Balint's syndrome
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What is Balint’s Syndrome?
Rezso (Rudolf) Balint identified Balint’s syndrome in 1909 as a disjointed and paralysis
of gazing ability with haphazard scanning skills. Balint’s syndrome is characterized by
optic ataxia (uncoordinated hand and eye movement) and optic apraxia (inability to
voluntarily guide eye movements and change locations of visual fixations). Due to the
combination of optic ataxia and optic apraxia, patients with Balint’s syndrome also
display simultanagnosia or the inability to perceive more then one object at a time even
when the objects are taking up the same area of the visual field. In some cases, the patient
may behave as if they are blind.
Simultanagnosia in Balint's Syndrome
What is really interesting about Balint’s syndrome is that the simultanagnosia involved
with Balint’s syndrome is not specific to one object or spatial location. For example, the
tester could hold up two objects that intersect each other on the patient’s visual field and
ask the patient what he sees. The patient is just as likely to pick one item over the other,
while being completely blind to the second object.
Jackson et al (2006) conducted perceptual priming tasks with a Balint's patient where 2
pictures were shown (either the same or different semantic categories), and the participant was
asked to either classify one of the pictures or name both pictures. The results indicate that
there was a significant decrease in classification performance when the 2 pictures were different
in semantic category. The surprising aspect of this result is that the patient rarely indicated
that he saw more than one object. Thus, Jackson et al (2006) found results pointing to a
theory that Balint’s patients do not have a difficulty in seeing more than one item at a
time, but they have a deficit in explicitly identifying one item at any given time.
They suggest that this could be from an inability to disengage attention from one object once
that object catches the patient's attention. When given more time, the patient with Balint’s
syndrome can sometimes identify more than one stimulus when asked.
A patient with Balint’s Syndrome, J.J., made significantly more classification errors when items
were presented sequentially in time instead of at the same time. This indicates that the priming
stimulus could have less of an influence when it is presented simultaneously with the probe item
than when it comes before the probe item. (Jackson et al, 2006)
It could be that there is a reduced amount of competition between items on a sequential
presentation in patients with Balint’s syndrome simply because when the stimuli are presented
simultaneously, the patient only consciously perceives one item instead of two, eliminating
competition between stimuli. (Jackson et al, 2006)
Brain Areas Involved
Balint’s syndrome has been associated with bilateral damage to the posterior parietal
cortex with a primary cause of the syndrome being multiple strokes, Alzheimer’s,
intracranial tumors or brain injury. Only recently has Balint’s syndrome been associated
with damage to the parietal-occipital vascular boarder zone and in children.
Refrences
Gillen, J.A. and Dutton, G.N. (2003). Balint's syndrome in a 10-year-old male. Developmental Medicine & Child Neurology, 45, (349-32).
From class discussions:
Jackson et al. (2006).dorsal simultanagnosia: An impairment of visual processing or visual awareness. Cortex. 42, 740-749.
Newport et al. (2006). The role of the posterior parietal lobe in prism adaptation: Failure to adapt to optical prisms in a patient with bilateral damage to posterior parietal cortex. Cortex. (2006) 42, 720-729.
