Pencil, Thumbtack and String
Purpose: To pattern accurate eye and hand movements while maintaining a stable total visual environment
Apparatus: A pencil, thumbtack, string and occluder
Method:
Phase I – Monocular
1. Tack a string to a pencil eraser.
2. Cover left eye.
Patient is instructed to:
3. Hold pencil in right hand and string to nose in left hand.
4. Move pencil in circles, figure eights, spirals and lines in all directions.
5. Keep watching thumbtack at all times–but maintain awareness of rest of room and the string. See and feel the length of the string. Does the string always look and feel the same length?
6. (The string can be seen in varying relationships with the tack. For example, it can be seen as always below the tack–aiming below it, that is. It can be seen, from another point of view, as relatively above the tack when the pencil is moved down, or to the left of the tack when the pencil is moved to the right, etc.)
7. Have the patient verbalize these changing relationships. Can he recognize that seeing the string differently, in relation to the tack, requires thinking about it from different points of view?
8. Patient is to alternate holding pencil with left hand while using left eye, with cover on right eye. Move eyes and arm only. No head or body movement.
Phase II – Binocular
1. Patient repeats the steps of Phase I, except does it with both eyes open.
2. Ask patient to describe the appearance of the string as it emerges from the thumbtack towards him. See Step #6, below.
Aspects to be Emphasized:
1. Maintain accurate ocular fixation on thumbtack.
2. Maintain awareness of seeing and feeling the length of the string.
3. Maintain awareness of the rest of the room. Is it stable?
4. Maintain awareness of the relative changes in orientation of the string to the tack as the pencil is moved into various positions of the visual field.
5. Maintain awareness of tack, string and room and the spatial relationships of one to the other.
6. During Phase II, maintain awareness of two apparent strings forming a V at the thumbtack.
