Direct realists might claim that indirect realists are confused about conventional idioms that may refer to perception. Perception exemplifies unmediated contact with the external world; examples of indirect perception might be seeing a photograph, or hearing a recorded voice. Against representationalists, direct realists often argue that the complex neurophysical processes by which we perceive objects do not entail indirect perception. These processes merely establish the complex route by which direct awareness of the world arrives. The inference from such a route to indirectness may be an instance of the genetic fallacy.
Direct realism proposes no physical theory of experience and does not identify experience with the experience of quantum phenomena or with the twin retinal images. This lack of supervenience of experience on the physical world means that direct realism is not a physical theory.
One of Reid's simplest arguments posits that if representationalism is correct, then we are forced to accept either skepticism or phenomenalism. But skepticism and phenomenalism are both absurd, according to Reid; there surely is an external world, and we surely do have knowledge of it. So, by reductio ad absurdum, we must reject any theory that would force us to accept either skepticism or phenomenalism. Accordingly, we must reject representationalism.
To reject representationalism would mean accepting that we do not perceive sense data at all. Someone looking at his hand does not immediately perceive a bundle or series of hand sense-data which represents the actual hand. Rather, he immediately perceives the hand. He does not perceive any hand sense-data at all. So the direct realist view up for consideration is that we perceive the external world immediately and directly.
Direct realism is the view that the immediate (direct) objects of perception are external objects, qualities, and events. It should not be confused with the more naïve view that the world is exactly as we perceive it to be. Obviously, we can misperceive the world. The direct realist does not deny that there are perceptual illusions. But the claim is that when we do perceive something, the immediate and direct object of perception is in the external world, not the mind.
A stick submerged in water looks bent. The direct realist is not compelled to say the stick actually is bent; rather, he can say that the straight stick can, in some unusual circumstances, look bent. To say that it looks bent is to say that light reflected from the stick arrives at one's eye in a crooked pattern. In short, the stick can have more than one appearance. But the appearance of a stick isn't necessarily a sense-datum in my mind, merely a pattern of ordinary light.
A similar argument can be made about the bluish color of distant hills. Hills, like anything, can appear with many different colors; but the color is simply the wavelength of light as it reaches my eye. If the light from the green hills has to traverse many miles, then it may be bluish on meeting the observer's eye. There is no need to posit bluish sense-data: only bluish light, which comes from the hills. The hills would reflect green light to a nearer observer's eyes.
Consider the case of pressing on your eyeball with a finger, creating a double image. Undeniably, such doubled vision implies that there are two of something. But assuming the existence of two sense-data is unnecessary under this paradigm. Instead, the direct realist can say that she has two eyes, each giving her a different view of the world. Usually the eyes are focused in the same direction; but sometimes they are not. Each eye may see things in a different way. It does not imply two visual sense-data in her mind; only that there are two slightly different acts of vision occurring.
Similar things can be said about the coin which appears circular from one vantage point and oval-shaped from another. The same coin can reflect different patterns of light to an eye. It does not imply two different sense-data. Rather, the coin is being perceived in two different ways.
Another potential counter-example involves vivid hallucinations: phantom elephants, for instance, indistinguishable from real elephants. This might be interpreted as the perception of sense-data; although the hallucinator is not perceiving real elephants, she certainly seems to be perceiving something. The hallucination seems to have an object, in some sense; but this object is only in the mind. A direct realist response would differentiate hallucination from genuine perception; in this case, no perception of elephants is going on, only the different and related mental process of hallucination. If visual images are present to those who hallucinate, this does not imply such images are present in actual sense-perception.
However, this may not be a particularly strong reply. If there are visual images when we hallucinate, it seems reasonable to think that there are visual images when we see. Similarly with dreams: if dreaming involves visual and auditory images in our minds, it seems reasonable to think there are visual and auditory images, or sense-data, when we are awake and perceiving things.
Direct realists can potentially deny the existence of any such thing as a mental image, but this is difficult to maintain, since we seem able to visually imagine all sorts of things with ease. Even if it should happen that perception does not involve images, other mental processes, like imagination, certainly seem to.
In the area of visual perception in psychology, the leading direct realist theorist was J. J. Gibson. Other psychologists were heavily influenced by this approach, including William Mace, Claire Michaels , Edward Reed , Robert Shaw, and Michael Turvey.
One considered view is similar to Reid's. It is that, in some sense, we do indeed have images of various sorts in our minds when we perceive, and dream, and hallucinate, and use our imaginations, but when we actually perceive things, our sensory images, or sensations, if you will (that's Reid's word), cannot be considered the objects of perception, or attention, in any sense whatsoever. The only objects of perception are external objects. Even if perception is accompanied by images, or sensations, it is wrong to say we perceive sensations.
This conclusion shows that direct realism simply defines perception as perception of external objects where an 'external object' is allowed to be a photon in the eye but not an impulse in a nerve leading from the eye. Recent work in neuroscience suggests a shared ontology for perception, imagination and dreaming, with similar areas of brain being used for all of these. Based on this work, le Morvan (2004) argues that such a shared ontology is fatal for direct realism.