The Maturation of the Acoustic Change Complex in Response to Iterated Ripple Noise in 'Normal'-Hearing Infants, Toddlers, and Adults.

BACKGROUND: Infants and toddlers are still being evaluated for their hearing sensitivity but not their auditory-processing skills. Iterated rippled noise (IRN) stimuli require the auditory system to utilize the temporal periodicity and autocorrelate the iterations to perceive pitch. PURPOSE: This study investigated the acoustic change complex (ACC) elicited by IRN in "normal"-hearing infants, toddlers, and adults to determine the maturation of cortical processing of IRN stimuli. DESIGN: Cortical responses to filtered white noise (onset) concatenated with IRN stimuli (d = 10 milliseconds, gain = 0.7 dB: 4-32 iterations) were recorded in quiet, alert participants. STUDY SAMPLE: Participants included 25 infants (2.5-15 months), 27 toddlers (22-59 months), and 8 adults (19-25 years) with "normal" hearing sensitivity. DATA COLLECTION AND ANALYSIS: Cortical auditory-evoked responses were recorded for each participant, including the onset response to the noise and an ACC to the transition from noise to IRN. Group differences were assessed using repeated-measures analyses of variance. RESULTS: Most infants had a replicable onset (P) response, while only about half had a measurable ACC (PACC) response to the high-saliency IRN condition. Most toddlers had onset responses and showed a P-NACC response to the IRN16 and IRN32 conditions. Most of the toddler group had responses present to the onset and showed a P-NACC response to all IRN conditions. Toddlers and adults showed similar P-NACC amplitudes; however, adults showed an increase in N1ACC amplitude with increase in IRN iterations (i.e., increased salience). CONCLUSION: While cortical responses to the percept of sound as determined by the onset response (P) to a stimulus are present in most infants, ACC responses to IRN stimuli are not mature in infancy. Most toddlers as young as 22 months, however, exhibited ACC responses to the IRN stimuli even when the pitch saliency was low (e.g., IRN4). The findings of the current study have implications for future research when investigating maturational effects on ACC and the optimal choice of stimuli.

Stereotypes of the elderly held by young, middle-aged, and elderly adults.

This two-part study extended the research on multiple stereotypes of elderly adults by examining the perceptions of young, middle-aged, and elderly adults. First, one set of participants engaged in a trait generation task which yielded a trait list for use in the second part of the study. Second, other participants sorted the set of traits into groups representing different types of elderly individuals. Trait groupings were analyzed with hierarchical cluster analysis. Results supported the hypothesis that older adults have more complex representations of aging than do middle-aged and young ones, and that middle-aged adults have more complex representations than do young ones. For example, middle-aged and elderly adults reported more stereotypes of the elderly than did young adults, and elderly adults reported more stereotypes than did middle-aged adults. Results also showed, as expected, that these differences in complexity exist against a background of general agreement about the nature of aging: Trait lists produced by those in the three age groups were significantly correlated, and the stereotype sets of the three age groups included seven shared stereotypes. Results are interpreted in terms of their support for two alternative explanations of the complexity differences: ingroup/outgroup and developmental.