Whose Thought Is This? When the Sense of Ownership Fails

The experience described is of a thought occurring in one's own mind while feeling that one is not its author, so that the person reports thinking it and simultaneously reports that it is not theirs. The distinction that makes this coherent is between ownership, the sense that an experience is occurring in me, and agency, the sense that I brought it about, and reports of this kind appear to preserve the first while losing the second. That is what separates the phenomenon from an ordinary unwanted or intrusive thought, which almost everyone has and which is recognised as one's own even when unwelcome. It is classified as one of a group of symptoms involving experiences of control, and it occurs mainly in schizophrenia.

Several reports form a cluster that appear to share a mechanism:

• •Thoughts experienced as inserted by an external source
• •Thoughts experienced as withdrawn or removed from the mind
• •Thoughts experienced as broadcast, audible or accessible to others
• •Movements experienced as made by someone else using one's body
• •Emotions and impulses experienced as imposed rather than arising
• •In each case the content is acknowledged as occurring and the authorship is not

The most developed account involves the mechanism by which the brain distinguishes self-generated from external events. When an action is initiated, a copy of the motor command is used to predict its sensory consequences, and the prediction is compared with what actually happens, which is how the system knows that a movement was self-produced and why self-produced touch is less intense than the same touch from another person, an effect demonstrable with a simple tickling experiment. Applying the same framework to inner speech and thought suggests that a failure in the prediction would leave a thought arriving without the marker indicating it was self-generated, which the person then experiences as foreign and explains by attributing it to an outside source. Evidence includes findings that affected individuals show reduced suppression of self-produced sensation.

The mechanism proposed to explain the clinical phenomenon operates in everyone and its ordinary effects are easy to notice. Self-produced touch feels weaker than identical touch from another person, which is why tickling oneself does not work and which has been measured with an apparatus that delays or displaces a self-produced touch and finds the sensation strengthens as the delay grows. The visual world stays still when the eyes move, because the system predicts the shift and cancels it, and pressing gently on the side of the eyeball makes the scene jump precisely because that movement was not predicted. Speaking aloud suppresses the auditory response to one's own voice. All of these involve the same prediction and comparison, and each can be disrupted experimentally, which is what makes the explanation testable rather than merely plausible.

The phenomenon bears directly on a claim that was long treated as beyond question, namely that one cannot be mistaken about whether one is the subject of one's own thought. If a person can be aware of a thought occurring in their own mind while sincerely denying that it is theirs, then that immunity is either false or needs restating more carefully, and most of the philosophical literature takes the second route by separating the various things the claim might mean. The debate has produced a considerably more precise vocabulary for describing the sense of self, distinguishing ownership from agency and both from the sense of being a continuing person. It has also prompted caution about building theories of mind on introspective reports assumed to be universal, since the reports considered here come from people whose experience differs.

The report is of a thought occurring in one's own mind while feeling one is not its author, which separates ownership from agency and distinguishes it from an ordinary intrusive thought. The leading account involves a failure in the mechanism that marks self-generated events, the same one that makes self-produced touch feel weaker. It challenges the claim that one cannot be mistaken about whose thought one is having.