Pupil Frequency Tagging: an on-line measure of visual attention
24.26, Saturday, May 11, 2:30 - 4:15 pm, Royal Ballroom 4-5
Marnix Naber1, George Alvarez1, Ken Nakayama1; 1Vision Sciences Laboratory, Department of Psychology, Harvard University
The muscles that control the pupil are richly innervated by the autonomic nervous system. While there are central pathways which modulate pupil size in relation to arousal, there is no anatomical evidence that centers involved with higher order cognition innervate the pupil. In this study, we show that such connections must exist and that they reflect the operation of visual selective attention. In our first study observers gazed at a fixation point while they attended one of four separate objects. Each object had a distinct location and flicker frequency (1.50, 1.75, 2.00, and 2.25Hz). Results showed that the frequency of the attended object was selectively enhanced in the pupil response dynamics. In the second experiment, our aim was to show that we could predict behavioral performance from the frequency tagged response. Here we had subjects centrally fixate while tracking a slowly moving flickering disk (2Hz). A stream of changing letters was superimposed on the disk and observers were instructed to hit a button whenever the target letter "x" was shown. Improved detection of the "x" was correlated with increased amplitude of the pupillary response. These surprising results taken together show that pupil responses closely follow the allocation and strength of focal visual attention. They provide a new opportunity to study visual attention and also invite investigation as to the pathways and mechanisms of this phenomena.