Presenting No Hurst for the weary: Suppressed scale-invariance in brain activity signifies effortful processesDespite being intuitive, cognitive effort has proven difficult to quantify. In Studies 1 and 2, we validated the correspondence between scale-invariance (H) of cortical activity recorded by EEG and task load during two working memory (WM) experiments with varying set sizes. We used this neural signature to disentangle cognitive effort from the number of items in WM. Our results showed monotonic decreases in H with increased set size, even after set size exceeded WM capacity. This behavior of H contrasted with behavioral performance and an oscillatory indicator of WM load (i.e., alpha-band desynchronization), both of which showed a plateau at difficulty levels surpassing WM capacity. In Study 3, we used H measured with fMRI to predict learning in a dual n-back working memory task. We hypothesized that low H during learning delineates effortful processing which can be used to predict improvement, or lack thereof, in task performance. Our results show that lower H during learning and during a resting interval prior to final task performance distinguished people who did not improve on the task (non-improvers) from those who improved, despite similar baseline performance. As a comparison, fMRI functional connectivity strength did not reliably classify improvers vs. non-improvers. Together these results provide the first evidence for the suppression of scale-invariance in EEG due to task difficulty, and suggest that H suppression may be used to quantify levels of cognitive effort absent of apparent behavioral performance differences which can be utilized to predict learning.