If a tree falls in the forest and no one there is there to hear it, does it make a sound? This is a traditional philosophical puzzle. The basic idea may be altered a bit. If perceptions of a tree (i.e., vision, hearing, and smell) cease in the forest when there is no one there to perceive the tree, can it still be said to exist? Whether it can be apprehended by the senses depends on one’s perceptual accruements of the seemingly material world: vision, hearing, smell, etc.. Most people would loudly proclaim “Yes!” to the tree’s existence, whether the tree is perceived or not.
A fully grown tree is easy to see, a healthy living thing secure deep in the ground. If someone walked away from the tree, would it be there while we are gone? As the wind blows, would the rustling of leaves still occur? If you walked away from roses, would they still smell sweet? If a newly planted tree is removed, we could not know it was removed unless we were there to perceive it. With normal vision, hearing and smell, the apparent displacement of the tree could be known.
Function and structure are intimately related. The perceptual state of the sensory apparatus depends on its structure (e.g., shape of the sensory organs, the nerves, and the health of the brain). If an external thing is known by an individual’s sensory activity, then this structure determines its nature: vision, sound, smell, cognition. A tree is said to exist by virtue of the dual dynamic of how it presents itself to another and as well as a thing in itself.
One would think that with the senses, the understanding of the tree, and the trees presentation to the world, can be easily understood through smell, vision, hearing, and cognition. This is not so because sensation is subject to the object of sensation, (the tree); through smell, vision, hearing, cognition, as well as a dynamic of all the senses acting together. This perception of the tree is transient and fleeting and therefore depends on the sense organs themselves acting together. The brain steps in to finally integrate the stimuli.
Vision is dependent on reception of light rays and the ear in modulation of vibration that travels through the air. Smell is the result of the air and its aromatic piggyback which stimulates the nose. There are the nerves in the sense organs which are forever in a state of flux. These types of perceptions depend on the nature of the relationship between the world and the sensory apparatus involved in the perception. Does the world show itself to another in a hard exact way? Is this understanding of the perceivers sense organs reliable? Can the receiver of the stimulus find its sensory accruements a reliable marker of an external reality?
Flies and bees see the world in very different ways than humans. A fly has a multitude of “eyes” which contribute toward an individual dynamic. A bee has different individual eyes. People depend on particular singular eye type with different assortments of rods and cones. These structures absorb the worlds light into different colours (or the lack of all colours if absent) resulting in different sorts of visual stimulation. As these perceptions differ, the external reality does not change. While the bee may perceive some things in the world differently (e.g., the tree), the thing perceived in itself does not change.
What is to be considered ones healthy vision? It is when one sees the rods and cones move the light impulses through nerves to the brain. Through this process one can enjoy the advantages of having excellent perception if the assortment of rods and cones are “normal.” But who can say what excellent perception is? What we see depends on the number and assortment of rods and cones.
For example, some people with less rods and cones may not enjoy the span of colours, and therefore be considered colour blind. While lacking to some degree colour, the vision could still have more acuity. Is this then a defect? Rods and cones that exist in the “optimal” range of vision, are dictated by inheritance.
In its representation of the external reality (e.g., the tree); the perceiver, may be claimed to be a direct recipient of the matter of the external thing. This thought is erroneous. The tree can only be known through the mediation of the senses. The trees bark is not flying into our eyes when seen. The tree taken as representing how this tree shows itself to the world would be considered normal vision with the appropriate distribution of rods and cones. This is assumed through common sense!
What about an eye which possesses additional rod and cone assortments? Also perhaps the assortment is different. This does happen, and therefore one perceives the world in different ways sometimes with particular advantages. With more acuity, the vision enables an environmental advantage. Evolution drives structure through function. If an organism sensory receptors become obsolete, the organism perishes or the senses go through necessary changes to adapt and survive.
Are a particular assortment of rods and cones representative of the external reality (e.g., the tree)? Who is to say any of these three different assortments of rods and cones (e.g., colour blindness, normal vision, and other idiosyncratic vision types) are superior to another? Different types of perceptions of the tree cannot be said to all reside in the tree itself. Ultimately to claim so implies a view from nowhere.
Clearly there are different dynamics involving acuity in vision, hearing and smell in its presentation to the human brain. If a thing exists, such as a tree, if we can know if it exists at all, it does not present itself to the world as it exists in itself. Rather when presenting itself for another it only stands in opposition. Further there may not be much more to say about the tree than to ask if it exists at all. More directly is how can we know?
It is counterintuitive to find that something perceived does not exist. Yet one can think of mirages in the desert or even mistaking a tadpole for a fish. The understanding of the object varies depending on the perception of the object, the “weight”on the perception. The way it present itself to the world differs, depending on the type of sense organ, the acuity of the organ, the species of the sense organs as well as brain health. Since these perceptions are ultimately rooted in the brain, the perception can also vary depending on damage or illness to the brain. For example Traumatic Brain Injury (TBI) can result in sensory abnormalities as noted by the Center for Disease Control https://www.cdc.gov/traumatic-brain-injury/about/potential-effects.html
Suffice it to say that our senses are reliable as shown by the advantages we acquire in the world as the result of evolution. It is less a question of are our senses reliable, but rather do we understand how they confer us access to the world?