Peggy Tausche

Roughness perception during the rubber hand illusion.

Watching a rubber hand being stroked by a paintbrush while feeling identical stroking of ones own occluded hand can create a compelling illusion that the seen hand becomes part of ones own body. It has been suggested that this so-called rubber hand illusion (RHI) does not simply reflect a bottom-up multisensory integration process but that the illusion is also modulated by top-down, cognitive factors. Here we investigated for the first time whether the conceptual interpretation of the sensory quality of the visuotactile stimulation in terms of roughness can influence the occurrence of the illusion and vice versa, whether the presence of the RHI can modulate the perceived sensory quality of a given tactile stimulus (i.e., in terms of roughness). We used a classical RHI paradigm in which participants watched a rubber hand being stroked by either a piece of soft or rough fabric while they received synchronous or asynchronous tactile stimulation that was either congruent or incongruent with respect to the sensory quality of the material touching the rubber hand. (In)congruencies between the visual and tactile stimulation did neither affect the RHI on an implicit level nor on an explicit level, and the experience of the RHI in turn did not cause any modulations of the felt sensory quality of touch on participants own hand. These findings first suggest that the RHI seems to be resistant to top-down knowledge in terms of a conceptual interpretation of tactile sensations. Second, they argue against the hypothesis that participants own hand tends to disappear during the illusion and that the rubber hand actively replaces it.

A novel approach to study audiovisual integration in speech perception: Localizer fMRI and sparse sampling

Speech comprehension in noisy environments is greatly improved by the availability of visual information, i.e. lip and facial movements. This suggests that the brain is in possession of an audiovisual integration mechanism supplementing speech comprehension. To reveal the respective brain areas, we used a step-wise functional neuroimaging approach in healthy German speaking subjects. First, a functional localizer session using a block design with auditory speech, visual speech (lip movements, no audio), and audiovisual speech (audio and video-signal in sync) was used to identify areas activated by auditory and visual speech, which showed in addition further increased activity in the audiovisual condition. This procedure revealed two clusters of brain activity in the posterior part of the superior temporal sulcus bilaterally. In a second session using slow-event-related imaging in conjunction with sparse sampling, these functionally defined volumes were further examined in a design crossing audiovisual congruity and intelligibility (with/without added noise). Within these areas, regions showing an interaction of audiovisual congruity and intelligibility were found with the greatest activity for incongruent speech stimuli with added noise. This underscores their role in audiovisual integration. We propose that the stepwise approach introduced here allows a finer analysis of audiovisual speech integration than previous methods.