Time course of movement preparation of rapid interceptive actions

Welber Marinovic (2008). Time course of movement preparation of rapid interceptive actions PhD Thesis, School of Human Movement Studies, The University of Queensland.

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Author Welber Marinovic
Thesis Title Time course of movement preparation of rapid interceptive actions
School, Centre or Institute School of Human Movement Studies
Institution The University of Queensland
Publication date 2008-08
Thesis type PhD Thesis
Supervisor Dr James Tresilian
Dr Annaliese Plooy
Total pages 132
Total black and white pages 132
Collection year 2009
Subjects 320000 Medical and Health Sciences
Formatted abstract
The aim of this thesis was to investigate the time course of the processes of motor preparation that
occur about 500ms prior to initiation of fast and brief interceptive actions.. More specifically, these
processes involve to the preparation of movement parameters (amplitude and direction) and the
triggering of interceptive actions both based on brief observations of a moving target during its final
approach towards an interception zone. Chapter 1 provides an introduction to the research program
and also reviews previous work - methods and main results - investigating the processes of motor
preparation in aiming at stationary targets. Chapter 6 presents a summary of the main research
findings of the present thesis. The remaining chapters (2-5) represent stand-alone scientific work.
In chapter 2, we sought to determine the critical moment at which people obtain time-to-contact
(TTC) information from the moving target in order to trigger an accurate interceptive action. To
achieve this goal we trained the participants to perform movements of a specific duration. This
method permitted an estimate of movement onset time. The efficacy of the training protocol was
tested in two experiments in which the accuracy of interception was examined under different
occlusion conditions. In the first experiment we examined the effect of changing the timing of an
occlusion period of fixed duration. In the second experiment we varied the duration of the occlusion
period as well as its timing. The results showed that the critical interval to trigger an interceptive
action occurs about 150 ms prior to movement initiation.
The studies described in chapter 3 further investigated the critical time interval to obtain TTC
information in a brief interceptive action. In experiment 1, participants were required to intercept
targets with a pre-trained MT and on random trials a stop-signal (SS) was presented indicating that
they should not make the interception. In experiment 2, the participants' primary task was to remain
stationary and on random go trials they were required to strike the target with the specified MT.
Experiment 1 was designed to examine whether interceptive actions can be suppressed by
presenting participants with a SS close to the time when the triggering is expected to occur and if
so, estimate the shortest time required for suppression. Experiment 2 aimed to provide an estimate
of the interval containing the criterion TTC information and also served as a control for experiment
1. The results of these experiments showed that the decision to make or suppress an interceptive
action must be taken about 200 ms before movement onset. The results also confirmed those
presented in chapter 2 by showing that performance in experiment 2 deteriorated when the go-signal
was delivered 150 ms or less prior to the expected time of movement onset.The experiments reported in chapter 4 sought to determine the last moment at which information
about the distance to move (amplitude) could be incorporated into a motor program. For this
purpose, we adopted an empirical protocol that allowed us to examine whether new amplitude
information is incorporated discretely or continuously into the program during short intervals prior
to movement onset – the preparation interval. Participants were trained to hit targets at two different
distances with movements of a specific duration (180ms): targets were moving in experiment 1 and
stationary in experiment 2. Preparation intervals were manipulated by delivering a stimulus cue for
movement amplitude at varying times prior to the estimated movement onset time. Results
demonstrated that amplitude information could be effectively incorporated into the program
provided the preparation interval was greater than about 200 ms. In addition, the results indicated
that amplitude was specified predominantly in a discrete manner, though the number of responses
directed towards a central default amplitude suggest that the distance between targets was near to a
threshold for continuous specification.
In chapter 5, we aimed to determine the last moment at which information about the direction of the
target could be incorporated into a motor program. The empirical protocol used in the study was
identical to that employed in chapter 4. Participants were trained to hit moving targets at two
directions with movements of a specific duration (180ms). Preparation intervals were controlled by
issuing a stimulus cue for movement direction at various times prior to the estimated movement
onset time. Results showed that direction information could be fully incorporated into the motor
program with a preparation interval as brief as 250ms. As for amplitude, the results indicated that
direction was specified predominantly in a discrete fashion even at short preparation intervals,
although it was evident that a significant number of movements were directed towards the middle
range of targets - typical behaviour expected in the continuous mode of specification.
Keyword human
motor preparation
motor control

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