Two-Stage Processing of Sounds during Attention Figure 7. Spatial extent of sustained activity and population-level frequency tuning. Similar to Figure 6, but for the sustained response range showing the most prominent attention effects (300–400 ms). The attention effects are more consistent in the left hemisphere, but show no clear within-hemisphere differences. The data in the right hemisphere are more variable and noisy, showing less consistent masker type specificity in the response magnitude than left hemisphere. Note that due to long latency, the evoked response visualization in the right hemisphere is showing activity already in frontal areas, possibly related to some higher-order cognitive processes not handled in this study. Notably this frontal activity did not show any masker dependency. doi:10.1371/journal.pone.0046872.g007 supporting previous findings [7]. These results revealed that a strong attentional demand induces changes almost instantaneous- ly, with earlier modulation of the neural population generating the M100 response in both left and right hemisphere posterior secondary auditory areas. After the initial onset response, sustained response at a somewhat later latency showed clear enhancement in sound-feature selectivity in more medial regions of the left hemisphere. Figure 8. Behavioral data. (A) Detectability (+SEM) and (B) reaction time (+SEM) measures show basically how the task requirements during AttAud condition changed, with gradual increase in d’ and decrease in RT with the wider notches. AttVis control task was intended to be comparable to AttAud, and d’ suggests that the difficulty level was well adjusted in comparison with AttAud, thus probably not causing changes in subjects’ vigilance level (see Fig. 9). doi:10.1371/journal.pone.0046872.g008 PLOS ONE | www.plosone.org 8 October 2012 | Volume 7 | Issue 10 | e46872