RESUMO
Multistable stimuli lead to the perception of two or more alternative perceptual experiences that spontaneously reverse from one to the other. This property allows researchers to study perceptual processes that endogenously generate and integrate perceptual information. These endogenous processes appear to be slowed down around the age of 55 where participants report significantly lower perceptual reversals. This study aimed to identify neural correlates of this aging effect during multistable perception utilizing a multistable version of the stroboscopic alternative motion paradigm (SAM: endogenous task) and a control condition (exogenous task). Specifically, age-related differences in perceptual destabilization and maintenance processes were examined through alpha responses. Electroencephalography (EEG) of 12 older and 12 young adults were recorded during SAM and control tasks. Alpha band activity (8-14 Hz) was obtained by wavelet-transformation of the EEG signal and analyzed for each experimental condition. Endogenous reversals induced gradual decrease in posterior alpha activity in young adults which is a replication of previous studies' findings. Alpha desynchronization was shifted to anterior areas and prevalent across the cortex except the occipital area for older adults. Alpha responses did not differ between the groups in the control condition. These findings point to recruitment of compensatory alpha networks for maintenance of endogenously generated percepts. Increased number of networks responsible for maintenance might have extended the neural satiation duration and led to decreased reversal rates in older adults.
RESUMO
Multistable stimuli are physically unchanging, but elicit spontaneous perceptual reversals between multiple internally generated perceptual alternatives. Perceptual reversal rates seem to decrease in older adults; however, there is no literature on the electrophysiological correlates of this performance decrease. Here, we aimed to identify age-related changes in theta activity that relate to decreased reversal rates of older adults. Electroencephalography (EEG) of young (n = 15) and older adults (n = 15) was recorded during presentation of stroboscopic alternative motion (SAM) and a control stimulus. Time-frequency amplitudes were extracted in 4-8 Hz via Morlet wavelet convolution. Older adults had lower SAM reversals as well as decreased accuracy, increased reaction time (RT) and increased RT variability in the control task. In older adults, reversal-related frontal theta response was diminished, yet parietal theta was intact. In the parietal area, the relationship between theta response and reversal rates was robust, but in the frontal area, was dependent on age-related variance. Result indicated that, in older adults, top-down facilitation of perceptual reversals was impaired. This appears to result in a predominantly bottom-up resolution of perceptual multistability. Age-related degradation of sensory areas in this bottom-up-driven resolution process might have slowed reversals. This study presents the first electrophysiological correlates of age-related impairment in multistable perceptual integration.
