Participants in the alcohol and placebo conditions did not differ on a range of demographic variables, including age, ethnicity, income, and drinking patterns (see Kirchner & Sayette, 2003
). Participants who drank alcohol reached a mean BAC of 0.067% just before the zoning-out task. As in prior research, SIS ratings indicated that participants who drank alcohol felt more intoxicated (M = 35.4, SD = 19.4) than did participants who drank placebo (M = 18.3, SD = 14.6), though on the postexperimental questionnaire, all participants reported drinking at least 1 oz of vodka (see Kirchner & Sayette, 2003
Data from 2 participants in the alcohol group and 2 in the placebo group were excluded from analyses because their reading comprehension was well below chance performance (i.e., proportion correct was at or below .33).1
Data from the remaining 50 participants were used in the following analyses. All inferential tests were nondirectional.
The placebo group (M = 1,439 s) and the alcohol group (M = 1,340 s) did not differ significantly in time spent reading (p = .22). The placebo group (M = .70) performed marginally better than the alcohol group (M = .61) on the comprehension test, t (48) = 2.50, p = .075, prep = .842.
Of particular relevance to our hypotheses were our two measures of mind wandering. The first was the mean proportion of probes to which participants responded affirmatively (i.e., that they had been zoning out). We used this measure to index the propensity to be caught zoning out by the prompts because it adjusts for the number of prompts and is therefore preferred to the absolute number of affirmative probe responses (Reichle et al., 2008
). Our second measure of mind wandering was the number of self-reported zoning-out episodes.
Results indicated that the alcohol group was significantly more likely than the control group to be caught mind-wandering by the prompts (M = .25, SE = .05, vs. M = .12, SE = .03), t (48) = 2.15, p = .036, prep = .900. (Means were computed by averaging across the ratios of individual participants.) The mean number of probe-caught zone-outs was 0.76 (SE = 0.19) for the placebo group and 1.52 (SE = 0.34) for the alcohol group. The number of prompts was similar for participants in the placebo group (M = 6.80, SE = 0.37) and those in the alcohol group (M = 6.60, SE = 0.41), t < 1, p > .7. Note that the slightly higher number of prompts in the placebo group actually worked against the observed difference in the proportion of probes that caught zoning out (i.e., participants in the alcohol group received fewer probes, but were nevertheless caught zoning out more often than participants in the placebo group).
The second mind-wandering measure putatively indexes meta-awareness of zoning out. Participants in the placebo group (M = 1.48, SE = 0.27) and those in the alcohol group (M = 1.24, SE = 0.29) were similar in the frequency with which they caught themselves zoning out (t < 1, n.s.). Despite zoning out more than twice as often as participants in the placebo group (as revealed by the probe measure), participants in the alcohol group were no more likely (and, indeed, were slightly less likely) to catch themselves zoning out. We quantified this observation by comparing the observed number of self-caught zone-outs in the alcohol group with the expected number of self-caught zone-outs in the alcohol group, given that participants in this group were approximately 2.09 times more likely than those in the placebo group to be caught (by probes) zoning out. To execute this analysis, we multiplied the mean number of self-caught episodes of mind wandering in the placebo group (1.48) by 2.09, and compared this value (3.09) with the observed number of self-caught zone-outs in the alcohol group (M = 1.24); the difference between these values (3.09 and 1.24) was significant, t (48) = 2.91, p < .007.
There were no significant associations between comprehension and either of the two mind-wandering measures in either condition. We also examined the responses that participants made to the computer-administered questions completed after each mind-wandering episode. Although the pattern of results was complex, it is important that participants reported thinking about a variety of different topics during the zoning-out intervals, and reported thinking about text-related topics (on average) only about 6.75% of the time. Moreover, alcohol seemed to particularly increase distraction related to sensory states, such as hunger, thirst, and other consummatory motives.