Neuropsychological Functioning in Danish Gulf War Veterans

Research has shown that Danish Gulf War (GW) veterans reported a significantly higher prevalence of neuropsychological symptoms than did military controls 6 years after GW deployment. To explore the possible central nervous system determinants of these complaints, neuropsychological tests were administered to stratified, random samples of the Danish cohort of 916 GW-deployed veterans and 236 non–GW-deployed participants. Multivariate analyses of covariance were used to analyze neuropsychological test outcomes among the 215 male participants (143 GW-deployed and 72 non–GW-deployed soldiers). No significant differences in neuropsychological test performances were found between the GW-deployed and non–GW-deployed groups. Troops deployed to the GW reported significantly more mood complaints (i.e., fatigue and confusion) than their nondeployed counterparts. Because they were assigned to the Gulf region during the postcombat phase, Danish GW soldiers differed from the majority of American GW-deployed troops in military assignments and possible toxicant exposures.     

Cognitive Functioning in Treatment-Seeking Gulf War Veterans: Pyridostigmine Bromide Use and PTSD

Gulf War (GW) deployed veterans have reported health symptoms since returning from the war that suggest dysfunction of the central nervous system (CNS). These symptoms include memory and concentration difficulties, fatigue, and headaches. Leading hypotheses for the etiology of these cognitive complaints include psychological factors and/or exposures to chemicals with neurotoxic properties. In this study, cognitive functioning was compared in treatment-seeking GW-deployed veterans and a treatment-seeking non–GW-deployed veteran control group. Results indicated that GW-deployed veterans performed significantly worse than the comparison group on tests of attention, visuospatial skills, visual memory, and mood. GW-deployed veterans who reported taking pyridostigmine bromide (PB) performed worse than GW-deployed veterans without PB use on executive system tasks. Treatment-seeking GW-deployed veterans with diagnoses of posttraumatic stress disorder (PTSD) did not differ on cognitive test measures compared with GW-deployed veterans without PTSD. No interaction effect of PTSD and PB use was found.     

A comparison of visual tilt illusions measured by the techniques of verticle setting, parallel matching, and dot alignment.

The tilt illusion (TI) was investigated by using both short (19 min) and long (2 deg 6 min) test lines, at three angles of test line-inducing line separation (15 degrees, 45 degrees, and 75 degrees). Three groups of ten observers each provided data under one of three task conditions: vertical judgment, parallel matching, and dot alignment on a common visual display. The main result was that both the vertical judgment and the parallel matching task provided similar, classic TI angular functions with the means ordered 15 degrees greater than 45 degrees greater than 75 degrees and with small attraction effects at 75 degrees in three of the four relevant functions. The third task, dot alignment, yielded results different from the average of the other two: no attraction effects occurred and, with the short test line, the obtained mean illusion at 45 degrees exceeded those at the other intersect angles. These results are consistent with alignment data reported by others. One explanation is that the inducing line produces an apparent bowing of the test line which would be reflected in dot alignments but not in vertical setting or in parallel matching. However, direct evidence does not support this hypothesis. An alternate hypothesis, for which independent evidence exists, is that alignment errors reflect perceptual mistracking but that the origin of these errors is not the tip of the test line but within it. Although this does not explain dot alignment errors, it highlights their complexity and the need to interpret them with caution.     

Successive independence and behavioral contrast in a closed economy.

Two pigeons had access to multiple concurrent schedules of reinforcement for 24 hours per day in their home cages. The variable-interval schedules comprising the multiple concurrent schedules were varied across 16 conditions. In three sets of conditions, one schedule was varied while its concurrent alternative and the concurrent schedules in the other component were held constant. Behavioral contrast was observed; that is, as the rate of reinforcement arranged by the varied schedule decreased, response rates on the constant schedules typically increased. These conditions formed part of two larger sets of conditions in which the concurrent schedules in one multiple-schedule component remained constant while the concurrent schedules in the other component were varied. Successive independence was found, in that behavior allocation during the constant component did not vary as a function of the reinforcer ratios in the varied component. Successive independence between components in multiple concurrent schedules is a robust result that occurs in closed economies and under conditions that promote behavioral contrast.     

Semantic priming in young and older adults: evidence for age constancy in automatic and attentional processes

Automatic and attentional components of semantic priming and the relation of each to episodic memory were evaluated in young and older adults. Category names served as prime words, and the relatedness of the prime to a subsequent lexical decision target was varied orthogonally with whether the target category was expected or unexpected. At a prime-target stimulus-onset asynchrony (SOA) of 410 ms, target words in the same category had faster lexical decision latencies than did different category targets. This effect was not significant at a 1,550-ms SOA and was attributed to automatic processes. Expected category targets had faster latencies than unexpected category targets at the 410-ms SOA, and the magnitude of the effect increased at the 1,550-ms SOA. This effect was attributed to attentional processes. These patterns of priming were obtained for both age groups, but in a surprise memory test older adults had poorer recall of primes and targets. We discuss the implications of these results for the hypothesis that older adults suffer deficits in selective attention and for the related hypothesis that attentional deficits impair semantic processing, which causes memory decrements in old age.