Effects of Decreased Variation in the Sensory Environment



This study began with a practical problem: the lapses of attention that may occur when a man must give close and prolonged attention to some aspect of an environment in which nothing is happening, or in which the changes are very regular. Watching a radar screen hour after hour is a prime example. As Mackworth (5) and others have shown, when at last something does happen in such circumstances the watcher may fail to respond. Such monotonous conditions exist in civilian occupations as well as in military ones (marine pilotage by radar, piloting aircraft on long flights), and here too lapses of attention may have extremely serious consequences. For example, such lapses may explain some otherwise inexplicable railroad and highway accidents.

Besides its practical significance this problem has theoretical implications of great interest. [There is much evidence from recent neurophysiological studies to indicate that the normal functioning of the waking brain depends on its being constantly exposed to sensory bombardment, which produces a continuing "arousal reaction."] Work now being done by S. K. Sharpless at McGill indicates, further, that when stimulation does not change it rapidly loses its power to cause the arousal reaction. Thus, although one function of a stimulus is to evoke or guide a specific bit of behaviour, it also has a non-specific function, that of maintaining "arousal," probably through the brain-stem reticular formation.

In other words, the maintenance of normal, intelligent, adaptive behaviour probably requires a continually varied sensory input. The brain is not like a calculating machine operated by an electric motor which is able to respond at once to specific cues after lying idle indefinitely. Instead it is like one that must be kept warmed up and working. It seemed, therefore, worth while to examine cognitive functioning during prolonged perceptual isolation, as far as this was practicable. Bremer (2) has achieved such isolation by cutting the brain stem; college students, however, are reluctant to undergo brain operations for experimental purposes, so we had to be satisfied with less extreme isolation from the environment.


The subjects, 22 male college students, were paid to lie on a comfortable bed in a lighted cubicle 24 hours a day, with time out for eating and going to the toilet. During the whole experimental period they wore translucent goggles which transmitted diffuse light but prevented pattern vision. Except when eating or at the toilet, the subject wore gloves and cardboard cuffs, the latter extending from below the elbow to beyond the fingertips. These permitted free joint movement but limited tactual perception. Communication between subject and experimenters was provided by a small speaker system, and was kept to a minimum. Auditory stimulation was limited by the partially sound-proof cubicle and by a U-shaped foam-rubber pillow in which the subject kept his head while in the cubicle. Moreover, the continuous hum provided by fans, air-conditioner, and the amplifier leading to earphones in the pillow produced fairly efficient masking noise.

General Effects

As might be expected from the evidence reviewed by Kleitman (3) for onset of sleep following reduced stimulation in man and other animals, the subjects tended to spend the earlier part of the experimental session in sleep. Later they slept less, became bored, and appeared eager for stimulation. They would sing, whistle, talk to themselves, tap the cuffs together, or explore the cubicle with them. This boredom seemed to be partly due to deterioration in the capacity to think systematically and productively–an effect described below. The subjects also became very restless, displaying constant random movement, and they described the restlessness as unpleasant. Hence it was difficult to keep subjects for more than two or three days, despite the fact that the pay ($20 for a 24-hour day) was more than double what they could normally earn. Some subjects, in fact, left before testing could be completed.

There seemed to be unusual emotional lability during the experimental period. When doing tests, for instance, the subjects would seem very pleased when they did well, and upset if they had difficulty. They commented more freely about test items than when they were tested outside. While many reported that they felt elated during the first part of their stay in the cubicle, there was a marked increase in irritability toward the end of the experimental period.

On coming out of the cubicle after the experimental session, when goggles, cuffs, and gloves had been removed, the subjects seemed at first dazed. There also appeared to be some disturbance in visual perception, usually lasting no longer than one or two minutes. Subjects reported difficulty in focussing; objects appeared fuzzy and did not stand out from their backgrounds. There was a tendency for the environment to appear two-dimensional and colours seemed more saturated than usual. The subjects also reported feelings of confusion, headaches, a mild nausea, and fatigue; these conditions persisted in some cases for 24 hours after the session.

Effects on Cognitive Processes

Our present concern is primarily with cognitive disturbances during the period of isolation and immediately afterwards. The subjects reported that they were unable to concentrate on any topic for long while in the cubicle. Those who tried to review their studies or solve self-initiated intellectual problems found it difficult to do so. As a result they lapsed into day-dreaming, abandoned attempts at organized thinking, and let their thoughts wander. There were also reports of "blank periods," during which they seemed unable to think of anything at all.

In an attempt to measure some of the effects on cognitive processes, various tests were given to the subjects before, during, and after the period of isolation.

First, the tests given during isolation. Twelve subjects were given the following types of problems to do in their heads: multiplying two and three-digit numbers; arithmetical problems (such as "how many times greater is twice than one-half ?"); completion of number series; making a word from jumbled letters; making as many words as possible from the letters of a given word. Each subject was tested on problems of this type before going into the cubicle, after he had been in for 12, 24, and 48 hours, and three days after coming out of the cubicle. Twelve control subjects were given the same series of tasks at the same intervals. The average performance of the experimental subjects was inferior to that of the controls on all tests performed during the cubicle session. With our present small number of subjects the differences are significant only for the error scores on the second anagram task (p5.01, see Figure 1). The groups are now being enlarged.

Secondly, tests given before entering the cubicle and immediately after leaving it. On the Kohs Block Test and the Wechsler Digit Symbol Test the experimental subjects were inferior to the controls on leaving the cubicle (p5.01). They also tended to be slower in copying a prose paragraph (p5.10). Figure 2 gives samples of handwriting before and after the experiment. The first is from one of the subjects showing the greatest effect, the second illustrates the average effect. As the third sample shows, some subjects were not affected. This disturbance in handwriting, though perhaps due to some sensori-motor disturbance, might also reflect cognitive or motivational changes.


Mean error scores for experimental and control subjects, before, during, and after the isolation period.


Specimens of handwriting before and after the isolation period.

Hallucinatory Activity

Finally there were the hallucinations reported by the subjects while in the experimental apparatus. Among our early subjects there were several references, rather puzzling at first, to what one of them called "having a dream while awake." Then one of us, while serving as a subject, observed the phenomenon and realized its peculiarity and extent.

The visual phenomena were actually quite similar to what have been described for mescal intoxication, and to what Grey Walter (6) has recently produced by exposure to flickering light. There have also been rare cases of hallucinations in aged persons without psychosis (1), which, like ours, involved no special chemical or visual stimulation. As we did not ask our first subjects specifically about these phenomena we do not know the frequency among them. The last 14 subjects, however, were asked to report any "visual imagery" they observed, and our report is based on them. In general, where more "formed" (i.e., more complex) hallucinations occurred they were usually preceded by simpler forms of the phenomenon. Levels of complexity could be differentiated as follows: In the simplest form the visual field, with the eyes closed, changed from dark to light colour; next in complexity were dots of light, lines, or simple geometrical patterns. All 14 subjects reported such imagery, and said it was a new experience to them. Still more complex forms consisted in "wall-paper patterns," reported by 11 subjects, and isolated figures or objects, without background (e.g., a row of little yellow men with black caps on and their mouths open; a German helmet), reported by seven subjects. Finally, there were integrated scenes (e.g., a procession of squirrels with sacks over their shoulders marching "purposefully" across a snow field and out of the field of "vision"; prehistoric animals walking about in a jungle). Three of the 14 subjects reported such scenes, frequently including dreamlike distortions, with the figures often being described as "like cartoons." One curious fact is that some of the hallucinations were reported as being inverted or tilted at an angle.

In general, the subjects were first surprised by these phenomena, and then amused or interested, waiting for what they would see next. Later, some subjects found them irritating, and complained that their vividness interfered with sleep. There was some control over content; by "trying," the subject might see certain objects suggested by the experimenter, but not always as he intended. Thus one subject, trying to "get" a pen, saw first an inkblot, then a pencil, a green horse, and finally a pen; trying to "get" a shoe, he saw first a ski boot, then a moccasin. The imagery usually disappeared when the subject was doing a complex task, such as multiplying three-place numbers in his head, but not if he did physical exercises, or talked to the experimenter.

There were also reports of hallucinations involving other senses. One subject could hear the people speaking in his visual hallucinations, and another repeatedly heard the playing of a music box. Four subjects described kinesthetic and somesthetic phenomena. One reported seeing a miniature rocket ship discharging pellets that kept striking his arm, and one reported reaching out to touch a doorknob he saw before him and feeling an electric shock. The other two subjects reported a phenomenon which they found difficult to describe. They said it was as if there were two bodies side by side in the cubicle; in one case the two bodies overlapped, partly occupying the same space. Figure 3 shows this subject’s subsequent drawing, made in an attempt to show what he meant.

In addition, there were reports of feelings of "otherness" and bodily "strangeness" in which it was hard to know exactly what the subject meant. One subject said "my mind seemed to be a ball of cotton-wool floating above my body"; another reported that his head felt detached from his body. These are familiar phenomena in certain cases of migraine, as described recently by Lippman (4), and earlier by Lewis Carroll in Alice in Wonder-land. As Lippman points out, Lewis Carroll was a sufferer from migraine, and it is suggested that Alice’s bodily distortions are actually descriptions of Carroll’s (i.e., Charles Dodgson’s) own experiences.

In summary, both the changes in intelligence-test performance and the hallucinatory activity, induced merely by limiting the variability of sensory input, provide direct evidence of a kind of dependence on the environment that has not been previously recognized. Further experimental study will be needed to elucidate the details of this relationship.


Drawing made by a subject to show how he felt at one period in the cubicle. He reported that it was as if "there were two of me," and was momentarily unable to decide whether he was A or B.


1. Bartlet, J. E. A. A case of organized visual hallucinations in an old man with cataract and their relation to the phenomena of the phantom limb. Brain, 1951, 74, 363—373.

2. Bremer, F. & Terzuolo, C. Nouvelles recherches sur le processus physiologique de réveil. Arch. internat. de Physiol., 1953, 61, 86—90.

3. Kleitman, N. Sleep and wakefulness. Chicago: Univer. of Chicago Press, 1939.

4. Lippman, Caro. Certain hallucinations peculiar to migraine. J. nerv. ment. Dis., 1952, 116, 346—351.

5. Mackworth, N. H. Researches on the measurement of human performance. Med. Res. Council, Spec. Rep. Ser., 1950, No. 268. London.

6. Walter, W. Grey. The living brain. New York: Norton, 1953.

Questions for Reflection and Discussion:

1. Why do the authors frame the research issue in terms of "lapses of attention"?

2. At the time this study was conducted, attention was being paid to the reticular activating system (RAS) and "arousal." Where is the RAS? What is meant by arousal?

3. What do the authors mean when they suggest, metaphorically, that the brain must be kept "warmed up and working"?

4. What was the treatment procedure? How did the authors produce sensory deprivation? Was deprivation complete? What were the limits?

5. Subjects were paid $20 a day to participate. How much would that be now? Would it be enough to keep you in the experiment? Are you sure?

6. What were the emotional and cognitive effects of the treatment?

7. Your authors write that the subjects experienced hallucinations? What are hallucinations? What kinds of "hallucinations" did the subjects report? What are the usual causes of hallucinations? What seems to have caused the sensory experiences during the experiment?

8. What do your authors conclude about the findings? Does the conclusion seem warranted by the method used and the results?

9. Do you consider the study to be ethical? Why or why not?


Bexton, W. H., Heron, W., & Scott, T. H. (1954). Effects of decreased variation in the sensory environment. Canadian Journal of Psychology, 8, 70—76. Copyright 1954. Canadian Psychological Association. Reprinted with permission.