Age-related changes in global motion coherence: conflicting haemodynamic and perceptual responses

Our aim was to use both behavioural and neuroimaging data to identify indicators of perceptual decline in motion processing. We employed a global motion coherence task and functional Near Infrared Spectroscopy (fNIRS). Healthy adults (n = 72, 18-85) were recruited into the following groups: young (n = 28, mean age = 28), middle-aged (n = 22, mean age = 50), and older adults (n = 23, mean age = 70). Participants were assessed on their motion coherence thresholds at 3 different speeds using a psychophysical design. As expected, we report age group differences in motion processing as demonstrated by higher motion coherence thresholds in older adults. Crucially, we add correlational data showing that global motion perception declines linearly as a function of age. The associated fNIRS recordings provide a clear physiological correlate of global motion perception. The crux of this study lies in the robust linear correlation between age and haemodynamic response for both measures of oxygenation. We hypothesise that there is an increase in neural recruitment, necessitating an increase in metabolic need and blood flow, which presents as a higher oxygenated haemoglobin response. We report age-related changes in motion perception with poorer behavioural performance (high motion coherence thresholds) associated with an increased haemodynamic response

The Effects of Alpha Oscillations on Touch Perception and Visuo-tactile Integration

Previous studies have shown that touch perception and visuo-tactile integration have large inter-subject/intra-subject variations. For example, touch perception varies across trials and the temporal binding windows of visuo-tactile integration varies across subjects. I hypothesized that the variations might be due to the change of power, phase and peak frequency of brain alpha oscillations. In the first set of experiments, I examined whether the power and phase of alpha oscillations predict successful conscious touch perception. Near-threshold tactile stimuli were applied to the left hand while electroencephalographic (EEG) activity and fast signal optical imaging were recorded over the somatosensory cortex. Alpha power desynchronizations and phase at stimulus onset influence touch perception. These findings suggest that spontaneous alpha oscillations in somatosensory areas exert a strong inhibitory control on touch perception and that pulsed inhibition by alpha oscillations shapes the state of brain activity necessary for conscious perception. In the second set of experiments, I extended those studies into the multisensory domain by presenting vision and touch with varying stimulus-onset asynchronies (SOAs) and investigated how alpha oscillations contribute to the temporal dynamics of visuo-tactile integration. In one experiment, near-threshold tactile stimuli and suprathreshold visual stimuli (LED flashes) were delivered on the left middle finger with varying SOAs. Touch detection rates were significantly higher than the touch only condition when visual stimuli occurred between -150 ms and 100 ms of the tactile stimulus. The results also demonstrated that visual stimuli desynchronize and phase reset ongoing alpha oscillations to facilitate touch detection. In another experiment, I used a simultaneity judgment paradigm with varying SOAs between suprathreshold tactile and visual stimuli. The temporal binding window was negatively correlated with individual alpha frequency peak. The results also showed that prestimulus alpha power desynchronizations were linked with variations of the temporal binding window across subjects. Together these results demonstrate that alpha oscillations shape the state of brain activity and contribute to sensory processing