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The validity of d', the signal detection theory measure of sensory efficiency, seems suspect in applications to vigilance and inspection, and it is suggested that the investigator should use an alternative, distribution-free measure instead. Three nonparametric measures of efficiency which seem particularly well suited to vigilance applications are considered. The measures, AG (Green and Swets, 1966), A' (Pollack and Norman, 1964), and E (McCornack, 1961) are defined and illustrated, and an example is provided demonstrating their use and suitability in analyzing data from a sustained monitoring task. Norman's (1964) nonmetric procedure for comparing performance efficiency is also applied to the data and is shown to provide a useful means for distinguishing between measure-dependent and measure-independent inferences about changes in efficiency. The relative merits of the three non-parametric measures are discussed.

The effects of intraduodenal and dietary lipid on alertness, mood and performance in a task requiring sustained attention were investigated in two studies. The first experiment compared the effect of duodenal infusion of either 100 g/l Intralipid (836 kJ/min) or isotonic saline (9 g NaCl/l) in paired studies carried out on two non-consecutive days on five male volunteers. Two consecutive 3 h infusions, one of lipid, the other saline, were given blind on each day using a crossover design. Analysis of variance indicated that lipid significantly reduced alertness (P < 0.05) and affected the speed and accuracy of performance in a sustained attention task (P < 0.05). A second experiment compared the effects on eight male volunteers of two isoenergetic lunches of similar appearance, taste and protein content but Wering fat and carbohydrate (CHO) contents (fat energy:CHO, 64:18 v. 7:76). Alertness was lower (P < 0.05) and responses to stimuli in a sustained attention task were slower after the high-fat meal than after the lowfat meal (P < 0.05). In conclusion, infusion of lipid into the small intestine, and the substitution of fat for carbohydrate while keeping energy and protein constant in a lunch, both cause an enhanced postprandial decline in alertness and concentration. This may be related to the presence of lipid in the small intestine.

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