Week 7. What’s suppressed during saccades?
– M and P pathway –
Hunjae Lee (VCC Lab)
Suppression of the magnocellular pathway during saccades has robust evidences since the research that unveils saccades in detail with analysis about saccadic time course and the effect of contrast backward / forward / simultaneous masking (Burr et al, 1994). On the other hand, recent experiment that shows even the stimuli under saccadic omission promotes a shape contrast illusion, suggesting something is still survived and processed in later stage after saccadic suppression of relatively early stage like LGN (Watson et al, 2009).
One possibility to break those conflicts is that higher brain area such as parietal and prefrontal cortices which is known to reflect our visual awareness (eg. Binocular rivalry, AB, CB and so on) also take some rolls in suppressing visual stimuli during saccades. fMRI data from humans’ eye blinking is supporting this hypothesis (Bristow et al, 2005). However Burr stick to saccadic suppression of M pathway in LGN, explaining that opposed phenomena can be result from reduced activity in early visual cortex that transmit information to parietal and prefrontal cortices (Burr, 2005).
At this very point, we can make a critical question about what suppressed during saccades with the same logic of Burr. If P pathway is relatively unimpaired compared to M pathway, ventral stream that wired mainly with P path has to be okay, while dorsal stream is under saccadic suppression and omission. Unlike this assumption, the average strength of the shape contrast illusion can vary with whether the inducer has seen or unseen, that implicating P pathway is affected somewhat by saccadic suppression (Watson et al, 2009). With this complex and interaction of two suppressions of distinct each two pathway, saccades seem to be reasonable that show various weird visual phenomena such as saccadic remapping, compression or mislocalization (Ross et al, 2001), that is kind of striving for visual stability but sometimes failure of it.
Besides things that are suppressed during saccades, the question about stage of saccadic suppression is still remained in this essay (Early at LGN, Burr et al, 1994; Later position-invariant at superior temporal sulcus or inferotemporal cortex, Watson et al, 2009). One idea to investigate this question pops up from studying saccades with comparing temporal masking (Ibbotson, 2009). Recording saccadic suppression and enhancement along the time course with differently manipulated stimuli such as color, shape, contrast, frequency, we may explore both M and P pathway more and where and what about suppression.
Ross, J., Morrone, M.C., Goldberg, M.E., and Burr, D.C. (2001). Changes in visual perception at the time of saccades. Trends in Neuroscience. 24, 113-121.
Burr, D. (2005). Vision: in the blink of an eye. Current Biology 15(14): R554-6.
Bristow, D., J. D. Haynes, et al. (2005). Blinking suppresses the neural response to unchanging retinal stimulation. Current Biology 15 (14): 1296-300.
Burr, D. C., M. C. Morrone, et al. (1994). Selective suppression of the magnocellular visual pathway during saccadic eye movements. Nature 371 (6497): 511-3.
Watson, T.L., and Krekelberg, B. (2009). The relationship between saccadic suppression and perceptual stability. Current Biology. 19, 1040–1043