FMRI adaptation (fMRIa) is an experimental tool which provides complementary results compared to conventional neuroimaging paradigms. We combined fMRIa with sparse-sampling to investigate the processing of common audio-visual (AV) objects.
Stimuli consisting of animal vocalizations and images were presented bimodally with an adapting stimulus S1 and a subsequent stimulus S2. Four experimental conditions involved in S1 and S2 either 1. the same image and vocalization, 2. the same image and a different vocalization, 3. a different image and the same vocalization, or 4. a different image and vocalization. S1 and S2 were always taken from the same basic-level category (e.g. cat).
Auditory and visual repetitions compared to the respective stimulus changes reduced the fMRI signal in regions of the superior temporal gyrus (STG) and the ventral visual cortex, respectively. Additionally, auditory regions particularly in the right STG showed a response profile which suggested an enhanced response to the repetition of visual stimuli. Interestingly, a left lateral occipital region exhibited a similar enhancement for repeated auditory stimuli.
These results suggest a complex interplay of human sensory cortices during the processing of repeated AV object stimuli as evidenced by the presence of both suppression and enhancement effects.