Figure 2.

Pupillary assessment of spatial focal attention. (A) Procedure of Experiment 2. Observers fixated at the screen center and counted the number of times the attended object flipped upside down. Each quadrant had an object within a white rectangle that flickered off-and-on at a separate frequency (1.5, 1.75, 2.0, and 2.25 Hz). (B) Example of an observer's pupil size during a single trial (black). The four flickering stimuli induced continuous pupil oscillations. (C) Example of a single trial FFT power spectrum analysis of the pupil trace in (B). The four peaks at the presented frequency indicate that each quadrant left an oscillatory trace in the pupil. In this trial, the observer specifically attended an object that flickered at 1.75 Hz. This frequency was the strongest represented oscillation in the pupil trace. (D) FFT Power values for attended frequencies as a function of power averaged across the unattended frequencies. Each data point represents the average power for an individual observer at a particular target frequency (see colored markers). Attended frequencies reliably induced enhanced pupil oscillations amplitudes as compared to unattended frequencies across observers. (E) Average FFT power spectrum analysis across observers as a function of attended frequency (see colors). Attended frequencies induced significantly higher power values than unattended frequencies (^*p < 0.05, ^***p < 0.001).