members the movement experience might be highly integrated. It meant that a single line travelled uniformly across the field changing in quality during movement. The fact that dissimilarly colored objects appear to incline the observer toward the apprehension of movement of the partial or dual type is important. If the perception of motion may be said to rest partly upon the successive apprehension of the same object through two moments of time and space it seems likely that where the successive phases are qualitatively different the continuity of the movement might easily be interrupted. Where successive lines of unlike hue are not apprehended as the same object O is led to report fewer cases of full and more cases of dual and partial movements. Much depends, it appears, upon the particular attitude or set of the observer. On the whole, we may say that where the objects are of similar hue, apparent motion tends more towards the optimal type. Qualitative peculiarities of the stimulus objects actually serve then to modify the extent of perceived motion, a mere change in hue being sufficient to change at times the character of the movement apprehended under discrete retinal stimulation.

What can we say of the qualitative aspects of the movement, i.e., of the hue of the movement? O reported that, where movement was seen, the meaning was that a colored object travelled part or all the way across the field. Movement in every case was of a colored object, the particular hue depending upon the hue of the stimulus. That is to say, O reported that where there was any relevant visual filling for the movement it was colored red or green. When we say that movement was of a colored object, we mean that O saw such an object move, although there might actually be no discernible visual material in parts of the field. We indicated in an earlier study that O may really apprehend movement of the clearest sort without being able to report the presence of anything other than the two lines or areal positions. O repeatedly claims that movement is continuous, uniform and clear; yet in the next breath remarks that there is nothing of a visual character filling the whole region between the lines to 5 Op. cit., 104 f.

5

carry the movement. The experience is so striking that even Os who have observed again and again will offer such comments as 'strange,' 'curious,' 'odd.' They unquestionably apprehend movement although a relevant visual filling is wanting. We cite a few reports from this series (1-16) upon the hue of the movement.

I saw only two extreme positions: an upper red oblique and a lower red horizontal. Between them there was only blackness. I definitely saw the oblique move continuously to the horizontal position (C, 75).

A red oblique moved to a horizontal position, paused for a moment and disappeared. I am sure of movement; it was quite clear, but I do not believe that there was any visual content (other than blackness) between the two positions (Y, 75).

Two green lines forming an angle; around the upper and lower thirds of the sector the field was green. Between these areas the field was black. I saw a green oblique move to a horizontal green line. Movement was uniform and continuous although the visual apprehension of color was not (C, 150).

A red horizontal line appeared; then a lower line similar to it. The field between was distinctly blackish, except for a colored haze around each line. A red horizontal line moved from upper to lower position (Y, 150).

I saw a green horizontal line move quickly to a lower position. When it stopped it was red. The middle of the field was quite black (Y, 75).

At times, O apprehended a single line as moving across the field changing in hue during the course of the experience. It was as if the visual field were covered with two adjacent pieces of glass unlike in hue. The object moving, as if behind this glass, was now of one color, now of the other. Or, as O sometimes said, it was as though an object 'moved from the sunshine into the shade.' O found it difficult to point out the exact place of qualitative transition. One second the hue was red, the next it was green. In general it appears that the change was effected nearer the second member than the first; although it might actually occur in the middle of the region of movement. It seemed that the hue of the first line was held over until the second line came, so that everything up to the time of the appearance of the second tended to partake of the hue of the first. Where the lines were dissimilar in quality the movement was no less colored that where the lines were alike. We cite the following as representative of the reports upon the qualitative aspects of the visual movement with objects of like and different hues upon a lightless

ground. In some of them the nature of the change in hue, as O observed it, is indicated.

A green oblique appeared surrounded by a greenish yellow haze. Then a red horizontal came in accompanied by a reddish glow. I saw the green line move down about 3/4 of the way toward the red stationary horizontal (Y, 150). A red line moved continuously from an upper oblique to a lower horizontal position. About 3 of the way down the oblique was clearly defined for a moment. It was, however, less saturated (C, 150).

A green line moved from an oblique to a horizontal position (Y, 150).

A well-defined red horizontal line appeared; then lower down I saw three vaguely outlined red lines of low chroma appear on a reddish field. At the end, a fourth line much like the first. The whole experience meant that a red line distinctly moved from an upper to a lower horizontal position (Y, 75).

Movement of a single line from an upper to a lower horizontal position. During the first half, the movement was red; but over the second half it was green (C, 150).

A greenish oblique appeared followed by a red horizontal. The field was almost black with just a trace of green extending over the sector except the lower part, where the field was reddish. I saw a green line move from an oblique to a horizontal position and just as it reached the horizontal it turned red (Y, 75).

(Serial exposition; red and green): Two parallel bars, the upper red and the lower green, moving discretely up and down. Each is independent of the other; but both are related in movement. When the red line moves down, the green shifts with it. When the green moves up, the red precedes it. The lines keep step during movement (C, 75).

(Serial): A single line changing in color moved clearly and uniformly up and down over a sector. It was green going down but suddenly turned red upon reaching the bottom. Going up, the line was red until it reached the top where it suddenly changed to a greenish hue and started down again (Y, 150).

One of our major problems was to determine the phenomenal nature of the field intermediate to the two positions, i.e., the qualitative aspects of the area over which the motion occurred. This region might be either partially or wholly colored. When partially colored the remainder was lightless or gray. Aside from the blacks and the greys, the visual filling, reds and greens, of various degrees of saturation and yellowishness, was referred to as being ill-defined, cloudlike, hazy, foggy or misty. The colors were blurry, sketchy, streaky or flashy. They either spread or shot out over the field much on the order of spilled paint, or else they were just there. These qualities were so obvious and so insistent that no one could possibly doubt their presence. Reports of such a positive character as these lead us to refer again to the at

tempt to reduce visual movement to an existential "grey." To resort to such an explanation in the presence of the facts at hand not only does violence in the worst possible manner to the facts of observation but also obscures the true status of the movement experience. We can say that upon three occasions only in these series did O use the descriptive term grey. Then the report ran that the area around the endpositions was colored but that the middle (1/3 or less) of the sector was greyish. We cite, as illustrative of the general nature of the observations, parts of a few reports upon the filling intermediate to the two members.

A green line appeared in an oblique position and spread quickly downward to a red horizontal. This spreading was of an ill-defined yellowish-green cloud-like film (Y, 150).

A red oblique; beneath it a reddish cloud-like content; then a reddish horizontal. The whole sector was red (Y, 75).

The red oblique and the green horizontal areas are sharply separated by a small black sector. The red extends downward about 4 inch and the green up a like distance (C, 150).

A red oblique and a horizontal green. A reddish-yellow cloud between (Y, 75).

The upper was a red; the lower, a green horizontal. A reddish haze extended down over of the field, and a greenish haze covered the lower . Between these the field was quite black (C, 150).

An oblique red line; then a low chroma orangish film around and beneath it and extending down to a reddish horizontal line (Y, 75).

A green oblique appeared and spread downward over 4 or % of the sector. Then the field was totally dark for a short distance and then a green line appeared and spread downward about ten degrees to form a horizontal (C, 150).

An angle formed by two green lines; the whole angle was filled with a greenish light (C, 75).

Two red lines forming an angle with a cloud-like blur, distinctly reddish in hue, between them (Y, 75).

A thin green horizontal appeared in the upper part of the visual field; then another similar line at the bottom. Between them the field was filled with a greenish haze (C, 75).

In addition to the vaguely defined colors intermediate to the end-positions Os reported the presence of secondary members or lines in a third (34 per cent.) of the observations. We have elsewhere indicated the theoretical significance of such 'accessory' objects, which have been observed in various major studies upon apparent visual movement of this type. They appear to contribute directly to the clear perception of

movement; for they are apparently seized upon and utilized by the organism as a resource in apprehending motion. They mean that a line is seen progressing across the field occupying these various positions. The chroma of these intermediates varied from time to time from a degree of saturation almost equal to that of the end lines to one of very little hue. In all cases but one, these lines were reported to be at least slightly colored. Where the two lines were complementary in hue, C reported once that at the point where the red and green films met, a colorless line was momentarily visible.

An interesting fact in connection with this matter of the secondary lines must be made clear. We believe that the particular hue of the intermediates when the end-positions were dissimilarly colored throws light upon certain functional operations of the organism. These lines, when colored, were always of the hue of the moving member. Now it is indeed strange that, where the two discrete positions were equal in intensity, brightness and extent, the hue of these secondary lines was always that of the object which moved. No report refers to the presence of intermediates like the unmoving member in quality. If these objects between are due merely to chance retinal irradiation of some sort why do they not occasionally assume the hue of the stationary member? As we regard the matter, the presence of these secondary lines indicates some functional peculiarity of the organism that may be of primary importance for the apprehension of visual movement. And it may be that the same functional conditions, which, at times, produce these linear extents serve likewise to create the vague, ill-defined and hazy colors which so frequently accompany the movement experience. Parts of a few reports are given below to show the general nature of . these intermediate members.

Two intermediate red oblique lines; over the rest of the field was a film of low chroma red (C, 150).

A green horizontal line followed by a yellowish film beneath. Then I saw a greenish line a little lower down and then a red line came in below the position of the second green horizontal (Y, 75).

A clearly defined intermediate position of a red oblique of the way down (C, 150).