van Diepen Rosanne M, Cohen Michael X, Denys Damiaan, Mazaheri Ali
Academic Medical Center Amsterdam.
University of Amsterdam.
J Cogn Neurosci. 2015 Aug;27(8):1573-86. doi: 10.1162/jocn_a_00803. Epub 2015 Mar 16.
The perception of near-threshold visual stimuli has been shown to depend in part on the phase (i.e., time in the cycle) of ongoing alpha (8-13 Hz) oscillations in the visual cortex relative to the onset of that stimulus. However, it is currently unknown whether the phase of the ongoing alpha activity can be manipulated by top-down factors such as attention or expectancy. Using three variants of a cross-modal attention paradigm with constant predictable stimulus onsets, we examined if cues signaling to attend to either the visual or the auditory domain influenced the phase of alpha oscillations in the associated sensory cortices. Importantly, intermixed in all three experiments, we included trials without a target to estimate the phase at target presentation without contamination from the early evoked responses. For these blank trials, at the time of expected target and distractor onset, we examined (1) the degree of the uniformity in phase angles across trials, (2) differences in phase angle uniformity compared with a pretarget baseline, and (3) phase angle differences between visual and auditory target conditions. Across all three experiments, we found that, although the cues induced a modulation in alpha power in occipital electrodes, neither the visual condition nor the auditory cue condition induced any significant phase-locking across trials during expected target or distractor presentation. These results suggest that, although alpha power can be modulated by top-down factors such as attention and expectation, the phase of the ongoing alpha oscillation is not under such control.
已表明对接近阈值视觉刺激的感知部分取决于视觉皮层中正在进行的阿尔法(8 - 13赫兹)振荡相对于该刺激开始的相位(即周期中的时间)。然而,目前尚不清楚正在进行的阿尔法活动的相位是否可以被诸如注意力或预期等自上而下的因素所操纵。我们使用具有恒定可预测刺激开始的跨模态注意力范式的三种变体,研究了指示关注视觉或听觉领域的线索是否会影响相关感觉皮层中阿尔法振荡的相位。重要的是,在所有三个实验中都穿插了无目标试验,以估计目标呈现时的相位,而不受早期诱发反应的干扰。对于这些空白试验,在预期目标和干扰物出现时,我们检查了:(1)各试验相位角的均匀程度;(2)与目标前基线相比的相位角均匀性差异;(3)视觉和听觉目标条件之间的相位角差异。在所有三个实验中,我们发现,尽管线索在枕叶电极中诱发了阿尔法功率的调制,但在预期目标或干扰物呈现期间,视觉条件和听觉线索条件在各试验中均未诱发任何显著的相位锁定。这些结果表明,尽管阿尔法功率可以被诸如注意力和预期等自上而下的因素所调制,但正在进行的阿尔法振荡的相位不受此类控制。