Abstract

In a loudness dependency (LDAEP) paradigm, auditory N1/P2 covaries with stimulus intensity. In a MMN paradigm, intensity deviants produce a MMN but it is unclear to what extent this effect is affected by loudness. These relations were explored in a modified MMN task in which binaural tones (1000 Hz; 40-ms; 500 ms ISI) were presented at four intensities (70-100 dB SPL), using one intensity in a block as standard (70%) and the remaining three as deviants (10% each). Standards (across blocks) and block order (across subjects) were counterbalanced. An additional block used equiprobable (25%) intensities to validate LDAEP effects. Healthy adults (N = 13) watched a silent film and reported its content (underwater scenes) after each block. Using 72-channel ERPs, temporal principal components derived from reference-free CSD waveforms characterized neuronal generator patterns underlying loudness dependency and MMN, which included: 1) N1 sink (113 ms peak; tangential sink/source topography); 2) temporal N1 sink (159 ms; radial temporal lobe sink); 3) P2 source (218; midline and bilateral temporal sources). These three factors revealed robust, monotonic relationships with intensity for standards and equiprobable stimuli. In marked contrast, tangential N1 was augmented with increases but not decreases in deviance. Whereas temporal N1 sink and temporal P2 sources for deviants showed a similar relationship with intensity, these factors had secondary midline topographies (N1: frontocentral; P2: midcentral) that were predominantly responsive to large increases (≥ 20 dB) but not decreases in deviance. These effects were also observed for factor score differences (deviant minus standard) revealing characteristic MMN (temporal N1 sink) and P3a (P2 source) topographies. These findings suggest that MMN of tone intensity is elicited primarily by louder rather than softer deviants, and that LDAEP effects may be affected by a selective MMN for loud tones. [Supported by NIMH MH036295]