Pupil dilation meaning3/10/2023 ![]() Few trials (circa 5%) were discounted after visual inspection of the pupil waveform for excessive blinking. The corresponding affected parts of the pupil record were recovered with cubic interpolation. Eye blink artifacts detected by the eye tracking software were automatically removed from the pupil data. The EyeLink 1000 head supported eye-tracker system ( ) that has a temporal resolution of 1000 Hz was used to track eye position and collect pupil diameter. The booth contained a chair and desk with the stimulus monitor and the eye-tracker apparatus. ![]() Subjects performed the experiments in a booth that isolated them from the surrounding laboratory. This was to avoid the mechanical muscle saturation at the two extremes of the pupil size where a significant amount of input excitation may generate undetectable pupil responses. In both experiments, the stimulus computer monitor was the only source of illumination in the environment surrounding the subject, consequently, the pupil operated approximately in the middle of the iris muscle length–tension curve where the relationship between excitation and amount of muscle response is linear. Two experiments were designed to examine the pupil responses associated with object detection under visual search conditions with limited image viewing time. This result differs from that of Hakerem and Sutton ( 1966) where dilations were not reported for the same condition. Under these conditions, we found that pupil dilation was associated with target detection even when subjects were not required to make an overt discrimination. Using the RSVP protocol, we have recorded the pupillary response during visual search with complex imagery. The rapid serial visual presentation protocol, RSVP, with a central fixation point is intended to simulate the rapid alternation of foveated regions of interest during normal viewing conditions while eliminating several complications due to tracking the pupil size during eye movements. Each fixation involves bottom-up signal processing and top-down higher level operations such as semantic binding and symbolic association of visual memory, which are basic to recognition (Privitera & Stark, 2003 Stark et al., 2001). Eye movements drive the fovea to fixate each part of a scene to enable processing with high resolution. Normal visual search in natural active looking is a complex set of component processes that may be compartmentalized into two interleaving phases of scanning and detection (Privitera & Stark, 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). 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). 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. ![]() ![]() 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. 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). Pupil size and dilation have been studied in relation to cognitive processing of visual information.
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