Contrast sensitivity in a harbor seal (Phoca vitulina)
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In this study, the contrast sensitivity function (CSF) of one harbor seal was determined behaviorally in a go-/no-go-experiment at an ambient light of 0.9 lx in air. Contrast sensitivity was assessed as the reciprocal value of the threshold contrast for spatial frequencies varying between 0.03 and 1.5 cycles/deg, which were displayed with contrast ranging from 0.02 to 1 on a TFT monitor with a mean luminance of 3.8 cd/m². The CSF of the harbor seal shows the general characteristics described for other species with a peak at an intermediate frequency, a low frequency roll-off and a high frequency cut-off towards the harbor seal’s resolution limit determined in a previous study. The position of the CSF’s peak lies at approximately 0.5 cycles/deg and adopts an absolute height of 40. These results compare well with the cat’s CSF assessed at a comparable adaptation light which might reflect similarities in lifestyle and optics.
KeywordsHarbor seal Phoca vitulina Vision Contrast sensitivity Resolution
The authors would like to acknowledge the valuable help of Viljami Salmela (Helsinki, Finland). Thanks is also expressed to Sophie Fiedler for assistance during data collection and to Christopher D. Marshall (Galveston, TX, USA) for critically reading the manuscript. This study was financially supported by a grant of the Studienstiftung des deutschen Volkes (2005 SA 0969) to FDH and of the Deutsche Forschungsgemeinschaft (SFB 509, DE 538/10-1) as well as the Volkswagenstiftung to GD. The experiments are in line with the current German law on the protection of animals.
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