Article

Rapid discrete goal-directed movements are characterized by a well
known coordination pattern between the gaze and the hand displacements. The gaze
always starts prior to the hand movement and reaches the target before hand
velocity peak. Surprisingly, the effect of the target size on the temporal
gaze-hand coordination has not been directly investigated. Moreover,
goal-directed movements are often produced in a reciprocal rather than in a
discrete manner. The objectives of this work were to assess the effect of the
target size on temporal gaze-hand coordination during fast 1) discrete and 2)
reciprocal pointings. METHODS: Subjects performed fast discrete (experiment 1)
and reciprocal (experiment 2) pointings with an amplitude of 50 cm and four
target diameters (7.6, 3.8, 1.9 and 0.95 cm) leading to indexes of difficulty (ID
= log2[2A/D]) of 3.7, 4.7, 5.7 and 6.7 bits. Gaze and hand displacements were
synchronously recorded. Temporal gaze-hand coordination parameters were compared
between experiments (discrete and reciprocal pointings) and IDs using analyses of
variance (ANOVAs). RESULTS: Data showed that the magnitude of the gaze-hand lead
pattern was much higher for discrete than for reciprocal pointings. Moreover,
while it was constant for discrete pointings, it decreased systematically with an
increasing ID for reciprocal pointings because of the longer duration of gaze
anchoring on target. CONCLUSION: Overall, the temporal gaze-hand coordination
analysis revealed that even for high IDs, fast reciprocal pointings could not be
considered as a concatenation of discrete units.
Moreover, our data clearly
illustrate the smooth adaptation of temporal gaze-hand coordination to terminal
accuracy requirements during fast reciprocal pointings. It will be interesting
for further researches to investigate if the methodology used in the experiment 2
allows assessing the effect of sensori-motor deficits on gaze-hand coordination.

Langue : ANGLAIS