Distractor removal amplifies spatial frequency-specific crossover of the attentional bias: a psychophysical and Monte Carlo simulation study.

Rarely noticed in daily life, attention may prefer the left side of space. Such attentional biases offer key insights into functions of spatial attention and visual awareness because they complement pathological biases in patients with spatial neglect who become largely unaware of the left side after right-brain damage. Yet there is little comprehensive understanding of these normal and pathological biases and how they relate to other attentional functions. Here we used a grating-scales task (GST) to test whether leftward biases and their spatial frequency-dependent crossover interact with attentional mechanisms of distractor removal. We asked healthy participants to make perceptual judgements to capture attentional biases in a high and a low spatial frequency condition (GST-HI and GST-LO), and we degraded stimuli with distracting pixel noise. We found that with noise, crossover grew, while biases remained positively correlated. Using Monte Carlo simulations, we probed the feasibility of three models and conclude that our data can only be explained by two, or more, biasing mechanisms, arguably interacting with each other through interhemispheric competition. Our study sets the stage for a new systematic approach to investigating the visuospatial mechanisms of the right hemisphere.