This article will help you to differentiate between Percept and Memory Images.
1. Fragmentariness of Images:
When you perceive a mango, you see its colour, form, size, etc., taste it, smell, its flavour, and touch it. These actual sense-experiences form a continuous totality. But when you remember the mango, you call up its visual image alone, and do not remember the images of other sense-experiences. Thus memory image is fragmentary; it is cut off from its context in the original experience.
2. Faintness of Images:
Percept are more intense than memory images. For David Hume, images or ideas are faint copies of original impressions or percept. They differ in intensity of degree. The image of a mango is fainter than the percept of it. But this is wrong.
Stout rightly points out, “at bottom the difference is a difference of kind, not merely of degree. Images do not strike the mind in the same way as actual sensations”. Percept are aggressive; they are thrust upon the mind from without. But memory images are not aggressive: they do not break in upon the mind and disturb the flow of consciousness.
3. Indistinctness of Images:
An image is sketchy, because it is an extract from the content of perception. A percept is full and detailed, while an image is sketchy and lacking in detail. Percept are distinct. You perceive a rose; your percept is clear and distinct.
But you call up the image of the rose; it is vague and hazy, because you cannot possibly remember all the features of the rose. An image is indistinct; a percept is distinct. Part of the content of perception fails to be recalled.
The indistinctness of the image is partly due to obliviscence and partly due to reduplication. Some elements of the original experience are forgotten. Some parts of the percept drop out simply because of a deficiency in our power to retain or at least recall them. The image is the product, not of a single perception, but of many perceptions which agree only in certain points, and differ in others.
Only the common features alone are retained and recalled. The divergent detail obstruct reproduction on account of their very divergence. Moreover, a train of ideation is conative. It serves a practical or theoretical purpose. Only so much is revived as may be required by the dominant interest of the moment.
4. Relation to Attention:
Percept are more steady than images which are fluctuating. The objects of percept have fixed positions in filled space, whereas images appear to exist in empty space—they appear to be projected in space. Percept are steady because they are produced and sustained by external stimuli.
Images are evolved by the mind from within and are sustained by attention. But attention is by nature flickering; it flits from object to object. So images are unsteady.
5. Relation to Motor Activity:
Percept are produced by external stimuli acting on the sense organs. So they vary with the movements of the organism and the sense-organs and their spatial relations to the stimuli in the environment. As we cast our eyes on different objects while we walk, they produce different percept in our minds.
But we can carry the same image (e.g., the image of a departed friend) in our minds while we walk along. The image is not affected by movements of the body. But if we turn our head away or close our eyes, we can no longer see what we saw before. The sensations vary with the adaptation of our sense-organs to different objects. But our images are not so affected by our movements.
But a memory image is not altogether different from a percept. It resembles a percept in many respects. A memory image is a reproduction of a past percept. Hence some qualities of the original percept must reappear in it.
Some qualities are possessed in common by a percept and its memory image:
i. The sensible, qualities (e.g., colour, sound, etc.,) of the original percept reappear in its memory image.
ii. The complication also, and in general,
iii. The spatial and temporal form of these qualities re-appear in the memory image. In the ease of an image, the same sense-organ or muscle is to be exerted, in a fainter degree, if it is required to reproduce its original percept. When you recall a tune, you have to partially adapt your ear to the image.
iv.A memory image is not merely reproduction of the original percept, but, to a certain extent, ideal revival and actual reinstatement of the physiological processes involved in the original percept. Percept and memory image are partly similar to, and partly different from each other.
v. They are relatively independent of each other. Gazing at the blue sky, we may imagine a portion of it as red instead of blue. Most people, while they are imagining a portion of the sky as red, do not cease to see it as blue. They may have a percept of it as blue and an image of it as red simultaneously. The percept and the image do not cancel each other, though they are conflicting in their nature.
They are independent of each other. Dip your hand into warm water. You have sensation of warmth. You can imagine at the same time how your hand would, if it were dipped in cold water. But your mental image does not annul your actual sensation.
You feel them both simultaneously. The relative independence of percept and image is probably due to the fact that the nervous tracts excited in perceptual process are not wholly coincident with those excited in ideational process.
6. Percept and After-Image or After-Sensation:
We look at the sun and have a percept of it. If we look at the sun for a few seconds and turn our eyes away from it, we see a disc of white light. This is a positive after-image. Gradually it turns into a patch of grey or black colour. This is a negative after-image.
A positive after-image due to the persistence of the original peripheral excitation after the stimulus is withdrawn. A negative afterimage is due to the effects of the exhaustion or the repair that immediately follows this excitation.
An after-image should properly be called an after-sensation because, it is due to the continued effect of a stimulus upon the sense-organ after the withdrawal of the stimulus. Thus an afterimage agrees with a percept inasmuch as both of them involve stimulation of the sense-organs.
In visual positive after-images the same qualities (e.g., colour) are reproduced as of the original percept. But the colours of the visual negative after-images are complementary to those of the percept.
There are some differences between a percept and an afterimage:
i. A percept is produced when the stimulus is present to the sense-organ, while an after-image emerges just after the stimulus is gone; it is a continuation of the percept due to the protracted stimulation of the sense-organ even after the stimulus is withdrawn.
ii. A percept can be maintained in the field of consciousness by attending to the stimulus present. But an after-image cannot be sustained by attention; it is a momentary act of consciousness independent of our will. A positive visual after-image possesses the sensible qualities of the corresponding percept, but a negative visual after-image possesses colours complementary to those of the original percept;
iii. Whatever may have been the spatial arrangement of the perceived objects, the corresponding after-images are spread out in a flat expanse.