EFTA01100146.pdf

Primary Auditory Cortex is Necessary for Fine-grained Loudness Perception Harvard-MIT Health Sciences & Technology Andrew R. Dykstra;1,2Christine K. Koh2,,3Louis D. Braida2, '3Mark Jude Tramo2,4 1Harvard-MIT Division of Health Sciences and Technologyl2Institute for Music and Brain Science,3Research Laboratory of Electronics, Massachusetts Institute of Technology, Department of Neurology, UCLA School of Medicine rteAT MIT 1. Introduction 3. Methods 1.A. Loudness perception is critical for understanding speech and appreciating music. 3.A. Stimulus delivery and data collection. - Participants sat a double-walled sound-attenuated booth and faced a computer monitor on which instructions and feedback were given. - The loudness of a sound source and its change over time convey information about source size, - Participants entered responses via a computer keyboard. location, trajectory, and identity. - All stimuli except pure-tone audiometry in normal controls were generated using MATLAB, DA-converted by 24-bit soundcard (Fs=32kHz), attenuated (TDT PA4), buffered (TDT HB6), and presented to the participant over Sennheiser HD580 open-air headphones. - Humans and animals use loudness to convey meaning and emotion. 3.B. Pure-tone detection. - Musical dynamics (i.e. changes in loudness) are important for musical aesthetics. - In Case A1+, thresholds were measured using a 2-interval, 2-alternative forced-choice procedure with a 2-down, 1-up rule (Levitt, 1971). Each 1.B. Humans demonstrate remarkably high perceptual acuity for changes in loudness. interval was indicated by a light flash. Target tone duration = 500ms. The target tone was randomly assigned to the first or second interval. Threshold was defined as the mean of the last six turnaround points after the lowest step-size had been reached. - At normal overal listening levels, pure-tone intensity discrimination thresholds are less than 1 dB - In controls, thresholds were measured with a modified Hughson-Westlake procedure using an Interacoustics Diagnostics Audiometer. for standard audiometric frequencies (0.2 - 8 kHz) (Yost, 2007). 3.C. Pure-tone loudness discrimination. - Threshold were measured using a 2I-2AFC procedure with a 2-down, 1-up rule. On each trial, two 500ms, lkHz pure tones were presented, one 1.C. It is well known that damage to the peripheral auditory system causes deficits in at reference intensity (40dB SL per ear for Case Al +; 65dB SPL for normal controls). Threshold was defined as the mean of the last six pure-tone detection as well as pitch and loudness discrimination. turnaround points after the smallest step size had been reached. 1.D. However, the extent to which the auditory cortex plays a critical role in processing 4. Results these basic features of sound remains unclear. A 1kHz detection thresholds C Loudness discrimination thresholds D Monaural loudness discrimination thresholds 35 35 12 —O— Rleh1Esc 10 2. Participants 30 —M— Left Est ANSI 3.8-2004 a. 30 O O e 2.A. Case Al + fi 28 co 25 o. co O O 4 to 3 46 year-old mixed-handed male who ro 20 20 suffered ischemic infarcts of right and left O 6) 0 O CC 2 2 middle cerebral arteries in 1980 and 1981, 15 • 15 A 10 1 respectively, leaving complete or near- O complete lesions of primary auditory 5 O Cabals o Controls COM Al+ 4 Case A14 cortex bilaterally. His second stroke (left x 1. 0 • • • • • hemisphere) was followed by a three-week 125 250 500 1000 2000 4000 0 5 10 15 20 25 30 35 1 2 3 4 5 8 7 89 Case Ai• Conkers Frequency (Hz) Left-ear threshold (dB SPL) AL (dB) - Left ear period of profound deafness during which Figure 2. (A) Case A1+ audiometric thresholds are near the average as measured by the ANSI standard and well within the patient did not respond to sound. He clinically-defined normal limits. (B) Audiometric thresholds at 1kHz for Case A1+ and normal controls are within the normal subsequently began to experience sound limits. Case Al + has thresholds that are lower than several of our normal control subjects. (C) Intensity discrimination as "buzzing noise," though pure-tone thresholds for Case Al + (X) are highly elevated compared with normal controls (O) in both ears. His average thresholds were thresholds remained markedly elevated. 6.5 dB in each ear, several standard deviations above the normal means of 1.6 and 1.7 dB in the left and right ear, respectively. Two months after deafness onset, pure- Error bars give the standard deviation across runs. (D) Individual run data for Case Al + (X) and normal controls (O). Box-and- tone thresholds reamined mildly elevated. whisker plots give the population median, interquartile range, and estimated 95% confidence interval. Eight years after onset, pure-tone detection thresholds were within clinically- 5. Discussion defined normal limits, though the patient 5.A. In Case Al-'-, intensity discrimination thresholds, like pitch discrimination thresholds measured reported difficulty in noisy situations and no longer enjoys listening to music. previously, were highly elevated compared to normal controls while absolute detection thresholds remained well within normal limits, suggesting that brain mechanisms for tone detection and intensity Figure 1. T2 fluid-attenuated inversion-recovery (FLAIR) sequence obtained with a Siemens TIM Trio 3T scanner. discrimination are neurologically dissociable. Continguous sections were 1.0mm thick; in-plane resolution is 0.94mmx0.94mm. TE=494ms, TR=6000ms, IT=2100ms, flip angle = 120 degrees. 5.B. Spared structures - specifically left anterior auditory association cortex and/or the auditory 2.B. Normal Controls brainstem - can mediate coarse loudness perception. - 11 age-matched (mean age = 41.5 ± 6.3) right-handed normal control participants (7 female) with 5.C. Based on the present study and our review of the literature, we propose a hierarchical model of clinically-normal pure-tone audiograms and no reported history of neurological disease. loudness perception in which the primary auditory cortex is necessary for fine-grained intensity discrimination and the auditory brainstem is sufficient for detection of sound. REFERENCE: Yost WA (2006) Burlington, MA: Academic Press. Tramo MJ, Shah GD, Braida LD (2002) J. Neurophysiol 87: 122-139. Levitt H (1971) J. Acoust. Soc. Am 49: Suppl 2:467+. Milner B (1967) Baltimore, MD. Johns Hopkins University Press. pp. 177-195. Swisher LP (1967) Cortex 3:179-193. Hodgson WR (1967) J. Speech Hear. Disord. 32:39-45. Baran JA, Bothfelt RW, Musiek FE (2004) J. Am. Acad. Audiol. 15:106-116. Jerger J, Weikers NJ, Sharbrough FW, Jerger S (1969) Acta Otolaryngol. Suppl. 258:1-51. Jerger J, Lovering L, Wertz M (1972) J. Speech Hear. Disord. 37:523-535. Baru A, Karaseva T (1972) New York, NY. 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