Shrinking the skin: Motion results in compressive mislocalization of
stimuli applied 10 s post-motion
Abstract
Localizing touch on the skin requires integration of multiple spatial
signals, including reference landmarks and motion cues. It is well known
that motion patterns can bias the perceived endpoint of motion. However,
it is unknown whether static touch presented post-motion is also
distorted. To investigate this, we presented space-changing motion
patterns and tested position perception 1 s and 10 s post motion. We
used a brush moving along the forearm at 15 cm s-1, brushing 4.5 cm skin
patches near the elbow and near the wrist, skipping a 10-cm long
metal-shielded patch in the middle (‘numb spot’). It accelerated to 100
cm s-1 across the shielded gap in an attempt to create an illusion of
continuous motion between the separate brushed areas. After several such
deceptive motions, 12 participants indicated the locations touched by a
von Frey filament near the elbow and wrist, all within the previously
brushed areas. Localization responses shifted 4 – 10 mm toward the numb
spot in the skipped-patch condition compared to controls with either
continuous brushing across the full forearm, or brushing the same
patches without acceleration. This spatial distortion was equally strong
1 s and 10 s after motion offset with only isolated location-specific
differences between delays. In addition, participants’ sketches
indicated a reduction in perceived gap size. We propose that
participants used the brushed fields as reference frame for
localisation, with the high-velocity motion compressing the perceived
space between them. This means that motion-defined boundaries can serve
as spatial landmarks for static touch.