Distortion products in auditory fMRI research: Measurements and solutions
Nonlinearities in the cochlea can introduce audio frequencies that are not present in the sound signal entering the ear. Known as distortion products (DPs), these added frequencies complicate the interpretation of auditory experiments. Sound production systems also introduce distortion via nonlinear...
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| Format: | Article |
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Elsevier
2017
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| Online Access: | http://hdl.handle.net/1721.1/112184 https://orcid.org/0000-0002-3965-2503 |
| _version_ | 1826198066176196608 |
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| author | Norman-Haignere, Samuel Victor McDermott, Joshua H. |
| author2 | Massachusetts Institute of Technology. Department of Brain and Cognitive Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Brain and Cognitive Sciences Norman-Haignere, Samuel Victor McDermott, Joshua H. |
| author_sort | Norman-Haignere, Samuel Victor |
| collection | MIT |
| description | Nonlinearities in the cochlea can introduce audio frequencies that are not present in the sound signal entering the ear. Known as distortion products (DPs), these added frequencies complicate the interpretation of auditory experiments. Sound production systems also introduce distortion via nonlinearities, a particular concern for fMRI research because the Sensimetrics earphones widely used for sound presentation are less linear than most high-end audio devices (due to design constraints). Here we describe the acoustic and neural effects of cochlear and earphone distortion in the context of fMRI studies of pitch perception, and discuss how their effects can be minimized with appropriate stimuli and masking noise. The amplitude of cochlear and Sensimetrics earphone DPs were measured for a large collection of harmonic stimuli to assess effects of level, frequency, and waveform amplitude. Cochlear DP amplitudes were highly sensitive to the absolute frequency of the DP, and were most prominent at frequencies below 300 Hz. Cochlear DPs could thus be effectively masked by low-frequency noise, as expected. Earphone DP amplitudes, in contrast, were highly sensitive to both stimulus and DP frequency (due to prominent resonances in the earphone's transfer function), and their levels grew more rapidly with increasing stimulus level than did cochlear DP amplitudes. As a result, earphone DP amplitudes often exceeded those of cochlear DPs. Using fMRI, we found that earphone DPs had a substantial effect on the response of pitch-sensitive cortical regions. In contrast, cochlear DPs had a small effect on cortical fMRI responses that did not reach statistical significance, consistent with their lower amplitudes. Based on these findings, we designed a set of pitch stimuli optimized for identifying pitch-responsive brain regions using fMRI. These stimuli robustly drive pitch-responsive brain regions while producing minimal cochlear and earphone distortion, and will hopefully aid fMRI researchers in avoiding distortion confounds. |
| first_indexed | 2024-09-23T10:58:19Z |
| format | Article |
| id | mit-1721.1/112184 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T10:58:19Z |
| publishDate | 2017 |
| publisher | Elsevier |
| record_format | dspace |
| spelling | mit-1721.1/1121842022-09-27T16:16:52Z Distortion products in auditory fMRI research: Measurements and solutions Norman-Haignere, Samuel Victor McDermott, Joshua H. Massachusetts Institute of Technology. Department of Brain and Cognitive Sciences Norman-Haignere, Samuel Victor McDermott, Joshua H. Nonlinearities in the cochlea can introduce audio frequencies that are not present in the sound signal entering the ear. Known as distortion products (DPs), these added frequencies complicate the interpretation of auditory experiments. Sound production systems also introduce distortion via nonlinearities, a particular concern for fMRI research because the Sensimetrics earphones widely used for sound presentation are less linear than most high-end audio devices (due to design constraints). Here we describe the acoustic and neural effects of cochlear and earphone distortion in the context of fMRI studies of pitch perception, and discuss how their effects can be minimized with appropriate stimuli and masking noise. The amplitude of cochlear and Sensimetrics earphone DPs were measured for a large collection of harmonic stimuli to assess effects of level, frequency, and waveform amplitude. Cochlear DP amplitudes were highly sensitive to the absolute frequency of the DP, and were most prominent at frequencies below 300 Hz. Cochlear DPs could thus be effectively masked by low-frequency noise, as expected. Earphone DP amplitudes, in contrast, were highly sensitive to both stimulus and DP frequency (due to prominent resonances in the earphone's transfer function), and their levels grew more rapidly with increasing stimulus level than did cochlear DP amplitudes. As a result, earphone DP amplitudes often exceeded those of cochlear DPs. Using fMRI, we found that earphone DPs had a substantial effect on the response of pitch-sensitive cortical regions. In contrast, cochlear DPs had a small effect on cortical fMRI responses that did not reach statistical significance, consistent with their lower amplitudes. Based on these findings, we designed a set of pitch stimuli optimized for identifying pitch-responsive brain regions using fMRI. These stimuli robustly drive pitch-responsive brain regions while producing minimal cochlear and earphone distortion, and will hopefully aid fMRI researchers in avoiding distortion confounds. 2017-11-14T18:38:27Z 2017-11-14T18:38:27Z 2016-01 2015-08 2017-11-14T18:25:06Z Article http://purl.org/eprint/type/JournalArticle 1053-8119 http://hdl.handle.net/1721.1/112184 Norman-Haignere, Sam, and McDermott, Josh H. “Distortion Products in Auditory fMRI Research: Measurements and Solutions.” NeuroImage 129 (April 2016): 401–413 © 2016 Elsevier https://orcid.org/0000-0002-3965-2503 http://dx.doi.org/10.1016/J.NEUROIMAGE.2016.01.050 NeuroImage Creative Commons Attribution-NonCommercial-NoDerivs License http://creativecommons.org/licenses/by-nc-nd/4.0/ application/pdf Elsevier PMC |
| spellingShingle | Norman-Haignere, Samuel Victor McDermott, Joshua H. Distortion products in auditory fMRI research: Measurements and solutions |
| title | Distortion products in auditory fMRI research: Measurements and solutions |
| title_full | Distortion products in auditory fMRI research: Measurements and solutions |
| title_fullStr | Distortion products in auditory fMRI research: Measurements and solutions |
| title_full_unstemmed | Distortion products in auditory fMRI research: Measurements and solutions |
| title_short | Distortion products in auditory fMRI research: Measurements and solutions |
| title_sort | distortion products in auditory fmri research measurements and solutions |
| url | http://hdl.handle.net/1721.1/112184 https://orcid.org/0000-0002-3965-2503 |
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