Archive for 09/11/2010

The clock speed of perceptual experience

Horowitz and group investigated the timing of attention shifts with a number of clever experiments aimed at separating the contributions to the total time of elements of attention shifts.

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.

I find this an excellent investigation except for the characterization ‘clock speed of free will’. They do describe this time in other words in the General Discussion.

It is possible to overrule this autonomous agent and select the next object of attention. This volitional deployment is much slower than the autonomous, priority-driven mode. We propose that the slower rate reflects the “clock speed of free will”. It might also reflect the clock speed of perceptual experience. Even if we can search through a display at 20-40 items/second, we do not experience 20-40 discrete selection events. We experience the search and its outcome but the rapid autonomous deployments of attention that are revealed by experiments are not available to consciousness. (underline added)

The ideas of free will and perceptual experience are distinct and different, very much so. The group’s careful experiments clearly showed a clock speed for perceptual experience and not for free will (whatever that is – as they do not define their use of the term). Scientists should be very careful about using terms with very wide range of meanings, in this case meanings ranging from the supernatural to the trivially mundane. It would also be wise to avoid terms that carry emotional, philosophical and political baggage unless this baggage is going to be ‘unpacked’.
Horowitz, T., Wolfe, J., Alvarez, G., Cohen, M., & Kuzmova, Y. (2009). The speed of free will The Quarterly Journal of Experimental Psychology, 62 (11), 2262-2288 DOI: 10.1080/17470210902732155