Abstract
Purpose: :
Speech perception is multimodal, intertwining auditory signals with lip reading. With inaccurate visual input, speech is heard incorrectly, as demonstrated from an illusion called the McGurk effect. Here, a video is presented of a person silently mouthing the sound "ka." The auditory output of the stimulus, however, is the sound "pa". When the signals are presented simultaneously, 70% of normal individuals hear "ta", a representation of visual-audio integration. Children with amblyopia may have missed the critical window for such integration to develop. The purpose of our study is to determine if speech perception is influenced by a history of amblyopia.
Methods: :
Our stimuli present the face of a person on a 13" monitor, 50 cm away, at 60 dB, with the output as visual "pa" with audio "pa" (i.e. an unedited video of the person saying "pa" normally), visual "ka" with audio "ka" (normal), and the McGurk stimulus of a silent visual "ka" lip movement superimposed over an audio output of "pa." Ten trials of each stimulus were presented in random order. Inclusion criteria for amblyopes were: 1) age at least 4 years; 2) amblyopia in only one eye; 3) stereopsis worse than 50 seconds; and 4) at least 20/25 acuity in the better-seeing eye at the time of testing. Inclusion criteria for control patients were: 1) age over 4 years; 2) 20/20 acuity in both eyes; and 3) 40 seconds of stereopsis. Test subjects viewed the stimulus binocularly, and were asked to choose what sound was heard: "pa", "ka", or "ta."
Results: :
Of the 50 trials among 5 control subjects, "ta" was perceived 33 (66%) times. In contrast, of the 110 trials among 11 amblyopic subjects, "ta" was perceived 21 (19%) times; two-tailed Fisher’s exact test p < 0.0001.
Conclusions: :
Children with a history of amblyopia, even if they are at least 20/25 in their better seeing eye and are tested binocularly, have impaired visual-audio fusion in speech perception.
Keywords: amblyopia • neuro-ophthalmology: cortical function/rehabilitation • visual development: infancy and childhood