Results from behavioral studies provide compelling evidence of large differences between infants and school-aged children on a variety of auditory skills (Buss, et al. In: Werner, Fay & Popper, eds. Springer, 2012). Converging data from electrophysiology and neuroimaging studies also indicate that significant changes in neural maturation and cortical organization occur between infancy and early school-age years (Eggermont, et al. In: Werner, Fay & Popper, eds. Springer, 2012). While these differences in auditory functioning are clear, how and when this process unfolds during the intervening years remain unknown. This gap in knowledge prevents us from having a comprehensive model of auditory development, and limits our ability to clinically manage toddlers and preschoolers with hearing loss.
The primary reason for this knowledge gap is that it is challenging to obtain reliable estimates of hearing for toddlers and preschoolers with rigorous psychophysical methods. One strategy that researchers have used is employing operant conditioning techniques that were originally developed to assess hearing in infants. However, toddlers and preschoolers tend to habituate faster than infants on these tasks. Another strategy is modifying forced-choice paradigms used for school-aged children. However, children often lack the cognitive maturity required to complete these paradigms.
In contrast to the limited success obtained by researchers with laboratory procedures, audiologists routinely obtain thresholds from 2- to 5-year-olds in the clinic with Conditioned Play Audiometry (CPA). In this task, the child is trained to respond to an auditory stimulus with a time-locked, play-based motor response (e.g., putting a peg into a board). However, CPA is susceptible to observer and listener response bias, making it difficult to compare thresholds across listener age groups and stimulus conditions. Thus, CPA is not well-suited for studies of auditory behavior.
One method that does control for bias is the observer-based psychophysical procedure used for testing infants (Dev Psychol. 1987;23:627). In this method, the experimenter judges the infant's behavior to determine whether a signal or no-signal trial has occurred. The observer-based procedure was adapted from a single- to a two-interval, forced-choice procedure (J Acoust Soc Am. 2014;136:EL236). Each trial contains two observation intervals in which the signal is randomly presented. Based on the infant's behavior, the observer must decide which interval contained the signal. Results indicated that a two-interval procedure is feasible and efficient for testing infants.
Building upon the work of Browning, et al., we adapted the two-interval, forced-choice procedure to evaluate its feasibility for measuring hearing in 2- to 4-year-olds (J Vis Exp. 2017; :54788). This method, called Play Observer-based, 2-Interval (PlayO2I), combines the psychometric rigor of the observer-based, two-interval procedure with the response method and behavioral-shaping strategies used in CPA (watch online video: http://bit.ly/2xF2Ot1). Although children are trained to perform a play-based and conditioned motor response when a signal is heard, the observer can use any consistent behavioral response that is time-locked with the presentation of the signal (e.g., eye movements). Our new method enables threshold collection while guarding against some forms of bias. It's also feasible for most 2- to 4-year-old children.