It follows that it is not necessary for the two successive series to be present in consciousness at the same time in order that they may be compared; but what is required is the union of all the impressions of one series together in a single unitary idea. The relatively fixed boundary of the scope of consciousness is clearly shown in the fact that the likeness of two temporal ideas is always recognized with certainty so long as they do not pass the bound that holds for the conditions under which they are given, while the judgement becomes absolutely uncertain when this limit is once crossed. The extent of the scope of consciousness as found in measurements made when the conditions of attention remain the same, depends partly on the rate of the successive impressions and partly on their more or less complete rhythmical combination. When the rate of succession is slower than about 4", it becomes impossible to combine sucessive impressions to a temporal idea; by the time a new impression arrives, the preceding one has already disappeared from consciousness. When the rate passes the upper limit of about 0.18", the formation of distinctly defined temporal ideas is impossible because the attention can not follow the impressions any longer. The most favorable rate is a succession of strokes every 0.2-0.3".
With this rate, and with the simplest rhythm, which generally arises of itself when the perception is uninfluenced by any special objective conditions, the 2/8-time 8 double or 16 single impressions can be just grasped together.
The best measure for the apprehension of the greatest possible number of single impressions is the 4/4 measure with the strong accent on the first stroke and the medium accent on the fifth. In this case a maximum of five feet or forty single impressions can be grasped at once. If these figures are compared with those obtained when the scope of attention was measured, putting simple and compound temporal impressions equal to the corresponding spacial impressions, we find that the scope of consciousness is about four times as great as that of attention. [p. 216]
7. Besides the properties of clearness and distinctness, which belong to conscious contents in themselves or in their, mutual relations to one another, there are regularly others which are immediately recognized as accompanying processes. These are partly affective processes that are characteristic for particular forms of apprehension and apperception, partly, sensations of a somewhat variable character. Especially the ways in which psychical contents enter the field and fixation-point of consciousness vary according to the different conditions under which this entrance may take place. When any psychical process rises above the threshold of consciousness, the affective elements, as soon as they are strong enough, are what first become noticeable. They begin to force themselves energetically into the fixation-point of consciousness before anything is perceived of the ideational elements. This is the case whether the impressions are new or revivals of earlier processes. This is what causes the peculiar states of mind which we are not exactly able to account for, some-times of a pleasurable or unpleasurable character, sometimes predominantly states of strained expectation. In this last case the sudden entrance of the ideational elements belonging to the feelings, into the scope of the attention, is accompanied by feelings of relief or satisfaction. When we are trying to recall something that has been forgotten, the same affective state may arise. Often there is vividly present in such a case, besides the regular feeling of strain, the special affective tone of the forgotten idea, although the idea itself still remains in the background of consciousness. In a similar manner, as we shall see later (§ 16), the clear apperception of ideas in acts of cognition and recognition is always preceded by special feelings. Similar affective states may be produced experimentally by the momentary illumination of a field of vision in which there are impressions of the strongest [p. 217] possible affective tone in the region of indirect vision. All these experiences seem to show that every content of consciousness has some influence on attention. It shows this regularly in its own affective coloring, partly in the feelings regularly connected with acts of attention. The whole effect of these obscure contents of consciousness on the attention fuses, according to the general law of the synthesis of affective components (p. 159), with the feelings attending the apperceived contents to form a single total feeling.
8. When psychical content enters the fixation point of consciousness, new and peculiar affective processes are added to those that have been described. These new feelings may be of a variety of kinds, according to the different conditions attending this entrance into the fixation-point. The conditions are of two classes, and are interconnected for the most part with the above described preparatory affective influences of the content not yet apperceived.