Sensory Gating Measured by Evoked Potentials in Children with Sensory Modulation Dysfunction
Patricia Davies*, William Gavin **
Colorado State University*, Colorado State University**
The purpose of proposed project was to explore whether typically developing children and children with sensory motor dysfunction (SMD) would exhibit the Sensory Gating response during EEG recording using the P50 paradigm. Two procedures to elicit sensory gating responses were investigated: 1) the standard adult paradigm where the participant is asked to focus or stare at a fixed target ("Auditory-only" condition) and, 2) a modified paradigm where the participant watches a silent movie while listening to the click sounds ("Auditory+Movie" condition). We reported findings of 4 studies. In Study 1, 87% of the 18 control adults demonstrated sensory gating in the Auditory-only condition and 67% in the Auditory+Movie condition when the intensity of the auditory stimuli, the click sound, was presented at approximately 50 dB SPL. In Study 2, we found that the majority of the 22 children (without disabilities) tested (73%) did exhibit evidence of sensory gating in either one or the other listening condition (Auditory-only or Auditory+Movie conditions). However, the gating responses of these children were not as reliable as in the adults. Sensory gating was observed in 50% of the children in the Auditory-only condition and in 64% of the children in the Auditory+Movie condition suggesting that unlike the adults, more children showed sensory gating while watching a movie instead of staring at a fixed, unmoving object. In a third study, 13 children with a diagnosis of Sensory Modulation Dysfunction (SMD) were tested using the modified sensory gating paradigm (Auditory+Movie). Sensory gating was observed in only 4 of the 13 children (31%) tested in the Auditory+Movie condition. Comparing the results of Study 2 and Study 3, when engaged in watching a silent movie, fewer children with SMD (31%) demonstrated evidence of sensory gating compared to children without disabilities (64%). In study 4, including 18 control adults, we implemented new testing protocols which assessed the hearing threshold of each participant and set the intensity levels of the click sounds to 50 dB above the obtained threshold, which results in an intensity of 75 dB SPL if the participant's threshold is 25 dB. The addition of this precise control, over the delivery of stimuli with louder intensity used in Study 4 not only resulted in all of the 18 adults (100%) showing sensory gating when tested in the Auditory+Movie condition but also substantially decreased the "within group" variability of the gating measure as well. Work to date has revealed that sensory gating is not as simple a phenomenon as is currently discussed in the literature. Considerable variability exists in performance in children. The degree of sensory gating in children may be a result of the interaction of several factors: stimulus intensity, attentional focus, and the nature as well as the severity of sensory-motor dysfunction. Additional methodological studies need to be conducted exploring other parameters of the sensory gating paradigm, such as intensity of auditory stimuli, to determine if the consistency of sensory gating in control children can be improved.
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