In this study, recordings from O1, O2, 5% above O1, 5% above O2, and Oz for 10 participants revealed that the HbO concentration showed a steady rise for approximately 10 seconds after onset. Changes in HbO (red line), Hb (blue line), and THb (green line) concentration levels averaged across 10 participants for five locations are shown in
Figure 4. Recordings from O1 (1.06 ± 0.09 μM) and O2 (1.2 ± 0.10 μM) showed the greatest change in HbO amplitude with recordings, from locations 5% above them following closely behind (0.62 ± 0.08 μM and 0.86 ± 0.10 μM, respectively). The main effects of location and condition and the interaction between the two were significant for all three chromophore concentrations, specifically for HbO (location [
F(4, 315) = 6.6,
P < 0.001], condition [
F(1, 89) = 191,
P < 0.01], interaction [
F(4, 298) = 7.9,
P < 0.001]), for Hb (location [
F(3, 262) = 3.9,
P < 0.05], condition [
F(1, 89) = 95,
P < 0.001], interaction [
F(3, 285) = 4.5,
P < 0.05]), and for THb (location [
F(3, 310) = 6.4,
P < 0.001], condition [
F(1, 89) = 274,
P < 0.001], interaction [
F(4, 318) = 7.7,
P < 0.001]). Subsequent analysis revealed that the responses at Oz were significantly smaller than those at O1 and at O2 (
P < 0.05) but did not differ significantly from the responses at the locations 5% above them. This was true for HbO, Hb, and THb. The increase observed in HbO concentration was greater than the decrease observed in Hb concentrations. The THb plots showed similar trends to the HbO plots.
Table 1 show the means and standard errors for all changes in chromophore concentrations over the five locations for 10 participants during the last 15 seconds of the 30-second pattern stimulation (after stabilization and before stimulus offset).