How visual experience modulates the ability to discriminate
faces from one another is still poorly understood. The aim of
this study is to investigate whether emotions may favor face
discrimination learning. To this purpose, we measured face
discrimination thresholds before and after a training phase,
where participants are exposed to (task-irrelevant) subtle
variations in face images from trial to trial. A task-irrelevant
perceptual learning paradigm was used because it closely
mimics the learning processes that daily occur, without a
conscious intention to learn and without a focused attention
on specific facial features. During the four sessions of
training, participants performed a contrast-discrimination task
on face images. The task-irrelevant features were face images
variations along the morphing continuum of facial identity
(Identity group) or face images variations along the morphing
continuum of emotional expressions (Emotion group). A
group of participants (Control group) did not perform the
contrast training, but their face discrimination thresholds were
measured with the same temporal gap between them as the
other two groups. Results indicate a face discrimination
improvement only for the Emotion group. Participants in the
Emotion Group showed a discrimination improvement when
tested with variations along the dimension of identity and
with variations along the dimension of expression, even if
identity variations were not used during training. The present
results suggest a role of emotions in face discrimination
learning and show that faces, differently from the other
classes of stimuli, may manifest a higher degree of learning
transfer.
