The type 1 submovement conundrum: an investigation into the function of velocity zero-crossings within two-component aiming movements


Specific target aiming contexts have shown a surprising prevalence of type 1 submovements (overshooting) as opposed to types 2 and 3 submovements (undershooting). It has been suggested that these type 1 submovements are in fact the product of highly rapid movements, and not necessarily a correction (Hsieh et al., 2021). Hence, our aim was to examine the function of type 1 submovements. We reanalysed data sets from three separate studies, and isolated those conditions where type 1 submovements appeared most prevalent. These type 1 submovements were categorised according to whether the secondary submovement moved the limb closer, (functional) or not (non-functional), to the target. Overall, there appeared both functional and non-functional submovements with a significantly higher proportion for the former. The displacement at the primary and secondary submovements was significantly greater in the functional compared to non-functional, which was significantly greater still compared to the type 2+3. There was a significantly more negative velocity peak within the secondary submovement for the functional compared to non-functional submovement. The influence of type on other movement characteristics was somewhat less clear. However, it appeared there was a larger positive velocity peak, and shorter time to the primary submovement for both the functional and non-functional submovements compared to type 2+3. These findings suggest a further need to categorise the function of type 1 submovements, although the majority of them can be attributed to a correction. The absence of any temporal cost may be attributed to a forward model that more readily anticipates overshooting.