Auditory brainstem potentials: comments on their use during infant development.

Auditory perception neurons, also called inner hair cells (IHCs) because of their physical shape, transform the mechanical movements of the basilar membrane into electrical impulses. The impulse coding of the IHC is the main information carrier in the auditory process and is the basis for improvements in cochlear implants as well as for low-rate, high-quality speech processing and compression. This paper compares biologically motivated models (Meddis, Cooke, Payton) with a newly developed model which is transfer function oriented. The new model has only three reservoirs and the parameters can be controlled through five small ROM tables. This model is compared with the often used Meddis model in terms of accuracy, system parameter flexibility, and hardware effort in an FPGA implementation.

Auditory Pathways↗

PubMed1997

Axogenesis in the human fetal auditory system, demonstrated by neurofilament immunohistochemistry.

Morphological, electrophysiological and behavioral evidence indicates that the onset of rapid, synchronized conduction of auditory impulses occurs in the human brainstem during the 28th-29th fetal weeks. This implies that axonal connections in the brainstem auditory pathway are generated prior to this time. In order to investigate the sequence of axogenic events in the human brainstem pathway, we employed immunohistochemical techniques and an antibody to neurofilament protein. Immunostaining for axonal neurofilaments in an age-graded series of fetal brains demonstrates that a small number of cochlear nerve axons have invaded the ventral cochlear nucleus by the 16th fetal week. By this same time point, a limited number of trapezoid body-lateral lemniscus axons have reached the superior olivary complex and inferior colliculus. Between gestational weeks 16 and 26, there is marked expansion and collateralization of the ascending pathway from cochlear nerve to inferior colliculus. By week 26, ascending axons have begun to form plexuses of terminal neuropil within all of the brainstem auditory nuclei. Beginning in week 22, there is development of commissural axons (dorsal commissure of the lateral lemniscus and commissure of the inferior colliculus) and descending projections (descending collicular axons and olivocochlear bundle). This early establishment of a mature pattern of axonal connections presumably forms the basis for the appearance of myelin, acousticomotor reflexes and recordable brainstem responses by fetal week 29.

Auditory Pathways↗

PubMed1997

Simulation of human sensory performance.

The capacity of human sensory systems for transmitting information has been approximated in the past by using statistical estimators. However, a substantial margin of error remained. The problem is that the error can be reduced to a negligible level only by increasing the number of human trials or tests to the order of about 10(4). Since a human subject can perform at peak only in the order of 10(2) trials per day, the requisite total number of trials could be obtained realistically only by pooling of data from several subjects. Following Houtsma, we have overcome this problem to a large extent by the use of computer simulation. By introducing parameters characteristic of a given subject into the simulation program, we are able to reproduce the subject's performance (say for 500 trials), and to extrapolate his or her performance using the simulation program to 30000 trials. In this way we can establish limits to the capacity of a single human being to transmit information.

Auditory Pathways↗