The magnitude of BOLD response at each point along the trajectory was established by taking the mean BOLD magnitude associated with every node which (i) lay within 2 mm of that point on the flat surface (ii) was closer to that point than to neighboring points on the trajectory.
Thus, our faces and animals stimuli were distinguished in terms of BOLD magnitude, but only in the FFA and the OFA, as expected.
Specifically, the CO/DA+ and FP clusters differed in terms of overall BOLD magnitude, time-to-peak and width of the HRF.
As we did for physical difference, we searched for regions showing repetition suppression effects, that is, linear decrease of BOLD magnitude as the perceptual difference between consecutive stimuli decreased.
For each condition the predicted BOLD magnitude was calculated by taking the cumulative sum of the full execution process over the length of each trial, then averaging across trials.
Both repeaters and non-repeaters showed significant stimulus-specific differences in BOLD response magnitude (for % magnitude in non-repeaters F = 3.69, p = 0.023; in repeaters F = 6.32, p = 0.002, one-way ANOVA).
The voxelwise linear coupling across the visual cortex strongly supports a homogeneous hemodynamic response in ER paradigms, though the BOLD response magnitude varies substantially over a wide range across the visual cortex.
There was also no correlation of % tutor-pupil song motif similarity with the mean BOLD response magnitude (r = 0.11, p = 0.79) in repeaters and non-repeaters (r = −0.2, p = 0.64).
Scatterplots of non-normalized BOLD response magnitude in Figure 3 highlight the weaker responses to TUT in repeaters by the fact that data points (red dots) from nearly every single repeater fall below the unity ratio diagonal when CON and BOS are plotted against TUT.
At each acquisition timepoint (i.e., for each of the 7 FIR regressors), we identified voxels in which BOLD response magnitude was systematically correlated with trial-by-trial RT differences (p<.05 uncorrected, one-tailed) in the same direction in all five samples (i.e., positively correlated in all samples or negatively correlated in all samples).
