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Brock String Instructions
A Brock string is simply a piece of white string, usually 3-4 feet (1-1.2m) long, with four movable color beads placed on it. One end can either be tied to a distant object, such as a doorknob, or held by a supervising person. The other end (whichever, it does not matter) is held to the tip of the nose. The beads should be positioned evenly from the first near the nose starting at approximately 10-15 inches (25-35 cm).
Note that when evaluating an athlete, it is appropriate to place the string in a position that relates to their sport. For example, instead of placing the distant end of the string on a doorknob in the straight-ahead position as you would for a baseball player, move it down to the floor for a hockey player, or place one end up at ten feet high for a basketball player. To accomplish this, a 20 feet string may be needed and is available.
When the subject looks at the first bead, he or she should see one bead with two short strings leading toward it and two longer strings leaving it. On the two strings which leave the bead there will be 3 pairs of beads.
Next, have the subject look at the second bead or the one at the 25 in distance from the nose. Here again the subject should see two strings entering the bead and two strings leaving it, making a large “X”. This will also mean that there are two beads ahead of and two behind the single second bead.
Finally, look at the one of the last two beads. You should notice the two strings making a “V” toward the bead and crossing exactly at the bead. The two closest beads will be double. The doorknob or whatever object the string was tied to may also appear doubled if there is adequate separation between it and last bead.
Results
If only one string is seen, the subject is suppressing one eye.
Absence of depth perception, poor overall performance.
If the strings seem to cross in front of the beads, this is referred to as an “eso-posture” and the subject will tend to perceive things as closer than they really are.
A baseball player might “pull” the ball, swinging early because the ball appears closer than it really is. A basketball player may consistently miss short.
Again, it is most appropriate to train athletes in a situation as normal to their sport as possible. It may be necessary to start with the string in a level or straight ahead position to begin with. After achieving all the goals set forth below, move the string to a position which is normal to the subject’s sport.
The object of any Brock string training is to be able to have the subject see the strings cross exactly at the bead they are looking at. Everything in front of and behind this bead should be doubled. If not, have the subject find some spot on the string where it is possible to achieve the proper image (strings crossing exactly at the bead). From this point they will slowly slide the bead closer, then further, maintaining proper alignment and fusion. The goal is to expand the range from this point until normal fixation can be obtained at all distances.
If there is no spot on the string where normal fixation can be achieved, the use of loose prisms may be necessary. This is done by finding the point on the string where the least amount of prism is needed to achieve fusion, and expanding the range from that point. Once the range is expanded to include the entire string, the prism is reduced and the process begins again.
Once normal fusion and fixation can be achieved at all distances, the next goal is to be able to jump quickly from one bead to another, achieving proper fixation each time. The position and separations of the beads should be varied during this part of the training to include many different possibilities. Once this has been successfully accomplished, the next goal is to be able to look away from the beads at a distant object and then look back at the beads and regain fusion, as well as alternate beads after each distance glance.
The Brock string may also be used in connection with prism flipper bars, accommodative flippers, balance boards, and other devices to make the task more challenging.
The object of any Brock string training is to be able to have the subject see the strings cross exactly at the bead they are looking at. Everything in front of and behind this bead should be doubled. If not, have the subject find some spot on the string where it is possible to achieve the proper image (strings crossing exactly at the bead). From this point they will slowly slide the bead closer, then further, maintaining proper alignment and fusion. The goal is to expand the range from this point until normal fixation can be obtained at all distances.
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