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G R Lightfoot

Publications and source records attributed to G R Lightfoot.

9 recordsLinked to original sources
PubMed2000

Audiometer calibration: interpreting and applying the standards.

A degree of judgement is required when applying the British Standard associated with the calibration and performance of audiometers, BS EN 60645-1 (IEC 645-1). Consequently there is potential for variation of practice between calibration agencies. This note addresses issues and makes suggestions relating to the measurement of distortion, on-off effect, cross talk, linearity, rise/fall time and to the positioning of the earphone on an artificial ear. The degree of precision appropriate to each measurement is suggested. A warning is given of the audiological consequences of excessive distortion produced by normally functioning audiometers.

Audiometry↗
PubMed1993

Bone conduction errors at high frequencies: implications for clinical and medico-legal practice.

The magnitude and origin of audiometric air-bone gaps in the range 3 kHz to 8 kHz was investigated in 20 normal subjects. The average gap ranged from a minimum of about 3 dB at 3 kHz to a maximum of about 19 dB at 6 kHz. Approximately 5 dB of the gap at high frequencies is caused by excess air-radiated sound from the bone vibrator. A larger error appears to result from discrepancies between the air and bone conduction standards to which audiometers are calibrated. These errors may influence diagnosis and we recommend that bone conduction tests at frequencies greater than 4 kHz are avoided. These findings have implications for medico-legal work where small air-bone gaps have diagnostic significance.

Audiometry, Pure-Tone↗
PubMed1993

Correcting for factors affecting ABR wave V latency.

The latency of auditory brainstem response (ABR) wave V has been shown to be affected by several subject and technical factors. Previous studies have often concluded with a recommendation to account or correct for one or more of these factors when latency is used as a means of detecting retrocochlear dysfunction. This study investigated the effect of subject age, sex, hearing loss and stimulus intensity on ABR wave V latency in a group of 189 clinical subjects in whom retrocochlear disease was effectively excluded. Regression analysis showed that all four factors exerted a significant influence on latency and that hearing loss and intensity were most effectively represented when combined to form a sensation level variable, together with a measure of audiogram slope.

Acoustic Stimulation↗
PubMed1992

ABR screening for acoustic neuromata: the role of rate-induced latency shift measurements.

The audiological assessment of patients considered 'at risk' for an acoustic neuroma is problematic when the patient has a severe hearing loss. The utility of ABR rate-induced latency shift (RLS) measurements was investigated in 189 patients who had passed a conventional assessment and 31 patients with an acoustic neuroma. A test based on the RLS of wave V using rates of 11.1 s-1 and 88.8 s-1 had a sensitivity of 89.5% and a specificity of 90.8% when applied with a dual interpretive criterion which included the loss of wave V at the higher rate. This test was included in an ABR screening protocol which had a sensitivity of 100% and a specificity of 97.9%. The RLS test requires no correction for age, sex, hearing loss or stimulus intensity and may be used in patients with severe hearing loss for whom other ABR tests are inappropriate.

Adult↗
PubMed1979

Air-borne radiation from bone conduction transducers.

The relative magnitudes of air-borne radiation and mechanical vibration from three types of bone conduction transducer have been measured. The study suggests that the presence of excess air-borne radiation can lead to the observation of a false air-bone gap in audiometry. Some methods of overcoming this effect are considered.

Air↗
PubMed1978

Some observations on the contralateral stapedial reflex artefact.

An artefact was observed whilst testing profoundly deaf children with a peters AP61c acoustic impedance meter, using the contralateral stapedial reflex technique at high stimulus levels. A study was carried out on cadavers which confirmed the earlier observation, and this pseudo-reflex was found to be caused by the transmission across the head of the stapedial reflex stimulus tone during contralateral testing. An electronic filter was designed and built which suppressed this artefact. It is suggested that this artefact could be mistaken for a stapedial reflex response.

Acoustic Stimulation↗