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J Physiol Vol 272, Issue 2 pp 247-281
Copyright © 1977 by The Physiological Society
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The dynamics of the {Pi}1 colour mechanism: further evidence for two sites of adaptation

E. J. Augenstein and E. N. Pugh, Jr

1. The visual pathway that determines Stiles's {Pi}1 colour mechanism was isolated by the auxiliary field technique and studied under dynamic conditions of light adaptation and recovery by threshold measurements.

2. The time courses of adaptation to {Pi}1-equated short wave-length ≤ 500 nm) and long wave-length (µ ≥ 550 nm) fields are very distinct: a large and relatively long-enduring transient threshold elevation occurs at the onset of the long wave-length, but not of the short wave-length fields.

3. Similarly, the time courses of recovery from {Pi}1-equated long and short wave-length fields are quite distinctive: a large and relatively long enduring transient (`transient tritanopia') occurs at the offset of the long wave-length, but not of the short wave-length fields.

4. The wave-lengths of the fields which cause the adaptation transients coincide with those shown previously (Pugh, 1976) to combine non-additively with µ = 430 nm fields in effecting {Pi}1 adaptation. The failure of the time course of {Pi}1 adaptation to be spectrally `univariant' combines with the failures of field-additivity to demonstrate that signals from the long and/or middle wave-length sensitive cones affect the adaptation state of the {Pi}1 pathway.

5. The adaptation transients are not observed in the pathways that determine {Pi}4 and {Pi}5. Thus, instantaneous signals from the middle and/or long wave-length sensitive cones are not the cause of the transients. Rather the cause must lie in the path by which those cones transmit their signals to the {Pi}1 pathway or in the {Pi}1 pathway itself.

6. The off-transient can be diminished by adding an adequately intense short wave-length field to a long wave-length field that would normally cause it. The {Pi}1 pathway must receive chromatically opponent signals.




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M. S. Tibber and A. J. Shepherd
Transient Tritanopia in Migraine: Evidence for a Large-Field Retinal Abnormality in Blue-Yellow Opponent Pathways
Invest. Ophthalmol. Vis. Sci., November 1, 2006; 47(11): 5125 - 5131.
[Abstract] [Full Text] [PDF]




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