DO EMOTIONAL DISTRACTOR PICTURES SUPPRESS SEMANTIC PROCESSING OF TARGET PICTURES?
Date
2017-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Emotionally charged stimuli swiftly grab our attention even when we are
deeply engrossed in other activities. This is readily apparent in a laboratory
phenomenon known as “emotion induced blindness” or EIB. EIB occurs when people
search a rapidly presented (RSVP) stream of scene pictures for a target picture, for
example, a picture outlined in red. These targets become virtually undetectable when
an irrelevant distractor picture containing negative emotional content precedes the
target picture by about two tenths of a second. Longer intervals between the distractor
and target restore detection to normal levels. What causes this brief period of
blindness? According to one theory, the emotional distractor doesn’t affect the
perceptual or semantic processing of the target but only interferes with late processes
responsible for awareness, similar to other observed attention capturing phenomena. A
competing theory holds that emotional pictures are special and suppress early
perceptual processing of the target. The late-interference theory predicts that people
should have full “knowledge” about the meaning of the target picture even when they
are unaware of it, while the early-interference theory predicts that both perceptual and
semantic information about the target is suppressed. These predictions were tested
using EEG to measure the electrical activity of the brain. A brain response known as
the N400 is smaller when two sequentially presented pictures are semantically related
(for example, doctor-nurse) than when they are unrelated (such as clock-nurse).
According to the late-processing theory, the N400 should depend on the semantic
relatedness of the target picture even when it cannot be reported. In contrast, the early interference theory predicts no effect of this semantic relationship because EIB
abolishes the perceptual and semantic processing of the target. Subjects were asked to
view an RSVP stream and decide whether or not a “prime” picture outlined in red was
related to a “test” picture at the end of the stream. The prime picture was preceded by
a negative, neutral, or baseline distractor picture. N400s elicited by the test picture
were completely suppressed during incorrect trials, regardless of distractor condition. I
conclude that semantic priming, as measured with the N400, critically depends on
awareness of the prime picture.
Description
Keywords
Neuroscience, semantic processing