Plasticity and Cross-modal Interactions in Profoundly Deaf Adults
Condition: Deafness; Perception, Bilateral
MeSH terms: Deafness; Hearing Loss, Sensorineural
Study type: Interventional

Summary: 
      The aim of this study is to evaluate cerebral asymmetry for face processing in a group of
      profoundly deaf participants and a group of hearing controls by the mean of fMRI measure. To
      this end, we present chimeric faces (faces split into different halves), entire faces, or
      faces presented in divided visual field, and subjects perform a gender categorization task
      while lying in a fMRI scanner.

      It is expected to find a reduced cerebral asymmetry in the Fusiform Face Area in deaf in
      comparison with hearing participants.
    

Detailed description: 
      A rightward asymmetry during face processing is well documented in hearing participants, in
      particular in the Fusiform Face Area, a cortical area underlying face processing. This
      rightward asymmetry seems to be very robust, present even with inverted faces or line
      drawings, and is already present at five years of age. If the brain asymmetry for face
      processing emerges during development, early deprivation or dramatic differences the infant's
      experience with the world should affect it. For example, infants treated for bilateral
      congenital cataracts after 7 weeks of age, who are deprived of patterned visual input for
      this duration, fail to develop some of the aspects associated with typical adult levels of
      face recognition. Non visual early deprivation can also affect the development of visual
      abilities. Several studies showed that deaf participants could detect targets at larger
      eccentricities, thus indicating larger visual field . Furthermore, better abilities have been
      found in deaf participants for the detection of motion, in particular in the visual periphery
      . Higher-level visual abilities have also been shown to be modified by early deafness, such
      as visual imagery (image generation, or rotation) or the processing of faces . Using the
      Benton Test of Facial Recognition, a previous study tested the recognition of individual
      faces in deaf participants. They obtained better scores than hearing non signers, but only in
      a difficult condition, in which faces were shadowed. This enhanced processing in deaf people
      could thus concern very particular aspects of face processing; it was found that deaf and
      normal hearing differed only by the detection of subtle facial features. Investigating
      configural processing during face perception, it was found an increased dependency on this
      mode of processing in deaf participants.

      If visual processing is affected by early deafness, what about visual asymmetries? Several
      experimental studies examining hemispheric asymmetry in congenitally deaf individuals found
      that it differs from the one observed in hearing individuals . Concerning face processing,
      few studies investigated hemispheric lateralization during the perception of faces in deaf
      people. When presenting briefly unfamiliar faces in either the left or right visual field and
      no differences between deaf and hearing participants were found. In a previous experiment,
      using chimeric faces (faces vertically split into two different parts, ie half male, half
      female) it was found a reduction of leftward asymmetry for face processing in deaf
      participants during a gender categorization task.

      The aim of the present study is to broaden the knowledge about asymmetry for face processing
      in deaf people, by evaluating if this reduction of asymmetry observed at the behavioral level
      results from a reduction of cerebral asymmetry at the level of Fusiform Face Area.

      Deaf participants and normal hearing controls will be presented face stimuli, composed of
      either chimeric male/female and female/male faces, entire faces or entire face presented in
      divided visual field, to investigate Fusiform Face Area asymmetry in these two groups.
      Participants will lie in an fMRI scanner, and their cerebral activity will be recorded while
      they perform a gender categorization task on our face stimuli.
    

Intervention name(s): fMRI measure
Intervention type(s): Other
Allocation: Randomized
Intervention model: Factorial Assignment
Masking: Single (Participant)
Primary purpose: Basic Science
Keywords: Face processing; asymmetry; deaf; fMRI