. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. spatial frequency (cycles/degree) spatial frequency (cycles/degree) Figure 4. Contrast as a function of spatial frequency for an object viewed from a distance of 5 m (modulation transfer function. MTFl. The contrast is normalized by the contrast at a distance of 0 m. (A) Coastal water at 5-m depth. (B) Oceanic water at 5-m depth. 1C) Oceanic water at 210-m depth. (D) Oceanic water at 800-m depth. The MTF is shown for two visual systems, one with resolution and one with ° resolution. At a spatial frequency of approxim
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. spatial frequency (cycles/degree) spatial frequency (cycles/degree) Figure 4. Contrast as a function of spatial frequency for an object viewed from a distance of 5 m (modulation transfer function. MTFl. The contrast is normalized by the contrast at a distance of 0 m. (A) Coastal water at 5-m depth. (B) Oceanic water at 5-m depth. 1C) Oceanic water at 210-m depth. (D) Oceanic water at 800-m depth. The MTF is shown for two visual systems, one with resolution and one with ° resolution. At a spatial frequency of approximately cycles/deg. the data split, with the lower trace denoting ° resolution. The two gray lines in (A) denote the MTF for the eyes alone. Because the MTF at 0 cycles/deg is important, the graphs include this point despite being logarithmic. Discussion This study shows that a counterilluminating individual faces a number of difficulties. First, an acute eye (° resolution) with moderate contrast sensitivity (33%) can detect the photophore patterns of both Ahnilia verunyi and Ceratoscopelus nwderensis at distances greater than 1 m. Second, even the water at the relatively turbid shallow coastal site blurred the counterillumination signals very little. Although all four water types did lower the overall contrast of the counterilluminator, the attenuation rate was quite low. particularly at mesopelagic (>200 m) depths. Finally, the spectrum of downwelling background light var- ied considerably with depth in the mesopelagic zone and was strongly affected by the source of nocturnal illumina- tion at the shallow depths. This suggests that counterillu- minating photophores must be spaced closely together when viewed by visually acute species, and that matching the background spectrum may be more difficult than previously considered. From the predator's point of view, this study suggests that high spatial resolution and color discrimina- tion in the blue-green portion o
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
