Cortical visuo-auditory interactions occurred initially in V1.

<p>(A) The averaged responses (average in the ROI of each animal followed by average among animals) to visual stimulation {V} (the black trace), auditory stimulation {A}, and combined presentation of visual and auditory stimuli {VA} (the dotted trace), were obtained from 10 animals in different cortical fields. The larger amplitude of ({VA}−{A}) (the red trace) compared to {V} suggests visuo-auditory interaction. (B) Visuo-auditory interactions estimated by {VA}−({V}+{A}). A <i>t</i>-score for {VA}–({V}+{A}) was calculated at each sampling point, and all calculated <i>t</i>-scores are presented as a time series. Shown here are V1 results, with simultaneous presentation of visual and auditory stimuli (simultaneous condition). The reddish shaded region shows the time window during which {VA}–({V}+{A}) is significantly different from zero (<i>p</i><0.05; Student's <i>t</i>-test). (C) Comparison of visuo-auditory interactions in different areas in the simultaneous condition. The green trace in each figure is the average of {V} (average in the ROI of each animal followed by average among animals), and the orange trace is the average of {A}. The average of {VA}−({V}+{A}) is shown as a black trace, and the SEM of {VA}−({V}+{A}) is illustrated as a dotted line. The black trace is drawn in red if {VA}–({V}+{A}) is significant, as tested in the way shown in (B). It is clear from the figure that significant visuo-auditory interaction occurs in all visual and auditory areas, and the interaction occurs initially in V1. Calibration scales apply to all traces. (D) Schematic illustration of visual response latencies (green lines) and auditory response latencies (orange lines; solid line represents negative response, and dotted line represents positive response), as well as the time window of significant visuo-auditory interaction (red) in the simultaneous condition. The number above each red box is the average of the ratio of ({VA}–{A}) to {V} in the time window. (E) Time series of <i>t</i>-score for {VA}–({V}+{A}) in V1, when auditory stimulation preceded visual stimulation. In this stimulation condition, significant {VA}–({V}+{A}) was observed only in V1.