Abstract
The tendency to generate head movements during saccades varies from person to person. Head movement tendencies can be measured as subjects fixate sequences of illuminated targets, but the extent to which such measures reflect eye–head coupling during more natural behaviors is unknown. We quantified head movement tendencies in 20 normal subjects in a conventional laboratory experiment and in an outdoor setting in which the subjects directed their gaze spontaneously. In the laboratory, head movement tendencies during centrifugal saccades could be described by the eye-only range (EOR), customary ocular motor range (COMR), and the customary head orientation range (CHOR). An analogous EOR, COMR, and CHOR could be extracted from the centrifugal saccades executed in the outdoor setting. An additional six measures were introduced to describe the preferred ranges of eyes-in-head and head-on-torso manifest throughout the outdoor recording, i.e., not limited to the orientations following centrifugal saccades. These 12 measured variables could be distilled by factor analysis to one indoor and six outdoor factors. The factors reflect separable tendencies related to preferred ranges of visual search, head eccentricity, and eye eccentricity. Multiple correlations were found between the indoor and outdoor factors. The results demonstrate that there are multiple types of head movement tendencies, but some of these influence behavior across rather different experimental settings and tasks. Thus behavior in the two settings likely relies on common neural mechanisms, and the laboratory assays of head movement tendencies succeed in probing the mechanisms underlying eye–head coupling during more natural behaviors.
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Notes
The original method of calculating COMR (Stahl 1999) was altered slightly to correspond with the method of calculating CHOR. In the original method, we generated a curve proportional to the frequency of final eye eccentricity and then adjusted for non-uniformity of the distribution of T H by dividing, point-by-point, by a curve proportional to the frequency of T H. The new technique, in which the kernel for each saccade is pre-scaled according to the frequency of that saccade’s T H, is more rigorously correct. The results of the two methods, however, are quite similar; for 35 measurements of COMR derived from 35 experimental sessions of 12 subjects, there was a strong linear relationship between the new and old measures, with a slope of 0.93 and a coefficient of determination (r 2) of 0.99.
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Supported by a Merit Award from the Department of Veterans Affairs.
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Thumser, Z.C., Oommen, B.S., Kofman, I.S. et al. Idiosyncratic variations in eye–head coupling observed in the laboratory also manifest during spontaneous behavior in a natural setting. Exp Brain Res 191, 419–434 (2008). https://doi.org/10.1007/s00221-008-1534-2
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DOI: https://doi.org/10.1007/s00221-008-1534-2