Auditory-Visual Localization in Hemianopia

Auditory-Visual Localization in Hemianopia
Neuropsychology
2013, Vol. 27, No. 5, 573–582
© 2013 American Psychological Association
0894-4105/13/$12.00 DOI: 10.1037/a0033451
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.
Auditory-Visual Localization in Hemianopia
Jörg Lewald
Robert W. Kentridge
Ruhr University Bochum and Leibniz Research Centre for
Working Environment and Human Factors, Dortmund, Germany
University of Durham
Sören Peters and Martin Tegenthoff
Charles A. Heywood and Markus Hausmann
Ruhr University Bochum
University of Durham
Objective: Beyond visual field defects, patients with hemianopia have been suggested to perceive
horizontal visual space in a distorted manner. However, the pattern of these distortions remained
debatable. The aim of this study was to estimate the geometry of the visual representation of space in
hemianopia using an auditory marker. Method: Patients with pure left or right hemianopia (without
neglect) were tested in tasks requiring them to bring a visual stimulus into spatial alignment with a target
sound (Experiment 1) or vice versa (Experiment 2). Results: In Experiment 1, patients adjusted the
location of a light such that it was displaced toward the anopic side with reference to the physical sound
position. In Experiment 2, patients adjusted the location of a sound such that it was displaced opposite
to the anopic side with reference to the actual position of the visual target. Both experiments consistently
indicated that hemianopic patients perceived a sound and a light to be in spatial alignment when the
physical position of the light deviated by several degrees from the sound toward the side of the anopic
hemifield, that is, to the contralesional side. Conclusions: Given that auditory localization in patients
with hemianopia has been previously shown to be only slightly biased toward the anopic side, the
observed distortion of visual space with reference to auditory space can be explained by assuming that
visual positions were, in absolute terms, perceived as shifted toward the intact side. As a result, HA
patients may perceive visual space as compressed on their ipsilesional (intact), in comparison with their
contralesional (anopic) side.
Keywords: hemianopia, visual space perception, sound localization, visual cortex,
multisensory integration
Supplemental materials: http://dx.doi.org/10.1037/a0033451.supp
Hemianopia (HA) is a visual field defect characterized by a loss
of vision in one hemifield. The visual defect is caused by unilateral
lesions in the cerebral hemisphere contralateral to the anopic side,
either in postchiasmatic optic tract, lateral geniculate nucleus,
optic radiation, or occipital lobe. HA has a relatively common
occurrence affecting approximately 20% of stroke patients and
severely affecting their quality of life (Schuett, Heywood, Kentridge, & Zihl, 2008). It has been suggested that patients with HA
perceive horizontal visual space in a distorted manner. The primary experimental evidence for this conclusion comes from visual
line bisection tasks. With these tasks, HA patients displace the
bisection mark toward the anopic side, which has been interpreted
as a bias of visual space toward the blind field (e.g., Axenfeld,
1894; Liepmann & Kalmus, 1900; Best, 1910, 1917; Strebel, 1924;
Barton & Black, 1998; Hausmann, Waldie, Allison, & Corballis,
2003a). In approaches using visual pointing or adjustment tasks,
the visual straight-ahead of HA patients was shown to be displaced
toward the anopic side (Zihl & Von Cramon, 1986; Ferber &
Karnath, 1999; Lewald, Peters, Tegenthoff, & Hausmann, 2009a).
The exact topography of the visual space in HA is, however, still
a matter of debate. In two studies, the horizontal angular distance
between visual stimuli (Zihl & Von Cramon, 1986) and the hori-
This article was published Online First August 12, 2013.
Jörg Lewald, Department of Cognitive Psychology, Faculty of Psychology, Ruhr University Bochum, Bochum, Germany, and Leibniz Research
Centre for Working Environment and Human Factors, Dortmund, Germany; Robert W. Kentridge, Department of Psychology, University of
Durham, Durham, United Kingdom; Sören Peters, Department of Radiology, BG-Kliniken Bergmannsheil, Ruhr University Bochum; Martin Tegenthoff, Department of Neurology, BG-Kliniken Bergmannsheil, Ruhr
University Bochum; Charles A. Heywood and Markus Hausmann, Department of Psychology, University of Durham.
We thank all participants for their willing cooperation, A. Stöbener and
V. Zimmermann for help with running the experiments, P. Dillmann for
preparing the software and parts of the electronic equipment, and H.-O.
Karnath for critical discussion of the results and valuable comments on the
manuscript. This research was supported by the Deutsche Forschungsgemeinschaft (FA 211/24-1).
Correspondence concerning this article should be addressed to Jörg
Lewald, Department of Cognitive Psychology, Faculty of Psychology,
Ruhr University Bochum, D-44780 Bochum, Germany. E-mail:
[email protected]
573
LEWALD ET AL.
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574
zontal size of rectangles (Ferber & Karnath, 2001a) was perceived
as smaller on the anopic side than on the intact side, thus suggesting a compression of visual space on the anopic side. Another
study (Doricchi, Onida, & Guariglia, 2002) obtained the opposite
result: HA patients estimated size and distance in the anopic
hemifield as being longer than equivalent sizes and distances in
intact hemifield. In each case, the most established result, that
visual straight ahead is displaced to the anopic side in HA, is
geometrically compatible only with both a bias of visual localization to the intact side and a compression and expansion of visual
space on the intact and anopic sides, respectively. The reasons for
these inconsistencies between studies are still unclear, but
might lie in the fact that previous approaches often did not
disentangle a putative distortion of space from accounts based
on spatial attention. In addition, paper/pencil tasks or tasks with
presentation of visual stimuli on a computer screen, as are often
used in this field of research, might not permit unequivocal
interpretations of the topography of visual space because stimuli are not seen in isolation but in relation to a visual surround.
Finally, compensatory strategies, using proprioceptive and vestibular cues from the eyes, the head and the arms (Doricchi et
al., 2002), may vary among individuals, in particular depending
on whether patients were tested in the acute or chronic phase of
brain injury. Thus, conclusions about the absolute localization
of a visual stimulus in space are difficult to draw from these
previous approaches.
The starting point of the present study was the growing evidence
that spatial hearing performance remains relatively unaffected in
HA. Zimmer, Lewald and Karnath (2003) did not find any significant bias of the auditory median plane in HA patients as measured
by variation of interaural time differences. In a direct comparison,
Lewald et al. (2009a) showed that subjective straight ahead deviates in hemianopia substantially for visual stimuli whereas it is
veridical for auditory stimuli. In a more detailed study (Lewald,
Peters, Tegenthoff, & Hausmann, 2009b) that focused on the
topography of auditory space in HA, there were statistically significant distortions of auditory space in HA patients which can be
interpreted by both rotation and compression of auditory space
toward the anopic side. However, the mean amplitude of these
distortions measured with a task of manual pointing was only 1.5°
in the auditory modality, which is relatively small compared with
the visual distortions that have been recently reported (4 – 8°; Zihl
& von Cramon, 1986; Ferber & Karnath, 1999; Lewald et al.,
2009a, 2009b).
In the present study, we thus asked subjects to match the
location of a single visual target with an auditory marker or vice
versa in totally dark surroundings. The rationale for our approach
was that accounts in which the relative attentional salience of
stimuli with different spatial locations determines spatial judgments in hemianopia cannot readily be applied to a task in which
there is only a single visual stimulus. For example, an attentional
gradient might affect the way in which patients with hemianopia
scan complex visual stimuli. It should not, however, affect simple
alignment judgments containing a single visual stimulus.
Using such simple alignment tasks, the present study sought to
establish whether more general distortions in the visual representation of space accompany deviations in visual straight ahead. In
other words, rather than asking participants to make judgments
about the relative locations of many visual stimuli (as is the case
of the visual line bisection task), the present experiment used an
auditory marker to indicate the location of a single visual stimulus.
From such judgments in HA patients and normal observers, we
aimed to estimate the potential distortions in the representation of
visual space accompanied by HA.
Method
Subjects
Results from 10 patients with brain lesions were included in this
study. All patients had received the diagnosis of persistent homonymous hemianopia (HA) confined to one hemifield, as confirmed by visual perimetry tests (see below). HA was left-sided
(LHA) in seven patients (LHA1-LHA7) and right-sided (RHA) in
three patients (RHA1-RHA3). Details on age, sex, visual field
defects, and lesion sites are reported in Table 1 and Supplemental
Table 1. All patients were congenitally right-handed, as assessed
by a German adaptation of Coren’s (1993) inventory (Siefer,
Ehrenstein, Arnold-Schulz-Gahmen, Sökeland, & Luttmann,
2003), with a criterion of an individual score of ⱖ2 (range from
⫺4 to 4) in the handedness section of this questionnaire. However,
hemiparesis prevented two patients (LHA5, RHA2) from use of
their contralesional hand, and one other patient showed mild
(LHA7) impairment with use of the contralesional hand as a result
Table 1
Summary of Clinical Data and Visual Field Defects of Patients With Hemianopia
Patient
Age
Sex
Side of HA
VF border
Time since onset
Ethiology
Lesion site
LHA1
LHA2
LHA3
LHA4
LHA5
LHA6
LHA7
RHA1
RHA2
RHA3
38
60
64
64
42
54
39
44
48
37
F
M
M
M
F
F
M
M
M
F
L
L
L
L
L
L
L
R
R
R
⫺1.2°
⫺2.9°
⫺1.7°
⫺4.6°
⫺0.3°
⫺0.2°
⫺1.8°
12.5°
0.4°
8.2°
7 months
7 years
6 months
5 years
35 months
19 months
5 years
5 months
33 months
6 months
AVM, ICH
ICH
CI
CI
CI
CI
CI
CI
CI
CI
R temporo-parieto-occipital
R temporal
R temporo-occipital
R occipital
R temporal
R temporo-parieto-occipital
R occipital
L temporo-occipital
L temporo-occipital
L parieto-occipital, R occipital
Note. AVM ⫽ cerebral arteriovenous malformation; CI ⫽ cerebral ischemia; F ⫽ female; ICH ⫽ intracerebral hemorrhage; HA ⫽ hemianopia; L ⫽ left;
M ⫽ male; R ⫽ right; VF ⫽ visual field. Negative angles are to the left, positive angles to the right.
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AUDITORY-VISUAL LOCALIZATION IN HEMIANOPIA
of hemiparesis. In addition to these 10 participants with HA, two
further patients (one LHA and one RHA patient) were also tested,
but were excluded from the study since they were unable to
adequately perform the acoustic pointing task, in particular when
visual targets were presented on the anopic side. For these two
subjects, linear regression analyses of the pointing responses to
targets on the anopic side resulted in rather poor coefficients of
determination (R2 of .06 and .17), which were more than four
standard deviations below the R2 values of the 10 subjects included
(range from .65 to .92, mean .78, SD .10; see Results).
All HA patients had circumscribed brain lesions as a result of
ischemic stroke or hemorrhage, demonstrated by MRI or computed
tomography (CT). In all patients, lesions were unilateral (i.e., on
the side contralateral to the anopic hemifield), with the exception
of patient RHA3 who showed some minor involvement of righthemispheric regions in addition to the predominant lefthemispheric lesion. Lesion sites of all patients are summarized in
detail in Supplemental Table 1 and Supplemental Figure 1.
To test whether HA patients suffer from spatial neglect a
neglect-test battery (Ferber & Karnath, 2001a) was applied, which
consisted of the following tests: (a) Letter Cancellation task
(Weintraub & Mesulam, 1985), which requires the patient to
cancel 60 target letters ‘A’ distributed amid distractors on a horizontally oriented standard page (DIN A4). Responses were coded
and the Center of Cancellation (CoC) index was measured using
the software (www.mricro.com/cancel/) by Rorden and Karnath
(2010). Patients are classified as suffering from spatial neglect
when they show a CoC index ⬎ .09 (Rorden & Karnath, 2010). (b)
Bells Test (Gauthier, Dehaut, & Joanette, 1998), which requires
the patient to identify 35 bell symbols distributed on a horizontally
oriented standard page with 40 distractor symbols. Responses were
analyzed by calculating the CoC index (Rorden & Karnath, 2010)
as with the Letter Cancellation Task, using the same cutoff threshold (⬎ .09) for the patient’s classification as suffering from spatial
neglect. (c) Baking Tray Test (Tham & Tegnér, 1996), which
requires the patient to place 16 identical items as evenly as possible on a blank standard page (8 on the left, and 8 on the right
side). Any distribution more skewed than seven items on the left
side and nine items on the right side are considered as a sign of
spatial neglect. (d) Copying task (Ferber & Karnath, 2001a; Johannsen & Karnath, 2004), in which patients are asked to copy a
complex multiobject scene consisting of four figures on a standard
page (two on the left, and two on the right side). Omission of one
left sided feature of each figure is scored as 1, and omission of
each whole figure is scored as 2, resulting in a maximum score of
8. A score higher than 1 (i.e., ⬎ 12.5% omissions) is considered as
a sign of spatial neglect. None of the HA patients exceeded the
limit values in at least two of these four tests, which has been
regarded as the criterion for presence of spatial neglect (Karnath,
Himmelbach, & Rorden, 2002).
In addition, we applied a line-bisection task which comprised 17
horizontal black lines of 1 mm width on a horizontally oriented
white standard page. The lines ranged from 100 to 260 mm long,
in steps of 20 mm. The mean length was 183.5 mm. Patients were
asked to bisect all lines into two parts of equal length by marking
the subjective midpoint of each line with a fine pencil (for details,
see, e.g., Hausmann et al., 2003a; Hausmann, Corballis, & Fabri,
2003b). The majority of neglect patients shows a large bisection
bias toward the right, although about 30% of patients with acute
575
neglect do not show any significant bias in line-bisection tasks
(Ferber & Karnath, 2001b). Here, HA patients showed a significant mean bisection bias of 4.77% (SE 1.67, range from ⫺2.15%
to 11.32%), t(9) ⫽ 2.85, p ⫽ .019, toward the side of the anopic
hemifield (LHA: mean leftward bias ⫺6.58%, SE 1.96; RHA:
mean rightward bias .53%, SE 1.47). This conforms with previous
findings of a contralesional bias in patients with HA (e.g., Barton
& Black, 1998; Hausmann et al., 2003a, 2003b).
Before experimentation, the presence of homonymous HA was
confirmed by visual static perimetry tests in all patients included in
this study. In addition, after completion of the experiments the
azimuthal dimensions of the visual field, and in particular the
position of the binocular vertical visual field border (see Table 1)
was measured in more detail using visual stimulation by the
experimental apparatus, as was already described in preceding
studies (Lewald et al., 2009b; Lewald, Tegenthoff, Peters, &
Hausmann, 2012). For this purpose, white light flashes (duration
50 ms), delivered by light-emitting diodes (LEDs; see below),
were presented in total darkness at random locations in the azimuthal plane over a range from ⫺90° on the left to 90° on the
right, in steps of 2°. Patients were instructed to fixate on a central
red light emitting diode, that was permanent on, and to press a
response button as soon as they perceived a white light flash.
Stimuli were presented with a randomly varied time interval between 1 s and 3 s (steps of .5 s) after the patients’ response. In one
block, each stimulus position was presented three times, resulting
in 273 trials. Data of four identical blocks (2 blocks conducted on
one day and 2 blocks on a separate day) were pooled. For computation of the visual field border, the number of correct responses
was plotted as a function of stimulus azimuth (␪) within the range
of ⫺46° on the left to 46° on the right, and fitted to the sigmoid
equation:
f ⫽ 100 ⁄ 共1 ⫹ e⫺k共␪⫺VFB兲兲
where f is the frequency of responses, given as percentage; VFB
(visual field border) is that ␪ where f is 50%; k is the slope of the
function at 50%; e the base of the natural logarithm (Lewald et al.,
2009b, 2012). The mean coefficient of determination (R2) of the fit
was .93 (range from .67 to 1.00; all p ⬍ .0001), indicating a sharp
boundary of the visual field for all patients. Patients detected the
vast majority of stimuli in the intact hemifield (mean 85.7%, SE
3.6) and only few in the anopic hemifield (7.7%, SE 2.2; measured
over the range from 90° to 2° eccentricity on the respective side).
Across all patients, the VFB was only slightly shifted toward the
side of the anopic field (mean 3.38°, SE 1.28). One of the patients
(LHA7) showed incomplete left HA, with a small peripheral area
of vision lying to the left of the anopic field.
Ten healthy right-handed subjects (4 females and 6 males),
ranging in age from 39 to 66 years (mean 49.9 years, SE 3.4),
participated in the study as normal controls. Each control subject
was matched with one of the 10 HA patients for sex and age (⫾ 3
years).
All subjects, HA patients and normal controls, were tested for
general hearing loss. For this purpose, white-noise bursts with a
duration of 1 s were presented monaurally via headphones (K271,
AKG Acoustics, Vienna, Austria) at various sound-pressure levels
(SPLs, range 10 – 80 dB re 20 ␮Pa, steps of 10 dB; onset/offset
time 50 ms), and subjects pressed a button as soon as they heard
a sound. A two-factor ANOVA with Ear (ipsilateral, contralateral)
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576
LEWALD ET AL.
as within-subject factor and Group (LHA patients, RHA patients,
controls) as three-level between-subjects factor revealed neither a
main effect nor interaction, all F ⱕ 2.77, p ⬎ .09. Most importantly, HA patients did not show any superiority of the ear on the
side of the intact (contralateral) or the anopic (ipsilateral) hemifield, t(9) ⫽ .00, p ⫽ 1.00.
A subsequent hearing test was focused on the symmetry in
loudness perception of the subjects’ left and right ears, which is
more relevant to the experiments conducted here than thresholds.
For this purpose, incoherent white-noise signals (preventing binaural fusion) were presented binaurally via headphones (as above).
Interaural SPL (average root mean square) differences for these
stimuli were varied between trials following a quasi-random order
over a range from 20 dB (higher SPL at the left ear) to 20 dB
(higher SPL at the right ear), in steps of 4 dB (duration 1 s;
onset/offset time 50 ms; mean SPL 70 dB). Subjects were instructed to make a two-alternative forced choice as to which of the
two sounds was louder, the one on the left or the one on the right.
The test was composed of 110 trials (10 presentations of each level
difference) and lasted about 5 min. The point of subjective equality
measured in HA patients (LHA: mean .05 dB, SE 1.33; RHA:
mean ⫺1.12 dB, SE 1.60) and controls (mean ⫺0.73 dB, SE .58)
did not differ, F(2, 17) ⫽ .45, p ⫽ .64, nor was there any bias
to the side of the intact or the anopic hemifield in HA patients,
t(9) ⫽ .37, p ⫽ .72. Taken together, with respect to these basic
auditory tests, the HA patients’ auditory performance of both ears
was symmetrical and normal.
This study conformed to the Code of Ethics of the World
Medical Association (Declaration of Helsinki), printed in the British Medical Journal (July 18, 1964). All subjects gave their informed consent to participate in the study, which was approved by
the Ethical Committee of the Medical Faculty of the Ruhr University Bochum.
Apparatus
The experiments took place in a sound-proof and anechoic room
(5.4 ⫻ 4.4 ⫻ 2.1 m3), which was insulated by 40 cm (height) ⫻ 40
cm (depth) ⫻ 15 cm (width at base) fiberglass wedges on each of
the six sides. A suspended mat of steel wires served as the floor.
The ambient background noise level was below 20 dB(A) SPL. All
experiments were conducted in total darkness.
The acoustic stimulus was band-pass-filtered noise (lower cutoff frequency .8 kHz; upper cut-off frequency 3 kHz) with a
maximum duration of 12 s (rise/fall Time 100 ms). Sound stimuli
were generated digitally and converted to analog form via a
computer-controlled external soundcard (Sound Blaster Audigy 2
NX, Creative Labs, Singapore) at a sampling rate of 96 kHz.
Sound stimuli were delivered via a semicircular loudspeaker system, with an SPL of 75 dB. The subject sat on a comfortable chair.
In front of the subject at a constant distance of 1.5 m from the
center of the head, 91 broad-band loudspeakers (5 ⫻ 9 cm2,
Visaton SC 5.9, Visaton, Haan, Germany) were mounted in the
subject’s horizontal plane. The azimuth of the loudspeakers ranged
from ⫺90° (left) to 90° (right), in steps of 2°, with the center
loudspeaker at 0°. For visual stimulation at corresponding azimuthal positions, at the lower edge of the chassis of each loudspeaker a white LED was mounted in a central position. The LED
(diameter 10 mm; luminance about 100 cd/m2) was mounted in a
small housing impermeable to light, with a central circular aperture
of 2 mm diameter immediately in front of the LED.
Procedure for Experiment 1:
Visual Pointing to Acoustic Targets
The subject’s head was fixed by a custom-made framework with
stabilizing rests for the chin, forehead, and occiput (see Lewald,
1997). In Experiment 1, subjects had to bring a visual stimulus into
spatial alignment with a target sound. This task is a modification
of the method originally described in Lewald and Ehrenstein
(1998). In each trial, a stationary target sound was presented.
Acoustic stimuli were presented from 21 loudspeaker positions:
straight ahead of the subject (0°), 10 positions on the left and 10
positions on the right with constant angular separation of 4°, thus
covering an angular range from 40° to the left to 40° to the right.
Each trial began with the onset of the sound stimulus at one of the
21 positions. The stimulus position changed in a quasi-random
order between trials. At the moment of sound onset, a continuous
light stimulus, delivered from an LED, was presented simultaneously at one out of nine locations (from ⫺24° to 24° azimuth, with
angular separation of 6°). The initial position of the light was
varied following a quasi-random order. The subject controlled the
azimuthal position of the light (over a total range of 180°, in steps
of 2°) by adjusting the knob of a potentiometer. The potentiometer
was mounted in a small case, so that the subject held it in one hand
while turning the knob with the other hand (see Figure 2 in Lewald
et al., 2009a). Subjects were instructed to direct their gaze to the
light and, while maintaining fixation on it, to adjust its position (by
turning the knob of the potentiometer) toward the position of the
sound until the locations of both these stimuli were perceived to be
in exact alignment. HA patients were explicitly encouraged to
search for the visual stimulus by eye movements, as it could start
in their anopic field. The subjects were instructed to press a button
(mounted beside the potentiometer knob on the case) as soon as the
adjustment was completed. At the moment the key was pressed,
both the light and the sound disappeared and the final position of
the visual stimulus was recorded. Each of the 21 loudspeaker
positions was presented in combination with each of the nine
starting positions of the LED, thus resulting in a total number of
189 trials plus repetitions. Two seconds after key pressing, the next
trial began. The sound and light stimuli had a maximum duration
of 12 s. After about 40 practice trials, all subjects were able to
perform the task within about 5– 8 s. In cases in which the key was
not pressed before the stimulus ended automatically (that is, within
12 s), the trial was repeated at the end of the experiment. Each
experiment comprised 168 trials plus repetitions (eight presentations of each stimulus position). The timing of the stimuli and the
recording of the subject’s responses were controlled by customwritten software.
Procedure for Experiment 2:
Acoustic Pointing to Visual Targets
In Experiment 2, subjects were asked to bring an acoustic
stimulus into spatial alignment with a visual target. The task was
conducted analog to that described for Experiment 1, with the only
difference that visual and auditory stimuli were interchanged.
Stationary visual target stimuli were presented from 21 LED
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AUDITORY-VISUAL LOCALIZATION IN HEMIANOPIA
577
positions: straight ahead of the subject (0°), 10 positions on the left
and 10 positions on the right with constant angular separation of 4°
(from ⫺40 to 40° azimuth). The light and sound stimuli had a
maximum duration of 12 s. The position of the target light changed
in quasi-random order between trials. In each trial, at the moment
of light onset a continuous sound stimulus (as described above)
was simultaneously delivered from a loudspeaker at one of nine
locations (from ⫺24° to 24° azimuth, with angular separation of
6°). The initial position of the sound was varied following a
quasi-random order. The subject controlled the azimuthal position
of the sound (over a total range of 180°, in steps of 2°) by adjusting
the knob of the potentiometer in an identical manner as described
above for adjustment of light stimuli. Subjects were instructed to
direct their gaze to the light and, while maintaining fixation on it,
to adjust the sound position (by turning the knob of the potentiometer) toward the position of the light until the locations of both
these stimuli were perceived to be in exact alignment. The subjects
pressed the button as soon as the adjustment was completed. HA
patients were able to perform this task with similar ease as that in
Experiment 1. At the moment the key was pressed, both the light
and the sound disappeared and the final position of the auditory
stimulus was recorded automatically. Each of the 21 LED positions was presented in combination with each of the nine starting
positions of the sound, thus resulting in a total number of 189 trials
plus repetitions. All other parameters and conditions were identical
to those in Experiment 1.
Data Analysis
For analysis of the data obtained in Experiments 1–2, the subject’s individual pointing responses were determined as a function
of target position, and were fitted to a regression line. Data
obtained for stimuli presented in the left and right hemispaces were
analyzed separately. Responses were normalized such that positive
angles indicate pointing toward the hemispace within which the
stimulus was presented, and negative angles indicate pointing
responses to the opposite hemispace (cf., e.g., Figure 1). Three
parameters, derived from the fit, were used to describe different
aspects of the subject’s individual performance (1). The y-intercept
of the regression line was taken as a measure of the subject’s
constant error in pointing to either side (2). The slope of the
regression line (a) was taken as a measure of the subject’s general
tendency to underestimate (a ⬍ 1) or overestimate (a ⬎ 1) the
distances between target positions (3). The coefficient of determination (R2) was taken as a measure of the subject’s precision in
pointing.
For statistical comparisons, results of LHA and RHA patients,
obtained in Experiments 1–2, were normalized and pooled. For
this purpose, data were classified according to whether they had
been obtained within the hemispace of the patient’s anopic or
intact field. As already mentioned, each HA patient was assigned
to a healthy control subject matched for age and sex. Each data set
of the control subject was treated in exactly the same way as the
data of the related patient. That is, as data obtained for the left
(right) hemispace in LHA patients and data obtained for the right
(left) hemispace in RHA patients were pooled, the data obtained
for the left (right) hemispace of the matched LHA controls and the
data obtained for the right (left) hemispace of matched RHA
Figure 1. Results of Experiment 1 (visual pointing to acoustic targets).
Final pointing eccentricities (mean values ⫾ SE) are plotted as a function
of target azimuth for patients with left (A) and right HA (B), and for
matched controls (C). Data obtained for stimuli presented in the left and
right hemispaces were analyzed separately. Responses were normalized
such that positive angles indicate pointing toward the hemispace within
which the stimulus was presented, and negative angles indicate pointing
responses to the opposite hemispace. Continuous lines indicate regression
lines, dotted lines indicate ideal performance.
controls were also pooled. This was mainly done to account for
effects of handedness on analyses of the normalized data.
Furthermore, y-intercepts resulting from analyses were normalized such that positive values indicate a bias in pointing toward the
anopic side and negative values a bias toward the intact side.
Finally, to adequately compare the y-intercepts obtained in Experiment 1 with those of Experiment 2, these values were normalized
such that in both experiments positive values indicate final deviations of the visual stimulus from the auditory stimulus toward the
anopic side, irrespective of whether the visual stimulus was
aligned with the auditory target (Experiment 1) or the auditory
stimulus was aligned with the visual target (Experiment 2).
LEWALD ET AL.
578
At the first stage of statistical analysis, multifactor analyses of
variance (ANOVAs) were conducted to compare performances of
HA patients and controls. In subsequent stages of analysis, onefactor ANOVAs were used to reveal differences between the
performances measured in the intact hemispace and in the anopic
hemispace of HA patients. For all computations, F statistics were
based on ε-corrected degrees of freedom (Greenhouse-Geisser
correction). Bonferroni-corrected p values were used for multiple
comparisons.
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Results
Although HA patients had some difficulties in performing these
tasks, linear regression of the pointing responses as a function of
target azimuth was significant (p ⬍ .0001) for all participants, both
in Experiment 1 (HA patients: mean R2 ⫽ .87, range from .48 to
.96; controls: mean R2 ⫽ .93, range from .82 to .97) and in
Experiment 2 (HA patients: mean R2 ⫽ .80, range from .65 to .94;
controls: mean R2 ⫽ .87, range from .71 to .95).
A 2 ⫻ 2 ⫻ 2 mixed ANOVA with Task [visual pointing,
acoustic pointing] and Hemispace [anopic, intact] as withinsubject factors and Group [HA, controls] as between-subjects
factor was conducted for the coefficient of determination (R2) of
the linear regression. The ANOVA revealed a main effect of Task,
F(1, 18) ⫽ 12.32, p ⫽ .003, ␩p2 ⫽ .41, indicating a generally higher
precision with light pointing than with acoustic pointing (Figures
1, 2). No further main effect or interaction was significant (all F ⱕ
3.71).
For the normalized y-intercept resulting from the linear regression, an analogous ANOVA was conducted. The ANOVA revealed a main effect of the factor Group, indicating the general
bias in adjustments with visual stimuli shifted, with reference to
auditory stimuli, to the side of the anopic hemifield, F(1, 18) ⫽
12.39, p ⫽ .002, ␩p2 ⫽ .41. Furthermore, a main effect of Hemispace, F(1, 18) ⫽ 6.19, p ⫽ .023, ␩p2 ⫽ .26, was in alignment with
the general asymmetry in displacements. Finally, a three-way
interaction of Task ⫻ Hemispace ⫻ Group, F(1, 18) ⫽ 5.08, p ⫽
.037, ␩p2 ⫽ .22, was found. Taken together, the findings of this
ANOVA confirmed the obvious influence of HA on cross-modal
constant error, as obtained concordantly in both tasks: Stimulus
pairs were adjusted such that visual stimuli were shifted toward the
anopic side with reference to the auditory stimuli. As confirmed by
the three-way interaction, this bias was stronger in the patients’
anopic hemispace than on the intact side, and the bilateral asymmetry was more prominent with the light-pointing task than with
acoustic pointing (Figures 1–3).
Finally, an ANOVA, computed for the slope of the regression
line, revealed a main effect of the factor Task, F(1, 18) ⫽ 31.33,
p ⬍ .0001, ␩p2 ⫽ .64, confirming that in the acoustic pointing task
(Experiment 2) lateral target positions were increasingly underestimated with increasing eccentricity, whereas in the light pointing
task (Experiment 1) the lateral target positions were increasingly
overestimated with increasing eccentricity (cf. Figures 1 and 2). In
addition, a Task ⫻ Hemispace ⫻ Group threefold interaction, F(1,
18) ⫽ 13.74, p ⫽ .002, ␩p2 ⫽ .43, indicated a differential influence
of HA on the slope in both tasks: The slope obtained with light
pointing was decreased in the patients’ anopic hemifield and
increased in the intact hemifield with reference to healthy controls,
Figure 2. Results of Experiment 2 (acoustic pointing to visual targets).
Final pointing eccentricities (mean values ⫾ SE) are plotted as a function
of target azimuth for patients with left (A) and right HA (B), and for
matched controls (C). Conventions are as in Figure 1.
whereas the opposite pattern was found with acoustic pointing
(Figure 3C and 3D).
If the ANOVAs for all three dependent variables were restricted
to HA patients with left hemispheric lesions (together with corresponding control subjects), the significance of the results (not
shown here) remained essentially unchanged (the 3-way interaction for the y-intercept dependent variable only approached significance, F(1, 12) ⫽ 4.43, p ⫽ .057).
If the three patients with lesions involving parietal areas and
their respective controls were excluded and the analyses were
restricted to patients with temporal and/or occipital lesions, all
main effects and interactions with Group as a factor remained the
same when analyzing the slope and R2. The only difference occurred for the y-intercept, for which the three-way interaction of
Task ⫻ Hemispace ⫻ Group only approached significance, F(1,
12) ⫽ 3.50, p ⫽ .086, ␩p2 ⫽ .23.
These results, and in particular the three-way interaction are
complicated by the fact that the slope for the auditory pointing task
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AUDITORY-VISUAL LOCALIZATION IN HEMIANOPIA
579
Figure 3. Linear regression analysis of the pointing responses for Experiments 1 and 2. Each panel shows data
(mean values ⫾ SEM) obtained in the anopic and intact hemispaces of patients with HA as well as data from
matched controls. For the control subjects the “anopic hemispaces” and “intact hemispaces” were that hemispaces that were assigned as controls to the anopic and intact hemispaces of patients with HA (see Method). A
and B, y-intercepts of the regression lines that were taken as a measure of constant error in pointing. Data were
normalized such that positive values indicate final deviations of the visual stimulus from the auditory stimulus
toward the anopic side, irrespective of whether the visual stimulus was aligned with the auditory target (A) or
the auditory stimulus was aligned with the visual target (B). C and D, Slopes of the regression lines that were
taken as a measure of the subject’s general tendency to underestimate (values ⬍1) or overestimate (values ⬎1)
distances between target positions. E and F, Coefficients of determination of the regression lines that were taken
as a measure of precision in light pointing (E) and acoustic pointing (F).
is in terms of degrees of auditory pointing location per degree of
change in visual location while the slopes for the visual pointing
task are in the inverse units. One means of clarifying the results for
slope is to recast the analysis so that, for both tasks, the dependent
variable slope is always the change in position of the auditory
stimulus obtained for a given change in location of the visual
stimulus (i.e., as in Figure 3C and 3D). When we did this, the
analysis revealed a significant effect of Task, F(1, 18) ⫽ 15.64,
p ⬍ .001, and an interaction between Group and Hemispace, F(1,
18) ⫽ 15.08, p ⬍ .001. The three-way interaction (which in the
original analysis merely reflected the fact that the auditory location
and visual location axes were interchanged in the two tasks)
disappeared. These results clarified the finding from the untransformed data insofar as visual space relative to the auditory representation of space was compressed more strongly on the intact,
than on the anopic, side in HA patients, whereas normal controls
performed essentially symmetrically.
Subsequent analyses for the group of HA patients were conducted for the three parameters resulting from the linear regression, using one-factor ANOVAs with Hemispace as factor. The
analysis for the coefficient of determination did not provide significant differences between hemispaces, thus suggesting equal
precision in pointing in both hemispaces (Experiment 1: F(1, 9) ⫽
2.20, p ⫽ .17, ␩p2 ⫽ .20; Experiment 2: F(1, 9) ⫽ 2.70, p ⫽ .14,
␩p2 ⫽ .23). However, an analogous ANOVA revealed a significant
difference in the position of the y-intercept between hemispaces
for Experiment 1, F(1, 9) ⫽ 7.29, p ⫽ .024, ␩p2 ⫽ .45: The bias of
visual pointing, with reference to auditory targets, toward the
anopic side was stronger within anopic hemispace (mean 6.72°, SE
1.15) than within intact hemispace (mean 2.96°, SE .98; Figure 3).
In Experiment 2, the bias of acoustic pointing was almost equal in
anopic (mean 4.39°, SE .83) and intact hemispaces (mean 3.83°,
SE .70), F(1, 9) ⫽ .64, p ⫽ .44, ␩p2 ⫽ .07 (see Figure 3). Finally,
an analogous one-factor ANOVA with Hemispace as factor indicated a significantly steeper slope of the regression line in anopic
(mean .86, SE .06), than in intact, hemispace (mean .77; SE .05) in
Experiment 2, F(1, 9) ⫽ 14.25, p ⫽ .004, ␩p2 ⫽ .61, thus suggesting that the effects of HA partially counteracted the normally
observed pattern of increasing underestimation with increasing
target eccentricity (see above). For Experiment 1, this approached
LEWALD ET AL.
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580
significance, F(1, 9) ⫽ 3.81, p ⫽ .08, ␩p2 ⫽ .30, suggesting that the
normally observed increase in overestimation with increasing target eccentricity was partially reduced in anopic hemispace (see
above).
It is important to note that these results describe divergences
between visual and auditory spatial representations, but not deviations of perceptual from physical spatial coordinates. As a consequence, these findings, if considered in isolation, did not allow
any conclusions of whether HA patients showed perceptual anomalies in audition or vision, or in both of these modalities. To clarify
this problem, data obtained in one modality are needed in addition.
In our preceding study (Lewald et al., 2009b), all HA patients
included here had been tested for auditory localization by using a
task of hand pointing to acoustic targets. In that study, these 10
individuals showed a constant error in pointing toward the anopic
side, that was, however, relatively small in amplitude (anopic side:
mean 2.63°, SE 1.54; intact side: mean .42°, SE 1.81). A statistical
comparison of the intermodal divergence between visual and auditory locations (mean normalized y-intercepts from Experiments
1 and 2; Figure 3A and 3B) and the unimodal auditory y-intercepts
taken from Lewald et al. (2009b) for both hemispaces revealed a
significantly larger bias in the present study (mean 4.47°, SE .67)
than in the preceding study (mean 1.52°, SE .50), t(9) ⫽ 4.00, p ⫽
.003. Also, the slope obtained by Lewald et al. (2009b) for the
regression line of hand pointing responses as a function of auditory
target position (mean .94, SE .05) was significantly flatter than the
mean slope obtained here after conversion of data such that visual
positions were always plotted as a function of sound position
(mean 1.18, SE .06), t(9) ⫽ 3.93, p ⫽ .003. Thus, given the
previous unimodal auditory results from the same HA patients
(Lewald et al., 2009b), the already known distortion of their
auditory space significantly differed from the intermodal distortion
found here.
Discussion
These results demonstrated a significant distortion of visual
space with reference to auditory space in patients with pure HA.
First, HA patients generally perceived visual locations to be displaced toward their intact hemifield. Second, HA patients perceived visual space relative to the auditory representation of space
as more compressed in their intact, than in their anopic, hemifield.
The interpretation of these findings is complicated by the fact
that HA patients might potentially exhibit distortions not only in
their visual representations of space (Zihl & von Cramon, 1986;
Ferber & Karnath, 1999) but also in the auditory modality (Lewald
et al., 2009a, 2009b), although these latter anomalies seemed to be
relatively slight. Nevertheless, unimodal auditory distortions of
space perception cannot explain the intermodal divergences found
here. The same patients who were participants in the current study
have also been tested in hand pointing to auditory targets (Lewald
et al., 2009b). The extent of the unimodal distortion found in that
previous study cannot account for the intermodal distortion found
here. Lewald et al. (2009b) reported constant errors that were
about half the values obtained here for intermodal bias. This
suggests that the results obtained in the current study had their
origin primarily in the anomalies of visual spatial perception,
rather than in the auditory domain. Lewald et al. (2009a) found the
auditory straight ahead of HA patients not to differ from that of
normal controls. It may therefore be reasonable to conclude that
constant errors in auditory localization, although statistically significant, are small in magnitude compared with the distortions of
visual space in HA. If one assumes that auditory space perception
is only subject to relatively small errors, the pointing bias obtained
in both experiments is consistent with a distortion of visual space
in which visual positions were mislocalized toward the unimpaired
hemifield (Figure 3A and 3B), suggesting visual space was perceived as compressed on the intact, compared with the anopic,
hemifield (Figure 3C and 3D).
This conclusion is in line with previous findings on the position
of the visual straight ahead in pure HA. Several studies consistently demonstrated a bias of the visual straight ahead toward the
anopic side (Zihl & von Cramon, 1986; Ferber & Karnath, 1999;
Lewald et al., 2009a). That is, if a visual stimulus is physically
located straight ahead, it will be mislocalized toward the intact
side. The amplitude of the shift in visual straight ahead was
reported to be about 4 – 8°, which is compatible with the average
bias of 4.47° obtained here given a substraction of the mean
unimodal auditory bias of 1.52° measured by Lewald et al.
(2009b). These earlier results are, however, based on estimates of
visual locations with reference to the subjective coordinates of the
body. They could be confounded by a proprioceptive bias that
might occur in addition to visual anomalies with HA (Lewald et
al., 2009a). Such proprioceptive factors cannot account for the
results obtained in the current study.
Unlike the previous findings on visual straight ahead, which
were restricted to one central point in space only, the present
results provide information on a broader topography of visual
space in HA patients. Taken together, our data indicate that the
rotation of the visual space along the horizontal axis results in a
perceptual expansion in the contralesional (blind) hemifield and a
compression in the ipsilesional (intact) hemifield. There is a conflict in the literature about the nature of visual space distortion in
HA. Our conclusion is consistent with findings of Doricchi et al.
(2002), showing that HA patients estimated lengths and distances
in the contralesional space as being larger than their equivalents in
the ipsilesional space. Our results are not consistent with studies
showing that the horizontal angular distances between visual stimuli (Zihl & Von Cramon, 1986) or sizes of rectangles along the
horizontal axis (Ferber & Karnath, 2001a) were perceived as
smaller on the anopic hemifield than on the intact side. The reasons
for this inconsistency between previous studies are not entirely
clear (see discussion in Ferber & Karnath, 2001a; Doricchi et al.,
2002).
From a methodological point of view, it is important to emphasize that in our experiments patients fixated a single light spot in
total darkness. In the studies of Zihl & Von Cramon (1986), Ferber
and Karnath (2001a), and Doricchi et al. (2002), patients had to
judge distances between simultaneously presented visual stimuli or
the size of visual objects in space. In the present study, subjects
were presented with single punctiform visual stimulus in otherwise
empty space. Their pointing responses (whether with a visual
pointer or with a visual target) are more likely to reflect absolute
judgments of localization than judgments of the relative locations
of pairs of points. Relative spatial judgment may engage processes
above and beyond those required to make a simple localization.
Our results may therefore provide a more direct estimate of space
distortion in HA.
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AUDITORY-VISUAL LOCALIZATION IN HEMIANOPIA
Several methodological issues have to be considered given our
use of two complementary tasks, The analyses of the coefficient of
determination (R2) showed that the acoustic-pointing responses
were more variable than light-pointing responses. This may reflect
greater uncertainty in the localization of the acoustic pointer compared with the light pointer and the fact that subjects were, doubtlessly, more familiar with pointing to objects visually in everyday
life. Critically, however, there were no significant differences in
variability between groups, suggesting that these task differences
did not have a differentially strong effect on HA patients. These
differences in task difficulty may have contributed to the taskrelated differences in slope as found in both normal controls and
HA patients. Although light pointing was nearly veridical, with
acoustic pointing subjects generally underestimated the eccentricity of the target, resulting in flatter slope of regression lines
(Figures 1, 2). Most likely, the acoustic marker was not moved far
enough because of the greater uncertainty in this task. In the
acoustic pointing task, the stationary visual target, which may have
been in a location initially invisible to HA patients, had to be
localized at the start of a trial. This imposed a visual search
demand that was not present in the light pointing task. There was,
however, no time pressure to respond and the opportunity to repeat
the trial if the target was not perceived in time. The results (see
Figure 2) suggest that HA patients did not have specific problems
in acoustic pointing (Experiment 2), compared with visual pointing
(Experiment 1).
There is another potential problem with using two modalities
simultaneously. In the so-called ventriloquism effect the location
of an auditory stimulus is captured by a simultaneously presented
visual stimulus. This effects is, however, unlikely to have affected
results in the current study because it is critically dependent on
synchronized transient or modulated signals in the auditory and
visual modalities (see, e.g., Lewald, Ehrenstein, & Guski, 2001).
In our experiment, visual and auditory stimuli were present continuously and so no such synchronized transients occurred.
The patients’ perceptual anomalies found here provide direct
evidence for substantial differences in the distortions of sensory
space between auditory and visual modalities. There is already a
large body of evidence showing significant differences between
uni-modal and cross-modal processing in brain-damaged patients,
including those with visual field defects. In fact, although HA
patients may exhibit distortions in their visual representations of
space as well as in the auditory modality, their cross-modal abilities might be preserved (e.g., Bolognini, Rasi, Coccia, & Làdavas,
2005; Leo, Bolognini, Passamonti, Stein, & Làdavas, 2008; Passamonti, Frissen, & Làdavas, 2009). However, had the distortions
of auditory and visual space been essentially similar, then in our
bimodal approach they would have cancelled each other out.
Pointing responses would appear to be veridical as the coordinates
in the distorted auditory and visual spaces would nevertheless be
congruent with one another. Our finding that these space distortions cannot be similar matches the direct comparison by Lewald
et al. (2009a), who showed a considerable divergence between the
subjective straight-ahead directions of HA patients in the visual
and auditory modalities. Based on the earlier literature on distortions of visual space in HA (see above), Lewald et al. (2009b)
originally assumed that processes of cross-modal spatial adaptation induced a visual miscalibration of auditory space, such that its
coordinates would be slightly shifted toward the point of alignment
581
with the distorted visual coordinates. Although the present experiments were not intended to test this hypothesis, the results shed
doubts on its validity. It seems reasonable to conclude that the
auditory space of patients with pure HA remained largely unaffected by the consistent auditory-visual disparity. If HA patients
retain an undistorted representation of auditory space, then it
should be possible to exploit the auditory system in rehabilitation
of visual field disorders, even when very severe impairment of
visual abilities limits the effectiveness of purely visual approaches
(Lewald et al., 2012).
References
Axenfeld, D. (1894). Eine einfache Methode Hemianopsie zu constatiren.
Neurologisches Centralblatt, 13, 437– 438.
Barton, J. J., & Black, S. E. (1998). Line bisection in hemianopia. Journal
of Neurology, Neurosurgery, and Psychiatry, 64, 660 – 662.
Best, F. (1910). Bemerkungen zur Hemianopsie. Graefes Archiv für Ophthalmologie, 74, 400 – 410.
Best, F. (1917). Hemianopsie und Seelenblindheit bei Hirnverletzungen.
Graefes Archiv für Ophthalmologie, 93, 49 –150.
Bolognini, N., Rasi, F., Coccia, M., & Làdavas, E. (2005). Visual search
improvement in hemianopic patients after audio-visual stimulation.
Brain, 128, 2630 –2642.
Coren, S. (1993). The lateral preference inventory for measurement of
handedness, footedness, eyedness, and earedness: Norms for young
adult. Bulletin of the Psychonomic Society, 31, 1–3.
Doricchi, F., Onida, A., & Guariglia, P. (2002). Horizontal space misrepresentation in unilateral brain damage. II. Eye– head centered modulation of visual misrepresentation in hemianopia without neglect Neuropsychologia, 40, 1118 –1128.
Ferber, S., & Karnath, H.-O. (1999). Parietal and occipital lobe contributions to perception of straight ahead orientation. Journal of Neurology,
Neurosurgery, and Psychiatry, 67, 572–578.
Ferber, S., & Karnath, H.-O. (2001a). Size perception in hemianopia and
neglect. Brain, 124, 527–536.
Ferber, S., & Karnath, H.-O. (2001b). How to assess spatial neglect - line
bisection or cancellation tasks? Journal of Clinical and Experimental
Neuropsychology, 23, 599 – 607.
Gauthier, L., Dehaut, F., & Joanette, Y. (1998). The bells test: A quantitative and qualitative test for visual neglect. International Journal of
Clinical Neuropsychology, 11, 49 –54.
Hausmann, M., Corballis, M. C., & Fabri, M. (2003b). Line bisection in the
split brain. Neuropsychology, 17, 602– 609.
Hausmann, M., Waldie, K. E., Allison, S. D., & Corballis, M. C. (2003a).
Line bisection following hemispherectomy. Neuropsychologia, 41,
1523–1530.
Johannsen, L., & Karnath, H.-O. (2004). How efficient is a simple copying
task to diagnose spatial neglect in its chronic phase. Journal of Clinical
and Experimental Neuropsychology, 26, 251–256.
Karnath, H.-O., Himmelbach, M., & Rorden, C. (2002). The subcortical
anatomy of human spatial neglect: Putamen, caudate nucleus and pulvinar. Brain, 125, 350 –360.
Leo, F., Bolognini, N., Passamonti, C., Stein, B. E., & Làdavas, E. (2008).
Cross-modal localization in hemianopia: New insights on multisensory
integration. Brain, 131, 855– 865.
Lewald, J. (1997). Eye-position effects in directional hearing. Behavioural
Brain Research, 87, 35– 48.
Lewald, J., & Ehrenstein, W. H. (1998). Auditory-visual spatial integration: A new psychophysical approach using laser pointing to acoustic
targets. Journal of the Acoustical Society of America, 104, 1586 –1597.
Lewald, J., Ehrenstein, W. H., & Guski, R. (2001). Spatio-temporal constraints for auditory-visual integration. Behavioural Brain Research,
121, 69 –79.
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.
582
LEWALD ET AL.
Lewald, J., Peters, S., Tegenthoff, M., & Hausmann, M. (2009a). Dissociation of auditory and visual straight ahead in hemianopia. Brain
Research, 1287, 111–117.
Lewald, J., Peters, S., Tegenthoff, M., & Hausmann, M. (2009b). Distortion of auditory space in hemianopia. European Journal of Neuroscience, 30, 1401–1411.
Lewald, J., Tegenthoff, M., Peters, S., & Hausmann, M. (2012). Passive
auditory stimulation improves vision in hemianopia. PLoS ONE, 7,
e31603.
Liepmann, H., & Kalmus, E. (1900). Über eine Augenmassstörung bei
Hemianopikern. Berliner Klinische Wochenschrift, 37, 838 – 842.
Passamonti, C., Frissen, I., & Làdavas, E. (2009). Visual recalibration of
auditory spatial perception: Two separate neural circuits for perceptual
learning. European Journal of Neuroscience, 30, 1141–1150.
Rorden, C., & Karnath, H.-O. (2010). A simple measure of neglect severity. Neuropsychologia, 48, 2758 –2763.
Schuett, S., Heywood, C., Kentridge, R. W., & Zihl, J. (2008). The
significance of visual information processing in reading: Insights from
hemianopic dyslexia. Neuropsychologia, 48, 2445–2462.
Siefer, A., Ehrenstein, W. H., Arnold-Schulz-Gahmen, B. E., Sökeland, J.,
& Luttmann, A. (2003). Populationsstatistik und Assoziationsanalyse
sensumotorischer Seitenbevorzugung und deren Relevanz für verschiedene berufliche Tätigkeitsfelder. Zentralblatt für Arbeitsmedizin, Arbeitsschutz und Ergonomie, 53, 346 –353.
Strebel, J. (1924). Über Hemianopien. Archiv für Augenheilkunde, 94,
27–55.
Tham, K., & Tegnér, R. (1996). The baking tray task: A test of spatial
neglect. Neuropsychological Rehabilitation, 6, 19 –25.
Weintraub, S., & Mesulam, M.-M. (1985). Mental state assessment of
young and elderly adults in behavioral neurology. In M.-M. Mesulam
(Ed.), Principles of behavioral neurology (pp. 71–123). Philadelphia,
PA: Davis.
Zihl, J., & von Cramon, D. (1986). Zerebrale Sehstörungen. Stuttgart,
Germany: Kohlhammer.
Zimmer, U., Lewald, J., & Karnath, H.-O. (2003). Disturbed sound lateralization in patients with spatial neglect. Journal of Cognitive Neuroscience, 15, 683– 693.
Received August 9, 2012
Revision received February 6, 2013
Accepted May 14, 2013 䡲
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