“Faster, but Not Smarter: An Experimental Analysis of the Relationship between Mental Speed and Mental Abilities”, 2018-10-11 (; backlinks):
Individual differences in the speed of information processing may contribute to individual differences in general intelligence by enhancing the efficiency of information processing. So far, this hypothesis is based on correlational data, and thus a causal relationship between mental speed and mental abilities has not yet been established.
In the present study, we used transdermal nicotine administration in a double-blind design to increase the speed of information processing and tested whether this increase in information processing speed affected performance in intelligence tests.
While nicotine administration decreased both reaction times and P3 latencies in the Sternberg memory scanning task, there was no effect of nicotine on intelligence test performance.
These results contradict theories proposing that a greater speed of information processing causes greater intelligence. Instead, they suggest that structural properties of the brain may affect both the speed of information processing and general intelligence and may thus give rise to the well-established association between mental speed and mental abilities.
…A recent meta-analysis of 48 experiments testing the effects of nicotine on cognitive processing reported consistent effects of nicotine administration on the speed of information processing in a variety of experimental tasks (Heishman et al 201014ya). On N-weighted average, the administration of nicotine led to an increase in reaction times of g = 0.33 in attention—and memory-related tasks. effect-sizes ranged from g = −0.16 to g = 1.42 for alerting attention RTs (g mean = 0.34), from g = 0.05 to g = 0.61 for orienting attention RTs (g mean = 0.30), and from g = 0.00 to g = 1.05 for short-term and working-memory RTs (gmean = 0.34). Despite the substantial variance in effect sizes, results from this meta-analysis suggest that nicotine administration overall has a small-to-medium positive effect on the speed of information processing. Moreover, there has been some evidence that nicotine administration decreases P3 latencies in comparison to a placebo condition (Edwards et al 198539ya; Houlihan et al 199628ya). For example, et al 1996 administered either a placebo cigarette with a nicotine yield of only 0.05 mg or a treatment cigarette with a nicotine yield of 1.1 mg to 32 overnight-abstaining regular smokers in a repeated measures design. They found that smoking decreased both reaction times, ω2 = 0.40, and P3 latencies, ω2 = 0.13.
However, the effect size of these pharmacological effects on P3 latencies were smaller than the effects on reaction times and some studies failed to find any effect on P3 latencies (eg. 1999; Knott et al 199925ya). In a study on 21 regular smokers, smoking a cigarette with a nicotine yield of 1.1 mg decreased N2, but not P3 latencies in a Sternberg short-term memory scanning task in comparison to smoking a placebo cigarette with a nicotine yield of only 0.05 mg (Houlihan et al 200123ya). This inconsistency in results is not surprising (Houlihan et al 200123ya) given the rather small sample sizes typical for electrophysiological studies, the probably small-to-moderate actual effect size, and the unreliability of ERP latencies (Cassidy, Robertson, & 2012; et al 2017). In a review of the existing literature on the effects of nicotine on ERP components, et al 2004 concluded that there probably were small effects of nicotine administration on P3 latencies, but that the existing literature was too heterogeneous in terms of sample composition, nicotine administration, and experimental procedure to allow for a systematization of boundary conditions.
Taken together, there is clear evidence that nicotine has an effect on reaction times that is not just a reversal of withdrawal-related symptoms (Heishman et al 201014ya), and some evidence that this effect may at least in part be due to an acceleration of stimulus-evaluation on a neural level (Pritchard et al 200420ya). If nicotine administration increases the speed of information processing, and if a greater speed of information processing positively affects general intelligence, then nicotine administration should enhance performance on standard intelligence tests. In fact, a first study supports this notion: In a study on 16 regular smokers who had to abstain from smoking two hours prior to their participation in the experiment, taking 6 puffs of a cigarette yielding 0.80 mg of nicotine prior to completing Raven’s Advanced Progressive Matrices and two additional puffs 10 minutes into the intelligence test, led to an average increase of 6 IQ points in comparison to a placebo condition, corresponding to a medium effect size of about d = 0.50 (Stough et al 199430ya).
However, the study does not allow a clear conclusion regarding the nature of the relationship between mental speed and mental abilities due to 4 limitations. First, because the speed of information processing was not measured in this study, it cannot be concluded if nicotine effects on intelligence test scores were mediated by changes in mental speed. Second, because only regular smokers participated in the study who had to abstain from smoking for two hours prior to participation, it is not clear if the results may not at least in part reflect the recovery from withdrawal symptoms. Third, the sample size was rather small, which may have led to an overestimation of the effects of nicotine on intelligence test performance and warrants replication of the study. Fourth, instead of a sham-smoking in the control condition, participants did not smoke at all in the control condition. Hence, the design was not double-blind and participant and experimenter expectancy effects may have biased the outcome (1966). Moreover, the experimental condition differed from the control condition not only in terms of nicotine administration, but also in the sensory and motoric components of smoking. Nevertheless, this study can be seen to yield the first preliminary evidence that nicotine administration might enhance performance in intelligence tests.