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1 colour mechanism: further evidence for two sites of adaptation
1. The visual pathway that determines Stiles's
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
1-equated short wave-length (µ
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
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
1 adaptation. The failure of the time course of
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
1 pathway.
5. The adaptation transients are not observed in the pathways that determine
4 and
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
1 pathway or in the
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
1 pathway must receive chromatically opponent signals.
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