There has recently been a renewed interest in the topic of minimal and mild hearing loss in children. Although the term minimal hearing loss has not been standardized, the Bess, Dodd-Murphy, and Parker (1998) definitions are commonly used and include:
Mild bilateral hearing loss - pure tone average at .5, 1.0, and 2.0 kHz between 20 and 40 dB hearing level (HL);
High-frequency hearing loss - pure tone thresholds worse than 20 dB HL at two or more frequencies above 2.0 kHz;
Unilateral hearing loss - pure tone average at .5, 1.0, and 2.0 kHz worse than or equal to 20 dB HL or pure tone thresholds worse than 25 dB HL at two or more frequencies above 2 kHz in the affected ear, with normal hearing in the contralateral ear.
For purposes of this review, only permanent, not transient, hearing loss is considered.
Prieve et al. (2000) reported 1 in 1000 infants are identified with unilateral hearing loss (UHL) as a newborn; whereas, Bess et al. (1998) reported 3 in 100 school-aged children have UHL. This difference in prevalence rates of UHL between the newborn and school-age periods may reflect poor follow-up rates from newborn screening programs resulting in fewer confirmed hearing losses, different screening criteria and definitions among hospitals and schools, progression of a mild hearing impairment, a late-onset hearing loss, or a combination of these factors. In any case, UHL is the most prevalent configuration of permanent hearing loss in school-aged children (Bess et al., 1998). When considering all configurations of permanent minimal and mild bilateral hearing loss (MBHL), as well as UHL, the prevalence increases to 5.4% of school-aged children.
Academic, Social, and Behavioral Outcomes
Unilateral hearing loss. Two decades ago, a flurry of research was conducted examining the effects of UHL on children (Bess & Tharpe, 1986; Bess, Tharpe, & Gibler, 1986; Bovo et al., 1988; Culbertson & Gilbert, 1986; Jensen, BØrre, & Johansen, 1989; Keller & Bundy, 1980; Klee & Davis-Dansky, 1986; Oyler, Oyler, & Matkin, 1988; Stein, 1983). Researchers at Vanderbilt University examined a cohort of 60 school-aged children with UHL (Bess & Tharpe, 1986). Most of their hearing losses were identified at five or six years of age upon school entry with some identified as late as 12 years of age. Interestingly, approximately 37% of these children failed at least one grade in school, and an additional 13% required academic assistance or resource help. This grade failure rate was 10 times that of the general school population for that geographic area. Also of interest was that the majority (62%) of the children who failed a grade had hearing loss in the right ear. In addition, children were at a higher risk for academic difficulty if the hearing loss was of a severe degree when compared to those children with lesser degrees of loss.
Upon closer examination of 25 of the original cohort of 60 children, Bess et al. (1986) found that children with UHL had more difficulty with speech understanding in the presence of background noise than their matched peers with normal hearing. Furthermore, even when the desired speech stimuli were directed toward the children's better ear in quiet conditions, the children with UHL still performed more poorly than their normal-hearing peers. Twenty percent of the children with UHL were also reported to have more behavior problems than their peers with normal hearing (Bess & Tharpe, 1986).
Currently, newborn hearing screenings accommodate earlier identification of UHL, and a growing number of individuals in the hearing health care and education settings are more aware of the risk for academic difficulties experienced by these children. One might expect that outcomes would improve over time; however, recent examination of the status of school-aged children with UHL suggested that 30-55% are still having academic difficulty (Brookhauser, Worthington, & Kelly, 1991; English & Church, 1999), regardless of the fact that it appears more of these children are receiving intervention than ever before (McKay, 2002; Reeve, Davis, & Hind, 2001).