Normal Aging Slows Spontaneous Switching in Auditory and Visual Bistability.

Age-related changes in auditory and visual perception have an impact on the quality of life. It has been debated how perceptual organization is influenced by advancing age. From the neurochemical perspective, we investigated age effects on auditory and visual bistability. In perceptual bistability, a sequence of sensory inputs induces spontaneous switching between different perceptual objects. We used different modality tasks of auditory streaming and visual plaids. Young and middle-aged participants (20-60years) were instructed to indicate by a button press whenever their perception changed from one stable state to the other. The number of perceptual switches decreased with participants' ages. We employed magnetic resonance spectroscopy to measure non-invasively concentrations of the inhibitory neurotransmitter (γ-aminobutyric acid, GABA) in the brain regions of interest. When participants were asked to voluntarily modulate their perception, the amount of effective volitional control was positively correlated with the GABA concentration in the auditory and motion-sensitive areas corresponding to each sensory modality. However, no correlation was found in the prefrontal cortex and anterior cingulate cortex. In addition, effective volitional control was reduced with advancing age. Our results suggest that sequential scene analysis in auditory and visual domains is influenced by both age-related and neurochemical factors.