Autismus und Sehen « Le Syndrome de Schorderet- Munier ... - ophta

ORIGINALIA
For pigeons to maximally benefit from
the information-processing «biases» of
both hemispheres, logic would dictate
for them to alternate the eye performing
primary, information-gathering. A moreforward-oriented
observation period of 7
to 8 seconds per view would seem reasonbeing
of the divergence-excess (excessive
innervation of the lateral rectus muscle)
or convergence-weakness (diminished
innervation of the medial rectus muscle)
types. With advancing age, the tendency
to diverge increases, and the deviation
becomes constant and permanent. An alternating
divergence tends to result. 7 This
condition has been reported to manifest
itself through corporal or emotional
stress, including insomnia due to shock,
mental duress, or illnesses with high fever,
such as mumps, measles, etc. Once
the illness or stress has passed, the strabismus
has become an acquired habit. 8 In
many cases, one eye becomes dominant, 9
but, when both eyes remain about equally
«competitive», alternation can result. 10
Thus, exophoria is often accompanied in
humans by binocular alternation: Thus,
they gaze at their listener first with one
eye, then, with the other. Individually,
each eye has normal function, but only
alternately (Figure 11a-b).
Morphometrical Review – Animal Studies
Eye-head coordination occurs in monkeys
and cats «when a visual target cannot
be foveated by an eye-and-head movement
because it is too eccentric...the body
is turned». 13 According to Walls, granivorous
birds never have over 25° of binocularity,
and many have less than 10°. It
seems that «most birds have little or no
spontaneous (eye) mobility, relying upon
the flexibility of the neck». 14 Even the
shape of pigeon eyes hinders more than
modest mobility (cf. Figures 12a,b). Close
observation revealed that «birds in flight
are commonly observed to tilt the head
on one side to look down to the ground
monocularly». 15 The homing pigeon, for
instance, has been found to have a 24°
binocular field upon full convergence
(Figure 12c), with a total field of 340° –
342°. 16 In discussing «eye-mindedness»,
Walls implies that granivorous birds do
not «need» binocularity to perceive their
food with sufficient accuracy to feed. 17
What advantage could homing pigeons
possibly gain from combining left- and
right-eye information garnered from gaze
alternation during flight?
In studies on lateralization of information-processing
in pigeon brains, a remarkably
distinct asymmetry has been
noted. 18–20 Ulrich et al. determined a
pronounced left hemispheric superiority
for visuospatial orientation in homing
pigeons. The opposite is true in the
right hemisphere, where higher resolution
seems to predominate. The right eye
provides the left hemisphere with information;
the left eye does so for the right
hemisphere.
a
b
b
a
c
Fig. 12a–c
Schematic of
proportional eye
cross-sections and
shapes in human (a)
and pigeons (b);
schematic of juxtaposition
of pigeon
eyes in the skull (c).
Fig. 11a–b Schematic of human exophoric
alternation of right- and left-eye gaze.
Clinical alternating exophoria and
«sidedness»
Visual field temporal characteristics in
binocular rivalry were observed to conform
to handedness in humans. In righthanded
persons, responses were faster
when visual stimuli were presented to the
right visual field, in left-handed persons,
the opposite held true. 11 Asymmetries in
binocular coordination were also seen in
alternating exophoria. 12
Fig. 13a–b Schematic of a visual-mechanical
explanation of head-turning alternation contributing
to regular undulations in flight-path.
ably adequate. Pigeon flight is just that, not
gliding; most of the time they flap their
wings continually. Thus, by turning their
heads from side-to-side to fully exploit
their «exophoric» and «visual lateralization»
maximally, pigeons could inadvertently
impart rhythmic asymmetry to their
flight exertions, and, thus, to their flightpath
(Figure 13). Try walking straight with
your head and hips turned to one side.
270 ophta • 4|2008