Localization of a remembered target under the influence of different head and body positions.

Previous investigations analyzed the effect of semicircular canal stimulation on the localization of a remembered target and found additional indications that different head positions affect the test results. Therefore, the aim of the present study was to analyze the influence of different head and body positions on the localization performance towards a remembered target. The pointing error (PE) towards a remembered target was investigated in 24 right-handed volunteers (12 females, 12 males; mean age 23 years) under six different head and body positions (sitting upright with the head tilted forward/backward by 45 degrees ; sitting upright with a head displacement of 90 degrees to the right/left relative to the body; lying on the right/left side of the body). Evaluation parameters were the horizontal and vertical PE (in degrees). Head displacement to the left relative to the body led to a PE to the right side and head displacement to the right led to a PE to the left (ANOVA P<0.001; df=5; F=16.92). An upward PE occurred when the head was tilted forward by 45 degrees and a downward PE could be proved when the head was tilted backward by 45 degrees (ANOVA P<0.001; df=5; F=35.78). In summary, any change in the relation between head and body position led to a systematic PE towards the frontal plane of the body (i.e. the plane located in the axis between both shoulders). Taken together, the systematic PE in direction to the frontal body plane suggests that the location of the remembered target is coded and remembered in a frame linked to the body and not transformed into a head-centered frame of reference.