Figural After-effects and q.i (was Re: Controlled Quantity)

[Martin Taylor 2018.]

When we consider whether a perception has a direct counterpart in the environment, we could recast the question, and ask two questions: 1) Can any external observer or experimenter perceive what we perceive if they look at what we look at, and 2) if the perceptual value of what we perceive to be a state of the environment changes when machines or other observers say that environmental state doesn't change, or vice-versa, can that environmental state be a property of Real Reality?

The example I want to use to exemplify these questions is a generic phenomenon that has been known for the best part of two centuries, figural after-effects. The earliest of these in public reports might be the "Waterfall Illusion". If you watch something moving in the same direction for a while and then look at something you believe to be stationary, it seems to move for a while in the opposite direction. Not only that, but while it seems to be moving, it is not perceived to be changing position.

Half a century ago, I did a tracking study of the inverse form of this. I had subjects watch for a prescribed period a circular disc, covered "randomly" with a blotchy pattern, rotating at a steady (slow) speed, after which the subject was allowed to influence the rotation speed with the instruction to keep the disc stationary. The machine-measurable speed was also subject to an external random influence added to the influence produced by the subject, in what I would now call a "compensatory tracking" experiment. They could do this pretty well, to judge by the smoothness of the curves of measured rotation speed (quite visible to an observer) that the subject claimed to be stationary over quite a long time (several minutes). The curves were precise exponential declines in measured rotary speed, except that if they had been looking at the disc for an exceptionally long time, the slope of the decline switched after a while to a much slower rate.

While the subjects were keeping the disc stationary, several of them spontaneously exclaimed that they could not keep it in the same position while it was stationary. The perceptions of position and velocity were decoupled. Velocity was not perceptually the derivative of position, because perceived rotary velocity was always zero.

In a very different situation, I had a personal experienced that surprised me as a Ph.D. student writing my thesis on perception. I spent maybe 16 hours a day for a week typing up my thesis on yellow paper (most of you won't remember manual typewriters; what you did was put a paper in behind a roller and feed it up manually line by line as you typed, so the paper was always in your line of vision). After a week of this, I started to type a letter on white paper, but as soon as I put the paper into the typewriter it turned a rich blue, to the extent that I thought I had taken the page from the wrong stack (I had stacks of white, yellow, pink, and blue paper beside me). So I took the "wrong" paper out of the typewriter and it immediately turned white. I put it back and it turned blue. This phenomenon took several days to fade away.

The point of mentioning these effects here and now is to illustrate the difficulty of determining q.i for a controlled perception. These may be extreme examples, but the point is general. For the rotating disk experiment, the perception of velocity at any one moment depends not only on the machine-measurable current velocity, but also on the average machine-measurable velocity to which the subject's visual system had been exposed, and the duration of that exposure. In the case of the paper colour, one assumes that in real reality the spectral reflectance of the paper did not change when I put it in and took it out of the typewriter. The perception of colour depended not only on the spatial context of the typewriter but also on the visual history over the previous week. No other observer would have seen the striking and sudden colour change when the paper was fed into the machine. (Side note: the typewriter experience led me to try for quite a while in 1960-61 without success to find what later became known as the McCollough effect (try it on Wikipedia)).

q.i is certainly the result of a function of many variables, but given these examples and many more, can any experimenter determine what is "the controlled variable" and its reference value? In the rotary disk after-effect, is the subject controlling for keeping the disk in a constant orientation? You wouldn't deduce that by observing and applying disturbances (as I did) to the velocity of rotation, because the observer can see the disk rotation and can measure how its orientation ha changed over time. Is the subject controlling for keeping the disc at zero rotary velocity, or any other constant velocity? You can't tell from the results.

They appeared to be controlling a perception of velocity according to a changing reference value -- changing in the externally observable environment, but not in their own hierarchy if they were following instructions, as they all (including me as a subject) said they were. No external observer could perceive their q.i without having had a goodly time having the same precursor visual experience. Their q.i did not exist in Real Reality, nor in the set of variables that would ordinarily be measured in a simple tracking study. It was purely synthetic.

And yet, and yet... Here's something you can try yourself if you can arrange to be a passenger while someone else drives. Look fixedly out of the back window at the distant road disappearing behind the car. When you get out, you will perceive the surroundings seeming to be coming toward you. This does not happen from watching the oncoming road when you sit normally in the passenger seat. When you get out, the surroundings are quite stable, perceptually. Why the difference? I suggest that your perceptual system has reorganized because you live in a world in which you may move toward things (and often do, both when walking and when in a car), but the whole world seldom if ever moves toward you. Your hierarchy has not reorganized for situations in which the world has been rushing away from you, so that perception is like most others -- a contrast between what was and what is provided by the sensors.