Marc Boillot

Disinhibited in vitro neocortical slices containing experimentally induced cortical dysplasia demonstrate hyperexcitability

Cortical dysplasia, a disorder of neuronal migration, has a strong association with intractable epilepsy in humans but little is known about the physiologic abnormalities that are present in this condition. Fetal rats were exposed to external irradiation to experimentally produce diffuse cortical dysplasia. In vitro neocortical slices from adult irradiated and control animals were examined in physiologic solution and in the presence of the A-type gamma-amino butyric acid (GABAA) receptor antagonist, bicuculline methiodide. Epileptiform bursts were quantified by counting the number of negative field potentials per epileptiform event. In the presence of bicuculline, neocortical slices with cortical dysplasia demonstrated more robust epileptiform activity in the form of an increased number of negative field potentials per epileptiform event. This demonstrates that areas of experimentally induced cortical dysplasia possess an inherent hyperexcitability when GABAA-mediated inhibition is effectively blocked.

A loudness enhancement technique for speech

We propose an application of the vocoder postfilter to increase perceived loudness of clean speech without increasing signal energy or degrading intelligibility. The critical band concept in auditory theory states that perceived loudness of a narrow-band signal will increase when the bandwidth of that signal increases beyond a critical band, even though the energy remains constant. Our post-filter technique applies formant bandwidth expansion to the vowel regions of speech without changing the vowel power to elevate perceived loudness. Vowels are known to contain the highest energy, have a smooth spectral envelope, long temporal sustenance, and for this reason are suitable candidates to target for a loudness enhancement technique. ISO-532B loudness analysis patterns and listening tests are provided to demonstrate a perceptual loudness improvement corresponding to a 2dB power gain.

A warped bandwidth expansion filter

A warped filter is presented as a new speech enhancement method to adjust formant bandwidths on a critical band scale. The warped filter enhances perceived loudness without adding signal energy by exploiting the psychoacoustic nature of the auditory system. The critical band concept in auditory theory states that when the energy in a signal remains constant, loudness increases when the energy spreads beyond a critical bandwidth. A warped filter is proposed and developed to elevate the perceived loudness of clean speech by applying nonlinear bandwidth expansion to the formant regions of vowels in accordance with the critical band scale. The filter has been inspired and motivated by the biological representation of loudness in the peripheral auditory system and the critical band concept of hearing.