Book Description

"Numerous studies have generated valuable data on the early visual system, but this information may be biased or at least incomplete since most studies have focused on terrestrial mammals. To better account for visual systems in different living environments and animal classes, we studied the function and structure of the early visual processing system of the archerfish, a species that is far removed evolutionarily from terrestrial mammals. To do so, we first studied what visual features guide attention in its early visual system. This was done by conducting search experiments on archerfish visual search in which its reaction time to detect a target against a backdrop of distractors that differed in their visual features from the target, was measured. If the archerfish detected the target quickly, independently of the number of distractors, this suggested that the visual feature was fundamental to its early visual system. We also compared the results to human performance in these experiments. We found that both species exhibit similar search behavior in terms of color, size, orientation and motion as well as in conjunction search tasks involving color and size. In contrast, performance differed between the two species on visual search tasks defined by shape. Next, to study how visual information is represented in the archerfish visual system we characterized the neural properties of the optic tectum, the main visual processing region in the fish brain. Receptive field structures were measured and linear non-linear cascades were used to analyze their properties. The findings indicated that the spatial receptive field structures lie on a continuum between circular and elliptical shapes. In addition, the cells' functional properties displayed a richness of response characteristics, since many cells could be captured by more than a single linear filter. Finally, the non-linear response functions that link linear filters and neuronal responses were found to be similar to the non-linear functions of models that describe terrestrial mammalian single cell activity. Overall, our findings illustrate the many functional and neuronal mechanism similarities between the archerfish and mammalian vertebrates and therefore suggest the existence of a universality in the visual system's processing algorithm across vertebrates."-- abstract.