Article Figures & Data
Figures
- Figure 1.
A, Schematic illustration of the stimulus sequence. Example shown is for a valid trial in which a target letter L was presented on the same side as the auditory cue. B, ACOP waveforms averaged over six pairs of posterior electrode sites ipsilateral and contralateral to the sound stimulus (see Materials and Methods) on sound-only (cue-only) trials. The ACOP (contralateral minus ipsilateral difference) begins at ∼200–250 ms and extends to ∼450 ms. The shaded area (300–400 ms) shows the interval in which the ACOP was quantified on the letter-present trials, which had a cue–target SOA of 400 ms. The ACOP difference amplitude averaged over the 300–400 ms interval was highly significant on these cue-only trials (contralateral vs ipsilateral, F(1,15) = 15.83, p < 0.002). Topographical map shows ACOP distribution with lateral occipital maximum. C, ACOP difference amplitudes mapped over successive 20 ms intervals within the 300–400 ms measurement window. The successive scalp distributions are highly similar, indicative of stable neural generators over the 300–400 ms interval.
- Figure 2.
ERP waveforms elicited by lateralized sounds and topographical distributions of lateralized N1 (92–140 ms) and ACOP (300–400 ms) components under valid conditions. N1 waveforms (left column) were averaged over seven homologous pairs of anterior temporal sites, and ACOP waveforms were averaged over six homologous pairs of occipital electrodes. ERP waveforms were collapsed over left and right sound locations and left and right hemispheres to form averaged waveforms recorded contralaterally and ipsilaterally with respect to sound location. Topographical voltage distributions are shown for the contralateral minus ipsilateral difference amplitude, projected onto the right hemisphere. Enlarged N1 negativities were observed for both correct trials (A) and incorrect trials (B), but the ACOP was only elicited on correct trials. The voltage scale shown for the top left pair of waveforms applies to all.
- Figure 3.
Same as Figure 2 but for invalid cueing condition. Enlarged N1 negativities and significant ACOPs were observed for both correct trials (A) and incorrect trials (B).
- Figure 4.
A, Mean ACOP difference amplitudes (contralateral minus ipsilateral) within the time window of 300–400 ms averaged over a cluster of six occipital electrodes. Note that the ACOP was significantly larger for correct than for incorrect trials under the valid cueing condition (p < 0.005) but not for the invalid condition. B, Estimated dipole sources of the ACOP difference amplitudes (300–400 ms), derived from the grand-averaged voltage topographies, were localized to the ventrolateral extrastriate visual cortex (Brodmann's area 19). Colored areas represent maximal current densities of the grand-averaged ACOP difference as determined by LAURA.
- Figure 5.
Left, ERPs to visual targets (letters), recorded at occipital sites I5/I6 contralateral to the target location. These waveforms were obtained by collapsing ERPs recorded from left and right hemispheres elicited by stimuli in the right and left visual fields, respectively. Measurement intervals for the P1 (120–140 ms), N1 (160–190 ms), and P3/P300 (400–500 ms) components are shaded. Right, Topographical voltage distributions for the correct minus incorrect difference amplitudes for each component. Maps depict voltages contralateral to the stimulus on the right side and ipsilateral on the left.
