# Auditory Coding of Reaching Space
Based on the considerations of [PERSON] (2018), we decided to use data of the right metacarpophalangeal joints to generate acoustic information about the target position and the reaching movement. For the acoustic representation of the target position of the hand, three- dimensional spatial coordinates were sonified. For the continuous representation of the reaching movement, acoustic information about movement velocity was added. The systematics of the sonification was adopted from [PERSON] et al. [PERSON] _et al._ (2018), who found a high efficacy of such a four- dimensional sonification of a continuous kinematic trajectory in the auditory discrimination of arm movements. The coding of the vertical spatial component by pitch was also in accordance with [PERSON] and [PERSON] [PERSON] and [PERSON] (2018) and [PERSON] et al. [PERSON] _et al._ (2018); [PERSON] _et al._ (2018). The results of [PERSON] et al. [PERSON] _et al._ (2018), who studied the relations between musical parameters and intuitive gestures and found a positive correlation between pitch and height, also supported the choice of this mapping. The horizontal coding by stereo characteristics conformed to that applied by [PERSON] et al. [PERSON] _et al._ (2018). The spatial depth was mapped on spectral composition. In this way, we intended to create an auditory space to enable the localization of reaching targets. Regarding the thoughts of [PERSON] et al. [PERSON] _et al._ (2018) and the findings of [PERSON] et al. [PERSON] _et al._ (2018), we added a velocity component to the spatial information for the movement sonification. In the light of the above-mentioned results of [PERSON] et al. [PERSON] _et al._ (2018) suggesting that the auditory position stimulus presentation of 0.25 s is too short for the generation of a precise and reliable target representation, our instruction sound was longer than 0.25 s in all conditions. In order to control the influence of the extent of given information, we worked with two different durations of target presentation. In contrast to [PERSON] et al. [PERSON] _et al._ (2018) and to facilitate the task, we chose to design the instruction and feedback in the same manner. That means that the subjects were prompted to produce by their reaching movement the same sound as they had heard for instruction. To realize a clear temporal separation between instruction and feedback to avoid confusion, the participants' movement did not start before the instruction was finished. We therefore accepted a reduced reaching performance observed by other authors for the removal of target presentation prior to the completion of the reaching movement ([PERSON] _et al._, 2018; [PERSON] _et al._, 2018). Since we think that it is possible to merely acoustically instruct target positions for reaching movements and that our kind of movement sonification is highly effective, we formulated the hypothesis that the blind as well as the sighted experimental group is able to hit the target points with a precision clearly above chance. In the light of the described important role of vision in reaching movements and the beneficial effects of audio-visual integration and audio-visuo-motor processing associated with movement sonification, we expect the sighted experimental group to be superior to the blind group in reaching precision. In spite of the merely acoustic target instruction, we suppose that the visibility of the moving arm enhances the precision of the reaching action. Furthermore, we hypothesize that additional continuous auditory instruction and real-time feedback about the movement is superior to a mere discrete sonification of target point. Considering the learning effect proved by [PERSON] et al. [14] and the improvement of the performance over time observed by [PERSON] et al. [27] even without the availability of feedback, we assume an improvement of the reaching performance over time in the present study.