Context-dependent role of selective attention for change detection in multi-speaker scenes

The impacts of training on change deafness and build-up in a flicker task

Performance on auditory change detection tasks can be improved by training. We examined the stimulus specificity of these training effects in behavior and ERPs. A flicker change detection task was employed in which spatialized auditory scenes were alternated until a "change" or "same" response was made. For half of the trials, scenes were identical. The other half contained changes in the spatial locations of objects from scene to scene. On Day 1, participants were either trained on this auditory change detection task (trained group), or trained on a non-auditory change detection task (control group). On Day 2, all participants were tested on the flicker task while EEG was recorded. The trained group showed greater change detection accuracy than the control group. They were less biased to respond "same" and showed full generalization of learning from trained to novel auditory objects. ERPs for "change" compared to "same" trials showed more negative going P1, N1, and P2 amplitudes, as well as a larger P3b amplitude. The P3b amplitude also differed between the trained and control group, with larger amplitudes for the trained group. Analysis of ERPs to scenes viewed prior to a decision revealed build-up of a difference between "change" and "same" trials in N1 and P2. Results demonstrate that training has an impact early in the "same" versus "change" decision-making process, and that the flicker paradigm combined with the ERP method can be used to study the build-up of change detection in auditory scenes.

Context-dependent role of selective attention for change detection in multi-speaker scenes

Disappearance of a voice or other sound source may often go unnoticed when the auditory scene is crowded. We explored the role of selective attention for this change deafness with magnetoencephalography in multi-speaker scenes. Each scene was presented two times in direct succession, and one target speaker was frequently omitted in Scene 2. When listeners were previously cued to the target speaker, activity in auditory cortex time locked to the target speaker's sound envelope was selectively enhanced in Scene 1, as was determined by a cross-correlation analysis. Moreover, the response was stronger for hit trials than for miss trials, confirming that selective attention played a role for subsequent change detection. If selective attention to the streams where the change occurred was generally required for successful change detection, neural enhancement of this stream would also be expected without cue in hit compared to miss trials. However, when listeners were not previously cued to the target, no enhanced activity for the target speaker was observed for hit trials, and there was no significant difference between hit and miss trials. These results, first, confirm a role for attention in change detection for situations where the target source is known. Second, they suggest that the omission of a speaker, or more generally an auditory stream, can alternatively be detected without selective attentional enhancement of the target stream. Several models and strategies could be envisaged for change detection in this case, including global comparison of the subsequent scenes.