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.

Infants' auditory detection thresholds are higher than adult thresholds. Since adults listen selectively for an expected test tone frequency, and selective listening improves their detection performance, one hypothesis about why infant thresholds are high is that infants do not listen selectively. This hypothesis was tested by obtaining listening bands from adults and from 7-to 9-month-old infants. The results replicate earlierfindings that adults listen selectively bllt indicate that infants do not. Lack of selective listening likely contributes to infants' high thresholds. Further, the finding that infants and adults have different listening strategies has implications for infants' auditory perception in general.

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Children with hearing loss are at risk for outcomes below their potential despite institution of educational approaches at increasingly younger ages. Research suggests some benefits of early intervention (EI) for these children and their families. However, previous investigators have not delineated broader family, child, and program variables that warrant consideration in understanding the role, success, and limitations of EI. The present study involved 28 hearing families and their children with hearing impairments aged 42 to 87 months, 9 to 42 months postgraduation from an EI program. The information gathered included demographics, duration and intensity of the EI, parent involvement, and educational and communication choices. Results provide a descriptive profile of children with hearing loss and their hearing families from EI through the preschool years. The discussion reflects upon EI in the context of this population's significant heterogeneity. Complex and confounding factors are presented that may affect children's and families' short- or long-term progress and the goals of EI.