Pupil size and dilation have been studied in relation to cognitive processing of visual information. For example, when subjects view ambiguous visual stimuli, pupil dilations were reported in anticipation of the rivalry switch and reflect the duration of perceptually rivalrous states (Einhäuser, Stout, Koch, & Carter,
2008). The emotional content in the visual stimulus might trigger a proportional pupil reaction as documented by Steinhauer, Boller, Zubin, and Pearlman (
1983) who showed that highly aversive or pleasant pictures were associated with large dilations. During visual-motor operations with a computer, the subject gains information about her task and thus changes her point of view, thinks of different goals, or modifies her scanpath or general behavior. This cognitive event (or task shift) is correlated with a series of abrupt pupil size enlargements over a period of time (Marshall,
2002; Marshall, Pleydell-Pearce, & Dickson,
2003). Task-evoked pupil dilations are widely reported in the literature (Beatty,
1982; Juris & Velden,
1977; Karatekin, Couperus, & Marcus,
2003) and the magnitude of the pupillary dilation appears to be a function of the cognitive workload and attention required to perform the task (see also Goldwater,
1972; Granholm, Asarnow, Sarkin, & Dykes,
1996; Hoecks & Levelt,
1993; Iqbal, Zheng, & Bailey,
2004; Janisse,
1977; Porter, Troscianko, & Gilchrist,
2007) and it could even reflect the general cognitive performance of individuals engaged in complex visual tasks (Verney, Granholm, & Marshall,
2004).