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Objectives Wideband acoustic transfer functions (WATF) measured in the ear canal have been shown to be effective in the diagnosis of middle ear dysfunction in adults and in newborn infants. Although these measures would be diagnostically useful in older infants, normative data on a large number of older infants are lacking. The goal of this study was to provide such normative data. Design The WATF of 458 infants aged 2 to 9 mos and of 210 adults were obtained. Wideband reactance (X), resistance (R), and energy reflectance (ER) were measured in third-octave bands between 250 and 8000 Hz. The effects of age and gender on the WATF were examined, and the WATF in the left and right ears were compared. Test–retest reliability was assessed, and the relationship between the 226-Hz tympanogram and the WATF was examined. Results The results agreed well with previous reports testing fewer subjects, which documented age-related change in these measures during infancy and between infancy and adulthood. Test–retest correlations within third octaves were 0.5 to 0.7 at best, but did not vary systematically with age. Infants’ test–retest absolute differences within third octaves for R and ER were similar to those of adults. The shape of the WATF on retest was highly repeatable, and the shapes of the WATF in the ears of the same individual were qualitatively similar. The wideband impedance results were not different in the left and right ears, but ER was slightly, but significantly, lower in the left ear than that in the right ear. Resistance and reactance magnitude were greater for females than males, but there was no effect of gender on ER. Infants whose 226-Hz tympanogram indicated reduced peak admittance (Types As and B) had greater resistance and reactance magnitude than those with normal peak admittance (Types A and C), but no tympanometry group differences were evident in ER. Conclusions Age-graded norms are essential to the successful clinical application of WATF. However, the effects of gender and laterality on the WATF are small.

Previous work has demonstrated that infants' thresholds for a pure tone are elevated by a masker more than would be predicted from their critical bandwidths. The present studies explored the nature of this additional masking. In Experiment 1, detection thresholds of6-month-old infants and of adults for a 1-kHz tone were estimated under three conditions: in quiet, in the presence of a 4-to 10-kHz bandpass noise at 40 dB SPL, and in the presence of the same noise at 50 dB SPL. The noise was gated on at the beginning of each trial. Adult thresholds were the same in all three conditions, indicating that little or no sensory masking took place in the presence of the noise. Infant thresholds were about 10 dB higher in the presence of the noise. We term this effect distraction masking. In Experiment 2, the effect of gating the noise on at trial onset was examined. Thresholds for the same tone were estimated in quiet and in the presence of the bandpass noise at 40 dB SPL, but the noise was presented continuously during the session. Under these conditions, distraction masking was still observed for infants. These findings suggest that a masker can have nonsensory effects on infants' performance in a psychoacoustic task. 405Masking has proved to be a powerful psychophysical paradigm for investigating the basic properties of sensory systems, and in recent years several investigations into the development of auditory masking have been published. Masked thresholds are often reported to be elevated in infants and children relative to adults (e.g., Allen, Wightman, Kistler, & Dolan, 1989;Nozza & Wilson, 1984;Schneider, Trehub, Morrongiello, & Thorpe, 1989), but this is not always the case, at least in older children (Veloso, Hall, & Grose, 1990). Even when the masked threshold is elevated, the amount of masking (i.e., the difference between masked and unmasked thresholds) is not always greater in younger subjects (Nozza & Wilson, 1984;Schneider et al., 1989). Olsho (1985), however, reported a case of tone-on-tone masking in 6-month-old infants where the amount of masking exhibited by the infants was about 14 dB greater than that exhibited by adults under the same condition. The purpose of the Olsho study was to estimate psychophysical tuning-eurve widths of infants and adults. The level of a .5-, 1-,2-, or 4-kHz tone, the probe, was set at 25 dB sensation level (SL). Thresholds for the probe in the presence of a second masking tone were obtained for three different masker frequencies to measure tuning- curve width, or QIO. Masker level was manipulated to define the threshold. At every masker frequency and every probe frequency, the infants exhibited masking at a masker level ranging from 11 to 16 dB lower than the level at which the adults exhibited masking. On the average, then, infants showed 14 dB more masking than did the adults. We refer to this additional masking shown by infants, relative to adults, as excess masking.Under traditional interpretation, the masked threshold is a measure of the frequency selectivity of the ...

Psychometric functions are described for individual 6- to 9-month-old infants and for individual adults for auditory detection of repeated, long- and short-duration tone bursts in quiet and for single, long-duration tone bursts in quiet and in noise. In general, infant psychometric functions have reduced upper asymptotes, shallower slopes, and poorer thresholds than adult psychometric functions. Infant-adult differences in slope and threshold are greater for short-duration tones than for other stimuli. Infant upper asymptotes are around 0.85 correct for all stimuli. One explantation for these findings is that infants are inattentive a certain proportion of time during the detection task. This model cannot account for the very shallow short-duration stimulus slope, nor can it account for infant-adult threshold differences for any stimulus. Other models of immature attention, or listening strategies, may be able to account for the slope and upper asymptote as well as the threshold of infant psychometric functions. Some combination of inattentiveness and primary neural immaturity may also account for the data. Although immaturities exist, some aspects of the detection process appear to be quantitatively similar in infants and adults.