| Summary: | All and only human languages are equipped with the possibility of negative
predications, but the neural and cognitive correlates of this ability are still unknown.
In particular, it is not clear whether negative sentence processing is intrinsically more
complex than affirmative sentence processing or not. On one hand, longer RTs and
lower accuracy observed with negative compared to affirmative sentences in
behavioral tasks have been traditionally linked to greater computational demands,
although recent studies reported cases where the behavioral patterns of affirmative
and negative sentences are aligned. On the other hand, the neurofunctional results
collected so far do not allow establishing if negative sentences actually recruit greater
computational resources than affirmative sentences. In particular, previous functional
Magnetic Resonance (fMRI) studies reported that, during sentence-verification tasks,
negative sentences compared to affirmatives are associated with increased BOLD
signal in left hemisphere language areas. However, when the effort imposed by the
task is limited as in passive listening or lexical decision paradigms, this pattern is not
observed. The current work integrates the research on linguistic negation with two
studies that explore the neural and behavioral correlates of affirmative and negative
sentence verification in healthy volunteers and brain-damaged population. The first
study tested nineteen healthy subjects with a sentence-picture verification paradigm
in a fMRI experiment. Increased activation in the left inferior frontal gyrus was found
with negative vs affirmative sentences, but also with false vs true affirmative
sentences. These results suggest that negative sentences are not intrinsically more
complex than affirmatives, but are at a disadvantage during tasks that involve
competing semantic representations. The second study tested t
hirty-one
individuals
with aphasia and thirty-seven individuals with diagnosed degenerative dementia with
an adaptation of the sentence-picture verification paradigm adopted in the first study.
The comparison between patients and the control group (n=50) revealed that sentence-
picture verification is overall problematic for people with brain injury, especially if
sentences contain negation. Moreover, in focal patients the sentence-picture
verification test allowed identifying distinct cognitive domains that may be selectively
interested by the damage. We propose that the complexity engaged by linguistic tasks
with negative sentences has not to do with negation processing per se, but with
domain-general cognitive mechanisms that go beyond pure language processing.
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