Balint Syndrome Overview

Zsuzsa Kaldy, “Parallel Pathways” Grad. Class, 2001 Spring)

-HISTORY:

ofirst description: Rezso Balint (1909), Holmes (1919)

osimultanagnosia: Wolpert (1924)

ostudied by Luria (~50), Kinsbourne and Warrington (~60)

- DIAGNOSIS - the triad of symptoms:

osimultanagnosia : constriction of visual attention

ovisuomotor problems:

§optic ataxia: misreaching (mislocalization is selective for visual stimuli)

§severe problems with fixation, saccade initiation and smooth pursuit

ospatial disorientation

(‘pure’ cases are extremely rare, often associated with:

alexia, prosopagnosia, visual field deficits)

The patient acts as if he / she would be blind (no reflex blink, bumping into things while walking, etc.)

- BUT: normal visual acuity, color vision, shape recognition,

NOT “shaft vision” as first noticed by Luria, 1954

-SITE OF LESION: bilateral lesions of the parieto-occipital junction (characteristically: posterior parietal lobe (angular gyrus), area 19, superior parietal lobe)

-CAUSES:

ostroke,

otumor (“butterfly” glioma),

ocerebral degenerative diseases (e.g. Alzheimer, PCA)

ohead traumas

-SOME EXPERIMENTAL APPROACHES:

oEgly et al. (1994)

§Right parietal lobe: shifting attention BETWEEN objects

Left parietal lobe: shifting attention WITHIN objects

oHumphrey and Riddoch (1993), Baylis et al. (1994) - reading

§simultanagnosia: object-based attentional deficit

oFriedmann-Hill et al. (1995)

§exceptional number of illusory conjunctions (problems with feature binding)

Comparative table based on Farah, M. (1990) Visual agnosia

Dorsal simultanagnosia	Ventral simultanagnosia
“piecemeal” character of perception; simultanagnosia: one object can be seen at one time, size does not matter
often have full visual field, normal visual acuity
description of complex scenes:  slow and fragmentary,  in 30-60 s: some details put together	description of complex scenes:  individual elements,  no understanding of the scene as a whole
lesion: bilateral parieto-occipital	lesion: left inferior temporo-occipital
observed in the context of Balint Syndrome: + optic ataxia  + ocular apraxia	other typical ventral dysfunctions: pure alexia, prosopagnosia, visual anomia,  visual form agnosia
act as if they were blind, spatial disorientation	able to manipulate objects,  walk around without bumping into obstacles
what they see, can recognize	can see multiple objects, given sufficient time, they can also recognize them
reading: difficult (words are recognized) or impossible	reading: impaired, letter-by-letter
not able to count (with haptic help: OK)	?
depth perception: impaired superimposed objects	depth and motion perception: normal
motion perception: slow, regular: OK  rapid, unpredictable: obj. disappear
no reflex blink to threatening movement toward the face (but normal reaction if own hand thrust by the experimenter, Holmes, 1919)	?

Auditory and visual space in Balint Syndrome

Phan ML, Schendel KL, Recanzone GH, Robertson LC (2000) Auditory and visual spatial localization deficits following bilateral parietal lobe lesions in a patient with Balint's syndrome. J Cogn Neurosci, 12(4), 583-600.

Parietal lobe functions

1.human studies:

·creating visual spatial representations

·directing and shifting spatial attention to visual stimuli

2.single-cell studies:

·attention

·preparation of executive motor commands (see also Snyder et al (2000))

·coordination of different spatial frames (see also Xing et al (2000))

·auditory spatial processing? relation to visual spatial processing?

in a Balint syndrome patient (RM)

-- unilateral parietal damage (hemineglect) patients: extent of auditory deficit, relationship to visual deficit is not clear

-- main questions:

1.if auditory and visual deficits are similar in bilateral damage

à parietal lobe integrates multisensory input

2.are they aligned into the same coordinate system?

Relative localization ability

Exp 1. Implicit rel. loc. (indicate change in location)

Result: RM deficit in visual localization, especially in the right hemifield

RM’s auditory deficit: smaller, almost symmetric (right hemifield worse)

Exp 2. Explicit rel. loc. (indicate direction of location change)

Result: RM more errors for left hemifield stimuli in the visual task + more Right

responses

no difference from age-matched controls in the auditory task

Reference frame: egocentric or allocentric (external)

Exp 3. Rel. loc. with changing reference point (-12º, 0, +12º)

Result: RM responses showed localization relative to his midline both in visual

and auditory tasks, in both hemifields. Position of fixation point (whether it was V or A) did not have an effect on him.

not simple misunderstanding of the instructions, rather inability to quickly shift reference points

Exp 4. Estimating egocentric midline (indicate if stimulus is aligned with body midline)

Result: RM visual: midline estimate shifted to the left by ~10º, precision worse

than age-matched controls

auditory: midline estimate shifted to the left by ~16º, precision similar to age-matched controls

Capture effects

parietal cortex: aligning different reference frames

·visual capture

·the ventriloquism aftereffect: a mismatch of 8 degrees for 20-30 min is sufficient to shift the perception of acoustic space by approximately the same amount across subjects and acoustic frequencies (Recanzone, 1998).

·McGurk effect: a heard /ba/ combines with a seen /ga/ gives the impression that /da/ has been heard.

which is the dominant? -- “modality appropriateness hypothesis” (Welch and Warren, 1980): “the sensory modality that best represents the stimulus feature to be judged will dominate”.

RM’s acuity in left hemifield: auditory similar to visual

rightauditory better than visual àpredicts auditory capture

Exp 5. Rel. loc. with distractors (indicate change in location)

RM visual

left hemifield: no effect of auditory stimulus (similar to controls)

right hemifield: Both Move is better than baseline in the periphery

Attended Moves is worse close to the midline

RM auditory

- Attended Moves is not different from baseline (similar to controls)

- visual distractor only captured auditory stimuli when it was close to midline, and the auditory stimulus was in the periphery (reduced spatial acuity)

- general conclusion:

·in attending to auditory stimulus conditions, RM is not different from controls

·auditory capture of the visual stimulus in right hemifield, in contrast to controls

RM: better auditory localization in right hemifield, V same as A in left hemifield (see also Exp 1.)

à A and V interacts in RM

the stimulus with the better spatial acuity captured the other one

(modality appropriateness hypothesis confirmed)

General conclusions

what does the damaged area do?

3 hypotheses:

·A and V spatial localization, planned motor movements (Andersen)

·Phan et al: although limited A and V localization still available, this area enhances V processing and selects a reference frame

this limited localization ablility can be served by the frontal cort. and the sup. coll.

·directs spatial attention (Posner, Vallar): imbalance between the two hemispheres -- but it does not account for all the results

the damage in the parietal areas (Br 7 and 39) in RM caused:

·relative auditory localization deficit, that is less severe than his relative visual localization (Exp 3)

·shifted egocentric reference frame to the left

·inability to use an external ref. point if it varied between trials [no explanation]

·interaction between A and V (auditory capture in the right hemifield, visual capture only when V stimulus close to midline) shows that capture effects, multisensory integration: not processed in the parietal lobe