The experiment reported in Chapter 4 made use of an embedded figures test (EFT) provided by Consulting Psychologists . This is a standardized measure of cognitive style and analytical ability. The test requires finding simple forms which are embedded in larger figures. The score is the average time in seconds to detect the simple forms. Thus, higher scores reflect greater difficulty in analyzing a part separately from a wider pattern. (Or, viewed more positively, a greater tendency to perceive complete patterns rather than their separate components.)
The EFT is closely associated with other perceptual measures which require the participant to analyze part of an organized field independently of the whole . These include tests of perception of orientation to the vertical (the rod-and-frame test and the body adjustment test); of certain illusions and reversible perspective; of similar auditory and tactile disembedding tasks; and of problem-solving which requires ``disembedding'' a part from its current environment.
The link between the EFT and ``field dependence'' is particularly interesting, for current purposes. Field dependence measures the degree to which an observer has difficulty analyzing part of an organized field independently of the field. For instance, the ``rod-and-frame'' test requires one to sit in a totally darkened room and adjust to the gravitational vertical a tilted luminous rod centered within a tilted luminous frame, while the frame remains in its initial position of tilt. ``Reflecting in each case the strong influence of the immediately surrounding field upon the way in which one of its parts is perceived, the person who takes very long to discover the simple figure in the complex EFT design is also likely to tilt the rod far toward the tilted frame and his own body far toward the tilted room.'' 
The visual-inertial conflict set up by the research of Chapter 4 required participants to extract inertial motion cues from conflicting visual motion cues. This bears a resemblance to the rod-and-frame test. A question addressed in Chapter 4 is therefore whether between-subject differences in the ease of visual-inertial disambiguation is related to EFT scores.
More generally, presence reflects the degree to which one is ``pulled into'' a (usually) visual environment, despite external cues. By analogy with the rod-and-frame experiment, one might expect between-subject differences in any valid presence measure to have at least some correlation with EFT scores.