We report a study designed to investigate the perspective that people take with respect to letters drawn on their body surface: Are the letters perceived from an external point of view (i.e., as if located in front of the observer) or from an internal point of view (i.e., as ‘mirror reversed’). We investigated the perspective taken by participants as a function of 3 parameters: Letters location (the letters were presented on the back or stomach), letter presentation (the letters were drawn from top-to-bottom or from bottom-to-top), and gaze direction (the participants were sometimes able to view the stimulated body part). In Experiment 1, the participants were presented with letters drawn on their stomach by means of a tactile ‘corset’ consisting of a 3x3 array of 9 vibrators. The participants made normal vs. mirror-reversed (i.e., left/right reversed) judgments concerning the letters C and L presented either ‘Normal’ or ‘Mirror reversed’. The participants completed the task while looking to the front, while looking down at their stomach, or while looking at the mirror image of their stomach in a mirror placed directly in front of them. Each condition was run with the two target letters drawn either from top-to-bottom or from bottom-to-top. In this, and in all the experiment reported here, there was no main effect of Gaze direction on the RT or error data. A significant effect of Letter direction in the error data reflected the fact that participants were more likely to consider the letters from an external point of view when presented from top-to-bottom (77%) than when presented from bottom-to-top (69%). The RT data revealed a similar pattern of results with participants responding faster for the letters presented from top-to-bottom.
In Experiment 2, participants performed the same task with the letters being presented on their back. The participants either looked at a blank screen or else at a real-time video recording of their back presented on the screen. The participants nearly always considered the letters from an external point of view. With respect to RTs, consistent with Experiment 1, the results revealed a significant effect of Letter direction with the participants responding faster for the letters presented from top-to-bottom. Finally, in Experiment 3, the participants had to recognize the letters b, d, p, and q that were presented either on their stomach or back, while looking either at a blank screen or at the stimulated body part (i.e., the back or stomach) on the screen. Participants responded more rapidly when the letters were presented on their back than when they were presented on their stomach.
Overall, this study revealed that the participants most often adopted an external point of view (i.e., they perceived the letters as being located in front of them) rather than an internal point of view. However, participants made more consistent (and faster) judgments for letters presented on their back than on their stomach. They also responded more rapidly to letters presented from top-to-bottom than from bottom-to-top. Performance was not influenced by whether participants viewed the stimulated body part or not.