Control de inventario

1.5.1. Chapter 2

Chapter 2 describes the common methodology used to generate, record and analyse the data for all experiments.

1.5.2. Chapter 3

To clarify the impact of attentional focus on motor imagery and performance, we directly compared the effects of external versus internal focus on physical and imagined instances of STS movements in young adults, as compared to older adults. We tested how focusing on the change in viewpoint relative to the environment (external focus) or the change in muscular load on the thighs, or cutaneous pressure under the feet (both internal focus), affected the self-reported movement times and the ground reaction forces of imagined STS movements. We also measured the self- reported, actual movement times, and the smoothness or stability (which we measured as the path length of the center of pressure during standing up) of the physical movements under these internal and external focus conditions. After the practice and test trials of each imagery condition, we also collected a rudimentary subjective measure of how vividly the participants felt they had managed to imagine the STS movements.

1.5.3. Chapter 4

In the second experiment, we manipulated the seat height from which participants made sit-to-stand movements (setting it to 100% or 80% of participants’ lower leg length). We introduced this manipulation of effort in order to amplify differences in timing between task conditions and age groups. We tested how

focusing on the change in viewpoint relative to the environment (external focus) or the change in muscular load on the thighs (internal focus), affected the self-reported movement times and the ground reaction forces of imagined STS movements. We also measured the self-reported and postural transition duration and stability during physical STS movements under the internal and external focus conditions.

1.5.4. Chapter 5

In the third experiment, we tested the impact of adding the manual task of holding a container filled with fluid in either hand and performing or imagining STS movements under external and internal attentional focus conditions. The participants’ task was to attempt standing up without spilling the fluid from the container. Thus, in effect, their task requirement now had an explicit component relating the body (or parts of it) to the environment. Again, we tested how focusing on the change in viewpoint relative to the environment (external focus) or the change in muscular load on the thighs (internal focus), affected the self-reported movement times and the ground reaction forces of imagined STS movements. We also measured the self-reported and postural transition duration and stability during physical STS movements under the internal and external focus conditions.

1.5.5. Chapter 6

In the fourth experiment, we carried out a preliminary study of how (or whether) attentional focus may influence the effectiveness of motor imagery training. During imagery training, participants’ task was to try to make their movement as laterally symmetrical as possible. We tested visual (external), muscular and somatosensory (internal) attentional focus during imagery training, and measured postural transition duration and stability and lateral symmetry of ground

reaction force during physical movements, both before and after the set of training sessions.

1.5.6 Chapter 7

In this concluding chapter, we provide a summary of our experimental results and discuss its possible implications for understanding the role of attention in motor imagery and for applications to clinical settings.

2.1. Introduction

This chapter describes the common methodology used to generate, record and analyse the data. Participant details, together with a specific experimental design, are presented with each experiment in the respective chapter.

2.2. Method

2.2.1. Apparatus

The experimental setup (Figure 2-1: A) consisted of a height-adjustable chair placed adjacent to an AMTIAccusway force platform (Watertown, MA) driven by AMTI’s Balance Clinic software. Sequencing of experimental trials and recording of self-reported movement time data at millisecond resolution was controlled by an E- Prime script (PST: Sharpsburg, PA)

2.2.2. Experimental procedures

The experiment was conducted in a quiet room within a laboratory suite. Participants were instructed to come dressed in comfortable clothing, and asked to take their seat on a vertically adjustable chair set to the height of their lower leg (Figure 2-1: A). Participants’ feet rested on the force platform with heels approximately 10 cm apart. Participants’ ankles were positioned with ~10° of dorsiflexion and knees with ~100 - 105° of flexion using a handheld goniometer. The position of the feet on the force platform was then marked with tape. Participants’ thighs were positioned with the edge of the chair at two-thirds of their thigh length. This position was marked with tape on the thighs and on the seat behind the buttocks. Participants were asked to keep their arms by the sides of their bodies.

Before each trial, the position of the trunk, the legs, and the feet, were checked and corrected if necessary.

Each participant performed the physical and imagined STS movements under three focus conditions – visual-external (focus on a fixation point on the wall), muscular-internal (focus on the load on thigh muscles), and somatosensory-internal (focus on the pressure under feet).The order in which participants encountered the focus conditions was counterbalanced. In each focus condition, participants first performed the physical movement (3 recorded trials) followed by the corresponding imagined movement (3 recorded trials), with 1 - 2 minutes of rest in between. Each set of 3 recorded trials was preceded by 2 practice trials. In conditions involving imagined movement, participants were asked to provide a vividness judgment after

the practice trials and then again after the experimental trials to record a subjective

impression of the strength of STS imagery.They indicate on a 5-point scale (see in Appendix 2) how vividly they felt they had been able to imagine the movement. At the beginning of each trial, participants were instructed to sit comfortably with their backs straight, and look forward at the fixation point on the wall, which was placed level with the participants’ eyes when standing on the force platform. Participants held a computer mouse in their right hand (to provide self-report of movement completion, see below), and then followed trial-specific instructions (see the details of specific instruction for each experiment in Appendix 3).

In each trial, the participant awaited a pre-recorded auditory “Ready … Go” signal played by the E-prime software, and then performed a physical or imagined STS movement. In the visual-external focus condition, their instruction was to stand up (or imagine standing up) at their natural speed while keeping their eyes on the fixation target, and focusing on the way their viewpoint’s position changed relative

to the fixation point. The fixation target was always positioned at the participants’ standing eye-height. In the muscular-internal focus condition, they were told “As you stand up (or imagine standing up), focus your attention on how the weight of your body feels in your thighs,” and in the somatosensory-internal focus condition, they were told to focus their attention on how “the pressure of your body weight feels under your feet.” They were also asked to press the left button of the handheld mouse when they felt they had completed the STS movement and were “standing comfortably and steadily” (or imagining doing so, according to the experimental condition) and then stay standing steadily until hearing the experimenter said DONE. Participants were then asked to sit down, relax, and prepare for the next trial.