________________
Perceiving-Touching/Pain, Secing and Hearing
69
the original picture is reproduced on the cortex, but modified and much expanded. We can regard all vision as a continual search for the answers to questions posed by the brain. The signals sent from the retina constitute 'messages' conveying these answers. The brain then uses this information to construct a suitable hypothesis about what is there and a program of action to meet the situation. The sequence of processes involved in the act of seeing do not therefore really begin in the retina, but involve the brain. Nevertheless it is convenient to ask just how the retina composes its messages. The rods and cones are the light-sensitive elements. They contain special pigments, which change when the intensity of light falling on them varies. This change alters the electrical potentials of the cells, so that the pattern of light thrown by the lens produces a corresponding pattern of electrical and chemical change in the various neurons which make up the retina. These impulses in the optic nerve-fibres at each moment of scanning a scene are the answers, in code, to the questions'that had been asked at the previous moment. Of course, if something quite unexpected happens, it is seen even though it bad not been anticipated. The point is that what goes on in the retina is not merely the recording of a 'picture', but the detection of a series of items, which are reported to the brain. If the eyes are prevented from moving, the signals fade within a second and no picture can be seen. C. Physiology of Vision
Human photoreception is a complicated process. We are able to encode all sorts of aspects of the world and to decode the signals and act accordingly. Our eyes have Jenses and we examine the pictures or patterns tbrown upon the retina. The task therefore is to understand how the brain is able to decide appropriate responses to many different
1. This is equivalent to indeterminate cognition (anākära upayoga or darsana), which
precedes every determinate cognition (sākāra upayoga orjñāna). In Jain Epistemology, anākāra upayoga consists of four classes of darsna viz. (i) caksuh-darsana (eye cognition or vision); (ii) acaksu-darsana (cognition by the mind as well as the senseorgans, other than the eye; (iii) avadhi-darśana and (iv) kevala-darśana, The last two art cases of direct cognition by the soul, without the help of any external instrument.
Subsequcnt use of this information by the brain to construct a suitable hypothesis is determinate upayoga or perceptual knowledge - mati-jñāna, which becomes the basis for a program of action.
