This paper describes a procedure for measuring hearing sensitivity in 2 to 4 year-old children. Children are trained to perform play-based responses when they hear a target signal. Thresholds are then estimated in a two-interval, two-alternative forced-choice paradigm, based on observations of the child's behaviors.
Collecting reliable behavioral data from toddlers and preschoolers is challenging. As a result, there are significant gaps in our understanding of human auditory development for these age groups. This paper describes an observer-based procedure for measuring hearing sensitivity with a two-interval, two-alternative forced-choice paradigm. Young children are trained to perform a play-based, motor response (e.g., putting a block in a bucket) whenever they hear a target signal. An experimenter observes the child's behavior and makes a judgment about whether the signal was presented during the first or second observation interval; the experimenter is blinded to the true signal interval, so this judgment is based solely on the child's behavior. These procedures were used to test 2 to 4 year-olds (n = 33) with no known hearing problems. The signal was a 1,000 Hz warble tone presented in quiet, and the signal level was adjusted to estimate a threshold corresponding to 71%-correct detection. A valid threshold was obtained for 82% of children. These results indicate that the two-interval procedure is both feasible and reliable for use with toddlers and preschoolers. The two-interval, observer-based procedure described in this paper is a powerful tool for evaluating hearing in young children because it guards against response bias on the part of the experimenter.
It is difficult to obtain reliable estimates of behavioral hearing thresholds for toddlers and preschoolers. The operant techniques used to test infants in the clinic and the laboratory do not generally work well with children in this age range because toddlers and preschoolers tend to habituate faster than infants1,2. On the other hand, toddlers and preschoolers often lack the cognitive maturity required to complete standard forced-choice behavioral testing procedures that are used to evaluate children 4 years of age and older3,4. Consequently, there are significant gaps in our understanding of human auditory development between infancy and early school age.
A single-interval, adaptive procedure called Conditioned Play Audiometry5 (CPA) is routinely used in the audiology clinic to assess hearing sensitivity for children with a developmental age falling between about 2.5 and 5 years6. CPA relies on the use of a play-based motor activity (e.g., stacking blocks) to establish a time-locked conditioned response to an auditory signal. A test assistant provides the child with positive social reinforcement, further shaping the response behavior. Results from several studies have shown that the use of CPA yields a conventional clinical audiogram for more than 90% of typically developing 3 year-olds7,8. Substantially lower yield rates have been reported for younger children. For example, Thompson et al.9 reported that a conditioned response to sound could be established using CPA in 68% of 2 year-olds.
Despite the widespread use of CPA in the audiology clinic, it is not well suited for most laboratory-based investigations of auditory behavior. CPA is a single-interval adaptive procedure designed to maximize both efficiency and patient acceptance, but it is susceptible to observer and listener response bias. The observer in the CPA procedure initiates signal presentations, and may thus be influenced by factors such as a priori expectations regarding the child's hearing sensitivity or their propensity to respond10. The inclusion of "catch" trials – trials in which no sound is presented – is sometimes used to quantify and accommodate examiner response bias11.
The overall goal of the method described in the present report is to efficiently estimate hearing thresholds in toddlers and preschoolers using a play-based, two-interval, forced-choice behavioral testing procedure. The rationale for using a forced-choice paradigm is that it guards against some forms of response bias10, thus permitting more direct comparisons across different ages and/or stimuli using an efficient adaptive procedure. Conventional two- and three-interval, forced-choice methods require a specific, prescribed response (e.g., pushing one of several buttons) on the part of the listener, to indicate which interval contains the signal. Children as young as 4 to 5 years of age can perform this task12, but the demands of the procedure make these methods unsuitable for younger listeners and for many listeners with developmental delays.
The method described here builds on the work of Browning et al.13, which evaluated the feasibility and efficiency of estimating infant behavioral thresholds using a two-interval, forced-choice adaptation of the observer-based psychophysical procedure14. In this method, the signal is presented during one of two observation intervals. Each interval is indicated to the observer in real time both visually and acoustically, but the observer is not told which interval contains the signal. The infant, on the other hand, is not given any indication of the occurrence of an observation interval apart from the presentation of a signal. After each trial, the observer selects the interval containing the signal based on the infant's behavior. The results reported by Browning et al.13 demonstrated that this procedure is both feasible and efficient for use with 7 to 9 month-old infants. The method for testing toddlers and preschoolers closely follows procedures for testing infants, with the caveat that children's responses to sound are shaped using methods common with CPA.
For this article, a simple experiment was designed to measure children's tone detection in quiet. The signal was a 500 msec, 1,000 Hz warble tone presented through an insert earphone. Note that we have also successfully used this protocol to assess performance in more complex listening tasks, such as speech detection in a noise masker15. In the protocol described below, children are taught to perform a play-based conditioned motor response when a signal is heard. However, any behavioral response can be used, provided it is time-locked to the presentation of the stimulus and can be reliably judged. As demonstrated here, this task is appropriate for testing typically developing children as young as 2 years of age.
The Institutional Review Board at The University of North Carolina at Chapel Hill approved this research.
1. Personnel and Space Requirements
Figure 1: Test environment. The assistant and the listener are seated at a table inside the sound booth. The child's parent may elect to sit inside or outside the booth. The observer sits outside the booth, positioned in front of the window for good visibility of the assistant and the child. The computer screen and keyboard controlling the run-time computer are accessible to the observer, allowing him/her to initiate trials and enter responses. Please click here to view a larger version of this figure.
2. Hardware and Software Configuration
3. Data Collection
4. Data Analysis
Thirty-three children were recruited from a database of children who are typically-developing, based on parental report. Inclusion criteria included no known history of hearing loss, no more than three episodes of otitis media, and no episodes of otitis media in the month prior to testing. Eight 2 year-olds, eighteen 3 year-olds, and seven 4 year-olds met these inclusion criteria. Of the children recruited, three would not tolerate the insert earphone and testing was not attempted.
Of the remaining 30 children, all but one child (a 2 year-old) successfully completed both training stages (Stage 1 and Stage 2). On average, children required 4.8 trials (SD = 2.4; max = 12) in Stage 1 and 4.1 trials (SD = 0.3; max = 5) in Stage 2. Two 2 year-olds and one 3 year-old were only able to complete training during the first visit; two of these children returned for a second visit and successfully completed Stage 3. All remaining children completed the protocol in a single session. On average, children required 40.0 trials to complete Stage 3 (SD = 7.9; min = 27; max = 57). All 28 children who completed Stage 3 of testing met the probe rate criterion of ≥0.80; all probe signal trials were correctly identified in 75% of testing sessions. Only one child's data were excluded based on excessive variability; in this case, the standard deviation of reversal values exceeded the criterion of 4.4 dB.
Figure 2 shows individual children's thresholds as a function of age. Thresholds for all children with normal middle ear functioning, based on tympanometry on the day of testing, are shown by the open circles. Six additional children (21%) had abnormal tympanograms, indicating possible middle ear dysfunction (e.g., middle ear fluid). Data shown with filled symbols indicate abnormal middle ear function based on tympanometry: reduced compliance (Type B; square) or excessive negative pressure (Type C; triangle). One additional child would not tolerate the test procedure for screening tympanometry, so his middle ear status is unknown (diamond). Interpret threshold values from children with abnormal middle ear function cautiously because abnormal middle ear status is associated with elevated thresholds19. Thresholds obtained from children are broadly consistent with previous data on this age group. For example, Schneider at al.20 estimated psychometric functions for detecting an octave-wide band of noise at 1,000 Hz in preschoolers. Defining threshold as the level associated with 65% correct, the mean threshold was approximately 21 dB SPL for 3 year-olds and 14 dB SPL for 4 year-olds.
Figure 2: Warble-tone detection thresholds. Detection thresholds are plotted as a function of child age. Only the first threshold obtained from each listener is shown. Symbol shape reflects the middle ear status of the listener: Type A (circle), Type B (square), Type C (triangle), or could not test (CNT; diamond). Whereas Type A indicates normal middle ear admittance, Type B (flat) and Type C (negative pressure) are typically associated with reduced middle ear function due to fluid, congestion, or ear infection. Please click here to view a larger version of this figure.
Thresholds were also measured for a group of young adults with normal hearing sensitivity and middle ear status on the day of testing (n = 8; 20-25 years). Due to procedural modifications between the two age groups, caution is warranted when comparing the child and adult data. The primary protocol difference between the two age groups was that an assistant inside of the booth was not present when testing adults. In contrast to children who were provided reinforcement through social engagement with the assistant, adults were provided only with trial-by-trial feedback through the activation of mechanical toys. Adults completed two consecutive adaptive tracks in a single testing session. However, only the threshold from the first adaptive track run was considered here. The mean adult threshold for the warble stimulus was 2.4 dB SPL (SD = 1.7 dB). In the present study, the group difference in threshold between adults and the 3 year-olds, with normal middle ear function, was 7.2 dB. This observed child-adult difference is smaller than has been reported in some studies20. However, the magnitude of the child-adult difference is likely influenced by both the overall procedure and any procedural modifications implemented between children and adults. Further research is needed to better understand how children's and adults' sensitivity to the stimulus is affected by modifications to the two-interval, observer-based procedure described in this paper.
This paper described a two-interval, forced-choice behavioral procedure for measuring hearing abilities in 2 to 4 year old children. In this procedure, an observer judges whether the signal is presented in interval 1 or interval 2 based solely on the listener's behavior. Children's behavior is shaped to be time-locked to the presentation of the signal by training them to perform a play-based response to the sound. Our preliminary results indicate this method is feasible and reliable for testing the hearing sensitivity of 2 to 4 year-olds.
Significance of the Procedure
There are several advantages associated with this method. The first advantage is that it can be used to test children as young as 2.0 years developmental age. Thresholds were successfully measured for 5 out of the 8 2-year-olds. A similar yield rate (~60-70%) has been reported in the literature for the measurement of hearing sensitivity in 2-year-olds using conditioned-play audiometry in the soundfield9,21. As with conditioned-play audiometry7,8, thresholds were successfully measured for all but one of the 3 year-olds, and all 4 year-olds. The second advantage of this method is that it guards against observer response bias. The observer must base his/her judgments solely on the child's behavior, so prior expectations regarding the child's sensitivity or behavior do not affect the results. The third advantage of this method is that it may be easier for the observer to judge which interval contains the signal than to make a yes-no decision regarding the presence or absence of a signal. In the present two-interval task, the observer is able to compare the child's behavior across the two intervals rather than comparing behavior across multiple trials, as is required in the single-interval task. Thus, the memory load on the observer may be smaller for the two-interval relative to the single-interval task. Moreover, looking for time-locked changes in behavior may allow the observer to adapt to changes in the child's behavior that occur during the testing session.
Limitations
There are a few limitations to consider when applying this method. First, pilot data are required to determine the appropriate parameters – training criteria, starting level, inter-stimulus interval value, and transducer – to use for different age groups and stimuli. In particular, adjusting testing parameters may affect the number of 2 year-olds who can successfully do the task and provide useable experimental data. Yield rate for 2 year-olds may be improved by presenting stimuli through the soundfield or headphones rather than an insert earphone. However, precautions must be taken when performing testing in the soundfield to prevent the assistant and parent from hearing the signal (see Leibold et al.22 for specifics.) A longer inter-stimulus interval may be required for younger children than for older children, if younger listeners take longer to complete the play-based response. Also, 2 year-olds may require greater training and may fatigue faster than older children. In order to guard against fatigue, it is recommended to change toys frequently9 and provide frequent breaks in testing. Recall that we tested three of the youngest children over two visits, rather than one. Second, it is not clear how much experience is required for observers and assistants to obtain reliable results using this procedure. In this example, all observers and assistants had at least two years of experience testing toddlers and preschoolers in the audiology clinic using play-based audiometry, as well as at least one additional year of experience in the laboratory testing infants and/or school-aged children. It is recommended to establish protocols for training new observers and to ensure consistent performance for trained observers. Further research is needed to determine the reliability of this method across observers and laboratories.
Future Applications
It may be possible to modify this procedure to test children who are unable to perform conventional motor responses. For example, the conditioned response could be an eye movement, head turn, or a change in activity level14. Previous work has shown that trained observers can reliably use these alternative behaviors to test infants as young as 1 month of age using a single-interval, observer-based method23. Furthermore, the single-interval, observer-based method has been used to measure hearing sensitivity in special populations, including 2 to 12 month-olds with Down Syndrome24 and 26 to 36 month-olds with cochlear implants25. Results from these previous studies support the feasibility of testing children who cannot produce a play-based, motor response with a two-interval paradigm.
Whereas the current study evaluated detection thresholds in quiet, this procedure can also be used to evaluate masked detection or discrimination. In the case of masking noise, previous studies of infants tested with the single-interval, observer-based procedure suggest that the masker be played continuously over the course of an adaptive track in order to avoid responses to masker onsets and/or offsets26. Similarly, to evaluate discrimination abilities, a standard sound is presented repeatedly apart from the signal interval, during which the signal stimulus would be presented27. For all stimulus conditions, the listener would be conditioned to respond when he/she detects a change in the stimulus, whether that change is the addition of a sound (detection) or a change in the sound (discrimination). While the current study used an adaptive procedure to estimate threshold, the same procedures could be used to evaluate percent correct performance at a fixed signal and/or masker level. Another possible modification is that the stimuli can be presented through other transducers, including the soundfield13,22.
In summary, the play-based, two-interval procedure described here provides reliable behavioral data on the hearing abilities of toddlers and preschoolers. Using this method, researchers will be able to study how the auditory system changes during the toddler and preschooler years – a time period where we know little about auditory behavior.
The authors have nothing to disclose.
Research reported in this publication was supported by the National Institute on Deafness and Other Communication Disorders of the National Institutes of Health under award number R01DC014460. Video production and editing was carried out by Robert Ladd and Barbara Rochen Renner of the Health Sciences Library at The University of North Carolina at Chapel Hill, with support from a National Library of Medicine of the National Institutes of Health Administrative Supplement for Informationist Services in NIH-funded Research Projects under award number R01DC011038. Children were recruited through the Research Participant Registries of the IDDRC at The University of North Carolina at Chapel Hill (NIH-NICHD award number U54HD079124). We appreciate Emily Buss’ comments on this procedure and a previous version of this article. The authors would also like to thank Steve Lockhart for programming support and members of the Human Auditory Development Laboratory for testing assistance: Jenna Browning, Lauren Charles, Nicole Corbin, Molly Drescher, Hannah Hodson McLean, Heather Porter and Dani Warmund. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
RZ6 auditory processor | Tucker-Davis Technologies (TDT) | ||
ER1 insert earphone | Etymotic Research | ||
IntellegentVRA mechanical toys and control box | Intelligent Hearing Systems | System modified by company to interfance with TDT system |