Why Can't You Tickle Yourself?

Try to tickle the centre of your own palm and an apparently trivial experiment becomes an epistemological oddity. The fingers move, the skin registers contact, the nerves convey their electrochemical dispatches and the brain receives the resultant commotion. Yet the expected frisson is conspicuously absent. Nothing in the corporeal choreography seems defective. What has vanished is surprise. Your hand can touch you with perfect anatomical fidelity, but it cannot quite take you unawares.

The cerebellum helps illuminate this curious insouciance. Among its functions is the prediction of the sensory consequences of voluntary movement. Before the fingers reach the skin, the nervous system has already conjectured the character of the impending sensation. When the anticipated consequence arrives, the corresponding sensory signal can consequently be attenuated. Conscious experience is thus not a passive receptacle into which sensations are deposited. It is partly constituted by the discrepancy between prognostication and occurrence. Where anticipation and actuality converge too perfectly, sensation forfeits some of its phenomenological salience.

This mundane neurological arrangement acquires an altogether less mundane significance when considered alongside the problem of self awareness. We habitually conceive consciousness as an inward theatre in which a sovereign subject surveys its own sensations, intentions and representations. Yet the failure of self tickling insinuates an inconvenient possibility. The self may be incapable of manufacturing, from within its own precincts, the very estrangement that renders experience arresting. Introspection can turn its gaze inward, but it cannot effortlessly conjure alterity. The observer and the observed remain implicated in the same predictive apparatus.

Perhaps this is why the presence of another consciousness possesses such extraordinary phenomenological potency. Another person introduces intentionality without granting us complete foreknowledge of its consequences. Their gesture can confound expectation. Their silence can acquire an almost sepulchral eloquence. Their expression can retroactively transfigure the meaning of words that moments earlier appeared unambiguous. Their refusal can expose the contingency concealed beneath our convictions. The other does not merely furnish companionship. The other punctures the presumptive sovereignty of the self.

An objection is readily available. Sensory attenuation demonstrates a neurological mechanism, not the metaphysical indispensability of another person. A sufficiently complex brain can generate prediction errors internally through conflicting representations, anomalous memories or unforeseen neural activity. To infer from the impossibility of self tickling that consciousness logically requires another mind would therefore be an instance of philosophical overreach.

Yet the more defensible proposition is subtler. What the other supplies is epistemic resistance. Another mind constitutes a source of intentional behaviour whose consequences cannot be completely precomputed from one's own standpoint. This resistance matters because an existence perfectly congruent with our predictions would gradually become experientially indistinguishable from an extension of ourselves. The other restores contingency to perception.

Consciousness may not be a hermetic chamber in which the subject finally discovers itself. It may be the perturbation that occurs when the subject encounters something its predictive sovereignty cannot absorb.

This may explain the strange ambivalence of human intimacy. We desire recognition from others while simultaneously resenting the jurisdiction their perceptions exercise over our self conception. A stranger's glance can suddenly disclose our posture. A lover's silence can render absence palpable. A child's question can anatomise an assumption that familiarity had rendered invisible. In each instance, another consciousness makes our own consciousness more conspicuous by refusing to become its obedient mirror.

The paradox is therefore almost perverse. We imagine self knowledge as the triumph of inward scrutiny, yet some of the most consequential knowledge of the self arrives through encounters with what the self cannot completely assimilate. Consciousness may not be a hermetic chamber in which the subject finally discovers itself. It may be the perturbation that occurs when the subject encounters something its predictive sovereignty cannot absorb.

Your own fingers cannot surprise you because they are already incorporated into the economy of your expectations. Another person can. And perhaps that infinitesimal difference between prediction and surprise is where the other begins, and where the self first becomes visible.