PDF (PhD Thesis Susan Chipchase) - Nottingham eTheses ...

designing and conducting experiments with the IAPS I have come across
several difficulties in using these stimuli to investigate cognitive processes.
There are perceptual differences in the characteristics of negative, neutral and
positive emotionally arousing stimuli from this source. These differences
include: the negative photographs tend to be darker, the positive photographs
tend to be of bolder colours and the neutral photographs tend to be less
complex as they often depict a single object on a relatively plain background. I
attempted to select stimuli in a way that would minimise these differences and
in chapter 3 adjusted the levels of colour saturation to obtain similarity across
positive, negative and neutral groups of stimuli.
Another difficulty in using the IAPS as a stimulus source is that by
controlling for the perceptual characteristics described it is very likely that the
final experimental set will be a mix of objects, animals, people and faces.
Research indicates that there may be specialised cognitive processes for
recognising human faces and interpreting emotions from facial expressions
(Adolphs, 2002) and therefore ideally, this could be controlled by either
exclusively using faces in emotional stimuli, excluding faces altogether or
specifically including them as a factor. An additional difficulty with the IAPS
is that some of the photographs are extracted from film stills or advertising
shots and may be very well known to some participants in the experiment,
introducing the problem that for some participants the study phase of the
experiment does not involve encoding of novel stimuli. The elicitation of
emotions by some of the pictures (for example American football games) may
depend on cultural relevance and as many of the pictures appear to be North
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