Cortical sensitivity to periodicity of speech sounds

Abstract

Previous non-invasive brain research has reported auditory cortical sensitivity to periodicity as reflected by larger and more anterior responses to periodic than to aperiodic vowels. The current study investigated whether there is a lower fundamental frequency (F0) limit for this effect. Auditory evoked fields (AEFs) elicited by natural-sounding 400 ms periodic and aperiodic vowel stimuli were measured with magnetoencephalography. Vowel F0 ranged from normal male speech (113 Hz) to exceptionally low values (9 Hz). Both the auditory N1m and sustained fields were larger in amplitude for periodic than for aperiodic vowels. The AEF sources for periodic vowels were also anterior to those for the aperiodic vowels. Importantly, the AEF amplitudes and locations were unaffected by the F0 decrement of the periodic vowels. However, the N1m latency increased monotonically as F0 was decreased down to 19 Hz, below which this trend broke down. Also, a cascade of transient N1m-like responses was observed in the lowest F0 condition. Thus, the auditory system seems capable of extracting the periodicity even from very low F0 vowels. The behavior of the N1m latency and the emergence of a response cascade at very low F0 values may reflect the lower limit of pitch perception.

Sustained responses for pitch and vowels map to similar sites in human auditory cortex

“…In MEG, the pitch specific response comprises a subcomponent of the N 1 m after pitch onset (Gutschalk et al, 2004;Krumbholz et al, 2003) and of the sustained response that continues for the duration of the periodic sound (Gutschalk et al, 2002) (also referred to as the "pitch onset response", POR, and the "sustained pitch response", SPR). A similar dependence of sustained activity on stimulus periodicity is observed for vowels, for which the degree of periodicity jitter determines the perceived vowel "roughness" (Yrttiaho et al, 2009;Yrttiaho et al, 2008).…”

Cortical encoding of aperiodic and periodic speech sounds: Evidence for distinct neural populations

“…vowel probes. The larger amplitude coupled with a more anterior source location in the periodic than in the aperiodic condition was similar to that found in several studies indicating cortical sensitivity to sound periodicity (Hertrich et al, 2000;Alku et al, 2001;Tiitinen et al, 2005;Lütkenhöner et al, 2006;Soeta and Nakagawa, 2008;Yrttiaho et al, 2008Yrttiaho et al, , 2009Yrttiaho et al, , 2010. This result might be taken to suggest that the population activated by the periodic stimulus is larger than that activated by the aperiodic stimulus and, thus, includes a distinct periodicity-sensitive subpopulation.…”

“…The periodicity-specific adaptation and the periodicityspecific displacement in the N1m source location were, however, observed for both the 800 ms-and the 200-ms ISI. Several studies addressing the encoding of sound periodicity have found evidence for a specialized cortical population or populations responsive to sound periodicity (Griffiths et al, 1998(Griffiths et al, , 2001Hertrich et al, 2000;Alku et al, 2001;Patterson et al, 2002;Gutschalk et al, 2004;Penagos et al, 2004;Tiitinen et al, 2005;Soeta et al, 2005;Soeta and Nakagawa, 2008;Lütkenhöner et al, 2006;Hall et al, 2006;Hall and Plack, 2009;Yrttiaho et al, 2008Yrttiaho et al, , 2009Yrttiaho et al, , 2010Lewis et al, 2009;Schönwiesner and Zatorre, 2008;Griffiths et al, 2010). However, the few data sets that pertain to whether aperiodicity is also encoded by the activation of a specialized population do not seem to converge on the issue.…”

“…The studies focusing on the N1m, a prominent response elicited around 100 ms after stimulus onset and generated in the auditory cortex , have revealed a larger response amplitude for auditory stimulation with a periodic as opposed to an aperiodic structure (Hertrich et al, 2000;Alku et al, 2001;Gutschalk et al, 2004;Tiitinen et al, 2005;Lütkenhöner et al, 2006;Yrttiaho et al, 2008Yrttiaho et al, , 2009Yrttiaho et al, , 2010Soeta et al, 2005;Soeta and Nakagawa, 2008). Such an amplitude increase in cortical population-level responses could be interpreted in terms of a larger neural population activated by the periodic than by the aperiodic stimulus.…”

“…In this view, the results seem to indicate the presence of a periodicity-sensitive population that is specifically activated in the periodic condition. This amplitude effect has typically been coupled with a more anterior source location of the response elicited by the periodic sound than that elicited by the aperiodic sound (Alku et al, 2001;Gutschalk et al, 2004;Tiitinen et al, 2005;Yrttiaho et al, 2008Yrttiaho et al, , 2009Yrttiaho et al, , 2010, providing further evidence for the distinction between the underlying neural generators of the responses elicited by varying degrees of stimulus periodicity. Imaging studies with positron emission tomography (Griffiths et al, 1998) and functional magnetic resonance imaging (Griffiths et al, 2001;Patterson et al, 2002;Penagos et al, 2004;Hall et al, 2006;Hall and Plack, 2009;Lewis et al, 2009;Garcia et al, 2010;Puschmann et al, 2010) along with invasive electrode recordings from human patients (Schönwiesner and Zatorre, 2008;Griffiths et al, 2010) have corroborated these results by showing that cortical areas are activated by sound periodicity.…”