Representation of the four energy ranges considered for the computation of spectral lags (shaded filled regions). Blocks defined by long and short dashed and dotted lines represent the full energy range of each Fermi detector (as labeled). For each GRB in the sample, the light curve extracted in Band 1 (10–100 keV) is cross-correlated (blue arrows) with those obtained in Band 2 (150–500 keV), Band 3 (500 keV–1 MeV), and Band 4 (30–100 MeV) in order to obtain the corresponding lags τ₁₂, τ₁₃ and τ₁₄.