title: Deficient Binocular Combination of Second-Order Stimuli in Amblyopia.
abstract: OBJECTIVE
  Sensory imbalances in humans with amblyopia have been well documented using luminance-modulated (first-order) stimuli. However, little is known regarding whether there is a deficient binocular combination in amblyopes for stimuli defined by modulations in contrast (second-order stimuli). To address this, we asked two questions: Does a sensory imbalance also exist in the binocular combination of second-order stimuli, and if so, is it more severe than that expected on the basis of the imbalance for first-order stimuli?
  
  
  METHODS
  The sensory imbalances of 14 adult amblyopes (mean age: 30.5 ± 11.5 years; 5 with strabismus and 9 without) were measured using a dichoptic phase combination task. Three types of second-order dichoptic stimulus pairs were used in the study, where the carriers in the two eyes were either correlated, anticorrelated, or uncorrelated. Results were compared with those obtained using first-order stimuli in all observers.
  
  
  RESULTS
  We found that second-order binocular combination in amblyopes was not affected by the interocular carrier correlations. The amblyopic eye's contribution to the binocularly fused percept was much less than that of the nonamblyopic eye. The resulting sensory imbalance in binocular combination for second-order images was comparable to that for first-order images in 8 of the observers but was more severe in the other 6 amblyopes.
  
  
  CONCLUSIONS
  These results indicate that amblyopia does not disrupt the normal architecture of binocular combination for second-order signals; however, there is an additional deficit in binocular combination of second-order image in some amblyopes that cannot be fully accounted for by the known first-order sensory imbalance.
authors.affiliation: School of Ophthalmology and Optometry and Eye Hospital Wenzhou Medical University, Wenzhou, Zhejiang, People's Republic of China 2McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
authors.forename: Jiawei
authors.initials: J
authors.lastname: Zhou
authors.affiliation: CAS Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, People's Republic of China.
authors.forename: Rong
authors.initials: R
authors.lastname: Liu
authors.affiliation: Department of Ophthalmology, First Affiliated Hospital, Anhui Medical University, Hefei, Anhui, People's Republic of China.
authors.forename: Lixia
authors.initials: L
authors.lastname: Feng
authors.affiliation: CAS Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, People's Republic of China.
authors.forename: Yifeng
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Hess
mesh_terms: D000293:Adolescent; D000328:Adult; D000550:Amblyopia / Q000503:physiopathology*; D015350:Contrast Sensitivity / Q000502:physiology; D003867:Depth Perception / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015348:Vision, Binocular / Q000502:physiology*; D055815:Young Adult