Leigh A. Thorpe

The role of recall time in producing hypermnesia

In two experiments subjects presented with either words or pictures showed improved recall over three successive recall tests for both types of materials, partially replicating Erdelyi’s finding of hypermnesia. However, these subjects did not recall more unique items than other subjects who received only one test equated in time with the three shorter ones. It is concluded that hypermnesia results from simply allowing subjects additional recall time. In a third experiment subjects were shown to recall additional information even after a long recall period employed during an experimental session. This surprising amount of item recovery during long recall periods is attributed to the use of subjective retrieval cues that are thought to function in a manner analogous to externally manipulated cues.In two experiments subjects presented with either words or pictures showed improved recall over three successive recall tests for both types of materials, partially replicating Erdelyi’s finding of hypermnesia. However, these subjects did not recall more unique items than other subjects who received only one test equated in time with the three shorter ones. It is concluded that hypermnesia results from simply allowing subjects additional recall time. In a third experiment subjects were shown to recall additional information even after a long recall period employed during an experimental session. This surprising amount of item recovery during long recall periods is attributed to the use of subjective retrieval cues that are thought to function in a manner analogous to externally manipulated cues.

Developmental changes in masked thresholds

Masked thresholds for octave-band noises with center frequencies of 0.4, 1, 2, 4, and 10 kHz and for a 1/3-octave-band noise centered at 10 kHz were obtained from listeners 6.5 months to 20.5 years of age at two levels of a broadband masker (0 and 10 dB/cycle). Thresholds declined exponentially as a function of age for all stimuli tested. The rate and extent of this decline, but not its asymptote, were independent of the frequency or bandwidth employed. The time course for this change parallels that found for electrophysiological maturation of more central auditory processes.

Development of the perception of musical relations: Semitone and diatonic structure.

In the present research we examined the development of sensitivity to two musical relations significant in Western tonal music, the semitone and diatonic structure. Infants and preschool children were tested for their detection of a semitone change in any position of a five-note melody. Two standard melodies were used, one composed of diatonic tones only and the other containing a non-diatonic tone. In Experiment 1, children from 4 to 6 years of age were superior in detecting the semitone change in the diatonic context compared with the nondiatonic context. In Experiment 2, infants 9 to 11 months of age detected the semitone change in all positions, but their performance was not influenced by diatonic context. These findings indicate that infants and children can discriminate a semitone in a musical context and that the priority of diatonic structure emerges by 4 to 6 years of age.

Auditory sensitivity in preschool children

Thresholds for octave-band noises with center frequencies of 0.4, 1, 2, 4, and 10 kHz, and 1/3-octave-band noises with center frequencies of 10 and 20 kHz, were obtained from children 3-5 years of age and from a comparison group of adults. Thresholds for all frequencies decreased between 3 and 5 years of age. Thresholds decreased further between 5 years of age and adulthood, except for the 20-kHz stimulus, for which children had lower thresholds than adults. These results are discussed in terms of possible age-related changes in the mechanical properties of the ear and in the efficiency of neural coding.

Infants' perception of melodies: Changes in a single tone*

Infants 6 to 8 months of age were exposed to repetitions of a 6-tone sequence or melody, then tested for their detection of six transformations of that sequence, each of which incorporated a frequency change in one of the six positions. In Experiment 1, infants showed evidence of discriminating all changes. Moreover, they performed significantly better on changes that extended the frequency range of the original melody. When the task was made more difficult in Experiment 2, performance deteriorated but frequency changes in all positions were still detectable.

Auditory sensitivity in school-age children

Thresholds for octave-band noises with center frequencies of 0.4, 1, 2, 4, and 10 kHz and 1/3-octave-band noises centered at 10 and 20 kHz were obtained from children 6 to 16 years of age. Such thresholds, combined with those obtained previously for infants, preschool children, and adults, provide a detailed picture of developing auditory sensitivity between infancy and maturity. Continuing improvements in sensitivity are evident from infancy through the preschool period, well into the school years. For stimuli with center frequencies of 0.4 and 1 kHz, maximal sensitivity is achieved at about 10 years of age, compared to 8 years for stimuli of 2 and 4 kHz. For 10-kHz stimuli, there is little change beyond 4 or 5 years of age. Finally, 20-kHz stimuli yield maximal sensitivity at about 6 or 8 years of age, followed by a progressive decline to adult levels. These findings are considered in relation to auditory sensitivity in nonhuman species, to structural and functional development of the ear, and to possible changes in the efficiency of neural processing.

Infants' Perception of Timbre: Classification of Complex Tones by Spectral Structure

Infants 7 to 8.5 months of age were tested for their discrimination of timbre or sound quality differences in the context of variable exemplars. They were familiarized with a set of complex tones with specified spectral structure; members of the set varied in fundamental frequency, intensity, or duration. Infants were then tested for their detection of tones that contrasted in spectral structure but were similar in other respects. They successfully differentiated the two spectral structures in the context of these variations, indicating that they can classify tonal stimuli on the basis of timbre. When the stimuli were organized into arbitrary categories, infants were unable to differentiate these categories, indicating that their performance with nonarbitrary categories was not attributable to memorization of the familiarized set.

Children's perception of melodies: The role of contour, frequency, and rate of presentation ☆

Children 4 to 6 years of age were exposed to repetitions of a six-tone melody, then tested for their detection of transformations that either preserved or changed the contour of the standard melody. Discrimination performance was examined as a function of contour condition, magnitude of contour change, rate of presentation, and the presence of novel frequencies. Performance was superior for transformations that changed contour compared to those that did not, for greater changes in contour, and for faster presentation rates. Melodies transformed by a reordering of component tones were no less discriminable than those transformed by the addition of novel frequencies.

Developmental Changes in High-Frequency Sensitivity

Sensitivity to 1/3-octave-band noises with centre frequencies of 10, 20, and 25 kHz was measured for 200 children between 1.5 and 16 years of age and for 20 young adults. In the case of the 25-kHz signal, listeners of 1.5 and 3 years of age as well as those 16 and 20 years of age were unable to detect it at its highest intensity (57 dB). In contrast, listeners 5-14 years of age could detect the 25-kHz signal. Sensitivity to the 20-kHz signal improved until about 8 years of age, deteriorating gradually thereafter. Finally, sensitivity to the 10-kHz signal improved rapidly, reaching young adult levels by 5 years of age, and remaining stable until 20 years of age. These findings are consistent with the onset of high-frequency hearing losses at around 10 years of age. Whether such hearing losses are due to normal aging (presbyacusis) or to noise exposure (socioacusis) remains to be determined.

Observational Measures of Auditory Sensitivity in Early Infancy.

A rigorous observational procedure is described for estimating the detectability of auditory signals in the first few months of life. This procedure, a modification of the observer-based psychoacoustic procedure, generates a bias-free estimate of auditory sensitivity and avoids some of the potential problems associated with alternative techniques.