The longer the reference, the shorter the legs: How response modality affects body perception.

There is a growing interest in the characterization of the internal body model: a stored representation of the metric properties of the body. Tactile Distance Task (TDT) is an experimental procedure for assessing the body metric, based on the perception of distances between tactile stimuli. We aimed at ruling out potential cognitive confounds: the body part being touched, the response estimation method being used, and the replicability of the results. Crucially, we compared two scoring indices (Global shape index vs. Misestimation of the distance) that have been used in the literature assessing the unique contribution of each score. Our data revealed a distortion of body metric perception of the leg. In particular, we found a more substantial reduction in proximo-distal distances rather than in the medio-lateral axis. TDT turned out to be a reliable and replicable method producing consistent results applicable to different body parts. The global shape index was shown to be particularly resistant to contextual experimental factors, while the Misestimation resulted in being affected by the estimation modalities, revealing that the verbal response was the most precise method. Finally, we provided substantial support for the combined use of the two indices as they were shown to give complementary information about body metric representation distortions.