Spontaneous Eye Movements following Touch Reflect Canonical Body Postures

Humans constantly move when interacting with their environment. This constant movement challenges the processing of tactile stimuli because localizing tactile input on the body requires considering postural information. According to a well-established view, stimuli are localized on the body based on information about the current body posture, via a process called tactile remapping. Recently, an alternative view has emerged, arguing that stimuli are rather localized based on prior information about the default body posture. We confronted these accounts by recording the spontaneous gaze behavior of human participants of either sex following tactile stimulation of the fingers of their right hand, placed in different postures. With the hand placed palm-down, the left-to-right direction of gaze shifts reflected the thumb-to-little finger arrangement of the digits. Placing the hand palm-up reversed this pattern. Critically, when the hand was placed in a mid-pronated posture, resting on its outer side, tactile stimuli induced horizontal gaze shifts similar to those observed in the palm-down posture, despite the vertical arrangement of the fingers. Moreover, crossing the right hand to the left of the body midline shifted the gaze rightward, opposite to the current hand position. Finally, when the five fingers were stimulated, the reference frame reflected in gaze behavior was centered on the middle finger, whereas it was centered on the ring finger when only the last three fingers were stimulated. These findings show that localizing tactile stimuli on the body activates priors about canonical body postures, and these priors are selected according to the stimulated area. Significance Statement Localizing tactile stimuli on the body requires access to postural information. Whether this information regards the current or the default body posture is debated. Using eye-tracking, we uncovered which postural information is activated while human participants localized stimuli on their hand placed in different configurations. The study provides straightforward evidence that we use information about the body in canonical postures to localize tactile stimuli on body parts. Hence, we show that tactile localization induces spontaneous gaze shifts whose direction depicts a hand in a palm-up or in a palm-down posture, even when a different hand posture is adopted. Moreover, the study provides compelling evidence that instead of a single default posture, different canonical postures are activated depending on the task.