Abstract
People with schizophrenia demonstrate impairments in predictive coding, particularly in laboratory tasks that assess high-level visual perception. However, it is unclear whether these abnormalities extend to the sensory level of vision. To date, only three studies have focused on retinal predictive processing within human subjects (Gowrisankaran et al., 2013; McAnany et al., 2013; McAnany & Alexander, 2009). This has been done through measurement of the omitted-stimulus response (OSR), which reflects the retinal response to an omission embedded within a highly repetitive stimulus train. The present study examined whether an OSR could be observed within human retinal activity to inform future studies focused on how these processes may be impaired in schizophrenia. Flash electroretinography (fERG) was recorded while eighteen subjects viewed a series of light flashes within two conditions: (1) a single-flash condition at 1.96 Hz and a luminance of 85 Td · s; and (2) a flicker condition at 28.3 Hz and a luminance of 16 Td · s. We examined the mean ERG waveforms of the retinal responses for present-stimulus and omitted-stimulus responses. Results demonstrated the absence of an OSR within the single-flash condition. We found the presence of a diminished (M=9.26) and delayed (Mdn=37.89) OSR peak within the flicker condition when compared to the present-stimulus amplitude (M=16.37) and implicit time (Mdn=29.70) measurements (t(17)=7.59, p<.001; z=2.12, p=.03, respectively). Additionally, OSR amplitude was highly correlated with number of flashes prior to first omission (rs=.56, p=.02). Overall, findings suggest that the retina elicits a response to an omitted stimulus embedded within a flicker train, although it is unclear whether this is representative of predictive or resonant activity. Additional studies are warranted to assess whether this activity is reduced in people with schizophrenia and whether it can serve as a marker of cortical predictive coding integrity.