Task demands affect spatial reference frame weighting during tactile localization in sighted and congenitally blind adults

Abstract

19Task demands modulate tactile localization in sighted humans, presumably through weight adjustments 20 in the spatial integration of anatomical, skin-based, and external, posture-based information. In contrast, 21 previous studies have suggested that congenitally blind humans, by default, refrain from automatic 22 spatial integration and localize touch using only skin-based information. Here, sighted and congenitally 23 blind participants localized tactile targets on the palm or back of one hand, while ignoring simultaneous 24 tactile distractors at congruent or incongruent locations on the other hand. We probed the interplay of 25 anatomical and external location codes for spatial congruency effects by varying hand posture: the palms 26 either both faced down, or one faced down and one up. In the latter posture, externally congruent target 27 and distractor locations were anatomically incongruent and vice versa. Target locations had to be 28 reported either anatomically ("palm" or "back" of the hand), or externally ("up" or "down" in space). 29Under anatomical instructions, performance was better for anatomically congruent than incongruent 30 target-distractor pairs. In contrast, under external instructions, performance was better for externally 31 congruent than incongruent pairs. These modulations were evident in sighted and blind individuals. 32Notably, distractor effects were overall far smaller in blind than in sighted participants, despite 33 comparable target-distractor identification performance. Thus, the absence of developmental vision 34 seems to be associated with an increased ability to focus tactile attention towards a non-spatially 35 defined target. Nevertheless, that blind individuals exhibited effects of hand posture and task 36 instructions in their congruency effects suggests that, like the sighted,, they automatically integrate 37 anatomical and external information during tactile localization. Moreover, spatial integration in tactile 38 processing is, thus, flexibly adapted by top-down information -here, task instruction -even in the 39 absence of developmental vision. 40 KEYWORDS 41 congenital blindness; selective attention; tactile reference frames; tactile remapping, multisensory 42