Decreased BOLD responses in audiovisual processing.

Audiovisual processing was studied in a functional magnetic resonance imaging study using the McGurk effect. Perceptual responses and the brain activity patterns were measured as a function of audiovisual delay. In several cortical and subcortical brain areas, BOLD responses correlated negatively with the perception of the McGurk effect. No brain areas with positively correlated BOLD responses were found. This was unexpected as most studies of audiovisual integration use additivity and super additivity - that is, increased BOLD responses after audiovisual stimulation compared with auditory-only and visual-only stimulation - as criteria for audiovisual integration. We argue that brain areas that show decreased BOLD responses that correlate with an integrated audiovisual percept should not be neglected from consideration as possibly involved in audiovisual integration.

Dominance of missing fundamental versus spectrally cued pitch: individual differences for complex tones with unresolved harmonics.

In a two-alternative, forced-choice experiment, subjects had to compare the pitches of two sounds, A and B. Each sound was composed of four successive harmonics of a fundamental frequency between 100 to 250 Hz, added in cosine or Schröder phase. The harmonic frequencies of A were lower than those of B; the missing fundamental frequency of A was higher than that of B. The dominance of the missing fundamental versus the spectrally cued pitch--a pitch percept corresponding to spectral components--was measured as a function of nA, the lowest harmonic in A. The pitch percept is dominated by the missing fundamental if the harmonics are resolved (nA<7). If the harmonics become unresolved and are added in Schröder phase, the dominance shifts to a spectrally cued pitch (720). For others, the transition was in the realm of partly resolved harmonics. This shows that the temporal envelope modulation of stimuli with only four unresolved harmonics can give a relatively clear fundamental pitch percept. However, this percept varies considerably among subjects.