Figure 2 . Topography of mean 15 Hz ssVEP activity averaged
across stimuli in Habituation and Acquisition (A) and the corresponding
FFT power at electrode Oz (B). The signal shows the involvement of the
visual cortical areas at the driving frequency of 15 Hz.
SCR was filtered offline with a high cutoff of 1 Hz and the signal was
segmented in epochs of -1000 ms to 8000 ms after stimulus onset. The
signal was quantified using a manual Foot-to-Peak method with a latency
time-window of 900 ms – 4000 ms after stimulus onset (Boucsein et al.,
2012). We considered the first response peak following the foot located
at 500 ms after the foot point until the end of the time window.
Responses below 0.02 μS were scored as zero. Finally, SCRs were log
transformed (log [1 + SCR]) to normalize the distribution and mean
responses were calculated per condition and phase. We decided not to
exclude non-learners based on SCR for two reasons: first, SCR is not a
direct measure of learning and excluding participants solely on this can
lead to sample bias (Lonsdorf et al., 2019). Second, since our
experimental manipulation included different reinforcement schedules
smaller SCR amplitude could be due to the experimental manipulation.