Head Displacement Shifts the Perceived Location of Touches in opposite Directions Depending on the Task

The perceived location of a touch shifts with eye or head position, suggesting touch is coded in a visual reference frame. Our lab has previously reported shifts in the direction of eccentricity, but Ho and Spence (2007, Brain Res. 1144: 136) reported head-related shifts in the opposite direction. These studies differed by body part touched (arm vs. torso), the nature of the touch (tap vs. vibration) and whether perceived touch location was recorded with head centered or eccentric. We performed a series of experiments applying vibration to the torso and measuring perceived location using a visual scale. We replicated Ho and Spence using trials blocked by head position and recording perceived position with the head displaced. A second experiment used randomized head displacements with the head centered before responding. In a control experiment head was centered during the touch and eccentric for response. Perceived touch location shifted in the direction opposite to head position under the blocked design, in the same direction as head position in the randomized design and not at all in the control. Results are discussed in terms of allocentric and egocentric coding mechanisms needed to complete each condition.