Neural oscillations associated with auditory duration maintenance in working memory

Abstract

The neural representation of auditory duration remains unknown. Here, we used electroencephalogram (EEG) recordings to investigate neural oscillations during the maintenance of auditory duration in working memory (WM). EEG analyses indicated that the auditory duration length was not associated with changes in the theta band amplitude, whereas the alpha band amplitudes during 3-s and 4-s auditory duration conditions were lower than during the 1-s and 2-s conditions. Moreover, the alpha band amplitude and accuracy were positively correlated in the 2-s duration condition. We also found that the neural representation of auditory duration is segmented, with a critical threshold point of approximately 2 s, which is shorter than that for visual duration (3 s). The results emphasised the involvement of the alpha band in auditory duration maintenance in WM. Our study's findings indicate that different internal representations of auditory durations are maintained in WM below and above 2 s from the perspective of electrophysiology. Additionally, the critical threshold point is related to the sensory modality of duration.

Figure 1

Trial sequences and durations of each screen presentation. Auditory stimuli were randomly presented for 1, 2, 3, or 4 s. Each trial starts with a pure tone (sample), followed by a 3-s interval (the delay/maintenance phase). Next, a second pure tone (probe) is presented. Participants press ‘1’, ‘2’, or ‘3’ correspondingly after estimating the duration of the second pure tone (probe) as shorter, equal to, or longer than the first tone (sample).

Figure 2

Theta and alpha effects for the whole epoch in the posterior parietal in the 1-s (A), 2-s (B), 3-s (C), and 4-s (D) auditory duration conditions. The decibel-transformed value is relative to the baseline interval (−0.4 s to −0.1 s) before the sample stimulus. The theta band is enhanced at the onset and offset of stimuli, whereas the alpha band is enhanced during encoding, especially in the delay phase.

Figure 3

Average theta (A) and alpha (B) band powers during the 1-s, 2-s, 3-s, and 4-s auditory duration maintenance in WM. Steady theta (4–8 Hz) and alpha (8–12 Hz) band activities are elicited during WM maintenance after averaging across frequency, and they are separately plotted for each of the nine analysed electrode clusters. Zero on the x-axis represents the onset of the delay phase. Red, green, blue, and black curves denote the 1-s, 2-s, 3-s, and 4-s auditory duration conditions, respectively.

Figure 4

Grand average theta and alpha band powers during auditory duration maintenance in WM in the 1-s, 2-s, 3-s, and 4-s conditions. Grand average theta and alpha band powers during the delay phase are computed for each duration condition, and they are separately plotted for each of the nine analysed electrode clusters. Red and green lines denote the alpha and theta band powers in each duration condition, respectively. Error bars represent the standard error of the mean across observers.

Figure 5

Topographies of theta and alpha activity during auditory duration maintenance in working memory in the 1-s, 2-s, 3-s, and 4-s conditions. Theta and alpha band powers are significantly activated in the posterior parietal cortex from the interval of 1 s to 3 s after the onset of delay.

Figure 6

Correlation between the amplitude of the alpha band power and accuracy in the posterior parietal during the 2-s auditory duration condition. The scatter plot depicts the amplitude of the alpha power (y-axis) relative to the accuracy of the behavioural performance (x-axis) in the 2-s auditory duration condition. Pearson product-moment correlation coefficient, r = 0.569.