Clinical Assessment of Speech Perception for Infants and Toddlers

Introduction

Early onset of hearing loss can impose substantial delays in communication and psychosocial development unless immediate and appropriate intervention is undertaken. The most obvious consequence of prelingual hearing loss is a decrease in the access to sound. Without maximal audibility, higher centers of auditory processing may receive stimuli devoid of important phonemic cues that contribute to speech understanding and language development. Even with optimum audibility, distortion of input may further affect recognition and comprehension. Development of spoken language for children with hearing loss requires the fitting of a sensory device followed by a well-designed habilitation program. The goal of prosthetic intervention is to maximize auditory capacity, thereby providing the sensory evidence necessary to perceive the acoustic cues of speech. We now have the tools to identify hearing loss at birth and to fit sensory devices soon thereafter. However, we are limited in the standardized behavioral tests required to assess auditory perceptual performance, particularly in babies from birth to 3 years of age.

The information required to assess higher level auditory processing and to appraise intervention outcomes depends, to a large extent, on speech perception data. According to Boothroyd (1991), speech perception is "the process by which a perceiver internally generates linguistic structures believed to correspond with those generated by a talker. (p.78)." Assessment of speech perception in the pediatric population is important for several reasons. First, results on speech perception measures help determine whether a child is benefiting from a hearing aid or should be considered for a cochlear implant. Although cochlear implants are approved for children 12 months of age and older, there is a growing trend in the United States to implant children under the age of 12 months (Luxford, Eisenberg, Johnson, & Mahnke, 2004), underscoring the need for measures that can be used with infants. Second, speech perception measures are important for comparing differences between sensory devices and/or processing algorithms. Third, follow-up assessments help track performance over time. Lastly, speech perception data in combination with speech and language outcomes are essential for establishing guidelines for habilitation.

In this overview, we highlight some of the important issues involved in speech perception assessment of hearing-impaired children with an emphasis on tests designed for children 3 years of age and younger. Illustrative cases are presented using several of these measures, including data from new implementations of established assessment techniques being developed at the House Ear Institute.

Considerations in Speech Perception Assessment

A number of important factors must be taken into consideration when assessing speech perception in children. These include a combination of child, task, tester, and environmental influences on test outcomes (Boothroyd, 2004). Child factors include the state of the child during testing, such as their attentiveness to the task. Moreover, children must demonstrate the requisite motor skills to perform the response task being asked of them (e.g., head turn, manipulation of objects, picture pointing, pushing a button), as well as the phonological, receptive and expressive language skills needed to participate in speech perception testing. Tester and environmental factors include the audiologist's aptitude to work with the pediatric hearing-impaired population, the general feel of the facility, and caregiver attitudes and behaviors.

Of those listed above, the task factors probably require the greatest consideration due to influences of maturation and language on test outcomes. A battery approach is needed to accommodate children of different ages (both chronological and linguistic), communication modes (oral vs. sign language), and auditory processing skills. For that reason, assessment batteries should include measures that vary from closed-set to open-set response formats, from live voice to recorded presentation, and from auditory-visual to auditory-only administration. In closed-set tasks, a limited number of choices are available to the listener. Words and nonsense syllables typically comprise the stimuli for these speech discrimination (two-alternative) or identification (multiple-choice) tasks. Phoneme identification tests are particularly useful for obtaining information about speech features (voicing, manner, and place) and do not rely on higher-level cognitive/linguistic processing, such as lexical, syntactic, and semantic knowledge. In contrast, there are no pre-defined response alternatives in open-set tasks, resulting in an unlimited number of choices. Open-set word and sentence recognition tests require higher-level cognitive/linguistic abilities than closed-set tasks and are more representative of real-life listening situations.

Assessing speech understanding in the presence of competition or background noise also expands the options used in speech perception testingas does testing under multimodal conditions (auditory-only, visual-only, and auditory-visual). With regard to the type of administration, live-voice affords the clinician greater efficiency and flexibility than the use of recorded stimuli, particularly when working with very young children. However, inter-talker variability makes it difficult to compare results obtained with live voice across different clinicians, let alone pediatric centers. Use of recorded stimuli provides for greater consistency in signal delivery across test sessions and test centers.