Selectivity and localization of cortical response to auditory and visual stimulation in awake infants aged 2 to 4 months.

To better understand the development of multimodal perception, we examined selectivity and localization of cortical responses to auditory and visual stimuli in young infants. Near-infrared optical topography with 24 channels was used to measure event-related cerebral oxygenation changes of the bilateral temporal cortex in 15 infants aged 2 to 4 months, when they were exposed to speech sounds lasting 3 s and checkerboard pattern reversals lasting 3 s, which were asynchronously presented with different alternating intervals. Group analysis revealed focal increases in oxy-hemoglobin and decreases in deoxy-hemoglobin in both hemispheres in response to auditory, but not to visual, stimulation. These results indicate that localized areas of the primary auditory cortex and the auditory association cortex are involved in auditory perception in infants as young as 2 months of age. In contrast to the hypothesis that perception of distinct sensory modalities may not be separated due to cross talk over the immature cortex in young infants, the present study suggests that unrelated visual events do not influence on the auditory perception of awake infants.