A Appendix

A.1 Data fMRI data fMRI activities differ when the same individual sees the same image at different times (Figure 1). Although we use activities and signals interchangeably throughout the paper, what we mean are fMRI betas in the NSD dataset. Betas are not direct measurements of BOLD (blood-oxygenationlevel dependent) changes, but the inferred activities from BOLD signals through GLM (general linear models). The reason for using betas instead of direct measurements is that image stimuli are shown consecutively to the subjects without prolonged delay, and activities triggered by the previous image can interfere with the next one if there is no proper separation. Authors of NSD proved the effectiveness of their GLM approach with much improved SNR in the betas over raw measurements [3].