Hearing an Illusory Vowel in Noise: Suppression of Auditory Cortical Activity

Abstract

Human hearing is constructive. For example, when a voice is partially replaced by an extraneous sound (e.g., on the telephone due to a transmission problem), the auditory system may restore the missing portion so that the voice can be perceived as continuous (Miller and Licklider, 1950; for review, see Bregman, 1990; Warren, 1999). The neural mechanisms underlying this continuity illusion have been studied mostly with schematic stimuli (e.g., simple tones) and are still a matter of debate (for review, see Petkov and Sutter, 2011). The goal of the present study was to elucidate how these mechanisms operate under more natural conditions. Using psychophysics and electroencephalography (EEG), we assessed simultaneously the perceived continuity of a human vowel sound through interrupting noise and the concurrent neural activity. We found that vowel continuity illusions were accompanied by a suppression of the 4 Hz EEG power in auditory cortex (AC) that was evoked by the vowel interruption. This suppression was stronger than the suppression accompanying continuity illusions of a simple tone. Finally, continuity perception and 4 Hz power depended on the intactness of the sound that preceded the vowel (i.e., the auditory context). These findings show that a natural sound may be restored during noise due to the suppression of 4 Hz AC activity evoked early during the noise. This mechanism may attenuate sudden pitch changes, adapt the resistance of the auditory system to extraneous sounds across auditory scenes, and provide a useful model for assisted hearing devices.

High-frequency neural activity predicts word parsing in ambiguous speech streams

“…The 3-Hz phase effects could then reflect the suppression of the irrelevant phonetic cues that would not be compatible with the perceived word. This would be consistent with recent findings showing that LFO encode phonemic information (Di Liberto et al 2015) and that theta (3-5 Hz) oscillations are involved in phonemic restoration (Riecke et al 2009(Riecke et al , 2012Strauss et al 2014;Sunami et al 2013).…”

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

“…Thus, neurons with complex tuning properties or even those modulated by components of a task (Brosch et al 2005;Fritz et al 2005) may contribute to the construction of a perceptual representation; but by themselves do not offer direct evidence of a perceptual representation. There has been a recent set of literature implicating A1 in auditory perceptual decision-making (Riecke et al 2009;Kilian-Hutten et al 2011;Niwa et al 2012;Riecke et al 2012;. In one study, ferrets were asked to report changes in a sound's pitch, and it was found that both local-field potentials and spiking activity in A1 were modulated by the ferrets' pitch judgments.…”

Dynamic cortical representations of perceptual filling-in for missing acoustic rhythm

“…Samuel's paradigm 22 ). Our method subscribes to the latter approach, also referred to as 'filling-in', which emphasizes the signal detection strategy followed in cases where a listener classification is inconsistent with the token absence in a gap 3,[23][24][25][26][27][28][29] . As has been noted 30 , from the listener's utilitarian perspective, this effect of induction in a challenging environment is not aimed at the production of decision errors (or illusions) but to assist against masking.…”

“…For human listeners, there is evidence that such compensatory principles may extend to disruptions to dynamically modulated sound, including amplitude-modulated (AM) sound, single vowels, and consonants within words 8,9,24,28,36,37 , the latter of which fall under the concept of phonemic restoration 1,3,22 . Depending on stimulus, neural correlates have been localized to different areas, including Heschl's gyrus for missing AM noise 36 , the posterior aspect of superior temporal gyrus for disrupted vowels 28 , and wider brain networks including the superior temporal lobe in the case of missed phonemes 24,37 .…”

“…Depending on stimulus, neural correlates have been localized to different areas, including Heschl's gyrus for missing AM noise 36 , the posterior aspect of superior temporal gyrus for disrupted vowels 28 , and wider brain networks including the superior temporal lobe in the case of missed phonemes 24,37 . In addition, mixed evidence points to a basis for restoration in terms of endogenous modulations to boundary encoding: on the one hand, the search for differential onset responses to noise when under restoration, indexing alternative encoding, has yielded negative results so far 27,28 ; on the other, induced narrow-band (3-4 Hz) desynchronizations that are restoration-specific, and occur after gap onset, have been suggested by results from EEG 28,38 .…”