Superadditive BOLD activation in superior temporal sulcus with threshold non-speech objects.

Evidence from neurophysiological studies has shown the superior temporal sulcus (STS) to be a site of audio-visual integration, with neuronal response to audio-visual stimuli exceeding the sum of independent responses to unisensory audio and visual stimuli. However, experimenters have yet to elicit superadditive (AV > A+V) blood oxygen-level dependent (BOLD) activation from STS in humans using non-speech objects. Other studies have found integration in the BOLD signal with objects, but only using less stringent criteria to define integration. Using video clips and sounds of hand held tools presented at psychophysical threshold, we were able to elicit BOLD activation to audio-visual objects that surpassed the sum of the BOLD activations to audio and visual stimuli presented independently. Our findings suggest that the properties of the BOLD signal do not limit our ability to detect and define sites of integration using stringent criteria.