Figure 1.

Adapted from Foxe et al. (1998). (A) Task schematic. Participants viewed a cue word (BEEP or FLASH) on a computer screen to start each trial. The cue indicated whether audition (BEEP) or vision (FLASH) was relevant for the trial. After a 1085-ms cue-target interval of no stimulation, the participants were presented with a pair of red disks on the screen and a concurrent pair of tones via headphones. For the visual target, one of the red disks was displaced slightly with respect to the reflection of the other disk across the vertical meridian (on standard trials, the two disks were symmetric about the vertical meridian). For the auditory target, the two tones had slightly different pitches (the two tones had the same pitch on standard trials). Participants were instructed to press a button upon detection of a target in the cued sensory modality, and to withhold response otherwise. Participants maintained central fixation throughout the trial. (B) Scalp current-density (SCD) waveforms from one subject (BH) at a right parieto-occipital scalp site to the beep (black trace) and flash (red trace) cues. (C) The same waveforms, band-pass filtered (8–14 Hz) reveal greater stimulus-locked alpha activity in the 300-ms (yellow box) before onset of the compound S2 (1085 ms, dashed blue line) when attention has been cued to the auditory modality. (D) Temporal–spectral evolution (TSE) waveforms for the alpha band, derived for the cue-target interval by full-wave rectifying the individual band-pass filtered trials prior to averaging, show a difference in the total alpha amplitude (i.e., both stimulus-locked and non-stimulus-locked). (E) Posterior view of the topographical distribution of current-density 975 ms following presentation of beep (top) and flash (bottom) cues for one subject (KH). Greater parietal field power is evident for the auditory cue compared to the visual cue. Red iso-contour lines (0.1 μV/cm² increments) indicate positive values and blue, negative.