MENTAL ROTATION IN A CALIFORNIA SEA LION (ZALOPHUS-CALIFORNIANUS)

Mental rotation is a widely accepted concept that suggests an analogue mode of visual information-processing in certain visuospatial tasks. Typically, these tasks demand the discrimination between the image and mirror-image of rotated figures, for which human subjects need an inc reasing reaction time depending on the angular disparity between the r otated figures. In pigeons, tests of this kind yielded a time-independ ent rotational invariance, suggested as being the result of a non-anal ogue information-processing that has evolved in response to the horizo ntal plane that birds perceive from above while flying. Given that mar ine mammals use the water surface as the horizontal plane for orientat ion while diving, the ability of a California sea lion to mentally rot ate two-dimensional shapes was tested. Using a successive two-alternat ive matching-to-sample procedure, the animal had to decide between the image and mirror-image of a previously shown sample. Both stimuli wer e rotated by a multiple of 30 degrees with respect to the sample. The animal's reaction time was measured by a computer-controlled touch-scr een device, rewarding the animal for pressing its snout against the st imulus matching the sample. A linear regression analysis of the animal 's mean reaction time against the angular rotation of the stimulus yie lded a significant correlation coefficient. Thus, the present data can be explained by the mental rotation model, predicting an image-like r epresentation of visual stimuli in this species, The present results t herefore correspond well with those found for human subjects, but are inconsistent with the data reported for pigeons.