Current Study
A simple behavioral tool to identify sensoryhyperexcitability is the Pattern Glare Test (PGT; Wilkins & Evans, 2001). Participants report visual illusions and sensationsdetected in static spatial gratings. Typical reports include illusory colors, stripes bending, moving, disappearing, blurring, andsensations of visual discomfort, such as pain and nausea (Evans & Stevenson, 2008; Wilkins et al., 1984). Higher numbers of illusions are reported when viewing the mid-range spatial frequency grating pattern, compared to the lower or high spatial frequency pattern, due to our visual systems being maximally sensitive between 1-5cpd (Campbell & Robson, 1968). Mid-range spatial frequencies tend to evoke a large metabolic response in the visual cortex that is even larger in those who are visually sensitive (Coutts et al., 2012; Huang et al., 2003). Certain clinical conditions such as those with migraine, stroke, autism, or synesthesia report higher numbers of illusions in the PGT and are all associated with a hyper-excitable cortex (Beasley & Davies, 2012; Fong et al., 2019, 2020; Harle et al., 2006; Ward et al., 2017). As a result, the illusions (i.e., visual perceptual distortions and sensations) induced by the PGT are thought to be due to excess cortical excitation in early visual cortex that spreads to neighboring parts of the cortex, creating the perception of illusions (Bargary et al., 2015; Evans & Stevenson, 2008). The relationship between the PGT and cortical hyperexcitability is so strong that the PGT is now being used to identify cortical hyperexcitability in other conditions such as major depressive disorder (Qi et al., 2019) and out-of-body experiences (Braithwaite et al., 2013). These illusions are not to be confused with visual hallucinations that manifest in the absence of external stimuli (Spencer & McCarley, 2005; Teeple et al., 2009).
Here, we used the PGT to test for behavioral evidence ofhyperexcitability as a function of schizotypy symptomatology in thenon-clinical population. Schizotypy refers to individuals in the general population that vary in schizotypal traits (Broyd et al., 2016; González-Rodríguez et al., 2021; Kwapil & Barrantes-Vidal, 2015). The non-clinical population is appealing because it avoids concerns related to the effects of antipsychotic medications (see Ettinger et al., 2015 for review; Kelemen et al., 2013), high schizotypy individuals have similar sensory profiles to SSD (Broyd et al., 2016; Moussa-Tooks et al., 2021; Myles et al., 2017; Nelson et al., 2013), and they are accessible.
Hyperexcitability predicts that individuals with higher schizotypy scores should report more illusions. If so, we can then examine whetherthe number of reported illusions loads on one or more factors of schizotypy symptomatology (e.g., cognitive perceptual, interpersonal, disorganization). Alternatively, hypore activity would be associated with reduced reports of illusions as a function of higher symptomatology. The value of clearer understanding of the pattern of behavior is to uncover links between anomalous sensory experiences and potential neural mechanisms in the pursuit of meaningful biomarkers in the SSD population.