Fig 1.
Panel A) Flowchart of the subject groups and stimulations. Box 1 illustrates the sample used to investigate the effect of age and flicker-rate on steady-state VEP power responses evoked by a complex image. Box 2 illustrates the sample used to investigate the correlation between intelligence and steady-state VEP measurements. Panel B) Schematic illustration of the stimulation procedure, with 6-second stimulation epochs, each indicated by a trigger. The abbreviation “ISI” denotes Inter-Stimulus Interval.
Fig 2.
Illustration of the electrophysiological response (steady-state evoked potential) when stimulating with 8 Hz and 36 Hz in, respectively, a young and an old adult from our sample.
Panel A) shows the amplitude at the Oz electrode, in the time domain filtered at the alpha range (8–12 Hz), and in the gamma range (30–70 Hz), with reference to M1 and M2. Panel B) shows time frequency spectrograms for the occipital electrodes (Oz) with data filtered at 0.5–250 Hz. The resolutions used are 126 ms in the alpha range, and 256 ms in the gamma range. The max frequency shown is 62.5 Hz. Note that stimulation with an 8 Hz flicker rate generated results suggestive of a sub-harmonic response. Panel C) shows 2D contour maps with a Laplacian transformation for 8 Hz (left) and 36 Hz (right). Panel D) shows 2D position plots of the spatial distribution filtered at 0.5–250 Hz, shown in the range of 6–10 Hz and 33–37 Hz. Clear peaks at 8 Hz and 36 Hz are seen for both age groups, with an indication of a greater response in the young adults.
Table 1.
The association between power responses and age group, flicker-rate, as well as scalp regions.
Table 2.
Correlation between the difference in relative occipital power and age.
Table 3.
Correlation between ΔRV and intelligence test score.
Table 4.
Correlation between ΔRV for the three main parts of the intelligence test score.
Fig 3.
Added-variable plot of the partial correlation between intelligence (measured with IST-2000-R) and the alpha-to-gamma difference in relative visual-area power (ΔRV).
The fit of the red line is generated by linear regression, estimated with OLS, when controlling for the individual alpha level (i.e., Rα,V), global cognition (measured with ACE), and speed of processing (i.e., minus-Trail-Making A, minus-Trail-Making B, and SDMT) (see Table 3, Column 10). The black line is fitted with LOESS smoothing. The gray area represents the 95% confidence limit. The dotted lines represent the bounds of the 95% prediction limits.