engleski

Unattended visual change detection: An MEG spatio-temporal source localization study

Detection of a change in the visual environment is an evolutionary important skill. In auditory modality, mismatch negativity (MMN) response is assumed to reflect an automatic detection of stimulus change. Visual analogue of MMN (vMMN) has also been reported [1] but it is not yet well explored. In this study we used magnetoencephalography (MEG) and spatio-temporal source localization to investigate vMMN response to simple visual stimuli. The evoked visual responses were measured on 10 subjects using Elekta 306-channel MEG system. Gratings of different spatial frequency were presented in an oddball paradigm in three experimental conditions as: 1) frequently-occurring standard stimulus (P = 0.8) ; 2) infrequent deviant stimulus (P = 0.2) ; 3) equiprobable stimulus (P = 0.2). The task in all conditions was discrimination of odd/even digits presented in the centre of the gratings. All subjects showed vMMN response to the deviant stimuli in the time interval 100-170 ms. The analysis of the evoked field amplitudes demonstrated differences between the responses to the same stimulus presented as deviant in one condition and equiprobable stimulus in the other condition. Spatio-temporal localization revealed neuromagnetic sources of the vMMN response in the occipital cortex. Our results suggested that unattended visual change was detected by sensory-memory comparison between deviants and standards in the occipital cortex.

MEG (magnetoencephalography); spatio-temporal source localization; vMMN (visual mismatch negativity); change detection; occipital cortex

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