A Performance in Low-Intensity Noise Study
During a grammatical reasoning task noise was suddenly interrupted, and error rates went down sharply.
The "Effects of simulated ventilation noise on performance of a grammatical reasoning task"  study showed a statistical significant decrease in error rates when low-intensity noise was shut off. The noise levels was somewhat high (47-57 dBD) compared to most ordinary personal computers. The so called weighting of the noise was also not comparable to ordinary PCs: PC noise is commonly weighted using the A-filter, while here the D-filter was used.
Nonetheless is the study most interesting reading since it is one of a few ones that has been able to show effects on performance in low-intensity noise. The article discussion is also of utmost value to anyone interested in problems that might arise when trying to study adverse effects of low-intensity noise.
The full text article is here provided free to download as pdf-file courtesy of Formas, the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning. The article is Copyright © Formas.
How Low-Intensity Noise May Affect
The following paragraph discusses in what way also low-intensity acoustic noise emissions may possess the power to decrease human performance and to adversely affect human health.
The hypothesis here presented is not based on scientific evidence: It is based on thoughts by The Silent PC Web site author. These thoughts are of course as everything else here, except cited items and others stated copyrighted items, the site author's copyrighted intellectual property ©.
Fujitsu Siemens Computers® has in 2003 with permission used part of these thoughts for marketing purpose. This writing has been further improved since then.
Fujitsu Siemens Computers is a registered trademark of Fujitsu Siemens Computers GmbH.
"Close your ears and relax"
Humans can not close their ears: Shutting out unwanted sound requires brain activity.
The human brain needs dynamic work for its functioning: All awake humans will therefore during all activity, most often unconsciously, include shorter or longer pauses in what tasks they are focusing on.
In the same way as science is beginning to understand that the mechanism behind the "burn-out syndrome" isn't primarily a too heavy workload, but the lack of necessary regular relaxation pauses, will continuous or too often repeated unwanted sounds hinder relaxation more than add to workload. This leads to the basic assumption:
The basic assumption
Non-auditory health effects and negative performance effects caused by acoustic noise emissions are all based on the fact that audible sound consciously or unconsciously calls for and competes for attention, and that monotonous sound decrease alertness.
Sound calls for and competes for attention
Attention is an active process. Active processes cost energy: In the same way as a personal computer, printer, fax machine or projector requires electric power to do its job does the human brain need energy to execute its tasks. Like the personal computer is the human brain limited in what it can accomplish. Each moment is only a certain amount of energy and capacity available. Like it costs electricity, processor power and consumes RAM (memory) to have many programs active in a PC, does it require brain energy to keep several tasks going on at the same time. (This is Psychology's and Neuroscience's theory of "Working Memory".)
The human brain processes information. IT acoustic noise emissions can in some aspects be regarded as information, but this information is limited to tell us that a machine is on, and how this machine sounds when on. Since most IT users will have other indications that the PC, printer, copier or projector is on, will their brains treat the sound telling that the machine is on as unnecessary and useless information. Hence do most of us not say that we are continuously listening to a PC's, printer's, copier's or projector's sound, but exposed to its noise.
Reactions to being subjected to repeated or continuous unnecessary and useless information include annoyance, feelings of lack of control and even helplessness; and second to this stress with its physiological and behavioral effects.
Note: Those people that like to continuously hear the kind of sound emitted from information technology equipment will of course not experience any adverse effects of listening to it; in the opposite will their health and performance probably benefit of it.
Annoyance and tiredness
Even if some people don't bother much about the sounds emitted from fans, hard disks, storage devices and other mechanical components of information technology equipment, would few choose to continuously listen to a recording of them: The unintentional continuous sound of information technology equipment is by most people regarded an unpleasant kind of sound. Most people dislike what is unpleasant, and want their world to be as comfortable and enjoyable as possible. Annoyance is a natural reaction to being exposed to something unpleasant.
A particular property of IT equipment noise is that it continues as long as the equipment is on. Because of this will we, if annoyed by the sound, continuously have to try to put it to an unconscious level of our minds. Since this continuous active suppression of information costs brain energy will it tire us. We want to be as alert as possible when using IT equipment. The tiring property of low-intensity noise will therefore add to our annoyance towards it.
The tiring aspect of continuous low-intensity noise will be most prominent as we already are tired. We will thus become more annoyed by noise when not thoroughfully rested than when we are, and more annoyed at the end of a working day than at the beginning. Most obvious is the tiring and annoying effect of noise for very tired users trying to focus by the PC late at night in a quiet working or home environment, and for a tired audience in a dark room having to stand the noise of an underdesigned projector.
Lack of control
Annoyance is a reaction that calls attention to the fact that something is wrong. Something wrong is natural to try to make right. Humans will therefore try to find a solution to what annoys them. If we can't find a solution to what annoys us will we experience lack of control.
Because of our World's imperfection there are numerous sources of annoyance humans can not avoid. Most people therefore have the capacity to handle annoyances that they can not respond to.
If humans experience too much of lack of control, will the total experience be perceived as helplessness. Today's working situations are often very hard, and humans do today often experience too little control over their situation. The amount of work in today's World is often more or less over the limit what a human can handle to feel comfortable. Lack of control on what repeated or continuous sounds one is exposed to can here become part of a feeling of helplessness.
The theories on so called "learned helplessness" are often applied on acoustic noise emissions. These theories focus on human reactions in prolonged or too often repeated unsolvable conflict situations.
In a more or less continuous feeling of helplessness at the same time as having to perform complicated tasks, humans will find themselves in a state of negative stress. Stress reactions include arousal, increased levels of hormones necessary for "fight and flight" reactions, elevated blood pressure and the heart beating faster.
If negative stress continues over too long time will secondary reactions occur: sleep disorders will be a first sign, and may be aggravated if one has to stand acoustic noise in the bed room. Secondary to too little or disturbed sleep, and too much of arousal at daytime, will one see changes in brain function, decreased performance, memory deficits, learning difficulties, headache, hypertension and stomach problems.
In the end of this spectrum of stress reactions can one see psychiatric disorders like depression, anxiety syndromes, abuse and "burn-out", musculosceletal disorders, coronary heart disease and stroke.
Note: The Silent PC Web site deals with acoustic noise emissions from information technology equipment. They can of course not alone be held responsible for reactions like the ones above, but it seems possible that they sometimes may take part. Scientific evidence here lacks, as said above.
The Feeling of Relief Sign
While many people these days are becoming aware of the fact that they easy become distracted by IT noise emissions, are many people not, and some can declare that they don't bother about low-intensity sound from machines and equipment at all, and never become distracted by it. People are also here different.
Annoyance caused by acoustic noise emissions is often unconscious. This is not to say that all people not bothered by the sounds that most other people define as noise emissions actually are, but many people will agree on that they have experienced a feeling of relief as the ventilation with its smooth almost non-hearable sound shuts off at a late working day. Other people will say the same on PC noise, and clearly declare that they don't let their machines and equipment be turned on a minute extra if not in use.
The exact meaning of the feeling of relief when low-intensity noise is shut off seems to require further research.