Study of vocal reaction times in subjects chronically exposed to neurotoxic solvents

The aim of this study was to evaluate the effects on a group of 35 laundry operators of exposure to the neurotoxic solvent perchloroethylene by means of Vocal Reaction Time (VRT) measurement. A group of 39 normal subjects comparable for age and educational level with the laundry workers constituted the controls. Vocal Reaction Times were measured by means of a device that presented Visual stimuli, acquired the acoustic signal and measured VRTs and durations. During each test a random sequence of words was presented to the subject under examination. The protocol consisted of an immediate reading task and two delayed reading tasks (the subject had to wait for. a response signal before starting to speak) in which the foreperiod was randomly selected (0.1 s or 1.5 s:). The test was performed using concrete and meaningless words. Analysis of the acoustic signals showed that reaction times were longer for the exposed group than for the controls. The differences between VRTs for the concrete words in all three tasks (immediate, 0.1 s and 1.5 s foreperiod) were statistically significant. The differences between durations were statistically significant for the delayed reading tasks using concrete words and for all tasks using meaningless words. Regression analysis showed a substantial correlation (r = 0.69, r = 0.73) between VRTs and an Exposure Index for concrete words in immediate and delayed (foreperiod = 1.5 s) reading tasks. This method can provide quantitative information about functional alterations of the nervous system areas related to speech production, in subjects exposed to neurotoxic solvents.