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Oren Yehezkel, Anna Sterkin, Uri Polat; Do the same lateral interactions support collinear facilitation and binocular summation?. Journal of Vision 2009;9(8):264. doi: 10.1167/9.8.264.
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© ARVO (1962-2015); The Authors (2016-present)
The two key components of the early visual processing architecture are ocular dominance columns (domains driven by either the left or right eye) and orientation preference domains that are selectively activated by a particular stimulus orientation. The pattern of these two circuits is shaped by selective local and long-range (tangential) lateral connections and is sensitive to changes in stimulus contrast and context manipulation with different levels of saturation.
In this study we recorded Event-Related Potenlials (ERPs) in 9 healthy volunteers in order to find the neuronal correlated of binocular processing of stimuli of similar orientation but with either similar or different contrast presented to the two eyes simultaneously. Our previous studies provided evidence for N1 peak amplitude modulation in by collinear context (Sterkin et al., 2008). Moreover, we also found a robust correlation between N1 peak amplitude and backward masking effect (Sterkin et al., 2007). Here we measured the latency and amplitude of P1 and N1 peaks (mean latencies of 219 and 278 ms, respectively) in ERPs using vertically orientated Gabor patches (GPs) of low (7%) and high (20%) contrast that were presented using either binocular, monocular or dichoptic stimulation, yielding a total of 8 conditions.
Saturation in P1 amplitude but not in latency was observed. Moreover, N1 amplitude was affected by robust contrast changes with no saturation in latency. Thus, changes in the P1 amplitude reflect binocular summation, whereas N1 amplitude are sensitive to contrast changes per se, indicating that P1 and N1 amplitude represent activity of different cortical sources and arguing against consecutive processing. Our results suggest that earlier P1 modulation reflects local processing, whereas later N1 effects underlie processes that are activated at a certain contrast threshold and initiate the spread of activity to other populations and horizontal summation.
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