if a subject responds 100 per cent correctly to three dots, 83.3 per cent to four dots and 66.67 per cent to five dots, his span lies between 4 and 5.
For experimental purposes the span can be defined as the maximum number of dots to which at least 75 per cent of correct responses are made, viz. The subject thus views each card twice and therefore there are 6 stimuli for each level, i.e., 6 exposures for 3 dots, 6 exposures for 4 dots, etc.Īfter exposing all the cards the experimenter finds out how many times the subject has responded correctly for each level out of the possible 6 times.
The complete set is exposed once and then exposed for a second time. After presenting each card, he makes a note of the actual number of dots as well as the subject’s response. The experimenter then shuffles the set of cards with single dots and exposes them one after the other, each time giving the ‘ready’ signal. The card will be exposed only for a short time”. You will see a card with a number of dots. The experiment has to be done separately for each of the five sets. The sets are shuffled separately and kept ready for the experiment. The experimenter sits on the other side of the apparatus keeping the five separate sets of cards with him. The subject is seated in front of the tachistoscope such that he has a good view of the window. It is sufficient to enable the subject to take a quick glance at the exposed material and at the same time short enough to prevent him from reading or memorising it. The exposure time is usually 1/10th of a second. This shutter can be closed or opened with the help of a lever which is behind the screen at the top. It consists of a wooden screen with a window in the middle which is covered by a movable falling shutter. For the present experiment, the simple falling-door type is adequate. There are other tachistoscopes which are operated electrically and the exposure is variable and adjustable (camera- shutter types). Falling-door type is the one which usually has a fixed exposure time. There are different types of tachistoscopes. (v) Cards with numbers ranging from 3 digit numbers to 10 digit numbers (again 3 cards at each stage with 3 different numbers having the same number of digits). (iv) Cards with meaningful words, again ranging from 3 letter words to 12 letter words (different words at each stage). (iii) Cards with nonsense syllables having 3 letter syllables to 10 letter syllables, 3 different combinations of letters at each level (3 cards with 3 letter syllables, 3 cards with 4 letter syllables etc.). (ii) Cards with 3 dots in each group ranging from 3 groups to 10 groups (having 3 dots corresponding to a single dot in the earlier set of cards.
The dots are to be arranged in different patterns. (i.e., 3 cards with 3 dots, 3 cards with 4 dots, etc.). (i) Each set of 3 Cards bearing 3 to 10 single dots. Nonsense Syllables (meaningless combinations of letters)Ī tachistoscope of the falling-door type, exposure cards having the following materials printed on them: Later experimenters have distinguished between span of attention and span of apprehension and also found that span of apprehension is greater than span of attention.ģ. After Cattell, a number of experimenters have studied the span of attention under different conditions. Cattell, who used the tachistoscope for this experiment. However, real scientific experimental work on the problem was started by J.M. The earliest psychologist to be interested in the problem was Sir William Hamilton, who made a very crude experimental attempt to study the problem.Īn advance was made on Hamilton’s method by Jevons, the logician. The span varies from individual to individual, from sense organ to sense organ, and also according to the nature of the stimuli. This limit is known as span of attention. However, our sense organs can respond to only a limited number of them at the same time. Span of Attention – Visual:Īt any given moment there are several stimuli in the environment competing for our attention. List of top two psychological experiments on attention! Experiment # 1.
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