Fig. 1.

(a) Experimental design for $n$-back tasks. (b) fNIRS headset with eight sources and seven detectors to give a total of 20 channels at source–detector distance of 3 cm. (c) An enlarged view of the schematic in (b) showing positions of the 10-10 system (Fp1, Fpz, Fp2, AF7, AF3, AFz, AF4, AF8, F5, F3, F1, Fz, F2, F4, and F6) and the 10-5 system (AFp3, AFp4, AF5h, AFF1h, AFF2h, and AFF6h) covered by the sources and detectors.