Effects of ethanol and tobacco on divided attention

Alcohol and human performance

The present paper presents a comprehensive review of studies concerned with the effects of alcohol on human performance. It attempts to review the studies within the framework of the information processing model. The effects of alcohol on information processing and transmission rates, sensory and perceptual processes, motorcontrol processes, attentional processes, and cognitive processes are described and discussed. It is proposed that such a processes analysis of human performance is a useful vehicle to describe the specific effects of alcohol. From the review it is concluded that much of the evidence from simple task description is equivocal. However, when information load is increased, when the stimulus-response incompatibility increases, and when the number of competing information processes occur in 'parallel', then a strong, consistent and coherent pattern of performance deterioration is associated with alcohol consumption.

Effects of nicotine on electroencephalographic (EEG) and behavioural measures of visual working memory in non-smokers during a dual-task paradigm

Research in smokers has shown that nicotine may have the ability to improve certain aspects of cognitive performance, including working memory and attention, processes which implicate frontal and frontal-parietal brain networks. There is limited research on the cognitive effects of nicotine and their associated neural underpinnings in non-smokers. This study examined the effects of acute nicotine on a working memory task alone or combined with a visual detection task (single- and dual-task conditions) using electroencephalographic (EEG) recordings and behavioural performance measures. Twenty non-smokers (13 females; 7 males) received nicotine gum (6 mg) in a double-blind, randomized, placebo-controlled, repeated measures design. Spectral EEG, together with response speed and accuracy measures, were obtained while participants completed a series of N-Back tasks under single- and dual-task conditions. Nicotine failed to exert any significant effects on performance measures, however, EEG changes were observed, primarily in frontal recordings, which varied with memory load, task condition and hemisphere. These findings, discussed in relation to previous studies in smokers, support the notion that nicotine may modulate central executive systems and contribute to smoking behaviour.

Positive and negative effects of alcohol and nicotine and their interactions: a mechanistic review

Nicotine and alcohol are two of the most commonly abused legal substances. Heavy use of one drug can often lead to, or is predictive of, heavy use of the other drug in adolescents and adults. Heavy drinking and smoking alone are of significant health hazard. The combination of the two, however, can result in synergistic adverse effects particularly in incidences of various cancers (e.g., esophagus). Although detrimental consequences of smoking are well established, nicotine by itself might possess positive and even therapeutic potential. Similarly, alcohol at low or moderated doses may confer beneficial health effects. These opposing findings have generated considerable interest in how these drugs act. Here we will briefly review the negative impact of drinking-smoking co-morbidity followed by factors that appear to contribute to the high rate of co-use of alcohol and nicotine. Our main focus will be on what research is telling us about the central actions and interactions of these drugs, and what has been elucidated about the mechanisms of their positive and negative effects. We will conclude by making suggestions for future research in this area.

Dose effects of triazolam and alcohol on cognitive performance in healthy volunteers

Benzodiazepines and alcohol are widely used psychoactive substances that have performance-impairing effects. Research suggests that the impairment profiles for benzodiazepines and alcohol differ, although few cognitive psychopharmacological studies have directly compared these drugs. This double-blind, double-dummy, placebo-controlled, repeated measures study directly compared the acute dose effects of triazolam (0.125, 0.25 mg/70 kg) and alcohol (0.40, 0.80 g/kg) in 20 social drinkers. At doses that produced comparable psychomotor impairment, triazolam was more likely to impair several objective measures of cognitive performance (e.g., episodic memory, divided attention) and to slow performance across several measures. However, only alcohol impaired accuracy on the digit symbol substitution and semantic memory tasks. In addition to objective measures, both drugs impaired awareness of performance impairments (i.e., metacognition) such that participants overestimated impairment, and the magnitude of this effect was generally larger for alcohol. Only triazolam impaired other measures of metacognition (e.g., error detection on a choice reaction time task). Future research might examine the clinical implications of the performance impairments reported here given the widespread use of benzodiazepines and alcohol.

The effect of acute ethanol challenge on global visuospatial attention: exaggeration of leftward bias in line bisection

Acute alcohol challenge has been associated with a selective impairment of right hemisphere function. A hallmark of visuospatial neglect syndrome is that patients with right hemisphere lesions misbisect horizontal lines far rightward of veridical centre. Neurologically intact participants misbisect lines with a systematic leftward bias (pseudoneglect). Neuroimaging studies in neurologically intact participants reveal predominant right hemisphere activation during performance of line bisection tasks. The current study assessed whether acute alcohol challenge alters global visuospatial attention. Participants (N=18; 10 male; strongly right-handed; mean age 23 years) engaged in a forced-choice tachistoscopic line bisection task in both ethanol challenge (mean BAC=.077) and no ethanol control conditions. Mean leftward bisection error in the control condition was -0.238 degrees visual angle (1.05% line length), and leftward bisection error significantly increased (p=.001) under ethanol challenge (-0.333 degrees visual angle, 1.47% line length). Mean bisection precision in the control condition was 0.358 degrees visual angle (1.58% line length); bisection precision significantly deteriorated (p=.008) under ethanol challenge (0.489 degrees, 2.17% line length). Decreased bisection precision indicates that ethanol disrupts the fidelity of visuospatial performance. The exaggerated leftward bisection error implies that ethanol may exert a differential effect on left versus right hemispheric function with respect to the control of global visuospatial attention.

Performance effects of nicotine during selective attention, divided attention, and simple stimulus detection: an fMRI study

Attention-enhancing effects of nicotine appear to depend on the nature of the attentional function. Underlying neuroanatomical mechanisms, too, may vary depending on the function modulated. This functional magnetic resonance imaging study recorded blood oxygen level-dependent (BOLD) activity in minimally deprived smokers during tasks of simple stimulus detection, selective attention, or divided attention after single-blind application of a transdermal nicotine (21 mg) or placebo patch. Smokers' performance in the placebo condition was unimpaired as compared with matched nonsmokers. Nicotine reduced reaction time (RT) in the stimulus detection and selective attention but not divided attention condition. Across all task conditions, nicotine reduced activation in frontal, temporal, thalamic, and visual regions and enhanced deactivation in so-called "default" regions. Thalamic effects correlated with RT reduction selectively during stimulus detection. An interaction with task condition was observed in middle and superior frontal gyri, where nicotine reduced activation only during stimulus detection. A visuomotor control experiment provided evidence against nonspecific effects of nicotine. In conclusion, although prefrontal activity partly displayed differential modulation by nicotine, most BOLD effects were identical across tasks, despite differential performance effects, suggesting that common neuronal mechanisms can selectively benefit different attentional functions. Overall, the effects of nicotine may be explained by increased functional efficiency and downregulated task-independent "default" functions.

Timevarying predictors of smoking cessation among individuals in treatment for alcohol abuse and dependence: findings from Project MATCH

AIMS

Individuals in treatment for alcohol use disorders are more likely to die from cigarette use than from alcohol consumption. Advanced statistical methodologies that increase study power and clinical relevance have been advocated to examine the timevarying nature of substance use relapse and abstinence, including drinking and smoking. The purpose of this investigation was to examine timevarying factors that are associated with smoking cessation among smokers in the general population, including alcohol use, self-efficacy, and depression, to determine if they were also related to smoking cessation during and after treatment for alcohol use disorders.

METHODS

Data were garnered from Project MATCH, a longitudinal prospective study of the efficacy of three behavioural treatments for alcohol use disorders. Timevarying covariate analyses were conducted to examine future smoking cessation.

RESULTS

Results showed that greater self-efficacy regarding resisting temptations to drink and lower levels of depression were independently associated with increased likelihood of stopping smoking. In contrast, drinks per drinking day and confidence regarding not drinking did not demonstrate such associations.

CONCLUSIONS

Clinical implications of these findings suggest that interventions to help alcoholics in recovery avoid temptations to drink, as well as decrease depression, may be warranted. By using advanced statistical techniques, these results can help clinicians and organizations working with smokers in treatment for alcohol use disorders to make informed decisions regarding how best to use limited resources.

Differential effects of alcohol on working memory: distinguishing multiple processes

The authors assessed effects of alcohol consumption on different types of working memory (WM) tasks in an attempt to characterize the nature of alcohol effects on cognition. The WM tasks varied in 2 properties of materials to be retained in a 2-stimulus comparison procedure. Conditions included (a) spatial arrays of colors, (b) temporal sequences of colors, (c) spatial arrays of spoken digits, and (d) temporal sequences of spoken digits. Alcohol consumption impaired memory for auditory and visual sequences but not memory for simultaneous arrays of auditory or visual stimuli. These results suggest that processes needed to encode and maintain stimulus sequences, such as rehearsal, are more sensitive to alcohol intoxication than other WM mechanisms needed to maintain multiple concurrent items, such as focusing attention on them. These findings help to resolve disparate findings from prior research on alcohol's effect on WM and on divided attention. The results suggest that moderate doses of alcohol impair WM by affecting certain mnemonic strategies and executive processes rather than by shrinking the basic holding capacity of WM.

Changes in cigarette consumption and drinking outcomes: findings from Project MATCH

Individuals undergoing treatment for alcohol use disorders smoke at rates that exceed those reported in the general population, and most patients will continue to smoke after treatment completion. A growing body of research indicates that quitting smoking is associated with better alcoholism treatment outcomes. Studies that dichotomize participants into smokers and nonsmokers, however, may be overlooking the possibility that even decreases in cigarette consumption over time among continuing smokers may also be related to improved alcohol use outcomes. The purpose of this article was to examine the relationship between cigarette consumption and alcohol use outcomes using data from Project MATCH. Smokers were divided into three groups according to whether their cigarette consumption decreased, increased, or remained constant from baseline to the 15-month follow-up. Results showed that smokers whose cigarette consumption decreased were significantly less likely to relapse to alcohol use than those whose consumption increased or remained unchanged. These findings suggest that even reductions in tobacco use may be associated with better drinking outcomes in alcoholism treatment.

Nicotine modulates reorienting of visuospatial attention and neural activity in human parietal cortex

Prior studies in animals and humans indicate that reorienting of visuospatial attention is modulated by the cholinergic agonist nicotine. We have previously identified neural correlates of alerting and reorienting attention in humans and found that the parietal cortex is specifically involved in reorienting. This study investigates whether the alerting and reorienting systems, especially in the parietal cortex, are modulated by nicotine. We used event-related functional magnetic resonance imaging (fMRI) and studied 15 nonsmoking volunteers under placebo and nicotine (NICORETTE) polacrilex gum 1 and 2 mg). Subjects performed a cued target detection task with four different types of randomly intermixed trials (no, neutral, valid, and invalid cue trials). Alerting was captured by comparing BOLD activity and reaction times (RTs) in neutrally cued trials with no cue trials. Reorienting was isolated by comparing invalidly with validly cued trials. On the behavioral level, nicotine affected reorienting of attention by speeding RTs in invalidly cued trials; alerting was not affected by nicotine. Neurally, however, nicotine modulated both attentional systems. Pharmacologic effects on alerting-related brain activity were mainly evident as modulation of BOLD responses in the right angular gyrus and right middle frontal gyrus due to a reduction of neural activity in no cue trials. In the reorienting system, effects of nicotine were mainly evident in the left intraparietal sulcus and precuneus and due to a reduction of neural activity in invalidly cued trials. We conclude that nicotine enhances reorienting of attention in visuospatial tasks and that one behavioral correlate of speeded RTs is reduced parietal activity.

Comprehensive deficits in performance of an attentional task produced by co-administering alcohol and nicotine to rats

BACKGROUND

Nicotine can improve and alcohol can impair attentional performance in rats, but little is known about the effects of mixtures of the two drugs with respect to attention.

AIMS

The aims were to investigate the effects of alcohol and nicotine alone and when co-administered on performance of a five-choice serial reaction time task, and to examine the impact of task difficulty by varying durations of the limited hold (LH) for availability of the reinforcer.

METHODS

Male hooded rats were trained to respond (nose-poke) to a 0.5 s light stimulus presented randomly in one of five apertures to obtain food reinforcers. Three groups of rats trained with different LH values were used (n = 10).

RESULTS

The first experiment showed that training at different LH values had little effect on performance when the LH value during testing was held constant. Experiment 2 showed that alcohol (0.4-1.6 g/kg, i.p.) had no effect on the percentage of correct responses (accuracy) but it impaired all speed-related indices. In the third experiment, the effects of nicotine (0.1 and 0.2 mg/kg, s.c.) were determined alone and on the dose-response curve for alcohol (0.4-1.2 g/kg, i.p.). Nicotine alone produced small improvements in performance whereas co-administration of nicotine and alcohol produced large decrements at doses of alcohol that themselves only slightly impaired performance. These decrements included impairments of accuracy as well as of anticipatory responding, omission errors, response latencies and reinforcers earned. There were no marked or consistent interactions of drug effects with LH values.

CONCLUSIONS

Task performance was disrupted to a much greater extent by co-administration of alcohol and nicotine than by alcohol alone; therefore, it seems unlikely that an ability of nicotine to reverse the effects of alcohol can account for associations between the use of the two substances.

Smoking and attention: a review and reformulation of the stimulus-filter hypothesis

An accumulation of evidence suggests that smoking may be reinforcing, in part, due to nicotine's capacity to enhance attentional processing. Correspondingly, the stimulus-filter model of nicotine reinforcement asserts that nicotine facilitates cognitive performance by acting as a stimulus-barrier, thereby screening irrelevant and annoying stimuli from the smoker's awareness. A review of the available data suggests that while nicotine does appear to reliably enhance sustained, divided, and focused attention, the stimulus-filter model falls short of adequately explaining the findings. An alternative, attention, allocation model of nicotine reinforcement is reviewed, the tenets of which suggest that nicotine differentially augments attentional processing via its propensity to: (a) induce attentional narrowing, and (b) increase perceptual processing capacity. The motivational implications of the model, including smokers' use of nicotine to dampen stress, are discussed.

Alcohol and vigilance performance: a review

In the literature on the effects of alcohol on driving-related skills, it is sometimes claimed that vigilance tasks are insensitive instruments whereas divided-attention tasks are extremely sensitive to the effects of alcohol. The results of the present review, based on the analysis of 38 comparisons of alcohol and placebo in vigilance tasks, require that these claims be restated. Both types of attentional task (concentrated and divided) are indispensable in test batteries, although not all types of vigilance and divided-attention task are equally sensitive, e.g. some types of vigilance task, using spatial stimuli, were sensitive to BAC levels of 0.03% whereas other types were insensitive to levels of 0.10%. In contrast, the usefulness of tasks of questionable validity and/or low sensitivity (such as the DSST, CFF, digit span, simple RT and choice RT) is questioned. Apart from issues of validity and sensitivity of tests, the ways in which alcohol may affect performance are also discussed. The main effect of moderate doses of alcohol is on attention and information processing. The capacity to divide and sustain attention is already impaired at BAC levels of 0.02-0.03%. Further, alcohol effects appear to some extent to be time-dependent, and are greatest during periods of sleepiness (the early afternoon and after midnight). Some current BAC levels concerning drinking and driving are far too generous. There is sufficient evidence from the literature on performance indicating that the BAC standard for driving should be lowered to 0.02% for driving after midnight and for special risk groups (young and less experienced drivers).

Effect of low and moderate doses of alcohol on driving hazard perception latency and driving speed

Both driving speed and speed of detection of potentially hazardous events while driving have been found to correlate positively with accident rates across individuals. Alcohol ingestion is also known to increase risk of a traffic accident. This paper reports two double-blind, placebo-controlled studies: one on the effect of alcohol on driving speed and the other on the effect of alcohol on time taken to detect potential traffic hazards. Moderate drinkers aged between 30 and 55 took part. Each subject underwent three experimental conditions on separate days: no alcohol, low alcohol (0.025% BAC) and moderate alcohol (0.05% BAC). The order of conditions was counterbalanced. The moderate alcohol dose increased mean time taken to respond to hazards (2.5 s in no alcohol condition compared with 3.2 s in moderate alcohol condition) but did not affect mean driving speed (indexed by time taken to travel sections of a fixed route; 19.3 s in no alcohol compared with 19.0 s in moderate alcohol). The results support the view that at least part of the excess risk of accident associated with alcohol ingestion is attributable to an increase in the time taken to respond to traffic hazards.

Stimulant drugs and vigilance performance: a review

The literature on the effects of some stimulant drugs (amphetamine, methylphenidate, caffeine, and nicotine) on vigilance performance is reviewed. Improvement of overall level of performance (both accuracy and speed) after the intake of amphetamine, caffeine, and nicotine has often been reported, and the decrement in performance with time has been shown to be prevented especially with amphetamine and nicotine. Effects on false alarms are negligible. In studies where a test battery was employed, vigilance tasks appeared to be the most sensitive performance tests in detecting the effects of stimulants; however, different vigilance tasks may measure different aspects of mental functions. There is no support for earlier conclusions that improvements are noticed only in fatigued subjects in protracted sessions. Evidence from several studies does not support the hypothesis that improvements are only a recovery of withdrawal-induced impairment. Because positive effects have been obtained with drugs possessing different mechanisms of action, there is as yet no clear support for a noradrenergic, dopaminergic, or cholinergic theory of sustained attention. Simple neurotransmitter theories of attention and information processing may be untenable.

Enhancement of continuous performance task reaction time by smoking in non-deprived smokers

In a test of the withdrawal-deficit hypothesis of the cognitive effects of cigarette smoking, non-deprived smokers participated in two sessions held on consecutive days. In both sessions, subjects performed two 20-min continuous performance tasks (CPTs). The CPT was a relatively "easy" version designed to require minimal practice (digit 0 target response; digits 1-9 nontarget response; 19% of stimuli targets). In one session, subjects smoked a cigarette prior to each CPT; in the other session they did not smoke (session order counterbalanced). Reaction time (RT) was significantly faster in the smoking session than in the non-smoking session with no difference in number of incorrect responses, a finding incompatible with the withdrawal-deficit hypothesis. Further, light inhalers (as assessed by pre-smoking to post-task increase in expired air carbon monoxide) appeared to process nontarget stimuli faster than deep inhalers, especially in the no smoking session. The results also indicated that, at least during the first CPT of each session, the performance of females in the no smoking session was poorer than in the smoking session and poorer than males regardless of session. In the latter part of the first CPT, the performance of males in the smoking session was better than their performance in the no smoking session. No clear pattern emerged for the second CPT.

Separate and combined effects of the social drugs on psychomotor performance

Ten female subjects (five smokers and five non-smokers) performed a choice reaction time task (CRT), a compensatory tracking task (CTT), a short-term memory task (STM) and were tested for their critical flicker fusion threshold (CFF) at set points over 4 h after the administration of each possible combination of nicotine (2 mg gum or placebo), caffeine (250 mg capsule or placebo) and alcohol (30 g or placebo). Memory and motor function were shown to be facilitated by nicotine or caffeine, and the debilitating effects of alcohol were frequently antagonised by either drug. In spite of the differences in their neuropharmacological actions, combinations of nicotine, caffeine and alcohol may be compared through their effects on common information processing mechanisms involved in psychomotor performance.

Smoking and drinking: a review of the literature

Smoking and drinking share many detrimental effects, some of which operate synergistically. Over 90% of alcoholic inpatients are smokers, with similar findings regarding outpatients. In the general population, the relationship between smoking and drinking appears positive but modest. Nicotine appears to facilitate ethanol consumption and vice versa. While ample theoretical viewpoints exist to explain the covariance of alcohol and cigarette consumption, conclusive data supporting one or another of these views are lacking. The assumption that alcoholics should be discouraged from quitting smoking as well as drinking is without empirical basis. Research should ascertain whether problem drinkers with greater positive association between alcohol and smoking benefit differentially from quitting both.

Effects of alcohol and extended practice on divided-attention performance

The effects of alcohol and extended practice on divided attention were investigated using a visual tracking task and an auditory detection task. Subjects performed the tasks with and without alcohol, under single-task (S) and dual-task (D) conditions, both before and after they had received extended practice under single-task conditions without alcohol. Tracking accuracy improved with practice and was impaired under divided-attention conditions but was not affected by alcohol. Speed of detection was impaired by alcohol, improved by practice, and impaired by divided attention. Extended practice did not reduce the influence of alcohol. The effects of both alcohol and practice on speed of detection were significantly greater under dual-task conditions than under single-task conditions. Analysis of detection-task reaction times in terms of relative divided-attention costs, (D-S)/S, showed no effect of alcohol, but a highly significant reduction in costs with extended practice. It is concluded that (1) alcohol and practice can have quantitatively, but not qualitatively, similar effects on speeded performance, and (2) the effect of alcohol is not influenced by the attentional requirements of the task.

Nicotine chewing gum (2 mg, 4 mg) and cigarette smoking: comparative effects upon vigilance and heart rate

Sixteen male smokers, abstinent the morning before testing, were assessed under four conditions: placebo chewing gum, 2 mg nicotine chewing gum, 4 mg nicotine gum, and cigarette smoking. Placebo gum was administered in the cigarette condition, while sham smoking occurred in the gum conditions. Pre-drug administration and post-drug difference scores were calculated for each assessment measure: rapid visual information processing (RVIP), memory for new information, and heart rate. Nicotine raised heart rate in a significant monotonic dose-related manner (P less than 0.001): placebo +0.2; 2 mg gum +5.1; 4 mg gum +9.8; cigarette +17.5 bpm. Rapid visual information processing target detections were also significantly related to dose (P less than 0.01), with this increased vigilance significant under 4 mg nicotine gum and cigarette smoking. Memory task performance was not significantly affected. Self-reported feelings of alertness/energy were higher while smoking than under placebo or 4 mg gum. Complaints about the taste of the 4 mg nicotine gum were frequent.

Acute effects of tobacco on human brain stem evoked potentials

Reports of tobacco-induced electrocortical activation have frequently indicated that this effect is mediated via nicotine's action on sub-cortical structures. This study focused on human brain stem involvement by examining the acute effects of tobacco smoking on brain stem auditory potentials (BSAEPs). Twelve regular smokers were tested on two separate sessions involving sham or real smoking. On each session, BSAEPs were recorded during a baseline period and immediately after smoking. BSAEPs, recorded from Cz, were elicited by presentation of 1,000 monaural, rare fraction click stimuli. Latency and amplitudes of peak components I, III and V were assessed and analysed. No significant effects were observed for latency measures or for amplitudes of peaks I and III. A significant effect was observed for peak V with tobacco resulting in larger amplitudes relative to sham smoking. Peak V reflects activity from upper pontine-lower midbrain sites and this tobacco-peak V finding is discussed in relation to arousal and information processing theories of smoking.

Investigating drug--ethanol interactions

Methodology developed in our laboratories for testing the interactive effects of ethanol and drugs on human psychomotor performance is discussed. An attempt has been made to relate the findings of our studies to the results of real-life impairment, particularly in traffic crashes. Proposals for more comprehensive testing of drug--ethanol interactions have been put forward which may increase the predictive value of such tests.

Urging the alcoholic client to quit smoking cigarettes

Cigarette smoking is highly correlated with alcohol abuse. Yet information regarding smoking cessation for alcoholics is largely absent. To begin addressing this gap, 311 alcohol treatment professionals staffing 23 inpatient facilities in Washington state reviewed a list of 8 different time points, including "never," at which an alcohol-involved adult could be urged to quit smoking cigarettes. Respondents first selected those time points at which they favored and then those at which they personally encouraged smoking cessation. One year after the onset of sobriety emerged as the preferred time point. Responses were analyzed according to the treatment staff's self-reported alcohol and smoking status. Staff who described themselves as alcoholics and smokers were significantly less likely than nonalcoholic-nonsmokers to urge smoking cessation efforts.

Laboratory performance during acute alcohol intoxication and hangover

Eleven private pilots (seven men and four women) were recruited and trained on the Multiple Task Performance Battery (MTPB), static and dynamic tracking of a localizer/glide slope instrument, and use of the Intoxilyzer. The experiment comprised four test sessions (vodka, bourbon, placebo, and control sessions) held at weekly intervals. Sessions began at about 5:00 p.m. and continued through midnight to about 11:00 a.m. the next day. Subjects were tested in groups of three or four and were not told whether they were drinking alcohol or placebo. The ordering of sessions was approximately counterbalanced. Subjects were given all tests in the evening (before and after a monitored dinner), drank prepared beverages from 8:30 p.m. to midnight, and were tested again. Subjects slept 4 to 5 hr. They were awakened around 7:00 a.m., fed, and asked to perform all tasks again, beginning at 8:00 a.m. (8 hr after they had finished drinking). Results showed clear deleterious effects of alcohol on the MTPB and the tracking tasks immediately following drinking. During the morning (hangover) tests, scores on the MTPB and on the static and dynamic tracking tasks showed small circadian effects (scores were better) without impairment due to the alcohol. There were no congener effects. These results offer no evidence contrary to the "8 hour rule."

Separate and combined effects of alcohol and tobacco on the amplitude of the contingent negative variation

To examine the separate and combined effects of alcohol and tobacco smoking on cortical functioning, the amplitude of the contingent negative variation (CNV) was studied during a simple reaction time task in non-smokers, tobacco-deprived smokers and non-deprived smokers in sessions involving administration of four cigarettes and/or 0.65 g/kg ethyl alcohol. Computer analysis indicated that alcohol and combined alcohol + tobacco significantly reduced the CNV amplitude in non-deprived smokers. Two sub-groups of non-smokers were identified, one showing large pre-drug CNV amplitudes and significant alcohol-induced reductions and the other showing small pre-drug amplitudes and no change in CNV amplitude after alcohol. No significant results were observed with alcohol, tobacco or alcohol + tobacco combined in tobacco-deprived smokers. The results are discussed in relation to previously reported studies which have indicated both synergistic and antagonistic interactions between alcohol and tobacco, and suggestions are forwarded regarding the experimental and clinical significance of tobacco-induced enhancement of CNV amplitude reduction by alcohol.