Ambient Prism Lenses Modulate Spatial Attention in Autism: An Event-Related Potential Study

Background: Autism is a developmental disorder marked by deficits in social interaction, communication, and behavior. One of the less studied deficits in autism is the dysfunction of the ambient visual system, which can affect attention, movement, and visuo-motor coordination. These deficits of the ambient vision may limit the ability to process information regarding gait, posture, movement, speech, and spatial attention.

Objectives: The proposed study aims to understand the abnormal neural and functional mechanisms underlying visual distortion in autism by incorporating neurophysiologic studies, behavioral studies, and qEEG/ERP measurements of spatial attention.

Methods: Individuals with ASD were recruited with the assistance of local autism treatment centers in Louisville. Pre-screening questionnaires were filled out by parents, while evaluation of visual abnormalities related to ambient vision deficits were conducted by Dr. Kaplan. Twenty subjects with autism screened and ambient correcting lenses were selected to match their visual deficits. The final sample consisted of 12 high-functioning ASD individuals (Mean age 13.9±3.0 years) who were able to tolerate EEG recording procedures for the ERP task. In this modified cued Posner spatial attention task, subjects were instructed to press a button to indicate which side of the screen the stimulus “X” appeared. Before the presentation of each stimulus, the subjects were shown a pre-cue (red square). The probability of correctly cued targets was 80%. The task consisted of 2 blocks lasting 10 minutes each, with a “horizontal” block (stimuli centered vertically), and a “diagonal” block (stimuli appeared in the corners). Each subject performed the task with ambient and placebo lenses which did not alter vision, and the order was counterbalanced. The ERP of interest included early (N100, P200) and late (N200, P300) components at frontal, centro-parietal, and occipital areas reflecting spatial attention processes.

Results: Reaction time in prism lenses condition tended to be faster than in placebo lenses condition. Accuracy of responses in lenses vs. placebo condition also showed lower percentage of errors (5.6% vs. 14.2%). Amplitude of the parieto-occipital N100 in horizontal congruent trial was significantly higher (-3.92 vs. -1.37 µV, F=7.79, p=0.012) in prism lens condition. Similar effect was significant for incongruent trials (0.21 µV in placebo vs. -3.33 µV in lenses condition, F1,23=6.40, p=0.021). Amplitude of the P3b during the more difficult diagonal incongruent condition was higher (4.65 vs. 2.05 µV, F=4.57 p=0.045) in ambient prism lenses condition, while latency of P3b was shorter (349.1 ms vs. 380.1 ms, F=7.72 p=0.012).

Conclusions: These ERP effects of wearing ambient prism lenses is indicative of more effective special attentional processing, especially in more complex diagonal incongruent trials. Our pilot study provides preliminary support to utility of wearing prism lenses to correct ambient vision in autism and sensitivity of ERP indices to detect spatial attention improvement. We have found that using prism lenses and comparing the autistic patients performance and ERPs with and without such lenses can be a very informative approach to understand the mechanisms of visual deficits and spatial orienting impairments typical for autism.