Pupillometric imaging reveals the spatiotemporal dynamics of covert attention

The visual system uses attention to process relevant aspects in the environment. Particularly covert attention plays an important role as it allows us to inspect information presented in the visual periphery before or without an eye movement. However, due to its latent and dynamic nature, it has been a challenge to characterize the spatial and temporal properties of covert attentional shifts. To date little is known about how the focus of attention moves across space and time. We developed a novel pupillometric imaging paradigm to directly probe and visualize spatiotemporal shifts of attention in observers that performed a classic Posner’s cueing task. The distribution of attentional resources was measured by proxy of the amplitude of pupil orienting responses to salient probes that sampled various positions and timepoints around cue and target onsets. The resulting attention maps confirm that the analogy of attention as a local spotlight holds when stationary. The analysis of its temporal dynamics indicate that the attentional spotlight, when shifting between peripheral locations, gradually fades out at start positions and fades in at end positions across time. When shifting from foveal to peripheral locations, the degree of attention only decreases at its start position (i.e., fixation), resulting in relatively more attention at start and end positions before and after a shift, respectively. As the first two-dimensional imaging effort of covert attention shifts across peripheral locations, this study lays the foundation to characterize attentional properties at an unprecedentedly high spatiotemporal resolution.