Investigating human audio-visual object perception with a combination of hypothesis-generating and hypothesis-testing fMRI analysis tools

Primate multisensory object perception involves distributed brain regions. To investigate the network character of these regions of the human brain, we applied data-driven group spatial independent component analysis (ICA) to a functional magnetic resonance imaging (fMRI) data set acquired during a passive audio-visual (AV) experiment with common object stimuli. We labeled three group-level independent component (IC) maps as auditory (A), visual (V), and AV, based on their spatial layouts and activation time courses. The overlap between these IC maps served as definition of a distributed network of multisensory candidate regions including superior temporal, ventral occipito-temporal, posterior parietal and prefrontal regions. During an independent second fMRI experiment, we explicitly tested their involvement in AV integration. Activations in nine out of these twelve regions met the max-criterion (A < AV > V) for multisensory integration. Comparison of this approach with a general linear model-based region-of-interest definition revealed its complementary value for multisensory neuroimaging. In conclusion, we estimated functional networks of uni- and multisensory functional connectivity from one dataset and validated their functional roles in an independent dataset. These findings demonstrate the particular value of ICA for multisensory neuroimaging research and using independent datasets to test hypotheses generated from a data-driven analysis.

A semi-structured interview to assess visual hallucinations in older people

OBJECTIVE: Visual hallucinations are under-reported by patients and are often undiscovered by health professionals. There is no gold standard available to assess hallucinations. Our objective was to develop a reliable, valid, semi-structured interview for identifying and assessing visual hallucinations in older people with eye disease and cognitive impairment. METHODS: We piloted the North-East Visual Hallucinations Interview (NEVHI) in 80 older people with visual and/or cognitive impairment (patient group) and 34 older people without known risks of hallucinations (control group). The informants of 11 patients were interviewed separately. We established face validity, content validity, criterion validity, inter-rater agreement and the internal consistency of the NEVHI, and assessed the factor structure for questions evaluating emotions, cognitions, and behaviours associated with hallucinations. RESULTS: Recurrent visual hallucinations were common in the patient group (68.8%) and absent in controls (0%). The criterion, face and content validities were good and the internal consistency of screening questions for hallucinations was high (Cronbach alpha: 0.71). The inter-rater agreements for simple and complex hallucinations were good (Kappa 0.72 and 0.83, respectively). Four factors associated with experiencing hallucinations (perceived control, pleasantness, distress and awareness) were identified and explained a total variance of 73%. Informants gave more 'don't know answers' than patients throughout the interview (p = 0.008), especially to questions evaluating cognitions and emotions associated with hallucinations (p = 0.02). CONCLUSIONS: NEVHI is a comprehensive assessment tool, helpful to identify the presence of visual hallucinations and to quantify cognitions, emotions and behaviours associated with hallucinations.