The visual acuity describes how thin a stripe of a stripe pattern can be in order to be resolved as a single item. The contrast sensitivity further takes the contrast of the stripe pattern into account. The contrast is important as it has been shown in all species analysed so far that e. g. if a stripe can be easily resolved because it is very broad it cannot be detected anymore if the contrast is only slightly reduced. We measured the contrast sensitivity curve of our harbour seals, and it generally resembles those of other animals and differs only in the position and the height of the maximum (Hanke et al. 2011).
In this video seal Sam shows how the contrast sensitivity function was determined at the Marine Science Center. If a stripe pattern with a defined stripe width and defined contrast is present on the monitor the experimental animal is required to move its snout to the response target on the right side. However, if the monitor appears grey (mean grey value of the stripe pattern) then the animal has to remain stationary. The experiments were conducted in an experimental chamber that was opened for demonstration purposes which led to reflections on the monitor.