ERP evidence of affective picture processing generally agrees with one of two dominant
theories. The first is that enhanced ERP responses to pleasant and unpleasant stimuli
relative to neutral reflects the processing of stimulus motivational relevance, referred to
as the quadratic effect, and the second is that enhanced ERP responses to unpleasant
stimuli compared to pleasant and neutral stimuli reflects a negativity bias. The
overarching aims of the current series of empirical studies were to identify which of the
two aforementioned theories can most definitively account for affective picture
processing (Phase 1); and to investigate how processes of attentional engagement and
disengagement are influenced by the presence of motivationally relevant stimuli (Phase
2). Pictorial affective stimuli (high and low arousing pleasant, unpleasant, sexual, and
neutral stimuli) were presented in a modified oddball paradigm to 38 participants (19
male, 19 female) in Experiment 1 and 34 participants (17 male, 17 female) in Experiment
2. A negativity bias was demonstrated for P3b amplitude in Experiment 1; however
significantly enhanced P3b amplitudes evoked in response to sexually explicit stimuli in
Experiment 2 was not consistent with either dominant theory, and raised questions as to
the separable effects of motivational relevance and sexual arousal on cognitive processes.
Experiment 3 was aimed at investigating whether ERP responses are differentially
modulated by the social content of affective picture stimuli. The same participants from
Experiment 2 participated in Experiment 3 and the oddball task involved the presentation
of low arousing social and non-social pleasant, unpleasant, and neutral stimuli. No
significant differences in ERP component measures were shown between social and nonsocial
pleasant, or between social and non-social unpleasant stimuli, however both P2 and
P3b component amplitudes were enhanced in response to neutral faces compared with
neutral objects. Factors associated with facial recognition and difficulties extracting
affective information from a somewhat ambiguous neutral expression were cited as
possible explanations for the observed ERP component modulations.
The principal aim of Phase 2 was to investigate whether the presentation of
appetitive and aversive cues influences the engagement and disengagement components
of covert visual attention as inferred by responses to validly and invalidly cued targets
respectively. Participants in Experiment 4 @=I9 female) and Experiment 5 @=I8
female) were presented with a modified peripheral cueing paradigm, where pictorial
stimuli (sexual, mutilation, threatening, and neutral) served as peripheral cues. Target
processing as indexed by P1 and P3b amplitude showed significant facilitation in both
Experiments 4 and 5 when targets were cued by sexual and mutilation stimuli, regardless
of whether cueing was valid or invalid. It was therefore concluded that the engagement
and disengagement components of covert visual attention are not differentially affected
by motivationally relevant cues; rather, normal participants demonstrate a global
response bias when respondmg to targets that are cued by motivationally relevant
appetitive and aversive cues. The same participants from Experiment 5 were presented
with a peripheral cueing paradigm in Experiment 6, which aimed to investigate the effect
of phylogenetically (biological) and ontogenetically (cultural) fear-relevant stimuli on
processes of covert visual attention. Pictorial stimuli depicting dangerous animals, human
threat, and neutral objects served as peripheral cues. In line with preparedness theory
(Seligman 1970, 1971), target processing was facilitated by the presence of animal threat
stimuli compared to human threat and neutral stimuli, and also the early level of visual
processing as indexed by cue-evoked P 1 amplitude was enhanced in response to
phylogenetically, fear-relevant animal stimuli. A global response bias was again
demonstrated in Experiment 6, and it was concluded that the attentional system of normal
participants is sensitive to stimuli that have been evolutionarily associated with threat
and/or fear. The current dissertation therefore has theoretical implications for the
systematic study of affective picture processing. Furthermore, the introduction of a
peripheral cueing paradigm to the study of affective picture processing provides a new
insight into the effect that both appetitive and aversive stimuli have on processes of
attentional orienting and target processing.
| Identifer | oai:union.ndltd.org:ADTP/246222 |
| Creators | Briggs, KE |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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