Enhancement of speech perception in noise by periodicity processing: A neurobiological model and signal processing algorithm

Abstract

The perceived loudness of sound increases with its tonality or periodicity, and the pitch strength of tones are linearly proportional to their sound pressure level. These observations suggest a fundamental relationship between pitch strength and loudness. This relationship may be explained by the superimposition of inputs to inferior colliculus neurons from cochlear nucleus chopper cells and phase locked spike trains from the lateral lemniscus. The regularity of chopper cell outputs increases for stimuli with periodicity at the same frequency as their intrinsic chopping rate. So inputs to inferior colliculus cells become synchronized for periodic stimuli, leading to increased likelihood that they will fire and increased salience of periodic signal components at the characteristic frequency of the inferior colliculus cell. A computer algorithm to enhance speech in noise was based on this model. The periodicity of the outputs of a Gammatone filter bank after each sound onset was determined by first sampling each filter channel at a range of typical chopper cell frequencies and then passing these amplitudes through a step function to simulate the firing of coincidence detecting neurons in the inferior colliculus. Filter channel amplification was based on the maximum accumulated spike count after each onset, resulting in increased amplitudes for filter channels with greater periodicity. The speech intelligibility of stimuli in noise was not changed when the algorithm was used to remove around 14 dB of noise from stimuli with signal-noise ratios of around 0 dB. This mechanism is a likely candidate for enhancing speech recognition in noise, and raises the proposition that pitch itself is an epiphenomenon that evolved from neural mechanisms that boost the hearing sensitivity of animals to vocalizations.

The Contribution of Brainstem and Cerebellar Pathways to Auditory Recognition

“…Pitch resolution is refined by waveform driven mechanisms in the IC to produce sharper frequency resolution after multiple stimulus periods ( Langner and Schreiner, 1988 ; de Cheveigné, 2005 ; Meddis and O’Mard, 2006 ; McLachlan, 2009 ; McLachlan and Grayden, 2014 ). According to McLachlan (2009 , 2011 ) the primed spectral pitch is associated with pitch dimension in a place code by neurons adjacent to the primary auditory cortex ( Bendor and Wang, 2005 ).…”

Pitch and Plasticity: Insights from the Pitch Matching of Chords by Musicians with Absolute and Relative Pitch

“…Furthermore, it is unlikely that periodicity information is used to segregate concurrent vowels presented at different pitches [25,26,27], because this information takes longer to accumulate than the duration of many speech phonemes [28,29]. …”

“…Micheyl et al [ 24 ] showed that good pitch discrimination of harmonic complexes in the presence of masking tones could only be achieved when several harmonics belonging to the target pitch were likely to be salient in tonotopic spike rate representations on the auditory nerve, providing further support for the importance of spectral information in concurrent pitch processing. Furthermore, it is unlikely that periodicity information is used to segregate concurrent vowels presented at different pitches [ 25 , 26 , 27 ], because this information takes longer to accumulate than the duration of many speech phonemes [ 28 , 29 ].…”