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Published clinical evidence has led us to hypothesize that there are parallel pathways which lead to the striate (V1) and prestriate cortex in the human brain. We have used the technique of visually evoked EEG coupled to magnetoencephalography (MEG) to test our hypothesis, by detecting the timing of arrival of signals into these visual areas, using published PET evidence to guide us in the location of the evoked response sources. We found that, if the moving stimulus has a speed of 22 degrees s-1, signals arrive in V5 before V1; with speeds of < 6 degrees s-1, signals arrive in V1 first. We conclude that, in addition to the classical picture of a sequential input to prestriate cortex through V1, there is also a fast parallel input which by-passes V1. The parallelism manifests itself only as a function of the characteristics of the visual stimulus, a phenomenon we describe as dynamic parallelism. The results obtained help us explain the residual motion vision of patients with lesions in V1 or V5.
ffytche et al. (Sun,) studied this question.