A nearly perfect recognition performance (mean = 98.3%, SD = 1.8) and reaction times (mean = 641.45 ms, SD = 68.5) were unaffected by any of the experimental factors. The subjects reported to be more “high” when given alcohol than when given juice regardless of the instruction they were given, F(1,11) = 11.56, p < 0.01. Similarly, the subjects’ self-ratings of intoxication indicate that they felt moderately intoxicated, mean = 2.67 (SD = 0.9) on a Likert 1–5 scale. They felt equally inebriated regardless of whether they were instructed that the drink contains alcohol or placebo.
depicts superimposed waveforms obtained in alcohol and placebo conditions averaged across all participants, sessions and repetition conditions for all electrode sites. Visual inspection of the waveforms reveals a large, sharp-onset deflection about 180 ms after stimulus onset which is negative at posterior temporal sites (T5 and T6) and inverts in polarity over central and frontal sites. It is followed by a series of superimposed broad negative deflections that could be observed at most sites, especially fronto-centrally, between about 230 to 450 ms.
Figure 2 Grand average waveforms obtained in alcohol and placebo conditions. The waveforms were averaged for both new and repeated words, across all participants and sessions. Alcohol intoxication resulted in a selective attenuation of N180 at lateral temporal (more ...)
Effects of beverage
None of the measures were affected by instructions as to the beverage content (expectancy). A significant beverage x sites interaction, [F(12,132) = 3.26, p < .01] was observed for the earliest measured time window, 135–265 ms post stimulus onset. The only scalp sites where ERPs were differentially affected by alcohol and placebo were T5 and T6, [F(1,11) = 12.21, p < .05]. At this latency, the overall event-related activity recorded over the posterior temporal sites (T5, T6) was by far the largest, as compared to other sites within the present montage. A closer look at the main effect of sites, [F(12,132) = 15.2, p < .001] revealed a laterality difference with larger potentials recorded over left parieto-temporal sites, [F(1,11) = 7.74, p < .05].
Whereas there was no significant effect of beverage on N310 (270–370 ms latency window), the overall laterality effect persisted with waveforms recorded on the left side being more negative than those on the right, [F(1,11) = 11.11, p < .05]. This effect was particularly prominent at temporal sites as potentials recorded at T5 were more negative than at T6, [F(1,11) = 16.23, p < .05].
The waveforms obtained in alcohol and placebo conditions clearly begin to diverge in most sites at about 330 ms after word onset. A significant beverage x sites interaction was obtained for the N450 area (420–480 ms), [F(12,132) = 2.59, p < .05], with alcohol increasing the amplitude of N450. As can be observed in , by this latency the waveform difference is quite pronounced over most scalp regions although it is negligible over posterior temporal sites.
Effects of repetition
As illustrated in , the main effect of repetition, with novel words evoking a more negative amplitude, was significant within all three measured time windows between 270 and 610 ms post-stimulus onset: N310 [F(1,11) = 10.4, p < .01], N450 [F(1,11) = 37.8, p < .0001], and P580 [F(1,11) = 19.3, p < .001]. Similarly, the repetition x sites interaction was very robust for these three latency windows (270 – 610 ms) as well, with the new-repeated difference increasing in the posterior sites: N310 [F(12,132) = 6.9, p < .001], N450 [F(12,132) = 13.9, p < .0001], and P580 [F(12,132) = 12.0, p < .0001]. Finally, the P580 peak latency was shorter for the repeated target (549 ms) than the novel words (605 ms), [F(1,11) = 53.4, p < .0001].
Figure 3 Grand average ERP waveforms to novel and repeated words at midline electrode sites, averaged for both beverage and instructions conditions and across all participants. Repetition resulted in a sustained attenuated negativity and increased positivity after (more ...)
Waveforms recorded from the three midline sites in alcohol and placebo conditions are presented separately for the novel and repeated target words in . There was no interaction between the factors of beverage and repetition indicating that although novel words evoked a larger negativity overall, alcohol intoxication affected the novel and target words in a comparable manner. Alcohol affected the series of superimposed negative components without exerting a significant influence on the peak amplitude of the late positivity P580. However, it has significantly prolonged its peak latency, F(1,11) = 8.84, p < .05, (alcohol: 583 ms and placebo: 571 ms).
Figure 4 Grand average waveforms obtained in alcohol and placebo conditions for novel and repeated target words separately for midline electrode sites. Alcohol increased the amplitude of N450 and the latency of P580 on both novel and target words in a comparable (more ...)
The main effect of stimulus type, [F(1,9) = 56.3, p < .0001] reflected larger average SCRs evoked by target than nontarget words, with the means of 0.22 √μS and 0.16 √μS respectively. Investigation of the dynamics across trials () revealed that the SCRs habituated markedly within the first ten trials resulting in the main effect of block, [F(19,171) = 7.2, p < .0001].
Average skin conductance responses (in √μ Siemens) measured across 5-trial blocks in alcohol and placebo conditions for the whole duration of the task. Alcohol tended to depress SCR amplitude in the last 16 blocks of the task.
Even though the dose used in this study may not have been sufficient to significantly alter skin conductance, alcohol exhibited a trend to depress SCR amplitude in the last 16 blocks of the task [F
(1,9) = 4.6, p
= 06], in agreement with other studies using higher doses (Carpenter, 1957
; Kilpatrick et al., 1980
ERPs as a Function of Electrodermal Responsivity
In addition to the analyses performed on event-related potentials and peripheral autonomic (i.e. electrodermal) responses separately, their concurrent recording during this task afforded an opportunity to compare directly the activity of the two physiological systems (Lyytinen et al., 1992
; Marinkovic et al., 2001
). The SCRs were used as a grouping criterion during ERP averaging for each participant and for the repeated and novel words separately. The SCR+ ERP averages contained only those trials on which a measurable phasic SCR was elicited. Conversely, no phasic SCRs were recorded on trials forming the SCR- average waveform. Since SCRs were evoked on fewer trials than not, care was taken to balance the averages with respect to the total number of trials and the ordinal trial number. Averaged ERPs were based on 17.6 and 19 trials for new and repeated words on average. Data of four participants were eliminated from the analyses due to an insufficient number of trials. The waveforms were quantified by obtaining an average voltage within 300–650 ms latency window as well as the peak amplitude and latency for the P580 component.
As shown in , the SCR+ and SCR- waveforms begin to diverge significantly at about 300 ms after word onset especially in the alcohol condition, with a large long-lasting negativity evoked on SCR+ trials. Interaction between the factors of SCR and sites [F(12,84) = 4.3, p < .001] was significant for the entire measured time window, 300–650 ms.
Figure 6 Grand average waveforms obtained on trials with (SCR+) and without (SCR-) accompanying electrodermal reactions recorded from midline electrode sites in alcohol (left column) and placebo (right column) conditions. Alcohol increased the negativity on trials (more ...)
Analysis of the peak amplitude and latency of the late positivity revealed that a smaller P580 was evoked on SCR+ trials, [F(1,7) = 5.69, p < .05]. This effect was primarily observed in alcohol condition at centro-posterior sites, [F(1,7) = 16.1, p < .05]. Finally, the P580 peak latency was longer on SCR+ as compared to SCR- trials under the alcohol condition only, as suggested by a beverage and SCR interaction [F(1,7) = 5.61, p < .05].