First of all, simultaneity is much more common in sign languages since these are visual languages. It has been shown that it is easier to perceive and produce visual information simultaneously, than auditory information. This is a processing argument based on characteristics of visual perception. In addition, and probably motivated by processing factors, in sign languages, every phonological parameter can in principle fulfill a morphological function, and multiple parameters can be modified at the same time without problems. This is a linguistic factor that favors simultaneity. (In spoken languages, morphemes can also be simultaneously realized at times – as in English sing – sang – sung – but this is usually limited to two pieces of morphemic information.)