Figure 1.

A, Tonotopic mapping was used to indentify primary auditory cortex in each subject individually (n = 6). In each hemisphere (n = 12), two mirror-symmetric gradients (high-to-low and low-to-high) corresponding the primary areas hA1 and hR were manually outlined on the medial two-thirds of Heschl's gyrus (one same right hemisphere shown). Each voxel within the selected region was labeled according to its preferred frequency between 88 and 8000 Hz in half-octave steps. B, Next, in the selective attention (dual-stream) experiment, low (250 Hz)- and high (4000 Hz)-frequency patterned tonal streams were presented concurrently to different ears. Subjects were cued to attend to only one stream at a time, alternating the attended stream every 30 s (blocks of attend high vs attend low). A 2-IFC experiment was used to focus attention on the cue stream (see Materials and Methods). The stimulus itself did not change across blocks, only the attentional state. Ear-side was counterbalanced across runs allowing the comparison of effects of frequency-specific attention (attend high vs attend low collapsed across sides) to effects of spatial-selective attention (attend contralateral vs attend ipsilateral collapsed across frequencies).