The sensory system of an octopus is very complex. Cephalopod brains, having evolved from a completely different branch of Eukaryota than humans, demonstrate a different structure of intelligent life. Their central brain, in control of the octopus’s wants and needs, sends signals to the clusters of neurons in the arms which carry out solutions to the wants and needs by sending its own motor and sensory signals to the effector nerves, bypassing the brain.
Approximately two thirds of the central brain is used for optical processing and sight alone. Octopus's eyes are similar to ours in terms of the lens and retina, except the cornea (1) of cephalopods is on top of the nerve fibres (2). Humans also have a blindspot (4) whereas octopuses don't.
The similarity between human and octopus eyes is an example of convergent evolution.
Octopuses are cery sensitive to light. It’s even thought that they can perceive light through their skin, suggested in a study where light was shone onto an octopus’s limb. 84% of the time, the limb would retract without the octopus seeing the light with its eyes.
An octopus’s sense of smell, however, is very different to ours. In fact, their method of taste and smell is so different that we would never be able to accurately imagine how an octopus feels these sensations. They use sensory nerves on their arms to gage a scent, even smelling predators from quite a distance and increasing the time it has to disguise itself or escape.
One sense they don’t rely on is their hearing. They have no structures that can detect sound like we can. It is likely they focus on the vibrations in water. In one study, scientists noticed octopuses elicited a response with sound frequencies varying between 400Hz and 1000Hz (the average human can hear frequencies between 20Hz to 20,000Hz). Vibration sensing can help to identify the calls of other animals, alongside their highly developed sense of taste and smell.
Being able to taste so well makes the octopus a picky eater. For all cephalopods, their main source of food is protein from dieting on crustaceans, other molluscs and fish.
REFERENCES
https://octonation.com/octopus-vulgaris-eyes/
The Eyes Of The Octopus Vulgaris: Let's take a peek!
OctoNation
(Year Unknown)
https://www.scientificamerican.com/article/the-mind-of-an-octopus/
The Mind of an Octopus
Peter Godfrey-Smith
January 2017
Date published: 30th July 2023
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