Perception

A theme running throughout the study of perception since the time of the ancient Greeks has been whether perceptual processes are learned or innate. Innate means existent or potential at birth due to genetic factors. Learned means that the ability is based on remembered past experience with similar or relevant stimuli.

One way to test these ideas is to examine humans or animals who from birth had no visual experience, and thus no opportunities for visual learning, and to test them when their sight is restored. Perceptual functions are then tested to see which, if any, are intact. This was done with human beings born blind because of cataracts before surgical methods were developed to safely remove them. Cataracts are a disease of the eye in which the crystalline lens or its capsule are or become opaque. It was found that after their cataracts were removed they were normally responsive to changes in color and light, but they were unable to tell when a figure was present, or to discriminate between simple shapes. It took a period of two to three months before they were able to perform these tasks with ease.

Along the same lines, research with animals deprived of visual experience from as close to birth as possible, finds that even without visual experience, some of the animals can perceive visual depth cues. Research also finds that animals raised without opportunities to see (for example if reared in the dark) sustain long-lasting deficits in their perceptual abilities. Indeed, such deprivation can even affect the weight and biochemistry of their brains.

Studies with human infants find that at even one or two days of age, they are able to perform detailed visual discriminations, and they show preferences for visually complex or novel stimuli. While this line of research cannot prove the ability is not learned, it does lend support to these abilities being present at birth in some form.

In sum, it seems that while some fundamental visual perceptual abilities are innate, visual experience is necessary to maintain and further develop them.