2.3.2. Multisensory Stimulation and Priming (MuSSAP) Training
The MuSSAP training was integrated into the EI-UL intervention; the total training frequency and duration was equal to the EI-UL intervention alone. With the integrated MuSSAP training, we aimed to increase infant's attention for the contralesional upper limb and facilitate readiness to initiate a goal-directed movement [Parents closely observed whether the infant looked at the wristband after it switched on and presented a toy to the infant as soon as the infant shifted its attention to the contralesional upper limb. The toy served as a reward for shifting attention to the wristband, and as a cue to provoke self-initiated goal-directed movements with the contralesional upper limb. In case no shift of attention by the infant was observed, parents prompted attention by bringing the contralesional upper limb into the infants' field of view. No toy was presented if the infant still did not look at the wristband. In case the infant shifted its attention to the contralesional upper limb, but no self-initiated movement was observed, parents placed a toy into infant's contralesional hand to stimulate holding. The infant was left to play with the toy for as long as the contralesional hand was involved and the infant payed attention to the contralesional upper limb (in unimanual or bimanual play). If the infant transferred the toy to its ipsilesional hand or the parent observed only mouthing behaviour, the parent removed the toy. Subsequently, parents started playing peek-a-boo, talking, or singing a song prompting the infant to shift its attention to the parent until the next stimulus by the wristband occurred. In addition to the instructions for the EI-UL intervention as described earlier, parents received a supplemental instructional video demonstrating the specific MuSSAP training procedure.