"PERCEPTION AND ILLUSIONS OF PERCEPTION.”

Shannon News, 29 June 1926, Page 3

"PERCEPTION AND ILLUSIONS OF PERCEPTION.”

W.E.A. LECTURE. The usual weekly gathering of the local branch of the W.E-.A. was held on Tuesday evening In the Century Hall. About 30 were present, and Mr R. McAllister occupied the chair.

The lecturer showed the- relationship between sensation and perception. Pure sensation being the first thing in the way of consciousness, and possible only to very young children; perception being sensational and reproductive brain' processes combined. When tin- facts with which one is dealing are- presented to the senses, one has sense perception. Prsented to the -eye, one has visual, to the -ear* auditory perception.' We can gain perception if only a sign is presented, i.e., we ‘‘see it is wet today”; “the slime looks heavy." Perception that Is not sense, perception takes place when, on putting together two facts, still another fact is’ discovered. Reading in the newspaper of a projected Polar expedition, and remembering that- both Poles have been discovered, one discovers, tor perceives that there is' something more in Polar exploration than a mere race for the Pole. Perception of this sort really merges into reasoning.

In perception the chain of events is: Stimulus, response of the sense organ affected and its sensory nerve, first critical or brain response, which is sensation, second critical response which is discovery or perception. When the-eye is stimulated, the nerve current first roaches the small .portion of the occipital lobe' called the visual sensory, area. But this is not enough. The regions of the cortex adjacent to this sensory area are necessary also, for if by injury or disease one’s adjacent region Is destroyed, the subject may still see but has no conception of the object seen. “I see men as trees, walking.” Sense perception Is the response of the whole area given by association fib-' res—lbis area being a kind of encyclopedia which holds from past experience all the information requisite to an understanding of the thing seen. The lecturer next dealt with what is called delayed perception, illustrating the point by reference to instances of post-war disability. In an ambiguous case the first perception may be wrong, it is quickly followed by a second, this may also be » wrong, but these perceptions do not j mix however, rapidly 'they follow 1 one anothett 1 . -When the brain’s functions are thrown Out of order as in aphasia, or when.one is very sleepy, one may gain ambiguous or wrong perceptions. Tin's leads on to the aspect of the subject called mistaken perception. In this case the stimuli arouse two or more perceptions and “the correct one is found only after trial and error investigation. In all these cases sensation remains to all intents and purposes the same. In dealing .with tire subject one must also take into consideration practised perception. A fact perceived for the first time must of necessity be attended to, in order that it may be perceived. This comes easier with practice; The linkage of stimulus with response becomes stronger and stronger until tbo stimulus is able to arouse the perceptive response almost automatically. A great deal of inattentive perception is constantly going on. Aside from sensation and from some of the reflexes, this kind of perception of familiar facts is the next practised and the easiest of all responses. The more intensely and the moire frequently a given fact is perceived the more readily is it perceived again. The next step is that of corrected perception. The first impression of a new object often needs revision because they do not work well. “On second thoughts 1. have decided, etc.” This gives use to analysis and discrimination, and a familiar instance is that of a child putting on her shoes—for a time there is confusion between left and right So also is the experience of the average non-mechanical person whose car. “konks out” on the road. In vestigation of a. “trial and - error’ kind is proceeded with—ignition, barburretiion—no result; finally investigation of petrol tank shows it to be bone dry and this explains the stoppage. The process is:—Blocked response—closer examination—new stimulus isolated that gives a satis factory response—finally perception that leads to the unravelling of the mystery. Mr McArthur at this stage dealt with what is known as one of the quarrelsome subjects in psychology—the perception of space. A sense of “voluminousness” is posses sed by us which contributes to our perception of distance and space just, as ke Know lhat as certain brain changes are followed by those men tal tacts which we call sensations, so the apprehension of certain char acteristics of our sensation is followed by the apprehension of space. Experience teaches. Some time was de voted to an examination of the pari played in these things by the eyes; ■and comparison made between a retinal pictures and that of an artist on canvas.

Illusions. — As the careful shipmaster adjusts his chronometer before .leaving port, so must .we adjust our perception from time h> time. „ It J 6 easy to “jump to conclusions.” An illusion consists in responding to a sensory stimulus tby perceiving something that is not- really theie. The stimulus is there but not the tact which' it is taken to indicate. Errors are due tft—

(1) Peculiarities of sense organs. A vertical line seems longer titan a horizontal line of same length. lan

is due to some, so far, undiscovered retinal defect, (2) Re-occupation or “mental set,” This is seen in many forms of insanity. (3) Optical illusion. Moving pictures—ill reality each picture is stationary. In cases of injury to ihe brain as in over indulgence in alcohol—delirium tremens—the patient feels, sees, hears,' or perceives mistakenly. At the close ol the lecture Mr McArthur showed about 20 slides illustrative of the subject. As usual the lecture was listened to with close attention throughout.