Measuring visual discomfort — a novel two-step method for reducing criterion effects when measuring subjective responses

Visual discomfort is a subjective experience, like many attributes of interest in the field of psychology. Measuring subjective phenomena can be difficult, as there is no ground truth against which to calibrate judgements. There is also a trade-off between the quality of the data and the time and effort of the participant - greater time investment should result in better data. However, whilst long, complex experiments might be possible in controlled lab settings with few observers, it becomes a barrier when attempting to estimate visual discomfort in less controlled but more ecologically valid spaces, and when investigating individual differences, for example young people and clinical populations. It is also difficult to calibrate judgements between participants due to individual variation in criterion - the idiosyncratic mapping of discomfort onto responses. We propose an intuitive method for participants to reduce criterion effects. This method maximises the amount of information gathered in a short space of time, and limits the risk of apparently estimating "discomfort" when the individual does not experience it. We apply this method to test two theoretical contributions to visual discomfort - cortical hyperexcitability (from spatial frequency (f), corresponding to stripe thickness) and ambiguous motion signals (from phase modulation wavelength (μ) corresponding to stripe waviness). Participants gave binary estimations that were used to scale their magnitude estimations. Using Bayesian methods, both these factors were found to affect discomfort judgements in both controlled lab environments (34 observers) and real-world estimations (47 observers).