Consciousness seems to have at its foundation the melding of information from all the senses into a integrated model of the world (and ourselves in it). It would be impossible to meld a sound with a sight, for example, without having a common framework of space and of time. And without the different senses informing one another, they would lose much of their usefulness. Therefore when we see melding of sensory information into a model, we can guess that there is a good probability that some level of consciousness exists. Two recent papers on fish show this sort of hint.
The first paper (Thompson, Vanwalleghem, Heap, Scott; Functional Profiles of Visual-, Auditory-, and Water Flow-Responsive Neurons in the Zebrafish Tectum; Current Biology 2016) shows that the tectum integrates sense information in a similar way to the human superior colliculus. “In order to function efficiently, fish and humans need a unified sensory view of the external world contributed to by multiple senses”, says Ethan Scott.
Using calcium imaging in transparent zebrafish, the dynamics of visual processing were shown to replicate previous studies. When sound or waterflow stimuli were used, a small number of cells in the tectum responded, similarly to the visual response but not showing the same cells. The visual response was somewhat less when other signals were present at the same time. This was similar to processes in the mammalian superior colliculus – information from various senses is integrated there.
The second paper (Schumacher, de Perera, Thenert, von der Emde; Cross-modal object recognition and dynamic weighting of sensory inputs in a fish; Proceedings of the National Academy of Sciences 2016) showed that fish can switch between senses as do monkeys, dophins, rats and humans.
The elephantnose fish explores objects in its surroundings by using its eyes or its electrical sense – sometimes both together. The skin contains numerous sensor organs that perceive objects in the water by means of the changed electrical field. “This is a case of active electrolocation, in principle the same as the active echolocation of bats, which use ultrasound to perceive a three- dimensional image of their environment.” Electrolocation is more useful at close range and vision is better at longer distances. The fish can, in effect, turn off one of the senses if the information from the other sense is more reliable.
Using darkness to force electrolocation and electrically transparent objects to force vision, the researchers could study the switching of the senses. They found that the fish could remember, find and recognize shapes experienced with one sense when using the other sense. They form a model of the space which could be used by either or both senses.
It seems that fish form a model of the their environment that all their senses can contribute to in an integrated way.