title: Visual perceptual strengths and weaknesses in adults with intellectual disabilities compared with a birth year-matched norm.
abstract: BACKGROUND
  The ventral and dorsal streams are considered to be the brain substrates of vision for perception and action, respectively. Using the Developmental Test of Visual Perception (DTVP), the current study examined whether visual perceptual strengths and weaknesses in adults with intellectual disabilities (ID) were attributable to the dichotomy of the visual streams.
  
  
  METHODS
  In study 1, DTVP performance was compared among mild, moderate and severe adult ID groups; study 2 contrasted adult ID groups with and without Down syndrome (DS). To prevent possible contamination by the Flynn effect, participants were matched by birth year with the norm of the DTVP original edition.
  
  
  RESULTS
  Independent of the extent of ID among the three groups in study 1 and the aetiological group difference in study 2, relative strength was found for two DTVP tasks: eye-hand coordination and distinguishing target figures from interference background. Relative weakness was obtained in identifying a figural category. Participants with DS demonstrated exceptional weakness in discerning a target from either mirror-imaged or rotated alternatives, in addition to figural-category detection.
  
  
  CONCLUSIONS
  Visual perceptual strengths and weaknesses in persons with ID were difficult to explain on the basis of two visual streams. An interpretation originating in a different research context (e.g. frontal-lobe dysfunction) appears to be required for explaining visual perceptual weaknesses in persons with ID. For persons with DS, strong frontal-lobe dysfunction with atypical lateralisation might be the pathological determinant of visual perceptual weaknesses.
authors.affiliation: Center for the Research and Support of Educational Practice, Tokyo Gakugei University, Koganei, Japan. kazunari@u-gakugei.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Ikeda
authors.forename: H
authors.initials: H
authors.lastname: Kasugai
authors.forename: A
authors.initials: A
authors.lastname: Yamaguchi
authors.forename: Y
authors.initials: Y
authors.lastname: Uchino
authors.forename: H
authors.initials: H
authors.lastname: Katase
authors.forename: A
authors.initials: A
authors.lastname: Kanno
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D004314:Down Syndrome / Q000150:complications / Q000503:physiopathology*; D005260:Female; D005625:Frontal Lobe / Q000502:physiology*; D006803:Human Development / Q000502:physiology; D006801:Humans; D008607:Intellectual Disability / Q000150:complications / Q000503:physiopathology*; D008297:Male; D016555:Matched-Pair Analysis; D008875:Middle Aged; D012720:Severity of Illness Index; D014786:Vision Disorders / Q000150:complications / Q000175:diagnosis*; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult