Load dependence of β and γ oscillations predicts individual capacity of visual attention

Human capability to concurrently attend and perceive multiple visual objects has a limited and individual capacity of 2-4 objects. Neuronal mechanisms that support the perception of multiple objects and underlie these attentional capacity limits have remained unclear. We investigated the role of neuronal oscillations in multiobject visual perception and in limiting the attentional capacity. To this end, we used parametric multiobject tracking tasks, MEG and EEG recordings, and data-driven source-space analyses to localize the neuronal substrates of task performance. Three lines of evidence suggested a mechanistic role for neuronal oscillations in multiobject attention. First, oscillation amplitudes preceding target events were distinct for subsequently detected and undetected targets and also predicted reaction times to the target events. Second, suppression of θ to low-β (<20 Hz) and strengthening of high-β to γ (20-90 Hz) oscillations in frontoparietal and visual regions were correlated with attentional load. Third, the load-dependent strengthening of γ (30-90 Hz) band oscillations in lateral prefrontal, posterior parietal, and visual cortices predicted interindividual variability in attentional capacity. A progressive recruitment of γ oscillations in sensory, attentional, and executive networks is thus directly correlated with multiobject attentional demands and, in particular, with the individual capability to consciously attend and perceive multiple visual objects concurrently. These data support the hypothesis that γ oscillations contribute both to neuronal object representations and to attentional and executive processing.