8/16/2023 0 Comments Hoy eyeconnectChanges in either of these variables can produce strong light reflexes that modulate pupil size by as much as 50 % ( Miller & Newman, 2005 Loewenfeld, 1993). The pupil diameter depends first and foremost on the luminance of the stimulus and the ambient illuminance of the experimental room. Most researchers are aware of the most serious confound-the pupillary light reflex. Pupil data can be collected inexpensively and noninvasively by most modern image-based eye-tracking systems, but researchers often underestimate the methodological challenges in producing well-controlled studies that allow for cognitive interpretations of the pupillary response ( Holmqvist et al., 2011). As a result of these recent developments, pupil size is increasingly being used by cognitive scientists as an important measure of cognitive processing. While the underlying mechanisms that drive cognitive pupillary effects are still an active topic of inquiry, recent data suggests that the pupillary response may reflect noradrenergic activity in the brain ( Murphy, O’Connell, O’Sullivan, Robertson, & Balsters, 2014 Aston-Jones & Cohen, 2005 Koss, 1986 Samuels & Szabadi, 2008). The human pupillary response correlates with a wide range of important cognitive variables including mental workload (e.g., Hess & Polt, 1964 Kahneman, 1973, Klingner, Tversky, & Hanrahan, 2011), emotional valence ( Partala & Surakka, 2003), attention ( Beatty, 1982), working memory ( Beatty & Kahneman, 1966), arousal ( Murphy, Robertson, Balsters, & O’Connell, 2011), decision-making ( Einhäuser, Koch, & Carter, 2010), surprise ( Preuschoff, Marius, & Einhäuser, 2011), and uncertainty ( Nassar et al., 2012). The model reduced the root mean squared error of pupil measurements by 82.5 % when the model parameters were pre-set to the physical layout dimensions, and by 97.5 % when they were optimized to fit the empirical error surface. The measured PFE was corrected by a geometric model that expressed the foreshortening of the pupil area as a function of the cosine of the angle between the eye-to-camera axis and the eye-to-stimulus axis. Large, systematic deviations in pupil size were observed across all nine maps. A grid-based map of pupil measurements was recorded with each artificial eye across three experimental layouts of the eye-tracking camera and display. Three artificial eyes with different fixed pupil sizes were used to systematically measure changes in pupil size as a function of gaze position with a desktop EyeLink 1000 tracker. Here we systematically map PFE using an artificial eye model and then apply a geometric model correction. One serious confound that is often not properly controlled is pupil foreshortening error (PFE)-the foreshortening of the pupil image as the eye rotates away from the camera. Despite the relative ease of data collection and increasing prevalence of pupil data in the cognitive literature, researchers often underestimate the methodological challenges associated with controlling for confounds that can result in misinterpretation of their data. Pupil data can be recorded inexpensively and non-invasively by many commonly used video-based eye-tracking cameras. Pupil size is correlated with a wide variety of important cognitive variables and is increasingly being used by cognitive scientists.
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