A BEHAVIOURAL AND ELECTROPHYSIOLOGICAL APPROACH TO THE STUDY OF AGE AND DRUG EFFECTS ON ATTENTION

Abstract

The three primary aims of the present study are: (i) to examine the theoretical perspective of Hasher and Zacks (1979) that organismic (e.g., age) and environmental (e.g., drugs) variables influence attentional capacity. The implications are that increased age and depressant drugs (e.g. diazepam) may reduce attentional resources and hence impair those cognitive functions that require allocation of attention. Conversely, stimulant drugs (eg., caffeine) may increase attentional capacity and therefore enhance those cognitive performance that require attention. (ii) to test the popular belief that elderly are more disadvantaged in divided and focused attention than the young. (iii) to assess the effects of low doses of caffeine and diazepam on attention, and to elucidate the locus of these drug actions on performance. The present study comprised three experiments which employed visual search/detection tasks to assess divided and focused attention. Experiment 1a and 1b examined the effects of caffeine and diazepam (respectively) on divided and focused attention of the young. Three levels of each drug were administered orally--- 0, 1, and 2 mg/kg for caffeine and 0, 0.05, and 0.1 mg/kg for diazepam. In addition, subjects in the drug experiments also performed a battery of behavioural tasks comprising addition, symbol cancellation, number learning, card sorting, and hand steadiness. Experiment 2 examined age-related differences in divided and focused attention performance among a group of elderly and young subjects. As no drugs were employed in this study, test battery was omitted, and subjects performed only the attentional tasks. Both behavioural (response accuracy and their reaction time) and electrophysiological (amplitude and latency of P3) measures were used as dependent variables in all three experiments. The results of Experiment 1a showed that caffeine has no effect on resource capacity. However, caffeine was found to impair encoding processes in divided attention. In addition, caffeine interacted with gender to impair focused attention in females. Experiment 1b found diazepam to act on resource capacity and focused attention. It is suggested that diazepam impairs divided attention by interfering with encoding of information. The effects of diazepam on focused attention is more complex, being dependent on a multitude of factors such as dose, gender, and tasks. Specifically, 0.1 mg/kg diazepam facilitated focused attention and symbol cancellation tasks. Facilitation in the latter task, was however, seen only in the performance of females. In contrast, the same diazepam dose impaired males in symbol cancellation task. Experiment 2 showed that increased age affected both divided and focused attention. As expected, age-related decline in capacity was evident in both behavioural (reaction time and response accuracy) and electrophysiological data (P3 amplitude). Results showed that the capacity of elderly were reduced by approximately 35%. As such, elderly were found to be more disadvantaged than the young in divided attention tasks. However, moderate caffeine usage was found to ameliorate this age-related decline in capacity. In addition, elderly were also found to be more susceptible than the young to focused attention deficits.