Auditory-evoked potentials to frequency increase and decrease of high- and low-frequency tones

Abstract

a b s t r a c tObjective: To define cortical brain responses to large and small frequency changes (increase and decrease) of high-and low-frequency tones. Methods: Event-Related Potentials (ERPs) were recorded in response to a 10% or a 50% frequency increase from 250 or 4000 Hz tones that were approximately 3 s in duration and presented at 500-ms intervals. Frequency increase was followed after 1 s by a decrease back to base frequency. Frequency changes occurred at least 1 s before or after tone onset or offset, respectively. Subjects were not attending to the stimuli. Latency, amplitude and source current density estimates of ERPs were compared across frequency changes. Results: All frequency changes evoked components P 50 , N 100 , and P 200 . N 100 and P 200 had double peaks at bilateral and right temporal sites, respectively. These components were followed by a slow negativity (SN). The constituents of N 100 were predominantly localized to temporo-parietal auditory areas. The potentials and their intracranial distributions were affected by both base frequency (larger potentials to low frequency) and direction of change (larger potentials to increase than decrease), as well as by change magnitude (larger potentials to larger change). The differences between frequency increase and decrease depended on base frequency (smaller difference to high frequency) and were localized to frontal areas. Conclusions: Brain activity varies according to frequency change direction and magnitude as well as base frequency. Significance: The effects of base frequency and direction of change may reflect brain networks involved in more complex processing such as speech that are differentially sensitive to frequency modulations of high (consonant discrimination) and low (vowels and prosody) frequencies.

Auditory cortical activity in normal hearing subjects to consonant vowels presented in quiet and in noise

“…Earlier studies (Dimitrijevic et al, 2008;Pratt et al, 2009) on the sources of the N100 component localized them to the right temporal lobe in response to acoustic change, similar to this study, whereas to low-frequency change the source was on the left (Pratt et al, 2009). Thus, assuming homology of N100 CV and the N100 component to frequency change, N100 CV is evoked by the high-frequency changes associated with the consonant.…”

“…The SN to VCVs (/utu/) persists beyond the VCV while the negativity to sustained tones terminates when the tone ends. The SN to VCV in the present study is similar to a negative potential that follows brief (100 ms) changes of pitch or intensity of continuous tones, a ''negative change potential'' (Dimitrijevic et al, , 2008Pratt et al, 2009) that was unrelated to the magnitude of the spectral or intensity change. However, the amplitude of the SN found in the present study to…”

“…In initial position cortical activities consisted of P50, N100, P200, and N200 components as in ''acoustic onset'' responses to tone bursts (Onishi and Davis, 1968). In contrast, CVs in second position (/udu/ and /utu/) evoked cortical activities consisting of N100 followed by a slow negativity (SN) as in ''acoustic change potentials'' to changes of pitch or intensity of ongoing tones (Dimitrijevic et al, 2008;Pratt et al, 2009); (2) Consonant VOT duration had different effects on ''onset'' and ''change potentials''. For CVs in initial position (e.g., /du/ and /tu/) N100 amplitudes decreased as VOT increased whereas N100 latency was not affected.…”

“…Aside from the temporal stimulus features, the spectral features of the stimulus will also affect the magnitude of the response. Picton et al (1978), Dimitrijevic et al (2008) and Pratt et al (2009) using non-speech sounds demonstrated that lower frequencies elicit larger responses compared to higher frequencies. In this study, the /du/ stimulus is lower in frequency than /tu/ given that voicing begins earlier.…”

“…Columns 3 to 6 indicate the mean (SD) percent of the trials (out of 20) where subjects reported hearing ''tu'' or ''utu'' as a function of VOT. The last column represents the mean (SD) VOT value for the estimated 50% performance, or equiprobable hearing of ''du'' and ''tu'' (or ''udu'' and ''utu'') /du-tu/ 1 (3) 8 (13) 96 (5) 100 (0) 33 (4) /udu-utu/ 3 (8) 21 (22) 94 (11) 97 (7) 32 (3) document differences of auditory cortical activity to CVs in initial position (acoustic onset) compared to CVs in second position when preceded by a vowel (acoustic change), similar to auditory cortical responses to pure tone onset (acoustic onset) and to a frequency change in an ongoing pure tone (acoustic change) (see Pratt et al, 2009). .…”