Evidence for Impaired Sound Intensity Processing in Schizophrenia
Dominik R. Bach1,2,4, Karin Buxtorf2, Werner K. Strik2,
John G. Neuhoff3, and Erich Seifritz2,5
2University Hospital of Psychiatry, University of Bern, Bern,
Switzerland;3Department of Psychology, College of Wooster,
Wooster, OH;4Wellcome Trust Centre for Neuroimaging,
University College London, London, UK;5Clinic for Affective
Disorders and General Psychiatry, Psychiatric University Hospital
Zurich, Zurich, Switzerland
Patients with schizophrenia are impaired in many aspects
of auditory processing, but indirect evidence suggests that
intensity perception is intact. However, because the extrac-
tion of meaning from dynamic intensity relies on structures
that appear to be altered in schizophrenia, we hypothesized
that the perception of auditory looming is impaired as well.
Twenty inpatients with schizophrenia and 20 control par-
ticipants, matched for age, gender, and education, gave
intensity ratings of rising (looming) and falling intensity
sounds with different mean intensities. Intensity change
was overestimated in looming as compared with receding
sounds in both groups. However, healthy individuals
showed a stronger effect at higher mean intensity, in keep-
lacked this modulation. We discuss how this might support
the notion of a more general deficit in extracting emotional
meaning from different sensory cues, including intensity
Key words: looming/perceptual bias/auditory/pitch
Alterations in auditory perception are widely recognized
in schizophrenia and are reflected—at different temporal
and hierarchical stages—eg, in sensory processing (P50
ratio,1prepulse inhibiton,2mismatch negativity3), im-
paired echoic memory for pitch,4–6and higher auditory
functions such as the extraction of emotional meaning
from speech melody or prosody.7–9
nia. For example, there seems to be no deficit in the per-
ception of soundsource motion when intensity is the only
cue provided10(as opposed to a deficit when relying on
intensity processing. In keeping with this idea, a recent
study on prosody perception reported that patients
with schizophrenia seem to overutilize sound intensity in-
formation to compensate for reduced pitch perception,
such that emotion ratings were biased by mean stimulus
intensity more than in healthy individuals.12This sug-
gests that in the perception of emotional meaning in au-
ditory cues, pitch extraction is impaired and intensity
extraction is not, thus alluding to a possibly distinct un-
derlying neural substrate.
However, alternative explanations for previous find-
ings are possible. Different from auditory cues in emo-
tional prosody, dynamic intensity in the study of
Balogh and Leventhal10did not carry emotional or be-
havioral relevance beyond source movement perception.
On the other hand, the overutilization of intensity cues in
the perception of emotional prosody only pertained to
mean intensity, rather than intensity changes.
Therefore, in order to study the extraction of meaning
from dynamic intensity in schizophrenia, a paradigm
where intensity change is the crucial stimulus dimension
to infer emotional meaning would be more sensitive. If
the notion of a distinctive neural deficit for extraction of
meaning from pitch would be supported, whereas other-
wise, one might conclude a more general impairment.
Auditory looming/receding stimuli offer such features,
where sound movement perception at slow sound source
speeds (ie, 10 m/s) relies mainly on monaural dynamic in-
tensity information, while other monaural and binaural
motion cues are less important.13–15Rising intensity in
such sounds is overestimated as compared with decreas-
ing intensity.15,16This reflects the observation that the
terminal distance of approaching sounds is perceived
sounds.17,18This perceptual priority for looming sounds
is also reflected by the recruitment of physiological
resources (ie, increased phasic attention to other stimuli
and enhanced skin conductance responses and heart rate
deceleration15,19). Thus, a model for looming sound per-
ception is that intensity change information is weighted
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Schizophrenia Bulletin Advance Access published September 3, 2009
more heavily when it has greater biological salience—
because the sound source could be approaching—and
in turn leads to preparatory physiological reactions.
This is a simple example for a mechanism of extracting
meaning from intensity change information.
ception is that the perceptual bias is stronger for sounds
with higher mean intensity than lower mean intensity.16
In the context of several similar sounds with different in-
tensity, higher mean intensity signals an approaching
sound that is either closer or louder and thus more salient
than one that is softer or (still) far away. Thus, the
effect of rising sound intensity is modulated by relevance
of the potentially approaching sound source. Both the
overestimation of rising sound intensity and its modula-
tion by mean intensity might be of biological relevance,
and it has been argued that they could be critical for
Monkey neurophysiology and human neuroimaging
research suggests that looming sound perception relies
on pathways including primary auditory regions (ie,
the auditory belt area), superior temporal sulci, middle
temporal gyri, frontal operculum, central and precentral
sulci, and the temporoparietal junction, encompassing
both the dorsal and ventral auditory pathways.19–22
This resembles findings on the neural correlates of im-
paired prosody and pitch perception in schizophrenia:
A diffusion tensor imaging study has provided evidence
that both impaired pitch perception and the extraction of
emotional meaning from prosody are related to struc-
tural changes in fiber tracts from primary auditory
Although overlapping on a macroscopic level, pitch
and intensity change information might be processed
by distinct neural pathways.24,25Thus, distinct deficits
are possible in schizophrenia. On the other hand, if
one assumes that white matter alterations in auditory
pathways23are generated by a process independent of
the functional specialization of individual neuron popu-
lations, one would expect a more general structural def-
icit in the described temporal regions rather than
a distinctive deficit relating to pitch perception. Hence,
we hypothesized that the extraction of meaning from in-
tensity change in looming sounds would be altered in
Study Design and Participants
Thisstudyfolloweda4(meanintensity) 32(risevsfall) 3
2 (group) factorial design. Twenty patients with paranoid
schizophrenia and 20 healthy control participants took
part in the study. Exclusion criteria for all participants
were psychiatric comorbidity, known organic brain dam-
age, mental retardation, epilepsy, and current drug or
alcohol abuse. This was checked by interview for all
participants and additionally by screening patients’ clin-
Patients were recruited as inpatients in the University
Hospital for Psychiatry, Bern, Switzerland. Diagnosis of
paranoid schizophrenia was made by the treating clini-
cian according to the International Classification of Dis-
eases, Tenth Revision26), and confirmed by a clinically
trained member of the study group (D.R.B.). To ensure
a stable diagnosis, it was additionally required that the
retrospectively assessed onset of first symptoms was
more than a year ago. Symptoms were assessed with
the Positive and Negative Symptom Scale (PANSS27).
All patients were approached as soon as the treating cli-
nician judged them to be able to give informed consent
and to maintain attention for the required amount of
time (about 30 min for the whole experiment, including
a preceding prosody experiment). Healthy control partic-
ipants were recruited from the general population by ad-
vertisement and were given no reward for their
The 2 groups were matched for gender and age with
a maximum difference of 5 years within each couple.
Nineteen of the 20 couples were also matched for second-
ary education. Sociodemographic and illness-related
characteristics of the sample, including chlorpromazine
(CPZ) equivalent doses, are listed in table 1. All partic-
ipants gave written informed consent, and the study was
approved by the local ethics committee.
Stimuli and Task
A pure sine tone of 2000-millisecond length that linearly
rose or fell in intensity was presented with 4 different ini-
sounds provide an easily quantifiable model for
approaching and receding sound sources and elicit a sim-
ilar perceptual bias.15Each combination of rise/fall and
mean intensity was presented 10 times, thus resulting in
80 trials. Participants were asked to estimate the intensity
change on a visual analog scale (VAS) as described pre-
viously.16The VAS was a horizontal line with no inter-
sections, anchored on the left and right with ‘‘no change’’
and ‘‘high change,’’ respectively. Using a computer
mouse, a rating arrow could be moved on this horizontal
line. Participants had as much time to respond as they
needed. The task lasted approximately 5–10 minutes
and was preceded by a test battery for emotion percep-
tion in prosody and face expression.28
The experiment was programmed in e-prime (version
18.104.22.168; Psychology Software Tools, Pittsburgh, PA)
and runon a laptop usingWindows XP.Auditory stimuli
were presented via headphones (SBC HP800; Philips,
D. R. Bach et al.
Amsterdam, The Netherlands). In all tasks, participants
selected the correct response with a computer mouse.
Data were averaged within participants and extracted
using R (www.r-project.org).
(rising/falling intensity) 3 2 (group) repeated-measures
analysis of variance in SPSS 12 (Chicago, IL). In order
and disorder-related variables (PANSS subscales, CPZ
equivalents, time since illness onset, time since first hospi-
talization, number of hospitalizations, duration of current
hospitalization), these were correlated with the within-
subject regression weight of perceptual bias increase with
increasingintensity. Also correlated were prosody identifi-
cation scores from a preceding experiment.28
Common Findings Across Both Groups
Descriptive results are shown in table 2. Across both
sity, reflected by higher intensity change ratings in these
Table 1. Sociodemographic and Illness-Related Data of the Study Participants
Age, y (mean 6 SD)32.9 6 12.9 33.4 6 12.1
Gender 11 male, 9 female in each group
Secondary education (%)
<9 y, or no degree
Tertiary education (%)
University degree (%)
Time since first symptoms in mo (median)84.5
Time since first hospitalization in mo (median)69
Duration of current hospitalization in wk (median)7.5
Number of previous hospitalizations (median)4
Percentage of patients receiving antipsychotic drugs95
Percentage of patients receiving antidepressants15
Percentage of patients receiving mood stabilizers25
Chlorpromazine equivalent dose (mg CPZ, mean 6 SD)722.1 6 620.7
PANSS positive symptoms subscale (mean 6 SD) 12.8 6 5.5
PANSS negative symptoms subscale (mean 6 SD) 17.2 6 7.7
PANSS general symptoms scale (mean 6 SD)28.2 6 9.0
Note: PANSS, Positive and Negative Symptom Scale.
Table2. IntensityChangeRatings(PercentVisualAnalogScale,Mean 6SE)forthe4MeanSoundIntensities,2Directions,and2Groups
Mean 6 Standard Error of the Mean
49.5 dB54.5 dB 59.5 dB 64.5 dB
34.04 6 2.94
16.18 6 2.12
47.02 6 2.52
23.32 6 3.05
63.19 6 2.26
30.80 6 4.50
80.45 6 2.54
44.32 6 6.34
41.85 6 4.94
23.85 6 3.32
49.86 6 4.68
28.37 6 3.98
57.70 6 4.41
37.58 6 3.64
71.51 6 4.52
49.05 6 4.51
Impaired Sound Intensity Processing in Schizophrenia
sounds than in falling sound intensity (F1,38 = 74.7,
were played at a higher mean intensity (F3,114= 97.9,
P < .0001), and the perceptual bias was also higher at
higher mean intensity (interaction mean intensity 3 rising/
falling: F3,114= 7.6, P < .001).
Across all sounds, intensity change was rated similarly in
both groups (main effect group: F1,38< 1), and across all
mean intensities, the perceptual bias was similar in both
groups (interaction group 3 rising/falling: F1,38= 1.6).
However, patients with schizophrenia showed less
increase in perceptual bias as mean intensity increased
(figure 1; interaction group 3 mean intensity 3 rising/
contrasts, a linear model provided best fit both for the
overall effect of mean intensity 3 rising/falling across
both groups (F1,38= 10.2, P = .003) and for the group
difference (F1,38 = 4.7, P = .036). This suggests that
healthy people have a linearly increasing perceptual
bias with linearly increasing mean intensity and that
the slope of this increase is smaller for patients than for
healthy individuals. Consequently, we estimated this
slope as within-subject regression weight for the correla-
tion of perceptual bias with mean intensity to test for
Within the schizophrenia group, we did not find any cor-
relation of age, gender, and disorder-related variables
(PANSS subscales, CPZ equivalents, time since illness
perceptual bias increase. Note however that sample size
was rather small for this kind of analysis. There was no
relation to prosody perception scores as assessed in a pre-
Both auditory pitch and intensity change perception rely
on overlapping neural pathways where macroscopic
alterations have been found in schizophrenia.23While
there is ample evidence for pitch perception deficits in
schizophrenia,4–6influencing higher cognitive functions
such as the extraction of emotional meaning from pitch
in prosody perception,9,12it has been suggested that in-
tensity perception and the extraction of meaning from in-
tensity might be intact.12Here, we show that patients
with schizophrenia are impaired in the extraction of
meaning from dynamic intensity. Specifically, while
they overestimated intensity change of rising intensity
sounds the same way as healthy people, they failed to
modulate this effect according to mean sound intensity.
This modulation in healthy persons allows for a stronger
effect of louder sounds that might also be closer. Failure
to do so could potentially be due to impaired perception
of mean intensity at an early stage of perception. How-
ever, the main effect of mean intensity (irrespective of
sound direction) did not differ between groups in the
ception has provided some evidence that patients with
schizophrenia are not impaired in perception of static in-
tensity12(although no studies to date have specifically
addressed this question). A perhaps more likely explana-
tion for our finding is that patients with schizophrenia do
perceive the difference in mean intensity but, in the con-
text of looming sounds, fail to interpret the higher mean
intensity in an adaptive manner or, in other words, that
they do not extract meaning from this information. This
could pertain to the interpretation of a louder sound
as being closer (ie, sound source localization based on in-
tensity information) or to the interpretation of a closer/
louder sound as more relevant.
Given that patients were not impaired at perceiving in-
tensity change and had the same overall perceptual bias
toward looming sounds, our data do not indicate im-
paired perceptual processing of dynamic intensity but
rather a failure to utilize this information in an adaptive
manner. This is paralleled by results from the perception
of emotional prosody where deficits in echoic pitch mem-
ory cannot explain all the emotion perception deficits,9,23
such that there appears to be an additional deficit in
extracting meaning from pitch. Parallel deficits in
Fig. 1. Perceptual Bias for the 4 Levels of Mean Sound Intensity.
Participants were asked to estimate the loudness change from ‘‘no
change’’ to ‘‘high change.’’ Perceptual bias was calculated as
estimated change (percent visual analog scale) in looming minus
estimated change in receding sounds. Data are given as mean 6 SE
for each of the 2 groups.
D. R. Bach et al.
interpreting pitch and intensity change are in keeping
with the suggestion that intensity change is highly corre-
lated with frequency change in prosodic vocal communi-
cation and other environmentally meaningful acoustic
signals. Vocal frequency tends to rise when vocal inten-
sity rises.29–32Birds also produce and attend more closely
to distress calls in which frequency and intensity rise and
fall together.33,34Moreover, music perception research
has shown that there is an expectation that melody lines
that rise in frequency will also rise in intensity.35This
makes a relation of systems for pitch and dynamic inten-
sity extraction—and deficits in these systems—plausible.
Also, there is evidence that the prosody perception
deficit in schizophrenia covaries with an impairment to
sion,7,8,28,36pointing toward a more general deficit in
the extraction of emotional meaning from sensory infor-
noise in respective neural structures: This deficit is more
pronounced for clear than for more ambiguous emotional
stimuli both in the visual37and auditory28domain, as
would be expected under this hypothesis.28Such a mecha-
nism could also explain the present results. However, one
would need to rule out some alternative explanations dis-
cussed above, such as deficits in static intensity perception
or in sound source localization based on intensity.
If the perceptual bias toward rising sound intensity is
not modified by mean intensity, this could imply stereo-
typed reactions to warning stimuli and therefore have
functional relevance. Rising sound intensity has been
shown to induce physiological reactions such as facili-
tated autonomic orienting response (as indicated in
skin conductance responses and heart rate) and increased
phasic alertness (as expressed in faster reaction to subse-
quent auditory targets).15,19Such measures could be
employed to expand the present findings.
The deficit we found was not related to any clinical
measure, including medication. However, given the small
sample size and consequent low sensitivity for detecting
correlations, this should not be construed as indicating
that there is no such relation. Also, the deficit was not
related to prosody perception as assessed in a preceding
experiment.28Here, equal power considerations apply,
although previous work already suggests that no such re-
lation of prosody and intensity perception exists.12
previous experiments that show overestimation of rising
sound intensity and a relation of this perceptual bias with
A limitation of our finding is the unclear specificity as
no clinical control group was included. In addition, the
present findings are limited to paranoid schizophrenia
and cannot be generalized to other subtypes of schizo-
phrenia. We did not control for subclinical hearing
impairments; as looming and receding sounds were phys-
ically equal, this should not have an influence but would
be useful to control in future studies. No relation of in-
tensity change perception and medication was observed,
such that the group differences found in the present study
can probably not be attributed to effects of medication
alone. However, studies on unmedicated patients, or in
larger samples with more power to detect medication
effects, are needed to confirm this conclusion.
To summarize, we present evidence for impaired ex-
traction of meaning from dynamic sound intensity in
schizophrenia. This, together with evidence of extraction
of emotional meaning from other sensory dimensions,
eg, pitch and visual cues, might suggest a common under-
Swiss National Science Foundation (PP00B-103012/1 to
No conflicts of interest. We appreciate the helpful
comments of 3 anonymous reviewers on a previous
version of this article.
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