Hard real-time closed-loop electrophysiology with the Real-Time eXperiment Interface (RTXI)
Fig 7
Hard RT distorted auditory feedback system.
(A) Simplified diagram of the acoustic feedback system. When not triggered (top), the system computes the root mean square (RMS) of the input signal. When the RMS exceeds the threshold, the system is triggered. When triggered (bottom), the system computes the spectrogram of the most recent 20ms of signal and computes the correlation coefficient of this spectrogram with the spectrogram of the template sound (e.g., song syllable). The template sound is detected when the correlation coefficient exceeds a threshold value; in this case, acoustic feedback can be generated. Both the input and the acoustic output are saved to the computer hard drive. (B) Spectrogram of the song of a Bengalese finch and the times of occurrence of one of the song syllables. The system was programmed to only detect the occurrences of the target syllable in real time, no acoustic feedback was generated. The detection times are shown as vertical red lines. Bottom: the system is detecting the target syllables (vertical red lines) and is generating acoustic feedback after detection. The acoustic feedback waveform is shown below. The feedback signal is one of the birdsong syllables; the acoustic feedback pickup by the microphone is visible on the spectrogram. The zoomed-in spectrogram of the template is shown on the right. (C) DAF increases the duration of the time interval between Bengalese finch song syllables. Histogram depicts the time intervals between two subsequent syllables in the song in the presence of DAF (blue) and without DAF (red). The means are: Δtmean = 74.8ms (control, N = 637 syllables) and Δtmean = 75.7ms (feedback, N = 97 syllables), the difference is statistically significant (p = 0.001, two-way Kolmogorov—Smirnov test). All figures obtained and modified with permission from [38].