| Abstract No.: | B-D2127 |
| Country: | Canada |
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| Title: | THE EFFECTS OF VISUAL FEEDBACK AND SELECTIVE ATTENTION ON SHAPE REPRODUCTION |
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| Authors/Affiliations: | 1 Blake Martin; 1 Blake Martin*; 1 Denise Henriques;
1 York University, Toronto, ON, Canada
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| Content: | Objectives: The role of Selective Attention (SA) has been studied in detail with respect to the sensory modalities of vision, hearing and touch, but remains largely unexplored for limb-position sense and motor planning. The purposes of this experiment are to examine how visual feedback of the hand impacts the drawing of a shape, and to gather baseline data for future investigations into the impact of attentional load on movement production.
Materials and Methods: With vision of the hand occluded, 15 right-handed participants used a stylus on a graphics tablet to trace a reference square (8 or 4 cm, square or diamond, centered or right-shifted) displayed on a video screen, and were thus provided with immediate visual feedback regarding performance on the tracing task by comparing the position of the cursor against the reference shape, although no trajectory was recorded on the screen. Immediately after the trace, the shape disappeared and the participant attempted to make three consecutive reproductions of the shape. In one condition, participants’ hand positions were represented by a cursor, although the resultant drawings could not be seen. In all other conditions, there was no visual feedback of the hand (“no cursor”). In a second experiment, the 15 participants drew the shapes without visual feedback while performing a secondary task of identifying the orientation of an arrow which appeared randomly on the screen. Participants indicated the direction of the arrow either verbally or pressing designed keys. In experiment 1, subjects completed eight repetitions of each combination of conditions of size, orientation and position, and in experiment 2 they completed 6 of each. Shapes were analyzed for scale, squareness, line straightness and drift. These variables were compared with respect to the reference shape and with respect to the preceding shape in each trial.
Results: Without vision of the trace shape or any line output to the screen as a consequence of the drawing, for both cursor and no cursor conditions the scale of each shape was significantly smaller than the reference shape, although the effect size was more dramatic for the no cursor condition. Equally, in both conditions shapes were skewed, with the longest side of the shape greater than the shortest by an average of 20%. Lastly, subjects drifted significantly from the position of the original shape, whether the cursor was visible or not. We are currently analyzing the effect of attentional load on these variables for the 15 participants in the second experiment.
Conclusion: Vision of the cursor is not adequate for accurately reproducing simple shapes such as squares and diamonds, although these drawings corresponded more accurately to the reference shape when visual feedback of the hand position was available. This suggests that in addition to knowledge of the hand’s position, we also need an external reference point against which to guide movement paths.
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