Auditory Mismatch Negativity in Response to Changes of Counter-Balanced Interaural Time and Level Differences

Comparison of sound location variations in free and reverberant fields: An event-related potential study

This study compares event-related potentials (ERPs) elicited by variations of sound location in free and reverberant fields. The virtual sound sources located at azimuths 0°-40° were synthesized with head-related transfer functions and binaural room impulse responses for free and reverberant fields, respectively. The sound stimulus at 0° was assigned as standard in the oddball paradigm. Results show that the P3 amplitude is larger in the free field and acoustical conditions have no significant effect on the amplitudes of N2 and mismatch negativity. Moreover, a linear relationship between sound angle and amplitude of ERP components is observed.

Influence of Audiovisual Training on Horizontal Sound Localization and Its Related ERP Response

The objective was to investigate the influence of audiovisual training on horizontal sound localization and the underlying neurological mechanisms using a combination of psychoacoustic and electrophysiological (i.e., event-related potential, ERP) measurements on sound localization. Audiovisual stimuli were used in the training group, whilst the control group was trained using auditory stimuli only. Training sessions were undertaken once per day for three consecutive days. Sound localization accuracy was evaluated daily after training, using psychoacoustic tests. ERP responses were measured on the first and last day of tasks. Sound localization was significantly improved in the audiovisual training group when compared to the control group. Moreover, a significantly greater reduction in front-back confusion ratio for both trained and untrained angles was found between pre- and post-test in the audiovisual training group. ERP measurement showed a decrease in N1 amplitude and an increase in P2 amplitude in both groups. However, changes in late components were only found in the audiovisual training group, with an increase in P400 amplitude and decrease in N500 amplitude. These results suggest that the interactive effect of audiovisual localization training is likely to be mediated at a relatively late cognitive processing stage.

Interaction of interaural cues and their contribution to the lateralisation of Mongolian gerbils (Meriones unguiculatus)

The main sound localisation cues in the horizontal plane are interaural time and level differences (ITDs and ILDs, respectively). ITDs are thought to be the dominant cue in the low-frequency range, ILDs the dominant cue in the high-frequency range. ITDs and ILDs co-occur. Their interaction and contribution to the lateralisation of pure tones by Mongolian gerbils was investigated behaviourally using cross-talk cancellation techniques for presenting ITDs and ILDs independently. First, ITDs were applied to pure tones with frequencies ≤ 2 kHz to the ongoing waveform, at the onsets and offsets, or in both the ongoing waveform and at the onsets and offsets. Gerbils could lateralise tones only if ongoing ITDs were present indicating that ongoing ITDs are decisive for the lateralisation of low-frequency tones. Second, an ITD was added to 2-to-6-kHz tones with varying ILD. Gerbils' lateralisation was unaffected by the ITD indicating that a large ILD provides a strong lateralisation cue at those frequencies. Finally, small ILDs were applied to 2-kHz tones with an ongoing ITD, pointing either to the same or opposing sides as the ITD. Gerbils' lateralisation was driven by the ITD but strongly affected by the ILD indicating that both interaural cues contribute to the lateralisation.