Figure 4. Effects of congruency on test sound ERPs. Congruent
(blue ) and incongruent (red ) test sound evoked
grand-averaged ERPs, as well as their difference wave (congruent –
incongruent, in black ) are plotted at the Fz and the Pz
electrodes. A series of topographical plots showing the difference
between congruent and incongruent sounds across time and sensor space
illustrates the spread of the significant positive cluster across time.
Sensors exhibiting significant differences across conditions are
highlighted in black.
Correlations between neural and behavioural effects of
agency
Differences in %Correct between the agent and observer condition
exhibited a great variability across individuals (M = 9.7%, SD = 7.1%,
range = 0-26%). Thus, active learning was more efficient than learning
from observation for some, but not all participants. Aiming to uncover
the neural underpinnings of active learning benefits, we tested for
possible correlations between the benefit that a participant would have
of agent over observer acquisition for their memory of the
movement-sound associations, and the degree to which agency modulated
auditory ERPs during early stages of acquisition, when the active
learning benefits were maximal.
We found a significant correlation between agency effects on N1
amplitude of acquisition sounds at Fz in the early learning stage and
agency effects in memory performance [r(21) = 0.6, p =
.002]. The stronger the N1 agency effect that a participant
experienced during early acquisition, the stronger the memory advantage
for the agent vs. the observer conditions (figure 5).
In order to visualize this finding, we decided to split the participants
into two groups, using the median of the difference between agent and
observer %Correct as a cutoff point (M = 7.8%).
Participants who had stronger behavioural agency effects than the median
were considered “active learners” (N = 11), and participants that fell
below that median of behavioural effects were considered “indifferent
learners” (N = 12).
We compared the overall performance (agent + observer condition) of
active and indifferent learners. Active learners performed overall
better in the behavioural task (M = 78%, SD = 13%) as compared to
indifferent learners (M = 68%, SD = 11%). A two-sample t-test showed
that this difference is statistically significant
[t(21) = 3.844, p < .001, d =
0.80].