Outpatients attending for conservative dental treatment were presented with eight instructions which they were asked to remember. The instructions were either written or spoken, and were in a positive or negative form. Patients treated with nitrous oxide remembered fewer instructions than those treated with local analgesia alone, and this effect of nitrous oxide was particularly marked for written instructions. Patients receiving local analgesia alone were more likely to remember positive than negative instructions in their original syntactical form, but this bias was not evident in the nitrous oxide group. In a second experiment both normal and dentally phobic patients were read dental and general instructions both before and during inhalation of 30 per cent nitrous oxide. Both groups showed a nitrous oxide-induced reduction in partially recalled instructions. There was interesting evidence for a different attentional bias in our two patient groups. The normal group remembered more general than dental instructions, whereas the phobic group showed the opposite pattern, yielding a significant patient group x type of instruction interaction.KEY woms-Nitrous oxide, memory, attention, syntax, cognitive bias.
INTRODUCTIONThere have been several reports of impairments in memory for lists of digits and nouns following inhalation of 30 per cent nitrous oxide (Steinberg, 1954;Kortilla et a/., 1981), the impairments being in acquisition (Steinberg and Summerfield, 1957;Block et al., 1988;Mewaldt et al., 1988). Impairments are not restricted to artificial material, but have also been found in recognition of faces (Norton et al., 1984) and memory for dental events (File et al., 1991).Task difficulty seems to determine whether or not memory impairments are detected after nitrous oxide. Thus. no impairments were found in an easy recall task (Norton et al., 1984) or in a recognition task made easier by repetitions (Block et al., 1988). The purpose of Experiment 1 was to investigate whether clinically used concentrations of nitrous oxide reduced memory for dental instructions and if any such reduction was dependent on the syntax of the instructions and whether they were written or spoken. Mehler (1963) found better recall of active, affirmative instructions than of passive or negative ones, and File and Jew (1973) also found * Author to whom correspondence should be addressed.better recall of airline safety instructions when these were positive, rather than negative, and when passengers heard them rather than read them.In Experiment 2 we investigated whether there was an interaction between the effects of nitrous oxide and the patient group. In Experiment 1 and the File et al. (1992) study the patients receiving nitrous oxide were dental phobics and their memory was compared with a control group receiving similar dental treatment under local analgesia alone. In Experiment 2 we therefore examined the effects of nitrous oxide on memory for instructions in a group of normal and a group of dentally phobic patients. There is some evi...