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The experience that I feel myself to be the agent of my own movements is inherent to any volitional action. Impairments of this basic experience both in normal subjects and in patients with focal brain lesions may help to shed light on the nature of this perceptual mechanism, entitled authorship processing. We here report a perceptual illusion during invasive electrical cortical stimulation in a patient who underwent presurgical evaluation for epilepsy surgery. While stimulating the right frontal eye field electrically, which induced a contralateral eye and head deviation, the patient repeatedly had the illusion of performing this movement volitionally. Our observation suggests that ambiguous contextual situations may produce impairment of authorship processing. The findings are in line with current neuroscientific data, suggesting that authorship knowledge is not inherent to any volitional act, but requires information and inference for any given action. This notion also shows striking similarities to the Freudian concept of the synthetic function of the ego. By harmonizing conflicting elements, the synthetic function of the ego ensures unanimity of action and—as shown in our patient—also of authorship and free will.