Planning of Sequential Motor Actions with Constrained Movement Time

In this study we aim to replicate previous findings dissociating between holistic and serial planning within one task, whilst constraining movement time. Previous studies suggest holistic planning of obtuse movements, but this is confounded by a quicker movement time in these movements compared to their acute counterparts. Therefore, we aim to show that behavioural signatures of holistic planning persist when movement time is constrained. We will use a two-stage sequential reaching task with a switch paradigm, where participants move through the start box to a centre target, followed by one of four surrounding targets (figure 1). This task has previously been used to distinguish between holistic and serial planning within the same task by switching the second target part way through the first movement. The holistic hypothesis suggests that if the whole movement is planned, participants will struggle to make the switch and move towards the original target before course correcting. The serial hypothesis however suggests that if participants have only planned the first movement, switching the second target will have no effect on performance and they will plan to move to the new target with ease. Previous studies suggest holistic planning of obtuse movements, but this is confounded by a quicker movement time in these movements compared to their acute counterparts. We propose that when we constrain the movement time of sequential reaches, fusion will remain in obtuse target configurations, as will behavioural indicators of holistic planning. Participants’ movement time will be constrained throughout the experiment using a reward manipulation to encourage participants to take around 1 second (1000ms) to complete each movement. The reward will be delivered by points as follows... • 5 points: movement time between 985ms and 1015ms • 3 points: movement time between 1015ms and 1045ms • 3 points: movement time between 955ms and 985ms • 1 point: movement time between 1045ms and 1075ms • 1 point: movement time between 925ms and 955ms • 0 points: movement time greater than 1075ms • 0 points: movement time less than 925ms Participants will be forced to repeat a trial if their movement time is... • Greater than 1090ms • Less than 910ms We hypothesize that participants will struggle to switch in obtuse conditions compared to acute conditions; there will be evidence of spatial reorganisation of the movement in obtuse trials; some participants fuse more than others, thus there will be clear groups of high and low fusers; and there will be a correlation between switch performance and fusion.