnitudes was evaluated. Individual reflex growth functions were measured as a function of activator SPL for a 1000-Hz tone, a 4000-Hz tone, and a broadband noise. These growth functions were measured within subjects (two trials) and across subjects in terms of (a) percentage acoustic-impedance change at LDL, (b) percentage acoustic-reactance change at LDL, (c) acoustic impedance at LDL, (d) relative change in acoustic impedance at LDL, and (e) ratio of static acoustic impedance to change in acoustic impedance at LDL. Although the loudness and acoustic-reflex measures demonstrated good reliability across trials, the data showed large variability across subjects and did not support the experimental hypothesis. It was concluded, therefore, that the use of acoustic-reflex measures in the estimation of an individual's LDL is unwarranted.

Use of multiple regression techniques in determining the surface of the cornea.

Many methods can be used to obtain specific values for relative corneal location. This paper derives a method in which those points can be used to generate a mathematical equation which will accurately describe the patient's corneal topology. After various dimensional methods are discussed, a three-dimensional mathematical method is derived.

Dynamics of acoustic reflex growth.

Acoustic reflex growth was measured as a function of activator bandwidth in 10 subjects with normal hearing and in 5 subjects with different configurations of sensorineural hearing loss. The activators consisted of tones with frequencies of 500, 1 000 and 4 000 Hz, fractions and multiples of octave bands centered at these frequencies, and broadband noise. Growth functions for the normal-hearing subjects measured with a 660-Hz probe tone had smaller peak magnitudes and shallower slopes than the growth functions measured with a 220-Hz probe tone. The slope of the growth function and the peak magnitude of acoustic impedance were not affected in any consistent manner by activator bandwidth or activator center frequency. The dynamic range of the growth function increased with an increase in activator bandwidth beyond 1 octave. The resistive component of acoustic impedance did not exhibit a consistent pattern of change with increasing activator intensity level. The reflex growth functions for normal-hearing subjects separated into two groups, those with steep slopes and large peak magnitudes and those with shallow slopes and small peak magnitudes. 3 out of the 5 cases with sensorineural hearing loss presented growth functions with shallower slopes, smaller dynamic ranges and smaller peak magnitudes than normal. The other 2 cases had steeper slopes and larger peak magnitudes than normal. The dynamic range did not increase with an increase in activator bandwidth beyond 1 octave. The differences in reflex growth functions with probe-tone frequency observed for the normal group were diminished or absent in 4 of the 5 cases of sensorineural hearing loss. The frequency of 4 000 Hz appeared to be the most sensitive to reflex manifestations of hearing loss.

Static acoustic-immittance measurements.

The basic principles of deriving static acoustic-immittance measurements in human ears are presented. Problems caused by differences in instrumentation, computations, and measurement technique are discussed in terms of the utility and comparisons of static acoustic-immittance measurements. Data are provided regarding the short- and long-term variabilities inherent to static measurements. Although our subject pool was relatively small, certain patterns were apparent in the short- and long-term variability inherent to static acoustic-impedance measurements. The intra-event variability about the mean static acoustic impedance was small and varied inversely with probe-tone frequency. Standard deviations were less than 50 acoustic ohms for a 220-Hz probe tone and less than 25 acoustic ohms for a 660-Hz probe tone. Session-to-session variability in static measurements varied little within subjects but varied greatly across subjects. There was little correlation between the mean and standard deviation for within-subject measurements. Standard deviations across subjects approximate a relatively constant proportion (30-40%) of the mean static value. The need for large population studies of static acoustic-immittance measurements is noted.

Acoustic-reflex growth and loudness.

Acoustic-reflex growth functions and loudness-balance judgments were obtained for three normal-hearing subjects with normal middle-ear function. The hypothesis that acoustic reflex-activating signals producing proportionately equal acoustic-impedance changes are judged equal in loudness was evaluated. The mean acoustic impedance and associated standard deviations were computed for the baseline (static) and activator (reflex) portions of each reflex event. An acoustic-impedance change exceeding two standard deviations of baseline was defined as the criterion acoustic-reflex response. Acoustic impedance was measured as a function of activator SPL for broadband noise and a 1000-Hz tone from criterion magnitude to the maximum acoustic impedance (or 120-dB SPL). This was defined as the dynamic range of reflex growth. Loudness-balance measurements were made for the 1000-Hz tone and broadband noise at SPL's representing 30, 50, and 70% of the individual dynamic range. The data supported the hypothesis.