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Divers breathing compressed air at depths beyond 30 m experience a type of behavioural impairment known as inert gas narcosis. This condition degrades performance on a wide range of tasks and has the potential to compromise safety. Symptoms associated with narcosis include slowed response time, amnesia, and euphoria. Studies have also found disturbances to mechanisms regulating ocular control in response to vestibular stimulation; however, these experiments have been limited to very low frequency head movement (0.2 Hz). Thus, to further examine the effects of narcosis on visual/vestibular mechanisms, the vestibular ocular reflex (VOR) was assessed across a range of higher frequencies more representative of natural head movement (2.0-4.7 Hz). Seven subjects were tested prior to, during and after exposure to narcosis which was induced using 30% nitrous oxide. Standard room air was breathed as a control. The results indicated that narcosis decreased the velocity of compensatory eye movements in response to head rotation (decrease in VOR-gain), with more pronounced decreases occurring at the higher frequencies. The lag between eye and head position (phase lag) was also decreased by nitrous oxide; an effect that was again more pronounced at higher frequencies. These results indicate that narcosis disrupts ocular regulatory mechanisms which help to stabilize images on the retina during head movement.

To assess the effects of nitrogen narcosis 16 male divers were tested on a digit-copying and a mental task. After a surface testing, the divers were tested under water; 8 started at 3 m followed by 30 m (Group A), and the other 8 at 30 m followed by 3 m (Group B). For all the divers, performance at 3 m and 30 m was compared and it was found that at 30 m the digit-copying was significantly impaired by 2L% (p 0.2). For digit-copying there was no significant difference between the impairment of Group A (19%) and that of Group B (23%). However, in the mental task analysis of variance revealed a significant Groups x Conditions interaction (p

Inert gas narcosis was induced with N20 and its effects on Fitts’ Law were studied using a reciprocal tapping task with different values of A(movement amplitude) and W (target width). In Experiment 1 it was found that N20 slowed MT (movement time) by increasing the slope of Fitts’ function and also increased variability of shots on the target. The slope increase was replicated in Experiment 2 but training and KR (knowledge of results) eliminated the increased variability found in Experiment 1. In Experiment 2, when MT was regressed on amplitude with accuracy constant and on accuracy with amplitude constant, N20 increased the slopes of the latter set of regression lines but not the former. This was taken as evidence that disruption of a control process concerned with error correction is implicated in the slope increase seen with Fitts’ Law. It was also concluded that increased variability is not a necessary concomitant of narcosis and its occurrence can be explained in terms of a trade-off between speed an...

Inert gas narcosis was induced in experiment 1 with compressed air using a hyperbaric chamber at 10 ata and in experiment 2 with 35% N2O-65% O2 and studied using a serial choice response time task. Both breathing mixtures degraded performance in an identical manner. There was a slowing of response latency with the frequency distribution of responses being shifted to the right. There was also increased positive skewing and variability of this distribution but no indication of extra-long ‘blocking’ responses. Number of errors increased and the latency pattern around an error did not change shape but showed an overall slowing. In addition, the effect of N2O on response latency was studied at two levels of stimulus brightness and an additive not an interactive relationship was found. It was concluded that these results support a model of inert gas narcosis effects on human performance which postulates that information processing throughout the perceptual-motor system is slowed but not disrupted, the exception...

The effects of ethyl alcohol (1·5 ml/kg body weight) and dextroamphetamine (15 mg) on nitrogen narcosis were investigated in two experiments using a 2-, 3- and 4-choice serial reaction time (RT) task with accuracy held constant. Narcosis was induced with air at 6·4 atmospheres absolute (ATA) and a heliox mixture was used as a control. Heliox at 6·4 ATA did not affect RT. Alcohol alone and air at 6·4 ATA increased the intercept of the Hick-Hyman function whereas amphetamine alone decreased it. The increased intercept with air at 6·4 ATA was exacerbated additively by alcohol and ameliorated antagonistically by amphetamine. The slope of the Hick-Hyman function was unaffected. Frequency distributions were shifted as a whole and their shapes were unaltered. It is concluded that these data are consistent with the slowed processing model which proposes that the effects of narcosis on performance are due to a decrease in arousal in conjunction with secondary changes in task strategy.