Auditory affective processing and the role of personality

Research on how the brain processes emotional information in the auditory
modality is relatively sparse. Two prominent carriers of emotional information
in the auditory modality are speech-prosody and music. The goal of the proposed
study is to examine how the brain processes emotional speech prosody and music.

How we say things can be more important than what we say in conveying an
emotional message. This prosodic layer of speech uses a variety of acoustic
cues such as pitch, rhythm and spectral balance to convey emotional as well as
non-emotional (linguistic-) information. Previous research suggests that a
bilateral temporofrontal network with relative rightward lateralization is
involved in the perception of emotional prosody. Two important questions
regarding the neural correlates of emotional prosodic perception remain
unresolved. Firstly, previous studies have almost exclusively presented
emotional prosody only. This raises the question whether the proposed bilateral
temporofrontal network is specifically involved with the extraction of
emotional prosody or with prosodic processing in general (including linguistic
prosody). Therefore in the present study emotional as well as linguistic
prosody will be presented while brain activity is recorded with fMRI. This
allows us to investigate which neural network is specifically involved in the
perception of emotional prosody. Secondly, there is discussion concerning the
nature of the relative right hemispheric lateralization that has been found
during emotional prosodic processing. Two hypotheses have been proposed.
Acoustic lateralization hypotheses propose that lateralization of prosodic
prosodic processing is driven by the acoustic nature of the prosodic material.
The functional lateralization hypothesis on the other hand posits that
lateralization of prosodic processing is determined by the communicative
function of the prosodic material: emotional prosodic processing is more
lateralized to the right cerebral hemisphere while linguistic prosodic
processing is relatively left lateralized. Testing these two hypotheses
requires that either the nature of the acoustic material is held constant while
the communicative function is being varied or vice versa. Therefore, in the
present study identical prosodic material will be presented while the
communicative function is varied and brain activity is measured with fMRI. This
manipulation allows us to directly test the two hypotheses of lateralized
prosodic processing.

Music uses a variety of acoustic parameters such as mode and tempo to convey
emotional information as well. Does affective music (despite its artificial
nature) interact with other affective stimuli? The so called *affective priming
paradigm* offers a means to investigate this issue. In this paradigm subjects
evaluate affective valence (positive versus negative) of a target stimulus: the
target is preceded by an affective prime that can be affectively congruent or
incongruent with the target. If participants need less time to judge the
affective connotation of a target (e.g., the word SUN) if it is preceded by an
affectively related prime (e.g., the word LOVE) an *affective priming effect*
is found. Two mechanisms have been proposed as an explanation of the affective
priming effect. The 'spreading of activation account' proposes that processing
of emotional congruent targets is facilitated by the prime because activation
of the prime spreads through a network of interconnected affective concepts,
pre-activating the target and hence facilitating performance in congruent
trials. The response competition account on the other hand, posits that an
affective prime automatically triggers a response tendency that corresponds to
its valence. This leads to response facilitation (and hence superior
performance) for targets with the same valence as the prime and to response
competition if the valence of the target is different from the valence of the
prime (i.e., a Stroop-like interference process). Note that the main difference
between these two accounts is that the spreading of activation account assumes
interaction of affective primes and targets at a conceptual level, while the
response competition account assumes interaction at the response level.
Using the affective priming paradigm a recent study claims to have found
evidence for interaction between affective music and language on the conceptual
level. Visually presented emotional words were presented and followed 200 msec
later by chords that either sounded pleasant (positive) or unpleasant
(negative). Participants had to judge whether the target chords were pleasant
or unpleasant. An affective priming affect was found and contrasting
incongruent with congruent conditions revealed activation in the superior
temporal sulcus (STS) of the right hemisphere. Although the authors suggested
that this affective priming effect and accompanying activation in the STS was
the result of interaction of language and music on the conceptual level, note
that response competition as an alternative explanation cannot be excluded.
Therefore, in the present study two affective musical priming tasks will be
used that present identical stimulus material but vary the possibility of
response competition to occur while brain activity is recorded using fMRI This
manipulation allows us to directly test which of the two proposed mechanisms is
responsible for musical affective priming effects.

Although the primary goal of the proposed study is to examine the neural
underpinnings of general affective information processing (that is stable
between individuals) it is known that there are individual differences in
affective processing. A better understanding of how personality traits modulate
affective processing on the neural level could have implications for the
prevention and treatment of affective disorders and is the secondary goal of
the proposed study. A problem with previous research on this subject is that
most studies have focused on the modulatory influence of only one personality
trait on the neural mechanism of affective processing. This raises the question
whether modulation of affective processing that has been found in earlier
studies is trait-specific. Therefore the present study examines how three
personality traits modulate affective processing on the neural level:
trait-anxiety, pessimism and alexithymia.

The primary goal of the proposed study is to examine the neural correlates of
affective processing in the auditory modality. Specifically, the primary goal
is to (1) examine which neural network is specifically involved in the
perception of emotional prosody and how this network is lateralized and (2)
investigate which mechanism underlies affective musical priming.

The secondary goal is to examine how personality traits modulate affective
processing on the neural level.

The proposed study uses a experimental within subjects design: every subject
will participate in every experimental condition of the experimental tasks in
random order while brain activity is recorder using (event related-) fMRI.
The role of personality will be examined by correlating scores on personality
questionnaires with the brain activity elicited by the experimental tasks.

Functional magnetic resonance imaging (fMRI) is a non-invasive technique that
has been used for decades without negative health consequences: there are no
known risks involved in participating in a fMRI-study.

The only burden that is placed on the subjects is a two hour investment of
their time. This time investment consists of a single 2 hour visit to the LUMC.
The two hours will be spent on practice of the experimental tasks outside the
scanner (15 minutes), performing the tasks in the scanner (one hour) and
filling in the personality questionnaires (30 minutes). Subjects will be
compensated for their efforts with 10 euros per hour .