The "Motor" in Implicit Motor Sequence Learning: A Foot-stepping Serial Reaction Time Task

Summary

We introduce the foot-stepping serial reaction time (SRT) task. This modified SRT task, complementing the classic SRT task that involves only finger-pressing movement, better approximates daily sequenced activities and allows researchers to study the dynamic processes underlying discrete response measures and disentangle the explicit process operating in implicit sequence learning.

Abstract

This protocol describes a modified serial reaction time (SRT) task used to study implicit motor sequence learning. Unlike the classic SRT task that involves finger-pressing movements while sitting, the modified SRT task requires participants to step with both feet while maintaining a standing posture. This stepping task necessitates whole body actions that impose postural challenges. The foot-stepping task complements the classic SRT task in several ways. The foot-stepping SRT task is a better proxy for the daily activities that require ongoing postural control, and thus may help us better understand sequence learning in real-life situations. In addition, response time serves as an indicator of sequence learning in the classic SRT task, but it is unclear whether response time, reaction time (RT) representing mental process, or movement time (MT) reflecting the movement itself, is a key player in motor sequence learning. The foot-stepping SRT task allows researchers to disentangle response time into RT and MT, which may clarify how motor planning and movement execution are involved in sequence learning. Lastly, postural control and cognition are interactively related, but little is known about how postural control interacts with learning motor sequences. With a motion capture system, the movement of the whole body (e.g., the center of mass (COM)) can be recorded. Such measures allow us to reveal the dynamic processes underlying discrete responses measured by RT and MT, and may aid in elucidating the relationship between postural control and the explicit and implicit processes involved in sequence learning. Details of the experimental set-up, procedure, and data processing are described. The representative data are adopted from one of our previous studies. Results are related to response time, RT, and MT, as well as the relationship between the anticipatory postural response and the explicit processes involved in implicit motor sequence learning.

Introduction

Implicit motor sequence learning, generally known as learning a sequence without knowing the sequence, is critical to our daily activities and has been well studied by a paradigmatic task named the serial reaction time (SRT) task designed by Nissen and Bullemer¹. In this classic SRT task, participants press keys to respond quickly and accurately to visual stimuli. To examine sequence learning, the appearance of visual stimuli is manipulated to follow either a pre-structured or random sequence, which is unknown to participants. Learning is evidenced by the faster response time to the pre-structured sequence (e.g., the training sequence)....

Protocol

The protocol was performed in accordance with the guidelines approved by the Institutional Review Board at the University of Maryland, College Park.

1. Experimental Set-up

1. Set up a motion capture system as shown in Figure 1a. Place eight cameras in a circle with a radius of 4 m.
   NOTE: The number and positions of cameras can be varied, provided all cameras are appropriately positioned to obtain a clear vision of all reflective markers attached to a participant's body.
2. Set up a stepping station in the center of the circle. Position a "home position" covered by dark blue fe....

Results

The above paradigm is implemented by Du and colleagues in a series of studies^3,4,5. We use a part of data adopted from one of these studies⁴ to represent the usage of the foot-stepping SRT task. In this study, there are 6 learning blocks and a RSI of 700 ms is used. Visual stimuli followed sequence A (i.e., 1423564215; Figure 1a) in b.......

Discussion

This protocol describes the experimental set-up and procedures for a modified SRT task. The modified SRT task shares its appealing simplicity with the classic SRT task, although the modified SRT task demands use of a motion capture technique. Like the classic SRT task, many parameters could be manipulated for specific research questions in the foot-stepping SRT task, including but not limited to: the length of interval-stimulus interval or response-stimulus interval²⁷, the type of sequence structu.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Vicon motion capture system	Vicon	Vicon T-40, T-160, calibration wand	Alternative systems may be used
50 mm reflective markers	Vicon	N/A	Numbers of markers may be varied
Labview software	National Instruments	N/A	Control visual stimuli. Use together with DAQ board. Alternative software may be used
DAQ board	National Instruments	BNC-2111; DAQCard-6024E
MATLAB	MathWorks	N/A	Alternative software may be used
double sided hypo-allergenic adhesive tape		N/A
pre-wrapping tape		N/A