Chap. 03 p.117-119

Chap. 03 p.117-119

It is also interesting to note that children do not begin to develop speech until their brains have attained a certain degree of electrophysiological maturity, defined in terms of an increase with age in the frequency of the dominant rhythm. Only when this rhythm is about 7 cps or faster (at about age two years) are they ready for speech development.
(g) Neurological Correlates; Pacing of Speech During Thalamic Stimulation. Deep electrical stimulation in the basal ganglia and thalamus is frequently performed in the course of surgical treatment of thalamic pain or certain extrapyramidal motor disorders. Guiot, Hertzog, Rondot, and Molina (1961) have reported that electrical stimulation in a particular place in the thalamus (the ventrolateral nucleus near its contact with the internal capsule) frequently interferes with the rate of speaking. Both slowing to the point of total arrest and acceleration of speech have been observed. The latter is the more interesting for our discussion. It is a behavioral derangement which may occur in complete isolation, that is, without any other observable motor manifestation or abnormal subjective experience. The patient is conscious and cooperative during part of the operation. He is encouraged to maintain spontaneous conversation and, failing this, is aked to count slowly at a rate of about one digit per second. It acceleration occurs with electrical stimulation, it may be sudden and immediate, or it may be a quick speeding up, the words at the end being generated so rapidly as to become unintelligible. It is significant that under conditions of evoked acceleration the shortest observed intervals between digits are about 170 msec.
Acceleration, uncontrollable by the patient, is occasionally associated with parkinsonism and goes under the name of tachyphemia.

(2) Final Comments on Speech Rhythmicity (Cultural, Individual and Biological Variations)
We have proposed that a rhythm exists in speech which serves as an organizing principle and perhaps a timing device for articulation. The basic time unit has a duration of one-sixth of a second. If this rhythm is due to physiological factors rather than cultural ones, it should be then present in all languages of the world. But what about the rhythm of Swedish, Chinese, or Navaho which sound so different to our English-trained ears? What about American Southern dialects which seem more deliberate than the dialect of Brooklyn, New York; and the British dialects which seem faster than American ones? These judgments are based on criteria such as intonation patterns and content of communications, which habe little in common with the potential underlying metric of speech movements. The rise and fall time in intonation patterns (non-tonal languages) are much slower than the phenomenon discussed here, usually extending over two seconds and more. With proper analysis, they may well reveal themselves to be multiples of the much faster basic units discussed above. On the other hand, the pitch-phonemes (also known as tonemes) are likely to fall within the same metric as other phonemes. Nor does our ability to speak slowly or fast have any bearing on the “six-per-second hypothesis,” because it should be possible to make different use of the time units available. There most likely is more than one way of distributing a train of syllables over the rhythmic vehicles.
On the other hand, physiological factors would allow for individual differences because organisms very one from the other. Moreover, the underlying rhythm may be expected to vary within an individual in accordance with physiological states and rates of metabolism. Such within-subject variations would, of course, be subtle, and detection would require statistical analysis of the periodic phenomena involved.
The statistic necessary to prove or reject our hypothesis is quite simple. At present the only obstacle is the necessity of making observations and measurements of hundreds of thousands of events. Suppose we programmed an electronic computer to search the electrical analogue of a speech signal for that point in time at which any voiceless stop is released. And then measured the time lapse between all such successive points. From these data we can make histograms (bar-charts) showing the frequency distribution of all measurements. Since our hypothesis assumes that the variable syllable-duration-time is not continuous and that there are time quanta, the frequency distribution should be multi-modal: and since the basic time unit is predicted to be 160 ± 20msec, the distance between the peaks should be equal to or multiples of this unit.
In a previous section of this chapter we have demonstrated certain formal properties of the ordering of speech events. In the discussion of rhythm we have added some temporal dimensions to those events. The rhythm we have added some temporal dimensions to those events. The rhythm we have added some temporal dimensions to those events. The rhythm is seen as the timing mechanism which should make the ordering phenomenon physically possible. The rhythm is the grid, so to speak. Into whose slots events may be intercalated.
It has long been known that the universally ovserved Rhythmicity of the vertebrate brain (Bremer, 1944; Holst, 1937) or central bervous tissue, in general (Adrian, 1937; Wall,1959) is the underlying motor for a vast variety of rhythmic movements found among vertebrates. If our hypothesis is correct, the motor mechanics of speech (and probably even syntax) is no exception to this generalization, and in this respect, then, speech is no different from many other types of animal behavior. In man, however, the rhythmic motor subserves a highly specialized activity, namely speech.