Measuring the Task-evoked Pupillary Response with a Remote Eye Tracker

Jeff Klingner

Stanford University

Rakshit Kumar

Stanford University

Pat Hanrahan

Stanford University

Proceedings of the 2008 Symposium on Eye Tracking Research & Applications


The pupil-measuring capability of video eye trackers can detect the task-evoked pupillary response: subtle changes in pupil size which indicate cognitive load. We performed several experiments to measure cognitive load using a remote video eye tracker, which demonstrate two extensions to current research in this area. First, we show that cognitive pupillometry can be extended from head-mounted to remote eye tracking systems. Second, we demonstrate the feasibility of a more fine-grained approach to analyzing pupil size data gathered with an eye tracker, which provides more detail about the timing and magnitude of changes in cognitive load.

Figure 1: Pupillary response during the mental multiplication task. There is a small (0.1 mm) increase in pupil size as the multiplicand is committed to short term memory and a larger, longer-lasting increase after the subjects hear the multiplier and begin computing the product. The graph on the left is from Ahern and Beatty [1979], reprinted with permission from AAAS. The graph on the right shows the results from our replication of their experiment. The two graphs are aligned and plotted at the same scale. Although we gave problems at all three difficulties, the easy level was the only one for which we collected sufficient correct responses for analysis. The pupillary response we observed for these easy problems resembles the prior result for medium and difficult problems. We speculate that students in 1979 had more practice with mental arithmetic.


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  author = {Klingner, Jeff and Kumar, Rakshit and Hanrahan, Pat},
  title = {Measuring the task-evoked pupillary response with a remote eye tracker},
  booktitle = {ETRA '08: Proceedings of the 2008 symposium on Eye tracking research & applications},
  year = {2008},
  isbn = {978-1-59593-982-1},
  pages = {69--72},
  location = {Savannah, Georgia},
  doi = {10.1145/1344471.1344489},
  publisher = {ACM},
  address = {New York, NY, USA},