Research Update: Fluency and time perception

This article was originally published in the winter 2011 issue of CSA Voices.

Are the brains of people who stutter bad timekeepers?

stopwatch

“I do not understand...the lateral movement of time. A clock ticks in an orderly fashion...My urge is always to telescope time into itself... and speed it up. People with a normal sense of time can count “one, two, three, four, five” systematically. I on the other hand, would count out five as ‘one, two threefourfive’ ”
Marty Jezer, Stuttering: a Life Bound up in Words

Marty Jezer’s impatience with time is typical of a lot of people who stutter. In fact, it has been a subject of study in speech pathology experiments as early as 1939. A faulty perception of time, known as a “temporal disorder”, is considered to be a factor in the stuttering condition by many researchers.

The technical term for the perception of time passing is protensity. We all know that “time flies when we are having fun” and crawls when we are being made to endure something unpleasant.  It makes sense, then, that a stutterer’s protensity is skewed while speaking, and that the length of blocks and stutters are drawn out in his or her mind. This has been proven by the results of experiments over the decades.

Actually, an experiment in 1966 found that all speakers, fluent and not, overestimated the duration of 10 seconds when reading aloud, reading silently and listening to others speak (but not when silent). Stuttering subjects scored the least accurately. In fact, researchers found that there was a positive correlation between the severity of the stuttering and the degree of impaired propensity. In other words, the worse the condition of the stuttering, the greater the inadequacy in the brain’s self timer to estimate short durations of time.

In one of the experiments the subjects were asked to estimate the duration of brief sounds, and to indicate the difference in duration between two tones. In another, they were tested in their ability to control the timing of repeated utterances. Participants were told to repeat a sound “the same way each time”. Again, in both cases, the degree of over-estimation correlated with the degree of disfluency in the subject.

It seems obvious from this that stuttering speakers have a less reliable “neural clock” than nonstutters, at least when it comes to short time periods. According to the later study, “there exists a connection between stuttering and difficulty in discriminating differences between short intervals.”

The most recent experiment along these lines ocurred in 2000, in which the goal was to compare protensity estimates between stutterers and nonstutterers, and to compare their ability to distinguish the relative lengths of short tones. The intervals between tones were also measured. The interesting thing about this test is that, instead of dividing into two groups, the participants were placed on a continuum of fluent to non-fluent speakers, meaning even non-stutters were divided into a subgroup of “less fluent”.  Each subject was interviewed in preparation for the experiment and the number of disfluencies for each participant counted.The less fluent non-stutterers had worse propensity than the fluent non-stutterers. Also, it was found that this propensity deficit only ocurred on short intervals and not longer time periods, such as 30 minutes.

Why does this occur, and what does it mean for people who stutter? The two hemispheres of the brain, as we know, are responsible for different things. The side that forms and speaks language – the left – is adept at controlling the short time intervals we experience in speech: the word and the pause, the slices of meaning that are a part of each phrase we speak. The right side of the brain is used more in non-verbal activities such as music, a task that involves working in longer intervals of time. As stutterers show abnormal activity on their brain’s right side while speaking, it makes sense that their ability to guage smaller time durations is compromised.
Further study is needed to determine how this knowledge can be used to benefit the analysis and treatment of  stuttering and other speech defects. In the meantime it is another piece of the neurological puzzle known as stuttering.

BIBLIOGRAPHY

Journal of Speech, Language and Hearing Research, Vol 43, December 2000.  “Disfluency and Time Perception”, by Charles T. Barasch, Barry Guitar, Rebecca J. McCauley, Richard G. Absher, University of Vermont, Burlington.