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Brandi Emerick, Tom Busey, Brian O'Donnell; Using SSVEPs to measure brain responses of chronic cannabis users and nonusers to during a visual recognition task . Journal of Vision 2016;16(12):530. doi: 10.1167/16.12.530.
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© 2017 Association for Research in Vision and Ophthalmology.
Much of the previous research on the effects of cannabis has focused on memory and executive function. Less is known about how cannabis affects visual perception. However, there are cannabinoid receptors in the retina, thalamus, and visual cortex (Schwitzer et al., 2014), and cannabis users frequently report changes in sensory perception (Green, Kavanagh, & Young, 2003). To determine whether chronic cannabis use affects how individuals attend to and recognize images, we used EEG to record steady-state visual evoked potentials (SSVEPs) during a visual recognition task. Images were degraded using Photoshop and embedded within visual noise to make recognition challenging. Two presentation frequencies were used to frequency-tag image and noise, allowing us to track the strength of brain responses to image and noise separately throughout recognition, despite image and noise being superimposed. In half the trials, images were flickered at 6.67 Hz and noise at 8.57 Hz, and image and noise were presented at 8.57 Hz and 6.67 Hz, respectively, for the other half. Participants were instructed to press a button once they recognized the image and to do their best to attend to images and ignore noise during the entire trial. Chronic cannabis users and nonusers showed qualitatively similar responses: SSVEPs to image and noise were typically greater after the image was recognized, and responses to image were generally stronger than responses to noise (likely due to the instruction to attend to image and ignore noise). However, SSVEPs recorded from chronic users were weaker than the responses from nonusers in many cases. Also, the difference between response strength for image versus noise was sometimes greater for nonusers. Results suggest that chronic cannabis use may affect one's ability to ignore noise and attend selectively to images, but this is somewhat dependent on presentation frequency and electrode location.
Meeting abstract presented at VSS 2016
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