Gordon Bauer, Debborah E. Colbert, & Wendi Fellner
Two male Florida manatees, 13 and 15 years of age, are being tested with black and white grating stimuli (ronchi rulings) in a simultaneous discrimination procedure using a modified staircase method followed by the method of constant stimuli. Two 32 cm, square targets are presented on each trial. One target with 1 mm stripes serves as a standard on all trials. The other, variable target, the "to-be selected target," has broader stripes. Subjects swim toward the targets until they reach a divider extending 1 m from the targets, where they have to make a left or right choice based on binocular discrimination of the grating stimuli. Placement of targets is counterbalanced using Gellerman or Fellows scales. The most recent trials indicate that Hugh's visual acuity is over one degree of visual arc. Buffett's threshold appears to be better than 27' although a curvilinear (cubic) trend in the data makes this difficult to interpret. Testing is continuing in order to verify threshold.