236
M. I. Baritz and A. M.Lazar
central nervous system. The main types of eye movements are: nystagmus, saccade,
miniature, pursuit, smooth, compensatory and vergence.
Nystagmus is a condition of involuntary movement acquired in the first years of
life or maybe even later. This form of eye movement results in a reduced or even
limited view of the axes of the visual system. These moves are even more evident
when the head rotates around an axis and the remote images of the visual system are
supported by turning the eyes in a direction opposite to the movement of the head to
compensate for the rotation.
From a functional point of view, there are two forms of manifestation of the
nystagmus: physiological and pathological, presenting, within each group, other
variants of manifestation. Forms of interest for oculographic computational analysis are represented by physiological nystagmus, the pathological one requiring
a medical approach of ophthalmological and neurological specialty. The forms of
nystagmus may be determined by a variety of causes, such as nervous system disorders, congenital disorders, acquired disorders, toxicity and medication. As mentioned
in many research papers, physiological nystagmus is a form of involuntary eye movement that is part of the vestibulo-ocular reflex (VOR), characterized by alternating
smooth pursuit in one direction and saccadic movement in the other direction [1].
In turn, the physiological nystagmus presents the following forms of manifestation:
downbeat nystagmus, upbeat nystagmus, seesaw nystagmus, periodically alternating
nystagmus.
Other forms of manifestation of physiological nystagmus, which are of interest
for studies on biomechanical posture, dynamical or static behavior of the human
body, are the form of opto-kinetic and post-trophic nystagmus, respectively. The
form of opto-kinetic nystagmus is induced by the pursuit of visual stimuli (vertical
or horizontal), the post-trophic form is determined by the rotation motion of the body
around the vertical axis, and the rapid phase of the nystagmus is performed in the
opposite direction of this rotation, trying to compensate some internal physiological
manifestations (Fig. 1).
Another form of movement determined in each ocular globe is saccade movement,
a rapid eye movement, conjugated and performed under voluntary control from the
central cortex (visual cortex). Generally, the purpose of these oscillatory movements
is to form the images of the surrounding space in the foveal area; therefore, the
saccade oscillations are considered as an important mechanism for characterization
of selective visual attention.
In the case of saccade movements, an important problem was identified, which is to
analyze how the visual system works during these movements (whether or not images
are formed on the retina to be transmitted to the visual cortex). Thus, it is stated in the
literature that in fact visual information, in this case, is obtained as sequential images
and interrupted by fixation processes, a phenomenon aware of the subject with this
form of eye movement [2]. Fixation periods last up to 200–300 ms, and the fixation
sequence is related to the sampling rate of the eye movement recording technique
that has been used. Saccade movements are very rapid, resulting in a phenomenon of
sacred suppression, a phenomenon during which visual perception is not completely
eliminated but only substantially reduced. From the experimental point of view, the
M. I. Baritz and A. M.Lazar
central nervous system. The main types of eye movements are: nystagmus, saccade,
miniature, pursuit, smooth, compensatory and vergence.
Nystagmus is a condition of involuntary movement acquired in the first years of
life or maybe even later. This form of eye movement results in a reduced or even
limited view of the axes of the visual system. These moves are even more evident
when the head rotates around an axis and the remote images of the visual system are
supported by turning the eyes in a direction opposite to the movement of the head to
compensate for the rotation.
From a functional point of view, there are two forms of manifestation of the
nystagmus: physiological and pathological, presenting, within each group, other
variants of manifestation. Forms of interest for oculographic computational analysis are represented by physiological nystagmus, the pathological one requiring
a medical approach of ophthalmological and neurological specialty. The forms of
nystagmus may be determined by a variety of causes, such as nervous system disorders, congenital disorders, acquired disorders, toxicity and medication. As mentioned
in many research papers, physiological nystagmus is a form of involuntary eye movement that is part of the vestibulo-ocular reflex (VOR), characterized by alternating
smooth pursuit in one direction and saccadic movement in the other direction [1].
In turn, the physiological nystagmus presents the following forms of manifestation:
downbeat nystagmus, upbeat nystagmus, seesaw nystagmus, periodically alternating
nystagmus.
Other forms of manifestation of physiological nystagmus, which are of interest
for studies on biomechanical posture, dynamical or static behavior of the human
body, are the form of opto-kinetic and post-trophic nystagmus, respectively. The
form of opto-kinetic nystagmus is induced by the pursuit of visual stimuli (vertical
or horizontal), the post-trophic form is determined by the rotation motion of the body
around the vertical axis, and the rapid phase of the nystagmus is performed in the
opposite direction of this rotation, trying to compensate some internal physiological
manifestations (Fig. 1).
Another form of movement determined in each ocular globe is saccade movement,
a rapid eye movement, conjugated and performed under voluntary control from the
central cortex (visual cortex). Generally, the purpose of these oscillatory movements
is to form the images of the surrounding space in the foveal area; therefore, the
saccade oscillations are considered as an important mechanism for characterization
of selective visual attention.
In the case of saccade movements, an important problem was identified, which is to
analyze how the visual system works during these movements (whether or not images
are formed on the retina to be transmitted to the visual cortex). Thus, it is stated in the
literature that in fact visual information, in this case, is obtained as sequential images
and interrupted by fixation processes, a phenomenon aware of the subject with this
form of eye movement [2]. Fixation periods last up to 200–300 ms, and the fixation
sequence is related to the sampling rate of the eye movement recording technique
that has been used. Saccade movements are very rapid, resulting in a phenomenon of
sacred suppression, a phenomenon during which visual perception is not completely
eliminated but only substantially reduced. From the experimental point of view, the