88. What essential difference between mental function and mechanical function is referred to by the word attention?
89. Can you illustrate the chief facts of attention and inattention?
90. Can you illustrate the parallelism between the laws of feeling and of attention?
91. How is attention mentally prepared for?
92. How is attention assisted by special muscular activity?
93. What causes the illusion that attention is a voluntary activity of the mind upon its contents?
94. What practical problems are connected with the law of the duration of attention?
§ [9]. Memory
While attention means limitation, memory means expansion. From the enormous number of impressions calling simultaneously for response, the mind selects a small group of those related to its present needs. But the mind may go beyond the limits of that which is presented and respond to impressions of a former time. We then speak of memory. When I hear the first verse of a poem which I have previously heard or read more than once, I continue to hear, in imagination, the following verses although the reader has stopped. When I see a black cloud drawing over the sky and the trees bowing under the pressure of the wind, I know that a thunderstorm is approaching. When I smell carbolic acid or iodoform, I look for a person wearing a bandage. In every case the mind tends toward expansion beyond the limits of the data presented at the moment. The mind thus restores the connections in which the accidentally isolated object of present interest has been experienced with other objects in the past.
We refer to this ability of expansion by the term memory, to the actual process of expansion by reproduction or association. The immense importance of memory for life is easily understood. Nature repeats itself—not without some variations of the accompanying phenomena; but no group of phenomena, aside from such variations, fails to recur at frequent intervals. In reproducing what previously existed under similar conditions, our mind possesses, as a rule, a real knowledge of what now exists but happens to remain hidden, and of what is about to occur. Thus our mind adapts itself to those parts of the world which are for spatial or temporal reasons beyond the reach of our sense organs.