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Special to MSNBC
updated 2/25/1999 8:11:43 AM ET 1999-02-25T13:11:43

We have to blink to cleanse and moisten the eye. Each time the eyelids close, salty secretions from the tear glands are swept over the surface of the eye, flushing away small dust particles and lubricating the exposed portion of the eyeball. Normally we blink every four to six seconds, but in irritating conditions such as a smoke-filled room, we blink more frequently to keep the eyes clean and moist.

PERHAPS THE more interesting thing about blinking is that we do it more frequently than is necessary to cleanse and moisten the cornea. Infants, for example, blink once every minute or so, but adults blink an average of 10 to 15 times a minute. This has lead scientists to discover other, more psychologically influenced reasons for blinking as frequently as we do.

Research has shown that when information acquisition is important, we actively inhibit blinking. We blink more often when we are not taking in and processing information. In this way, blinks are like punctuation marks of the mind, signaling a pause in the activity in your head.

For example, when reading interesting material, we blink an average of three to eight times per minute as opposed to 15 times per minute when we are not engaged in an attention-demanding activity. We are also most likely to blink as our eyes shift from one page of text to the next or from the end of a line of text to the beginning of the next line. This phenomenon has also been demonstrated with auditory input when someone is listening attentively and thus is not unique to visually presented information.

One blink isn’t always like the next. Scientists have shown that frequency and duration varies under different conditions. Air Force pilots flying simulators over “friendly” territory have been shown to blink more frequently and to have longer closure durations of the eyelids than when flying over “enemy” territory. In the latter case, information acquisition is more important, and the pilots blink less frequently and more crisply. Pilots inhibit blinking the most when they have been “painted” by enemy radar and are attempting to find and evade missiles or while landing an aircraft.

There is also a relationship between blink frequency and one’s emotional state. Someone who is tired will blink more frequently and for a longer duration than someone who is well rested.

And during the Watergate hearings, for example, President Nixon’s blink rate markedly increased when asked a question that he was not prepared to answer.

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