Comparing Methods for Analysis of Pupillary Response

Changes in eye-pupil size index a range of cognitive processes. However, variation exists in the protocols to analyse such data in the psychological literature. This raises the question of whether different approaches to pupillary response data influence the outcome of its analysis. To address this question, four methods of analysis were compared, using pupillary responses to sexually appetitive visual content as example data. These methods comprised analysis of unadjusted (raw) pupillary response data, z-scored data, percentage change data, and data transformed by a pre-stimulus baseline correction. Across two experiments, these methods yielded near-identical outcomes, leading to similar conclusions. This suggests that the range of approaches that are employed in the psychological literature to analyse pupillary response data do not fundamentally influence the outcome of its analysis. However, some systematic carry-over effects were observed when a pre-stimulus baseline correction was applied, whereby dilation effects from an arousing target on one trial were still influencing pupil size on the next trial. This indicates that the appropriate application of this analysis may require additional information, such as prior knowledge of the duration of carry-over effects.