Oscillatory neural activity associated with cognitive processes affected by spatial frequency

Abstract

The spatial frequency contained in visual objects is known to affect human psychophysiology. In our previous study, we showed that event-related potentials are affected by spatial frequency during a simple calculation task. In that study, however, we did not investigate the contribution of oscillatory neural activities. The purpose of the present study is to characterize the changes in oscillatory neural activity associated with cognitive processes, and to investigate how these signals are affected by the spatial frequency of a visual stimulus during simple calculation tasks. We investigate these issues by analyzing our previously collected electroencephalography (EEG) dataset using the same visual stimulus, tasks, subjects, and EEG recordings. In that study, four types of vertically striped visual stimuli were used. The visual stimuli contained embedded numbers (from 0 to 9) that possessed the following frequency (f ) characteristics: white noise, 1/f , 1/f 2 , and 1/f 3 . The subjects were instructed to perform two tasks: 'add numbers' (addition task) and 'do not add numbers' (reference task). EEG data were recorded, and event-related synchronization (ERS) and desynchronization (ERD) for each visual stimulus were analyzed on the basis of the intertrial variances of wavelet coefficients for theta, alpha, low-beta, and gamma band activity. Eight healthy men (21-23 years) were recruited to participate in the study. Our results suggest the presence of a frequency discrimination function in the theta band activity in the fronto-central area at the latency of 198 ms during the addition task. The alpha-band ERD during completion of the reference task also showed a spatial frequency dependency. This phenomenon was observed in the left temporal-parietal area at a latency of 376 ms, and is thought to be related to the perceptual filter. We conclude that the observed changes in oscillatory neural activity associated with cognitive processes are affected by spatial frequency.

Oscillatory Neural Activity during Performance of a Cognitive Task in the Presence of Fluctuating Ambient Noise

“…The value of the pre-stimulus period from 2,000 ms pre-stimulus to 0 ms served as the 100% value for baseline normalization. The band-averaged variances in the theta (4-8 Hz), alpha (8-13 Hz), beta (13-30 Hz), and gamma bands (30-80 Hz) were then calculated, and the resulting time functions were smoothed with a low-pass digital filter with a 4 Hz cutoff frequency [10].…”

“…Epochs including artifacts exceeding 100 μV between 500 ms pre-stimulus and 1,000 ms post-stimulus were excluded. The intertrial variances of the wavelet coefficients were calculated for each frequency using the equation below (1) [10].…”

“…In the present study, instead of ERPs, we focused on the oscillatory neural activities seen in the electroencephalogram (EEG), grouped in ascending frequency bands as theta, alpha, and beta rhythms, to study the functioning of cognitive process such as working memory, attention, and visual awareness [5]- [10]. This paradigm could be expected to reveal novel associations between the auditory environment and cognitive function.…”