The speed of free will

Abstract

Do voluntary and task-driven shifts of attention have the same time course? In order to measure the time needed to voluntarily shift attention, we devised several novel visual search tasks that elicited multiple sequential attentional shifts. Participants could only respond correctly if they attended to the right place at the right time. In control conditions, search tasks were similar but participants were not required to shift attention in any order. Across five experiments, voluntary shifts of attention required 200–300 ms. Control conditions yielded estimates of 35–100 ms for task-driven shifts. We suggest that the slower speed of voluntary shifts reflects the “clock speed of free will”. Wishing to attend to something takes more time than shifting attention in response to sensory input.

Keywords:

• Selective attention
• Visual search
• Volition

Acknowledgments

We would like to thank Aude Oliva for graciously allowing us to use her eye tracker, Winston Chang and Barbara Hidalgo-Sotelo for assistance with setting up the eye-tracking experiments, and Naomi Kenner for piloting the eye-tracking experiments. We would also like to thank Ulrich Ansorge, Artem Belopolsky, David Rosenbaum, Shui-I Shih, Sandy Pollatsek, and an anonymous reviewer for helpful comments on various versions of the manuscript. This work was funded by Grant F49620–01–1–0071 from the Air Force Office of Scientific Research to J.M.W.

Notes

¹ Actually, Reeves and Sperling (1986) asked observers to report the first four letters they detected in the central stream. The order in which letters were reported was of interest to them. However, these effects are more germane for a discussion of visual memory; the time course results are similar whether one uses four letters or just the first letter.