The participants in this study were part of a larger group of children participating in a comprehensive study investigating auditory processing disorders. School-aged children were recruited from the London, Ontario and surrounding area by way of the letter of information that invited typically developing children and children with, or suspected as having, an auditory processing deficit to participate in a study of hearing and auditory processing (listening). The letter was provided to local schools and audiology clinics for distribution to families. Individuals who contacted the researchers after hearing about the study through other sources were provided with the letter of information and, if interested, also participated in the study. All participants were native English speakers. Because the participants were involved in a larger project the number, age range and gender of children varied across signal feature encoding study. A total of 59 children, 21 female and 38 male, ages 7.2 to 16.6 and 7.2 to 17.6 years respectively, participated in the studies. Some children may have completed more than one signal encoding study, depending on the date of entry and continuing participation in the project. Of the 59
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children enrolled, 12 completed all 5 of the signal feature encoding studies. Figure 1 displays the age and gender distribution for overall study participation. It shows that the male participants outnumber the females by a factor of two, reflecting the general
reports of referral demographics for auditory processing assessment in clinical settings (Keith, 2004). Anecdotal reports from typical audiology clinics and some prevalence reports (Chermak, 2002; Keith, 2004) suggest that a higher number of boys than girls are referred for auditory processing assessment and that children are referred at younger rather than older ages.
To be enrolled in the study the participants were required to demonstrate normal pure tone thresholds and middle ear function (ASHA 1988, 1997). During the hearing test, participants sat comfortably in an IAC double-walled sound isolation room (controlled acoustical environment) where pure tone thresholds for 250, 500, 1000, 2000, 4000 and 8000 Hz were obtained bilaterally, employing conventional test methods. The
Interacoustics AC40 Clinical Audiometer was used to obtain the hearing thresholds. Signals from the AC40 were routed through Etymotic Research EAR 5A insert
earphones coupled to the ear with sponge insert eartips. Participants sat comfortably in a quiet room adjacent to the sound isolation rooms for the assessment of middle ear
function. The Grason Stadler Tympstar diagnostic middle ear analyzer assessed middle ear function for both ears by obtaining tympanograms as well as ipsilateral and
contralateral acoustic reflexes at 500, 1000, and 2000 Hz. Following the hearing assessment children with normal hearing sensitivity were entered into the study. If a child was excluded from the study due to hearing loss and/or middle ear dysfunction, their parents were informed of their child’s hearing assessment results and they were referred to the appropriate community professionals for follow-up. Thresholds for individual listeners fell within the normal range. Hearing thresholds, averaged across the frequency range, for the group of 59 children were 2.89 dB HL with a standard deviation of 4.61 dB in the right ear and 4.24 dB HL with a standard deviation of 4.39 dB in the left ear.
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Figure 1 Age and gender distribution for all project participants.
0 2 4 6 8 10 12 14 7 8 9 10 to 11 12 to 17 N u m b e r o f P a rt ic ip a n ts Age in Years Boys Girls
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The cognitive, academic and language abilities of the participants were assessed as part of the larger project. One participant did not undergo assessment in these areas. Standard scores were obtained for 58 participants on the Peabody Picture Vocabulary Test (Dunn & Dunn, 1997) (PPVT), the Oral and Written Language Scales (Carrow- Woolfolk, 1996) (OWLS), the Wide Range Achievement Test (Wilkinson, 1993) (WRAT), and the Wechsler Abbreviated Scales of Intelligence (Wechsler, 1999) (WASI). The average standard score (standard deviation) on the PPVT, a test of receptive vocabulary, was 101.66 (14.52), revealing that the group had age appropriate receptive vocabulary abilities. The WRAT Reading and Arithmetic average standard test scores (standard deviation) were 87.91 (16.33) and 87.90 (15.06) respectively. The scores reflect the lower than average academic performance of this group of children. The average WASI Full Scale IQ standard score (standard deviation) for the group of children was 99.62 (15.81) showing that the children participating in this study have intelligence scores within the normal range. The mean standard scores (standard deviation) for the OWLS Comprehension and Oral Expression tests were 90.74 (13.53) and 91.03 (13.29) respectively for the group of participants. These results show that the receptive and expressive language abilities for this sample of children fall within the normal range.
As would be expected in a clinical population of children referred for auditory
processing assessment, the children participating in this study were experiencing some level of academic failure. The children had either been identified as having an auditory processing deficit (determined by a community audiologist using a typical clinical test battery) or, as in most cases, concern was being expressed by teachers and/or parents about the participant’s auditory skills and their ability to listen in a classroom setting. The reported auditory difficulties experienced by the participants were representative of referrals to community clinics for assessment of auditory processing abilities and for this reason qualified the group as a typical clinical population.
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