Speech discrimination skills in deaf infants before and after cochlear implantation

Abstract

The benefit of early cochlear implantation (CI) to later speech perception outcomes in prelingually deaf (PLD) children is well established and implantation of infants has become more prevalent. The aim of this study was to determine whether or not deaf infants could discriminate audiovisual non-words shortly after CI and whether their attention to speech and non-speech audiovisual stimuli was similar to infants with normal hearing (NH). Three groups of participants were tested: PLD infants tested prior to CI (pre-CI), PLD infants tested post-implantation (post-CI), and a group of age-matched NH infants. A novel version of the visual habituation (VH) procedure was used. Infants were presented repetitions of an audiovisual non-word until their looking-time decreased to a predetermined criterion. They were then presented two types of test trials: repetitions of the old word (non-alternating (NA) trials) and repetitions of a novel non-word alternating with the old word (alternating (A) trials). Longer looking times to the A relative to the NA trials was taken as evidence of discriminating the non-words. An audiovisual non-speech trial was presented at the beginning and the end of each experiment and looking times between speech and non-speech trials were compared. Analyses revealed that pre- and post-CI infants had significantly shorter looking times than NH infants for speech but not non-speech trials. Furthermore, deaf infants often did not look long enough to be exposed to the novel non-word during the A trials. When trials with less than three seconds of looking were removed, analyses revealed that both NH infants and post-CI infants discriminated the non-words but pre-CI infants did not. Pre-implant hearing, age at implantation, and length of CI use were not related to visual preference for A trials. These results suggest that PLD infants show less visual interest in speech stimuli than NH infants. Despite this, PLD infants appear to be able to discriminate audiovisual non-words within three months after implantation.

• cochlear implant
• infant speech perception
• visual habituation
• outcomes

Notes

1. In an earlier version of the protocol, seven A and seven NA trials were presented in alternating order. Two of the pre-implant and two of the post-implant sessions were conducted in this way. Testing with normal-hearing infants later showed that making the A trials less frequent made the visual preference for A vs. NA trials more robust (20) Houston D, Horn D, Qi R, Ting J, Gao S. Assessing Speech Discrimination in Individual Infants. Infancy. 2007;12: In press

2. To prevent redundancy, the post-hoc tests for looking times during the test phase are excluded here as they essentially mirror the results of the repeated measures ANOVA described earlier