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Ž.
Psychiatry Research 87 1999 65]75
Contralateral induction by frequency spectrum in
hallucinating schizophrenics
Olle OlssonU, Soren Nielzen
¨´
Di¨ision of Psychiatry, Department of Clinical Neuroscience, Uni¨ersity Hospital, SE-221 85 Lund, Sweden
Received 29 May 1998; received in revised form 10 November 1998; accepted 29 December 1998
Abstract
Seventeen schizophrenic patients who had all experienced auditory hallucinations were compared with 14 subjects
of a reference group on a test of contralateral induction. Contralateral induction means that a sound is illusively
heard as coming from a location where it belongs according to its spectral content. The phenomenon is connected
with a simultaneous relative elimination of masking. The schizophrenic subjects deviated from the reference group in
several aspects. Some of them did not hear the sound being induced to the contralateral side, which it was for all
reference subjects. Another subgroup of the schizophrenics noticed the induction unusually early with a prolonged
experience of it, and finally some of them experienced the induction now and then. The aberrations were interpreted
as rigidity of adaptation on the one hand and as effects of an enhanced sensitivity on the other. Discontinuity,
meaning that the fluency in mental processing is broken, was interpreted to cause the ratings of the third group of
schizophrenics in this sample, who heard the contralateral induction now and then. These phenomena are clearly
reminiscent of descriptions in research reports, and witnessed by clinical experience of the schizophrenic disturbance.
The results represent another example of discontinuous neurophysiological functions between neural systems and
between individuals suffering from schizophrenia. Q1999 Elsevier Science Ireland Ltd. All rights reserved.
Keywords: Sound localization; Laterality; Masking; Auditory hallucinations
UCorresponding author. Tel.: q46-46-1738-88; fax: q46-46-1738-84.
Ž.
E-mail address: olle.olsson@psykiatr.lu.se O. Olsson
0165-1781r99r$ - see front matter Q1999 Elsevier Science Ireland Ltd. All rights reserved.
Ž.
PII: S 0 1 6 5 - 1 7 8 1 9 9 0 0 0 4 0 - 2
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O. Olsson, S. Nielzen rPsychiatry Research 87 1999 65]75
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1. Introduction
1.1. Psychoacoustic background
The ability to localize sound rests on the fact
Ž.
that interaural time differences ITDs from the
right to the left ear offer a phase displacement
which is liable to neurophysiological analysis. One
of the ears will as well most of the time find itself
in a shadow in relation to the other one. This
Ž.
causes an interaural intensity difference IID
between the ears. These two circumstances con-
stitute the basis for a theory of localization called
‘Duplex Theory’. However, many other physical
properties determining localization of the sound
wave are watched by the analysing hearing sys-
tem. As examples may be mentioned different
Ž
high frequency filtering by the two pinnae outer
.
ear cartilage , which helps vertical orientation
Ž.
Lackner, 1974; Guterman and Klein, 1992 , bin-
aural masking, dichotic pitch, and binaural beats
Ž.
Yost and Dye, 1991 .
The acoustic phenomenon of contralateral in-
duction may occur under specific circumstances,
and it was partly described for different cases by
Ž.
Egan 1958 . It consists of the fact that brain
processes compare and segregate input to the two
Ž.
ears Warren and Bashford, 1976 . This means,
for example, that a tone, noise, or complex sound
presented to one ear may-be localized to the
middle or opposite side, if on the opposite side
there is a simultaneous stimulation with spectral
components corresponding to the former side.
The phenomenon is related to masking, release
from masking, fusion, fission, and possibly other
mechanisms, but constitutes a separate feature as
well. It may be most importantly seen as a com-
pound process based on spatial estimates of con-
flicting cues in the spectral domain for the two
ears. Spatial origin is important as a cue for
auditory scene analysis, but can be overwhelmed
by other cues. Therefore, contralateral induction
may be studied best in strict laboratory situations.
In everyday life it is a useful means to avoid
Ž
confusion of spatial origin of sounds Bregman,
.
1990 .
Neurophysiologically, the nervous system con-
structs percepts by collected and purified infor-
mation from the two ears. Bushy cells in the
anterior ventral cochlear nucleus put their elec-
trical discharge representing specific frequencies
into the same phase, and thereby a safe bilateral
system of transmitting ITD differences is consti-
tuted. IID differences are treated by a circuitry
involving basically the anterior ventral cochlear
nucleus, the lateral superior oliva, and the medial
Ž.
nucleus of the trapezoid body Brugge, 1988 . The
coding of lateralization takes place by unilateral
and contralateral inhibition, facilitation, and
adaptation under the influence of superimposed
efferent activity. In this process various forms of
coding are used by the nervous system, effectu-
ated by the sensitivity of cells for stimulus-rate
variations, by synchronization coincidences, and
by cells especially developed to react to amplitude
modulation, phase modulation, and frequency
ŽLindemann, 1986; Hafter et al., 1988; Schreiner
.
and Langner, 1988; Yin and Chan, 1988 .
A possibility to trace the origin of lateralization
in humans is offered by the study of brainstem
auditory evoked potentials in combination with
Ž.
other methods. Levin et al. 1993 have traced
deficient acuity of localization in patients with
multiple sclerosis due to different lesions in the
superior olivar complex-trapezoid body system,
the ventral acoustic stria, and the nuclei of the
lateral lemniscus. Spatial tuning within superior
levels is based on this primary information and is
elaborated within colliculus inferior and cortex
Ž.
Ehret, 1988; Middlebrooks, 1988 . The circuitry
serving processes like masking are but incom-
pletely elucidated. The same applies to the
phenomenon of contralateral induction. However,
contralateral induction is considered to be a pri-
mary psychoacoustical process, dominantly han-
dled at evolutionarily low levels in the brain stem
Ž.
Hafter et al., 1988 .
1.2. The schizophrenic context
Few studies on schizophrenics and sound local-
ization have been performed. In a study by
()
O. Olsson, S. Nielzen rPsychiatry Research 87 1999 65]75
´67
Ž.
Gruzelier and Hammond 1979 , dichotic stimula-
tion and various verbal and non-verbal tests were
used to assess hemispheric differences. An indica-
tion of deficient pathways to the left hemisphere
was obtained and the hippocampus was assumed
to be implicated due to results of impaired short-
term memory retrieval and efferent control of
sensory input.
Ž.
In a study by Bruder and Yozawitz 1979 no
evidence of abnormal auditory lateralization
asymmetries was noticed. Guterman and Klein
Ž.
1992 described deficiencies of vertical localiza-
tion ability among schizophrenics. There was a
different function between pinnae-dependent and
ITD-dependent information, compared to normal
Ž.
subjects. Lackner 1974 took the body position
Fig. 1. Display of the experimental situation. Top left distractor sound, top right target sound.
()
O. Olsson, S. Nielzen rPsychiatry Research 87 1999 65]75
´
68
into acount. Schizophrenics seemed to have a
deficient ability to correctly localize a sound when
asked to relate it to the proprioceptive experi-
ence.
These studies suggest that there are subtle
differences of various complex functions in
schizophrenics with regard to localization tasks,
although no indications of basic hearing function
deficits, such as threshold differences, etc., are
found. It might therefore be reasonable to as-
sume that the psychophysical task planned for the
present study will cause a difference betweeen
healthy subjects and schizophrenics, due to its
challenge of an integrated grouping function.
The schizophrenic auditory hallucination dif-
fers from organic, epileptic or toxic hallucinations
Ž.
Walter et al., 1990; Steinberg et al., 1998 . In the
beginning of the illness there are primary delu-
sions and misperceptions reminiscent of elemen-
tary psychoacoustical disturbances. These may
consist of hearing minute sounds as disturbingly
loud, distorted or impossible to locate. Not until
later stages of the illness are the hallucinations
interpreted in constant patterns, and filled with
Ž.
content Conrad, 1958 .
The rationale for this study is the assumption
that primary schizophrenic disturbances might ex-
press themselves in processes demanding a group-
ing activity of the percept by the brain. This may
apply to individuals with auditory hallucinations
in their past history, where auditory function is
involved in the development of psychopathologi-
cal symptoms. An experiment offering a conflict
between localization and recognition of a sound,
depending on its spectral content, will be used.
2. Aims of the study
The aim of this study is to investigate the
functioning of a psychoacoustic separation
process, where the perception of localization is
‘released’ by the influence of a second sound.
Cues of frequency content ‘extract’ the first sound
from its original location. This is called contralat-
eral induction. It is assumed that schizophrenics
Fig. 2. Frequency distribution of individuals who have heard
Ž.
the movement of the target sound right towards the distrac-
Ž. Ž .
tor left . Unfilled bars sreference group ns14 and filled
Ž.
bars sschizophrenics ns17 .
with auditory hallucinations in their past history
will show impairments of this integrative function.
3. Methods
3.1. Stimuli
Two stimuli were created, one to be used as
target and the other as distractor. The first was
Ž.
constructed in MATLAB 5.1 by collecting 12
Ž
sinewaves 100, 200, 300, 400, 500, 600, 700, 800,
.
900, 1000, 1100, and 1200 Hz . The second was
Ž
combined of five sinewaves 100, 200, 400, 800,
.
and 1200 Hz . All sinewaves had the same ampli-
tude and starting phase angle. The envelope fol-
lows the formula:
The rise time becomes 0.16 s, the decay time
0.27 s, as the total duration was set to 0.5 s. These
()
O. Olsson, S. Nielzen rPsychiatry Research 87 1999 65]75
´69
values were chosen in order to avoid distortion in
the experiment due to too short rise times.
3.2. Equipment
The stimulus was constructed by the use of the
Ž.
software MATLAB 5.1 , Signal Processing Tool-
box and a Macinthosh Quadra 650 with a built-in
Power PC 601 card. The stimuli were sampled
into a Kurzweil K2000 and MIDI-controlled by
the software Digital Performer on a Macintosh
LCIII. The stimuli were presented via a Teac
W-900RX cassette tape recorder and a Yamaha
CA610 amplifier with two Heybrook HB1 loud-
speakers.
3.3. Procedure
The subjects were seated in a laboratory at a
distance of 1.5 m from each loudspeaker. The
azimuth angle between the loudspeakers was 908
Ž.
Fig. 1 .
They were presented with a written instruction
describing target and distractor, and the mode of
presentation. Thereafter, they had the opportu-
nity to listen to the separate sounds and were
asked to discuss the experiment with the test
leader in order to ensure that they had under-
stood the meaning of the experiment.
The test was divided into 16 presentations. In
Ž.
each of them the distractor the 12 partial sound
was delivered through the left loudspeaker, first
with 0 dB. From the second presentation an in-
crease by 4.5 dB in amplitude was made from the
base value of 39 dB arriving at 76 dB at the
eighth presentation. The amplitude of the ninth
presentation was equally 76 dB and then the
amplitude decreased by 4.5 dB until the 16th
Ž.
presentation. The target the five partial sound
was presented simultaneously through the right
loudspeaker at a constant amplitude of 68 dB.
The subjects were asked to mark a 0 when they
could hear the target clearly coming from the
right loudspeaker and an X if they heard it move
towards the left one. When the SPL of the dis-
Table 1
Some identifying and background variables of the subjects with schizophrenic symptoms
a
Ind. Age Sex Medication No. of Duration of DSM-IV No. of months
Ž. Ž.
no. mgrweek admissions illness years diagnosis as inpatient
1 44 M Zuclopenthixole 4 11 295.30 8
decanoate, 100
2 37 F Zuclopenthixole 5 8 295.10 3
decanoate. 50
3 35 M Clozapine, 4200 7 7 295.30 15
4 34 F Clozapine, 350 8 4 295.30 14
5 22 F Perphenazine, 84 1 3 295.10 1
6 27 F Clomipramine, 525 4 8 295.40 15
746M ]1 10 295.90 1
8 36 F Roxiam, 4800 2 9 295.30 1.5
9 38 M Roxiam, 5250 10 12 295.30 17
10 46 M Haloperidol 5 4 295.30 1
depot, 50
11 30 F Perphenazine, 280 6 4 295.30 6
12 31 F Perphenazine, 280 4 5 295.30 4
13 28 F Clozapine, 2100 6 12 295.30 8
14 32 M Clozapine, 1750 6 7 295.30 13
15 49 F ]0 1 295.30 0
16 33 M Clozapine, 1750 2 12 295.30 7
17 34 M Perphenazine, 84 1 2 295.30 3
aMsmale and Fsfemale.
()
O. Olsson, S. Nielzen rPsychiatry Research 87 1999 65]75
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Table 2
Ž.
Number of Xs perception of contralateral induction for 16 presentations to the test groups
12345 6 7 8 9 10111213141516
a
RG0002 5 710141211 7 21000
b
S 134813151314141310109551
2
x0.01 1.09 1.98 2.42 3.70 3.75 0.09 1.09 0.56 0.85 0.17 4.68 5.42 2.98 2.98 0.01
P0.92 0.30 0.16 0.12 0.05 0.05 0.92 0.30 0.81 0.77 0.90 0.03 0.02 0.08 0.08 0.92
aŽ.
RG, reference group ns14 .
bŽ.
S, schizophrenics ns17 .
()
O. Olsson, S. Nielzen rPsychiatry Research 87 1999 65]75
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tractor becomes equal to, or louder than the
target, the sounds are generally perceived as one
sound coming from the middle or from near the
left.
3.4. Subjects
Seventeen former in-patients at the University
Hospital in Lund were asked to take part in the
study. The inclusion criteria were: a diagnosis of
schizophrenia with typical schizophrenic auditory
hallucinations in the past history, but no present
hallucinations during testing. The diagnosis should
have been established on clinical examination by
a senior medical doctor. It had to comply with the
criteria of schizophrenic psychosis as defined in
Ž
DSM-IV American Psychiatric Association, 1994,
.
pp. 285]286 . Exclusion criteria were organic
brain diseases, alcohol or drug abuse, or the
presence of additional psychiatric diagnoses. A
formal consent was ascertained in accordance with
Ž
the requirements of the ethical committee LU
.
171-94 . Table 1 presents the patient sample.
The reference subjects were recruited among
medical students and staff. There were eight fe-
males and six males, the mean age being 29 with
S.D.s8.
Eight patients with panic disorder, according to
the criteria of DSM-IV, were additionally in-
cluded in the study. Their ages ranged from 30 to
55 years, and there were five females and three
males.
4. Results
The frequency distribution of all individuals
Ž.
divided into a schizophrenic black bars and a
Ž.
reference group white bars is presented in Fig. 2
and Table 2.
Obviously, schizophrenics differ from the sub-
jects of the reference group in the beginning
Ž.
presentation 1]6 of the experiment and in the
Ž.
end presentation 12]16 . There is a statistically
significant difference between the group of refer-
ence subjects and that of schizophrenics
ŽKolmogorov]Smirnov tested for the entire dis-
.
tribution, Zs2, Ps0.03 . In other words, some
of the schizophrenic patients must experience the
movement of the target earlier than the reference
subjects do, and some of them hear the pheno-
menon longer than the reference subjects. How-
ever, where contralateral induction becomes com-
Ž
plete among the reference subjects around pre-
.
sentation 8 , it is also at hand among most of the
schizophrenics. The irregularity of the frequency
distribution of the schizophrenics calls for a closer
analysis regarding the existence of different rat-
Ž.
ing strategies in subgroups see Table 3 . It turns
Ž.
out that one subgroup ns7 seems to experi-
ence the contralateral induction in a quite normal
way. For two individuals no contralateral induc-
tion seems to take place, and they experience the
target sound as coming from the right loud-
Ž.
speaker all the time. A few schizophrenics ns4
start earlier and keep their impression of a fused
sound to late stages. Finally, four individuals hear
the target sound coming from the right and the
left loudspeaker intermittently.
In order to test the validity of the rating proce-
dure among the schizophrenics, a comparison was
made with data achieved in another experiment
performed by all subjects on the same occasion.
This experiment was one of streaming which is a
test on grouping of high and low sounds depend-
Ž.
ing on amplitude Nielzen and Olsson, 1997 . It
´
was similarly organized in 16 presentations. It
turned out that the schizophrenic probands could
be sorted out in the same different rating sub-
groups as in the present study. A Mann]Whitney
test between streaming and contralateral induc-
tion regarding the different response categories
Žno recognition of target phenomenon, starting to
.
hear it earlier, and hearing it intermittently
yielded Z, corrected for ties sy2.154; Ps0.03.
The rating responses are therefore not random,
but varying, depending on different experiments.
A test was made to look for a possible influ-
ence of anxiety on test results. The compari-
son was made on a sample of anxiety patients
Ž. Ž .
ns8 , the reference group ns14 , and the
Ž.
schizophrenic group ns17 . A Kruskal]Wallis
variance test showed a difference at a highly
Ž.
significant level Hs12; d.f.s2; Ps0.0002 . A
pair-wise comparison by Mann]Whitney tests
between the three groups gives the following re-
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O. Olsson, S. Nielzen rPsychiatry Research 87 1999 65]75
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72
Table 3
The distribution of the individual schizophrenic probands regarding different strategies of perception
Normal No induction Earlyrlate Induction now and then
induction
Ind. no. 1, 2, 9, 10, 14, 3, 11 4,6,7,8 5, 12, 13, 16
15, 17
sult: schizophrenicsranxiety patients; Z, cor-
rected for ties sy3; Ps0.002, anxietyrrefer-
ences; Z, corrected for ties sy6; Ps0.0001,
schizophrenicsrreferences; Z, corrected for ties
sy3; Ps0.0005. The mean number of presen-
tations, when the movement was identified was
about the fifth for the reference subjects, about
the sixth for the schizophrenics, and the eighth
for the anxiety group.
This means that schizophrenics and anxiety
patients tend to hear the phenomenon late and
Ž.
much too late, respectively cf. Section 5 .
Comparisons were further performed on clini-
Ž.
cal measures Table 1 , but no correlations or
differences were statistically significant. There
were also no age differences. Sex, however, dif-
ferentiated the ratings. Schizophrenic women
differed from women in the group of reference
subjects in a statistically significant way
Ž.
Mann]Whitney, Ps0.0001 . Schizophrenic men
differed from men in the group of reference
subjects, in the same direction as schizophrenic
Ž
women, but in a non-significant way Mann]
.
Whitney, Ps0.25 .
Although several schizophrenic subjects seem
to perceive the contralateral induction in a nor-
mal way, there is a considerable number of them
who do not. This circumstance necessitates fur-
Ž.
ther considerations and a discussion Table 3 .
5. Discussion
Contralateral induction operates on the condi-
tion that a target sound may he relocated in the
hearing system by an inducing sound. For this to
happen, the inducer must contain the same fre-
quency components as the target and it must
supply the nervous system with sufficient energy
Ž.
high amplitude . The induction will not occur if
the target and inducer do not have exactly the
Ž
same duration, phase, and envelope Bregman,
.
1990 . On the psychoacoustic level one percept is
extracted from its original position and relocated
to a surrounding where there is pattern evidence
of similarity. This process is intimately connected
with masking.
This study was undertaken on the assumption
that schizophrenia is connected with perceptual
disturbances including primary psychoacustical
malfunctioning. Such a disturbance may be of
importance for further investigations regarding
relations to localization processes and auditory
hallucinations.
Before further discussion of the present results,
a few aspects may be discussed regarding method-
ology.
Some researchers claim that schizophrenics are
not able to handle a test situation. The impact of
the illness may be considered to hamper the
results due to lack of attention, preoccupation of
symptoms, motoric incapability, etc. On the other
hand, schizophrenics sometimes perform better
Ž.
than normal subjects do, as Hemsley 1993
pointed out in connection with cognitive experi-
mentation.
A comparison was made between the present
Ž
psychoacoustic test and another one cf. Section
.
4 performed at the same time by the same
schizophrenic subjects. It showed that the rating
responses varied from experiment-to-experiment
at a statistically significant level. This supports the
validity of the rating performance of the
schizophrenic probands. The reliability was fur-
ther checked by comparisons made in this and
earlier psychoacoustic experiments. No statisti-
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O. Olsson, S. Nielzen rPsychiatry Research 87 1999 65]75
´73
cally significant differences from reference sub-
jects were found on this general level, which
supports the existence of a sufficient reliability.
However, there still remains a question whether
the schizophrenics rate according to what is really
heard or in response to their subjective impres-
sion, influenced by interfering mental processing.
This question, inherent in most studies of percep-
tion, could only be answered by means of comple-
mentary correlative studies with various objective
measures.
It is likewise necessary to consider the fact that
ratings may be influenced not only by the
schizophrenic illness but by other background
factors. Generally, the impact of schizophrenia is
much greater than any other psychiatric illness as
seen from many investigations of this kind. The
influence of other background factors such as
age, sex, education, etc., is usually still less than
Ž
the influence of schizophrenia Nielzen, 1982;
´
.
Steinberg, 1986 . In order to test the possible
influence of a common confounding symptom,
namely anxiety, a sample of eight panic disorder
patients was included for the purpose of compar-
ison. It turned out that schizophrenics, anxiety
patients, and subjects of the reference groups
differed significantly. The subjects of the anxiety
group tended to rate a hearing of the contralat-
eral effect much later than the subjects of the
other two groups. Furthermore, a computation of
correlation with other psychoacoustical tests per-
formed at the same occasion showed no signifi-
cant correlations between anxiety and schizo-
phrenic subjects.
No statistically significant differences were
observed for any of the available clinical mea-
sures. An explanation may be that the inclusion
criteria limited the sample to a narrow group of
mainly paranoid schizophrenics, even perhaps
mostly phonemic paraphrenics. The lack of sig-
nificant influences from symptoms, medication,
duration of illness, etc., could mean that the
altered perception depends on more fundamental
factors of the illness. Age also had no significant
influence on the ratings, but there was an interac-
tion by sex. The schizophrenic women contribute
more to the group differences than schizophrenic
men do. Evidently, there are sex-related factors
that enhance the contralateral induction. A gen-
eral sensitivity factor in women could be one, but
the question requires further studies to be an-
swered.
The major finding of the study is that these
schizophrenics respond differently compared to
the subjects in the reference group. In order to
try to understand what the difference means, a
closer look at details of the rating responses has
to be taken.
Four subgroups of rating strategies among the
schizophrenics were identified. One of these sub-
groups showed a pattern coinciding with the re-
sponses in the reference group. The meaning of
this finding is that contralateral induction func-
tions in a normal way. The main hypothesis of the
study has to be rejected regarding these patients.
The majority of the patients in this study show
other patterns of rating, indicating that in certain
cases of schizophrenia there might still be some
disturbing influence upon mechanisms determin-
ing contralateral induction.
Two schizophrenics never heard any move-
ment. The suspicion that they were subjected to
some bias could be strong. However, one must
realize that not hearing the induction means that
the subject manages to hear the target sound in
the right loudspeaker all the time. This does not
occur for any non-schizophrenic person, or most
other schizophrenics. It implies such a strong
release from masking that induction is inhibited.
A psychoacoustic way of explaining what may
have happened is that for these schizophrenics,
recognition of the sound character, by suppress-
ing masking, has a priority over localization.
The third group is characterized by hearing the
movement of the target earlier, and holding onto
this percept for a long time. In opposition to the
former group, the schizophrenics in this group are
more ready to fuse the target and the inducer
than the reference group is. For these patients
masking has a dominant role.
In the last group there are four subjects who
mark an experience of the moving target in an
inconsistent way, thus noting the phenomenon
now and then. In one case there is even a motion
towards the distractor in the first presentation,
when no stimulation is given in the left speaker.
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O. Olsson, S. Nielzen rPsychiatry Research 87 1999 65]75
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74
One would be inclined to assign these aberrations
to the influences of random factors, but it is
important to remember that the probands had
been acquainted with the experiment by listening
to it just before testing. Similar patterns of rating
have been noted in perceptual experiments by
other researchers on schizophrenic psychophysi-
ology, and they have been interpreted as signs of
regression, which coincides with the clinical symp-
Ž.
tom discontinuity Smith et al., 1972 .
A few unquestionable basic phenomena are
connected with the schizophrenic disease. One is
dishabituation, a lack of adaptation to new sti-
muli. Not hearing contralateral induction may be
interpreted as an effect of this phenomenon.
Those who start to hear it early are obviously
sensitive, another undisputed attribute connected
with the disease. Thirdly, perceptual discontinuity
is an uncontroverted feature of the disease. Those
who heard the induction now and then may show
precisely this disturbance.
Important parts of systems serving the mecha-
nism of localization operate in the brainstem.
They are structurally separated from systems in-
volved in the analysis of frequency, envelope, and
other features. The differences found here con-
trast to the current neurophysiological models of
explanations of schizophrenia. These are focused
on prefrontal cortex, the limbic system, and the
left temporal cortex. In view of the sparse litera-
ture on schizophrenia and psychoacoustics, forth-
coming research efforts in this field will in time
give valuable information about more neural net-
works related to schizophrenic symptoms.
To conclude, the results show that aberrant
perception of contralateral induction occurs in
this schizophrenic group in eight of 17 probands.
The schizophrenic probands have shown one type
Ž.
of disturbance response strategy in the present
experiment, but a different one in another psy-
choacoustic test. There seems to be an intraindi-
vidual variation in schizophrenic influences of
different psychoacoustic mechanisms. Overall, the
study has shown aberrations reminiscent of some
characteristic schizophrenic perceptual aberra-
tions, dishabituation, sensitivity, and discon-
tinuity.
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