Class III with constricted maxilla treated without surgery.
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Adolescent↗
Biomedical subjects
J F Lawson
Publications and source records attributed to J F Lawson.
Head-free pursuit in the human of a visual target moving in a pseudo-random manner.
1. Head and eye movements have been recorded in man during head-free pursuit of a target moving in a pseudo-random manner in the horizontal plane with a motion stimulus composed of the sum of four sinusoids. 2. In an initial experiment the three lowest frequencies remained constant at 0.11, 0.24 and 0.37 Hz, whilst the highest frequency (F4) took values of 0.39, 0.78, 1.56 and 2.08 Hz. Peak velocity of each component was 10 deg/s. When F4 was 0.39 Hz gaze displacement (i.e. the sum of head and eye displacement) was relatively smooth and had a mean velocity gain of 0.95. As F4 was increased gaze displacement contained more saccadic activity and gaze velocity gain for the three lower-frequency components was significantly (P less than 0.001) reduced to a minimum level of 0.66 when F4 was 1.56 Hz. 3. A similar reduction in gain of the lower-frequency components was obtained when the velocity of F4 was increased as a ratio of the velocity of the lower frequencies from 0 to 4. 4. When the frequency composition of the stimulus was varied so that the two highest frequencies were closely spaced, gaze velocity gain for the highest frequency was always significantly higher than that of the next lower frequency, indicating a true enhancement of the highest-frequency component. 5. Changing the lowest-frequency component of the stimulus resulted in a significant shift in the gaze velocity phase profile as a function of frequency, so that phase advance was always associated with the lowest frequency even when this was as high as 0.89 Hz. 6. These changes in gain and phase of gaze velocity with the frequency content of the stimulus were similar to those previously described for head-fixed pursuit and visual suppression of the vestibulo-ocular reflex (VOR) and implicate the frequency-dependent, non-linear visual feed-back mechanisms in gaze control. 7. A number of the non-linear characteristics of gaze velocity were also observed in a somewhat modified form in the head displacement gains and phases, implying that the drive to the neck muscles is also derived from the same non-linear visual feed-back source. 8. The role of the VOR in head-free pursuit was tested by exposing the subject to whole-body motion on a turntable which countered the volitional head movement generated by the subject.(ABSTRACT TRUNCATED AT 400 WORDS)
Eye Movements↗
Head-free pursuit of pseudo-random target motion.
Experiments have been conducted in which subjects were required to pursue a target moving in the horizontal plane with co-ordinated movements of the head and eyes. Target motion was pseudo-random in form, composed of four sinusoids. The three lower frequencies of the stimulus were maintained at 0.11, 0.24 and 0.37 Hz with a peak velocity of 10 degrees/s, whilst the frequency and velocity of the highest frequency component (F4) were varied. When all frequencies were below 0.4 Hz, eye movements were smooth and gaze velocity gain was high (0.95), but when F4 was increased up to 1.56 Hz or when the velocity of F4 was increased up to 40 degrees/s, gaze velocity gain decreased significantly. When voluntary head movements were countered by whole-body rotation to eliminate the input to the semicircular canals, gaze velocity gain increased because there was no longer any requirement to suppress the vestibulo-ocular response to head rotation. The results are in accord with those of previous experiments involving head-fixed pursuit and vestibulo-ocular suppression.
Eye Movements↗