Formation and decay of auditory short-term memory in the macaque monkey

Echoic memory (EM) is a short-lived, precategorical, and passive form of auditory short-term memory (STM). A key hallmark of EM is its rapid exponential decay with a time constant between 1 and 2 s. It is not clear whether auditory STM in the rhesus, an important model system, shares this rapid exponential decay. To resolve this shortcoming, two rhesus macaques were trained to perform a delayed frequency discrimination task. Discriminability of delayed tones was measured as a function of retention duration and the number of times the standard had been repeated before the target. Like in the human, our results show a rapid decline of discriminability with retention duration. In addition, the results suggest a gradual strengthening of discriminability with repetition number. Model-based analyses suggest the presence of two components of auditory STM: a short-lived component with a time constant on the order of 550 ms that most likely corresponds to EM and a more stable memory trace with time constants on the order of 10 s that strengthens with repetition and most likely corresponds to auditory recognition memory. NEW & NOTEWORTHY This is the first detailed quantification of the rapid temporal dynamics of auditory short-term memory in the rhesus. Much of the auditory information in short-term memory is lost within the first couple of seconds. Repeated presentations of a tone strengthen its encoding into short-term memory. Model-based analyses suggest two distinct components: an echoic memory homolog that mediates the rapid decay and a more stable but less detail-rich component that mediates strengthening of the trace with repetition.

Noise Equally Degrades Central Auditory Processing in 2- and 4-Year-Old Children

Purpose The aim of this study was to investigate developmental and noise-induced changes in central auditory processing indexed by event-related potentials in typically developing children. Method P1, N2, and N4 responses as well as mismatch negativities (MMNs) were recorded for standard syllables and consonants, frequency, intensity, vowel, and vowel duration changes in silent and noisy conditions in the same 14 children at the ages of 2 and 4 years. Results The P1 and N2 latencies decreased and the N2, N4, and MMN amplitudes increased with development of the children. The amplitude changes were strongest at frontal electrodes. At both ages, background noise decreased the P1 amplitude, increased the N2 amplitude, and shortened the N4 latency. The noise-induced amplitude changes of P1, N2, and N4 were strongest frontally. Furthermore, background noise degraded the MMN. At both ages, MMN was significantly elicited only by the consonant change, and at the age of 4 years, also by the vowel duration change during noise. Conclusions Developmental changes indexing maturation of central auditory processing were found from every response studied. Noise degraded sound encoding and echoic memory and impaired auditory discrimination at both ages. The older children were as vulnerable to the impact of noise as the younger children. Supplemental materials https://doi.org/10.23641/asha.5233939

Is there a bilingual advantage in phonetic and phonological acquisition? The initial learning of word-final coronal stop realization in a novel accent of English

Research question: We address the question of whether the cognitive advantage of the bilingual mind, already demonstrated in the case of auditory processing or novel word acquisition, also applies to other linguistic domains, specifically to phonetic and phonological learning. Design: We compare the performance of 17 monolinguals and 25 bilinguals from Canada in a production experiment with two tasks: imitation and spontaneous reproduction of a novel foreign accent, specifically Sussex English. Data and analysis: To eliminate potential sources of variability, our focus is on a sound already existing in the subjects’ production (the glottal stop), but differently mapped to surface representations in the novel accent to which they were exposed (i.e., as an allophone of coronal stops in word-final position). We measured the glottal stop rates of our subjects in baseline, training, and post-training. Results: The two groups behaved differently, with bilinguals showing a larger increase of their glottal stop rate post-training. Our results are thus consistent with a bilingual advantage in phonetic and phonological learning. Originality: We interpret these findings in light of recent psycholinguistic work and conclude that echoic memory strategies, possibly underlain by stronger subcortical encoding of sound in bilinguals, may account for our results by facilitating the re-mapping between existing mental representations of sounds and existing articulatory command configurations. Significance: Our study adds to the body of work suggesting that there may be an advantage of bilingualism in second dialect learning in adulthood, and provides an explanation in terms of perceptual strategies in which echoic memory is involved. We also contribute to the body of research suggesting that imitation of an action can result in improved understanding of that action.