Distinguishing cognitive effort and working memory load using scale-invariance and alpha suppression in EEG

Area of Science:

• Neuroscience
• Cognitive Science
• Brain Activity Analysis

Background:

• Cognitive effort is difficult to quantify, despite its intuitive nature.
• Brain activity's default state is scale-invariant; deviations may indicate cognitive effort.
• fMRI studies show promise, but EEG is better suited for scale-invariance analysis due to its wider frequency range.

Purpose of the Study:

• To validate the relationship between EEG-measured cortical activity scale-invariance (H) and task load.
• To use scale-invariance as a neural signature to differentiate cognitive effort from working memory load.
• To investigate EEG scale-invariance suppression as a proxy for cognitive effort.

Main Methods:

• Conducted two working memory (WM) experiments with varying set sizes.
• Recorded cortical activity using electroencephalography (EEG).
• Analyzed scale-invariance (H) of EEG signals and compared it with behavioral performance and alpha-band desynchronization.

Main Results:

• Scale-invariance (H) monotonically decreased as WM set size increased.
• This decrease in H continued even when set size exceeded WM capacity.
• H suppression contrasted with behavioral performance and alpha-band activity, which plateaued at maximum WM capacity.

Conclusions:

• This study provides the first evidence of scale-invariance suppression in EEG due to task difficulty.
• Scale-invariance suppression (H) can quantify cognitive effort, even at maximum working memory capacity.
• EEG-based scale-invariance offers a novel method for measuring cognitive effort.