Building a Lego wall: Sequential action selection.

The present study draws together two distinct lines of enquiry into the selection and control of sequential action: motor sequence production and action selection in everyday tasks.Participants were asked to build two different Lego walls.The walls were designed to have hierarchical structures with shared and dissociated colors and spatial components.Participants built one wall at a time, under low and high load cognitive states.Selection times for correctly completed trials were measured using 3D motion tracking.The paradigm enabled precise measurement of the timing of actions, whilst using real objects to create an end product.The experiment demonstrated that action selection was slowed at decision boundary points, relative to boundaries where no between-wall decision was required.Decision points also affected selection time prior to the actual selection window.Dual task conditions increased selection errors.Errors mostly occurred at the boundary between chunks and especially when these required decisions.The data support hierarchical control of sequenced behavior.Public significance Activity of daily living (ADL) can be described as a sequence of actions that are hierarchically organized.For example, the task of making an instant coffee, can be broken down to more specific sequence of actions: boiling the kettle, adding coffee to the mug, pouring boiling water etc… Apraxia and action disorganization are neurological syndromes (AADS) associated with failure to execute sequenced actions, leading to loss of independence.In the context of laboratory experiment, the mechanism underlying learning and execution of sequenced actions has been investigated using simple key pressing tasks.There are many differences between action sequence in the context of ADL and key pressing tasks.The present study aimed to bridge between the two research fields.We designed a novel Lego building task that comes midway between laboratory key pressing and ADL tasks.Our main aim was to identify weak points in the sequence that are susceptible for errors.Participants were asked to build two partially similar Lego walls.We found that error and slow responses occurred at the dissimilarity points between the walls.This suggest that rehabilitation of patients who suffer from AADS should account for overlap in action units across ADL tasks.