Photoglottography or photo-electric glottography is a

laboratory technique A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physici ...

for investigating the opening and closing of the

glottis The glottis is the opening between the vocal folds (the rima glottidis). The glottis is crucial in producing vowels and voiced consonants. Etymology From Ancient Greek ''γλωττίς'' (glōttís), derived from ''γλῶττα'' (glôtta), va ...

in the

larynx The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about ...

. It detects variations in the amount of light that can pass through the glottis as it opens and closes.

Transillumination of the glottis

It was observed by Czermak in 1861 that the inside of the

trachea The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...

could be illuminated from outside the neck, in what he called ''illumination by transparency'', and the resulting light passing through the glottis observed with a laryngoscopic mirror. Electronic techniques making use of this observation began to be used in the mid-twentieth century. Instruments such as that designed and manufactured by B. Frøkjaer-Jensen, have used the combination of a light source illuminating the trachea from below, and a light-sensitive cell positioned above the glottis in the

pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...

to detect light passing through the glottis. This cell is fixed near the end of a thin tube inserted through the nose and nasal passages (which leaves the articulators relatively free to move in speech); in the Frøkjaer-Jensen instrument the tube is extended so that a few centimetres can be swallowed into the

oesophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

in order to anchor the light-sensitive cell securely in place. The light from a light source is carried to the neck by a tapered perspex rod pressed against the neck immediately below the thyroid cartilage; alternatively, a cold light source may be applied directly to the neck.

Photoglottography in speech research

Two main areas have been explored with this technique.

Examination of vocal fold vibration

A number of researchers have attempted to compare the photoglottograph output with measurements of glottal opening based on high-speed or stroboscopic film during

phonation The term phonation has slightly different meanings depending on the subfield of phonetics. Among some phoneticians, ''phonation'' is the process by which the vocal folds produce certain sounds through quasi-periodic vibration. This is the defini ...

. If the two were closely similar, the photoglottograph would represent a quicker and cheaper method of analysis of phonation. However, Baken reports variable results: a study by Coleman and Wendahl concluded that "relating photoglottographic waveforms ... to glottal area is not only hazardous but invalid in many cases", while a later study by Harden found that the photoglottograph provided "essentially the same information on glottal area function as that provided by ultrahigh-speed photography"

Detection of large-scale glottal opening and closing

In addition to the study of vocal fold vibratory patterns, the technique may be used to detect the opening of the glottis for voiceless consonants or the closure of the glottis for

glottalic consonant In phonetics, a glottalic consonant is a consonant produced with some important contribution (movement or closure) of the glottis. Glottalic sounds may involve motion of the larynx upward or downward, as the initiator of an egressive or ingre ...

s and

glottal stop The glottal plosive or stop is a type of consonantal sound used in many spoken languages, produced by obstructing airflow in the vocal tract or, more precisely, the glottis. The symbol in the International Phonetic Alphabet that represents thi ...

Clinical applications

Photoglottography has been evaluated for usefulness in the study of

dysphonic A hoarse voice, also known as dysphonia or hoarseness, is when the voice involuntarily sounds breathy, raspy, or strained, or is softer in volume or lower in pitch. A hoarse voice, can be associated with a feeling of unease or scratchiness in the ...

patients in the clinic. The technique is thought to be useful in reflecting the

phonatory The term phonation has slightly different meanings depending on the subfield of phonetics. Among some phoneticians, ''phonation'' is the process by which the vocal folds produce certain sounds through quasi-periodic vibration. This is the defini ...

effect of

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...

References