Failed to get the word of reasoning: therefore

"visual evoked potentials (VEPs)" is itself physiologic (or is itself both physiologic and psychological - that is, a psychological phenomenon has its physiological base), thus, "therefore" should be removed from the sentence "VEPs therefore do not allow separating psychogenic blindness from organic disruption of the visual pathway."

What do you think?

Context:

Sight and blindness in the same person: Gating in the visual system.

Abstract

We present the case of a patient having dissociative identity disorder (DID) who-after 15 years of misdiagnosed cortical blindness-step-by-step regained sight during psychotherapeutic treatment. At first only a few personality states regained vision whereas others remained blind. This could be confirmed by electrophysiological measurement, in which visual evoked potentials (VEPs) were absent in the blind personality states but were normal and stable in the seeing states. A switch between these states could happen within seconds. We assume a top-down modulation of activity in the primary visual pathway as a neural basis of such psychogenic blindness, possibly at the level of the thalamus. VEPs therefore do not allow separating psychogenic blindness from organic disruption of the visual pathway. In summary, psychogenic blindness seems to suppress visual information at an early neural stage.

More:
http://www.ncbi.nlm.nih.gov/pubmed/26468893