Tuning of single fibers in the cochlear nerve of the alligator lizard: relation to receptor morphology.

(1) The general anatomy of the peripheral portion of the cochlear nerve in the alligator lizard is described. (2) Spike discharges of single units were recorded with micropipets placed in the peripheral portion of the cochlear nerve of anesthetized lizards. (3) In response to tone bursts, each unit is maximally sensitive to a charactertistic frequency (CF). There are two distinct populations of units having different CFs: a low CF population (CF in the range 0.2-0.8 kHz) recorded in the portion of the nerve that enters the apical region of the basilar papilla and a high CF population (CF in the range 0.9-4.0 kHz) recorded in the portion of the nerve that enters the basal region. The low CF units are more sharply tuned than the high CF units. (4) Comparison of cochlear nerve units of the alligator lizard with those of mammals shows that the tuning of low CF units resembles that of mammalian units of the same CF. The tuning of high CF lizard units differs significantly from mammalian units. (5) The distinct differences in tuning of low and high CF units are correlated with distinct differences in the structure of the basilar papilla in the apical and basal regions rather than with differences in the width of the basilar membrane.

Neuro-ophthalmic sarcoidosis.

Sarcoidosis is a multisystem disorder in which ocular involvement occurs in about one-quarter and neurosarcoidosis in 7 per cent of patients. When the retina is involved, the reported incidence of central nervous system sarcoidosis is 37 per cent. The patient described had a transient papular eruption of the legs, bilateral hilar lymphadenopathy, polyarthralgia with knee effusions, and bilateral facial and peripheral neuropathy. Ocular involvement was characterized by anterior uveitis (in the initial stages), vitreous flare, bilateral disc oedema, macular oedema, streak haemorrhages, peripheral periphlebitis, nerve fibre bundle defects, and candle-wax spots. Fluorescein angiography showed no fluorescence of the candle-wax spots nor of the adjacent vessels. However, there was hyperfluorescence of two retinal lesions. This patient had unilateral internal ophthalmoplegia, only three cases of which have been reported in the literature. Her health was restored by heavy, prolonged corticosteroid therapy. Her family history revealed that an uncle died of sarcoidosis complicated by cryptococcal meningitis. The literature on retinopathy in sarcoidosis is reviewed and the lesions noted in the posterior segment are listed.

Neural tuning in the granite spiny lizard.

Scanning electron microscopy was used to examine the basilar papilla of the granite spiny lizard. The papilla contains three distinct hair cell populations: an apical and a basal population with free-standing cilia, and a central population with a tectorial membrane. In the free-standing populations, stereocilium length decreases towards the ends of the papilla. Ciliary tuft morphology differs in the free-standing and the tectorial membrane populations, except that several of the free-standing hair cells with the shortest stereocilia have a tuft morphology like the hair cells in the tectorial membrane population. On the basis of single-fiber physiology, auditory nerve fibers can be divided into a low characteristic frequency (CF) and a high CF population. Mappings of the tonotopic organization of the nerve demonstrated two groups of high CF fibers that correspond to the two free-standing hair cell populations. The low CF fibers are associated with the tectorial membrane hair cell population. Fiber CF correlated with hair cell cilium length, not position on basilar membrane, for hair cells with free-standing cilia. Tonotopic organization of high CF fibers could be predicted reasonably well from the histogram of fiber CFs.

Factors that determine the cost and performance of early identification protocols.

In this paper, a simple model is used to examine the relation between important factors, such as prevalence of hearing loss, and protocol performance and cost. Protocol hit rate is determined primarily by the hit rate of the screening protocol and follow-up percentage, the percentage of infants who return for diagnostic testing. Many factors influence protocol cost. Not only does absolute cost change as certain model parameters are varied, but the relative cost of different protocols can change as well. The false alarm rate of the screening protocol and the follow-up percentage have the greatest impact on protocol cost.

Modeling the cost and performance of early identification protocols.

This is the first in a series of three papers concerned with the early identification of hearing loss. In this paper, a simple model is presented that permits the calculation of the performance and cost of early identification protocols. In the second paper (Turner, in press), this model is used to compare four early identification protocols that differ in hearing screening strategies. The third paper (Turner, in press) examines the factors that influence the early identification protocol. The model described in this paper is sufficiently general to accommodate most early identification strategies including those that meet the goal of identification and habilitation by 6 months. The model measures protocol performance using hit rate, false alarm rate, and selected posterior probabilities. The model also calculates two measures of the financial cost. One measure reflects the cost of implementing the protocol; the other reflects the cost-effectiveness of the protocol. The parameters required by the model are also specified and are based on published clinical data. The model is provided to help audiologists design and select early identification protocols that are optimum for their particular clinical situation.

Comparison of four hearing screening protocols.

This is the second in a series of three papers concerned with the early identification of hearing loss. In the first paper (Turner, 1991), a simple model that permits the calculation of the performance and cost of early identification protocols is presented. In this paper, the model is used to compare four protocols that differ only in their hearing screening strategies. The high-risk register and auditory brainstem response screening are used to construct the four screening protocols. The cost and performance of the four early identification protocols are calculated using base model parameters derived from the clinical literature. The protocols are evaluated separately for the intensive care nursery and the well-baby nursery.

Comparison of self-report and performance measures of attention.

The attentional scales of the Test of Attentional and Interpersonal Style were correlated with performance measures of attention, the Digit Span and Block Design subtests of the WAIS. Of the 24 correlations computed only one was statistically significant. The need for the construct validity of these scales to be established against some behavioral measure of attentional focus was emphasized.

Techniques to determine test protocol performance.

This paper considers the problem of determining the performance of test protocols, i.e., combinations of diagnostic tests. Two techniques are developed which provide quantitative measures of performance. First, protocol performance can be calculated from clinical data. This technique is simple and straightforward. The primary limitation is that the necessary clinical data may not be available. A second technique is developed to predict protocol performance based on (1) protocol design, (2) individual test performance, and (3) test correlation. This second technique is applied to two types of audiological protocols: those to determine retrocochlear site-of-lesion, and those to identify hearing loss in newborns. Both techniques provide information essential to the design and selection of test protocols. The ability to predict performance is extremely important because clinical studies to evaluate protocols can take years to complete, or may be impractical.

Recommended guidelines for infant hearing screening: analysis.

This paper has identified problems with the guidelines and the disadvantages of the ASHA protocol. Some of these are significant. Others are less important but represent issues that should be considered when designing an EID protocol. The problems and disadvantages are summarized below. 1. The guidelines should have estimated and cost and performance of the recommended protocol. 2. The guidelines should have identified the true advantage of ABR screening (lower cost) and the disadvantage (lower hit rate) as compared to other protocols. 3. The guidelines should have evaluated other possible protocols. 4. The guidelines recommended the same protocol for all facilities (with adequate resources) independent of local factors. 5. The guidelines recommended the same screening strategy for the ICN and the WBN when different protocols may be appropriate. 6. The guidelines reject ABR screening of all WBN infants as too expensive without estimates of cost. More importantly, this is a decision that should be made by local institutions or governments. 7. The screening protocol was developed without a detailed description of the diagnostic component of the EID protocol. 8. The guidelines should have provided more information to hospitals that do not have the resources necessary to implement the recommended protocol. 9. The recommended protocol requires significant in-patient testing that can cause problems with reimbursement. 10. Some infants at risk for progressive loss can be lost from follow-up. Apparently, the guidelines were developed using a subjective, experiential approach. Although clinical experience is important, subjective impressions can be subject to bias and error. Some type of quantitative analysis is essential when developing test protocols. Perhaps a more rigorous theoretical foundation is needed to focus research and guide the development of EID protocols. The ASHA protocol is reasonable, but there is little evidence indicating that it is superior to, or even as good as, other possible protocols. Like all protocols, it has advantages and disadvantages. That is not to say that all possible protocols are appropriate. For example, protocols that delay diagnostic testing beyond 6 months should be rejected if the goal is habilitation by 6 months. Protocols that use screening tests with extremely poor hit rates may be undesirable in most situations. There remains one fundamental question. Is it even appropriate to recommend a particular protocol when, by necessity, many important local factors must be ignored? Perhaps it would be better to provide the basic data and techniques that would permit audiologists to design EID protocols that are optimum for their own circumstances.