Lecture Four Origin and effects of hearing loss

Lecture Four – Origin and effects of hearing loss A closer look at the anatomy of the middle and inner ear systems. Details of the haircells. Conductive Main problem is during development otitis media (glue ear) Ways in which specific hearing disorders affect speech and what can be done about the ensuing problems Relatively mild – otitis media More severe (operations to treat destroyed parts of the hearing system) – cochlear implants Otitis media (OM) Definition OM is an infectious disease that is a result of the interplay between microbial load (viral and bacterial) and immune response. Microbial infection arises when pathogens in the nasopharyngeal region enter into the middle ear system through the Eustachian tube. Entry of these pathogens into the middle ear is common in childhood because children‟s Eustachian tubes are short, floppy, horizontal and function poorly (Bluestone, 1996: Bluestone, 1999). OM varies in acuity from simple OM, through OM with effusion from the middle ear (OME) to acute OM (AOM). AOM, like OME, has middle ear effusions but also has signs or symptoms of inflammation in the middle ear (e.g. fever or irritability) (Rovers, Schilderm, Zielhuis & Rosenfield, 2004). Otitis media (OM) Host and environment risk factors Risk factors can be broadly distinguished that derive from the host and the environment. Host The immune system‟s response is one host factor (Rovers et al., 2004). Others (also associated with stuttering), are age (Zielhuis, Rach, van den Bosch & van den Broek, 1990) and genetic predisposition (Kvaerner, Harris, Tambs & Magnus, 1997; Rovers, Haggard, Gannon, Koeppen-Schnomerus & Plomin, 2002). DS as a host factor (return to later) Environment The environment the child experiences affects contagion and progress of the disease by increasing microbial load. Environmental factors that have this effect include whether the child has siblings (usually older), whether the child attends a day-care group and season of the year (Rovers et al., 2004). Otitis media (OM) Assessment, pure tone audiometry not designed to detect OM. Tympanometry is the appropriate procedure (Brooks, 1968). Treatment Treatments usually involve antibiotics or tympanostomy tubes (ventilation tubes inserted through the tympanic membrane) though these only have moderate efficacy (Rovers et al., 2004). A drawback to treatment with antibiotics is that resistance can build up (a particular problem with DS children). Based on what has been said so far, there appears to be little to recommend antibiotic or surgical treatment. Offset against this, OM can lead to hearing loss and concomitant problems in language development (as well as associated behavioral problems) (see Roberts, Hunter, Gravel, Rosenfield, Berman, Haggard, Hall, Lannon, Moore, Vernon-Feagans & Wallace, 2004 for a recent review of work on both these topics). The high rate of spontaneous recovery from OM during childhood suggests that OM is an epiphenomenon associated with the normal course of development of the immune system (Rovers et al., 2004). Otitis media (OM) Treatment of OME and effect on speech: Typanostomy tube reduces OME prevalence by 115 days per child year which represents as 67% relative risk reduction . Otitis media (OM) Roberts et al. (2004). “Conductive hearing loss secondary to OME reduces sound intensity, delays sound passing through the middle ear and often results in asymmetrical hearing levels for the right and left ears.” How it affects hearing - Stephenson et al. (1993) “interaural fluctuations occurring over a prolonged period could give rise to development of abnormal ratios of ipsi- and contra-lateral connections required for binaural hearing.” Sensorineural: OME induces (simulated in animals by plugging the ear) leads to neural changes. Poor performance on central hearing tests with animals and children with OME. Prolongation and asymmetry of ABR waveforms suggesting lateral asymmetries and poor binaural interaction in children with OME. Children with retrospectively documented prolonged OME history had poorer MLDs before and after tympanostomy tubes (consistent with long-term central auditory changes). Resolve slowly after surgery. Cochlear implants and speech development (sensori-neural) Overview If the view is taken that the development of speech is extremely limited without adequate auditory input and feedback, then auditory input ought to be encouraged whenever possible. One way this can be done is by giving a child a cochlear implant. This does not „restore hearing‟ but does give a child the sense of sound input and this can be tailored to be effective for communication. Cochlear implants and speech development (sensori-neural) How is speech development affected in hearing impaired children Fluent children Babbling begins around 5-6 months of age. Verbal expression starts around 12 months of age. Speech production skills continue to be refined through the school-age years and beyond. E.g. vowel space, voice-onset times, and vocal control adjust throughout early childhood (Assmann & Katz, 2000; Koenig, 2001; Lee, Pontamianos, & Narayanan, 1999). Evidence for development of coarticulation, literature is not definitive. Children appear to be less able than adults to coarticulate their speech gestures in a consistent manner, and as a consequence, their speech is less intelligible than that of adults (Katz, Kripke, & Tallal, 1991; Nittrouer, 1993). Auditory processing of speech also appears to be more susceptible to acoustic and linguistic perturbations than is observed with adults. Children are more adversely affected than adults by background noise, reverberation, talker variability, reductions in signal bandwidth, and the number of signal channels (Eisenberg et al., 2000; Ryalls & Pisoni, 1997; Kortekaas & Stelmachowicz, 2000). Cochlear implants and speech development (sensori-neural) Hearing Loss and Speech Production Hearing loss is most pronounced with individuals whose hearing loss is congenital or acquired in early childhood. Most adults who acquire their hearing losses later in life suffer little or no deterioration in intelligibility, likely because their residual hearing provides sufficient feedback since their mature speech production systems rely more on orosensory than auditory information to maintain proper control (Guenther, 1995; Goehl & Kaufman, 1984; Perkell et al., 1997). Some adventitiously deafened adults exhibit reduced speaking rate, and compromised articulatory and phonatory precision (Kishon-Rabin et al., 1999; Lane & Webster, 1991; Lane et al., 1995; Leder et al., 1987; Perkell et al., 1992; Waldstein, 1990). These speech differences are similar in nature, but not in severity, to those observed with prelingually deafened speakers. Cochlear implants and speech development (sensori-neural) Hearing Loss and Speech Production (cont.) Most infants and young children with hearing loss demonstrate disordered phonation and articulation, as well as delays in the acquisition of sound categories. The entire speech production system can be affected, from respiratory support to the coarticulation of ongoing speech (Pratt & Tye-Murray, 1997). More marked if the hearing loss is identified late or after a period of protracted hearing loss. Babbling generally does not appear before 12 months of age (Oller et al., 1985). Infants include a more limited range of consonants in their babble (StoelGammon, 1988; Stoel-Gammon & Otomo, 1986; Wallace, et al., 2000). The phonetic repertoires of infants with severe-to-profound hearing loss often are restricted Cochlear implants and speech development (sensori-neural) Hearing Loss and Speech Production (cont.) The early speech inventories of infants with severe-to-profound hearing loss predominately consist of motorically easy sounds such as vowels and bilabial consonants. The sounds of their inventories also contain more low frequency information, which is more audible. For example, the babbling of infants with hearing loss often has a high concentration of nasals and glides, which include low-frequency continuant cues (Stoel-Gammon & Otomo, 1986). Sensory aids have a substantial impact on speech outcomes, butthe age at which infants and young children are fitted with cochlear implants has not surfaced in studies of speech production as a significant predictor of later speech intelligibility (Geers et al., 2002; Tobey et al., 2003). Early implantation (less than 2 years) is, however, related to more normal oral communication development as a whole (both speech and oral language). Cochlear implants and speech development (sensori-neural) Sensory Aids in Treatment Cochlear implants have a positive impact on speech development (Geers et al., 2002; Tobey et al., 2003). Augmenting the communication channel Cochlear implants and hearing aids are one way of doing this Speaker effects Speakers who are hard of hearing report being able to understand males better than females. Why might this be so? Females have higher voice pitch and this leads to poorer registration of the formants Speaking clearly for the hearing impaired leads to roughly 10% improved word recognition scores (Picheny Durlach and Braida, 1986).