In some studies a light emitting rod, or a rod and a frame have been adjusted using a mechanical device, in others they have been projected onto a screen.
The test is simple but a number of different systems have been used. Measurement of subjective visual vertical (SVV) or horizontal (SVH) using the rod and frame test, pioneered by Witkin, is an established way of investigating spatial orientation. This reduces clues provided to the subject by the appearance of the rod on the screen. The computerized rod and frame system may be improved by replacement of the line with two dots. Changing the rod from a line to dots in the computer system resulted in errors for both SVV and SVH that were comparable to previous studies using manual systems. Bland and Altman analysis showed no difference between the rod and dots presentations in the measurement of SVV, but confirmed a fixed error of -0.93° between rods and dots for SVH. In a second investigation 30 subjects were tested using both the "rod as line" and "rod as dots" presentation. A solution to this problem was sought by replacing the rod by two dots to mark its ends. This was attributed to additional visual cues provided by the changing appearance of the rod as it approached the horizontal. Preliminary results showed a higher than expected percentage of individuals with SVH errors < 0.5°. This was done by comparing two groups of subjects (n = 103) randomly assigned to be tested for SVV or SVH. We have expanded the use of this system by testing its feasibility to measure SVH.
The computerised rod and frame (CRAF) system has previously only been used to measure SVV. Perception of subjective visual vertical (SVV) and horizontal (SVH) has traditionally been measured by rotating a mechanical rod either with or without a frame present.
0 kommentar(er)
