Light-adaptation properties of the ultraviolet-sensitive cone mechanism in comparison to the other receptor mechanisms of goldfish.
The light-adaptation properties of goldfish photoreceptor mechanisms were examined using Stiles' two-color threshold technique. Threshold vs. background intensity (TVI) curves were determined for isolated cone and rod mechanisms using the heart-rate conditioning technique. The principal aim of this study was to compare the light-adaptation properties of the ultraviolet (UV)-sensitive cone mechanism to the other receptor mechanisms of goldfish. This examination revealed several striking functional differences: (1) The UV-sensitive cone mechanism threshold vs. background intensity (TVI) exhibited a slope of 0.65 (compared to the approximate 1.0 for the other cone mechanisms on a log/log plot) and thus was not in accordance with Weber's law. This may in part be related to the intrusion of the blue-sensitive mechanism at the upper radiance range. (2) The operation of the UV-sensitive cone mechanism was limited to intermediate intensities (i.e. not very dim or bright). (3) The UV-sensitive cone mechanism exhibited a Weber fraction or luminance contrast threshold of 0.316 that was approximately six times larger than the other cone mechanisms but comparable to the rod mechanism. This indicates that the UV-sensitive cone mechanism performs relatively poorly in terms of brightness contrast detection.
Hawryshyn
C W
CW
Department of Biology, University of Victoria, British Columbia, Canada.
D000221:Adaptation, Ocular / Q000502:physiology*; D000818:Animals; D006054:Goldfish; D008027:Light; D010786:Photoreceptor Cells / Q000502:physiology*; D012684:Sensory Thresholds; D014466:Ultraviolet Rays; D014787:Vision Tests