Participants who indicated on the post-acquisition questionnaire they were ‘completely’ or ‘fairly’ certain that the US was paired with the CS+ were considered contingency aware. Although this method is consistent with past research (e.g., Grillon, 2002
), it does not account for the fact that participants who did not accurately select the CS+ on the questionnaire may have failed to do so for reasons other than an unawareness of the CS+/US contingency, such as lack of confidence about their perceptual experience or retrospective biases in reporting (e.g., Lovibond & Shanks, 2002
). Thus, online expectancy ratings to CSs were used to identify participants who answered the post-acquisition questionnaire incorrectly, but who were likely aware of the CS+/US contingency. Participants’ differential expectancy, or CS+ expectancy minus CS− expectancy, was calculated for pre-acquisition and acquisition. If participants’ acquisition differential expectancy exceeded zero by two standard deviations (based on the pre-acquisition distribution), it was deemed highly unlikely that they were unaware of the contingency.
Of the 80 participants with no technical problems who completed all three days, 52 (65%) were designated aware of the CS+/US contingency based on the criteria above. Although the percentage of aware participants did not differ by Group (1-min, 2-min, and 4-min extinction CS durations), χ2(2) = 5.34, p = 0.07, unaware participants were excluded from analyses because the present study sought to determine the effect of extinction on those who learned the CS+/US association. Further, the pattern of results described below for those who were considered contingency aware (n = 52) was virtually identical to that observed for all participants who completed the 3 days without technical problems (n = 80). Generally, effect sizes for the contingency aware group (presented here) were larger than those for all participants who completed the 3 days without technical problems.
It was not expected that there would be between group differences for Day 1 fear conditioning as individuals in different Groups were not treated differently until Day 2. Consistent with this, no significant main or interactive effects involving Group (all F < 2.7, p > 0.09) were found for any dependent variables during acquisition when Group × CS-type (CS− and CS+) × Time (early CS and late CS) × Trial (acquisition trials 1–4) repeated measures analyses of variance (ANOVAs) were conducted with Group as a between-subjects factor. Thus, acquisition data (dependent variable means and standard errors) are presented for all participants, collapsed across Group in .
Figure 3 Acquisition dependent variable means and standard errors, collapsed across Group (1-, 2-, and 4-min) because there were no significant Group effects for acquisition. 3a: US expectancy ratings (0 = ‘certain no stimulation’, 5 = ‘uncertain’, (more ...)
For dependent variables where Time could not be examined as a factor (subjective fear ratings and SCRs), it was hypothesized that participants would learn to fear the CS+ to a greater extent than the CS− during acquisition. As seen in , this was seen for subjective fear ratings: the difference between CS+ and CS− prior to acquisition was not significant, F(1,49) = .3, p = .64, but subjective fear to the CS+ was significantly greater than that to the CS− post-acquisition, F(1,49) = 63.0, p < .001, η2 = .56; the expected CS-type × Phase (pre-acquisition and post-acquisition) interaction was significant, F(1,49) = 56.6, p < .001, η2 = .54. As seen in , this same pattern was observed for SCRs: the difference between CS+ and CS− for Trial 1 was not significant F(1,24) = .01, p = .92, but SCRs to the CS+ were significantly greater than that to the CS− by the last trial, F(1,24) = 11.1, p = .003, η2 = .32. However, the expected CS-type × Trial interaction did not reach significance for SCRs, F(3,72) = 1.2, p = .32.
For dependent variables where Time could be examined as a factor (US expectancy ratings and SRs) it was hypothesized that participants would develop a temporal expectation of the US during acquisition for the CS+, but not the CS−. In other words, fear would not increase during the course of the CS at the beginning of acquisition for either CS+ or CS−, but fear would increase from early to late in the CS trial for only the CS+ by the end of acquisition. As seen in , this pattern was observed for US expectancy ratings; the expected CS-type × Time × Trial interaction was significant, F(3,114) = 21.3, p < .001, η2 = .36. Within CS+ trials, there was no change in US expectancy from the early to late time period for the first CS+ acquisition trial, F(1,38) = .35, p = .56, but there was a large, significant increase for the final CS+ trial, F(1,38) = 73.0, p < .001, η2 = .66. The expected CS-type × Time × Trial finteraction did not reach the level of significance for SRs, F(3,69) = .5, p = .69. However, as seen in , SRs generally decreased during the course of CSs, but for the CS+, this decrease turned into a slight increase by the end of acquisition. In fact, examination of simple effects for the final acquisition trial revealed there was no significant difference in SRs between the CS+ and CS− at the early time point, F(1,40) = 0.1, p = .82, but the difference approached significance at the late timepoint, F(1,40) = 3.3, p = .07, η2 = .08.
Because Groups have different number of trials and trial durations during extinction, comparisons for expectancy ratings and SRs are based on duration of CS exposure rather than number of trials. The majority of models discussed above would indicate that there would be a significant difference in change in fear responding to the CS+ across extinction among the Groups; the only exception would be RET because the present study holds total duration of exposure constant across Groups. Thus, it was hypothesized that the Groups would show a significant difference in the amount of fear reduction to the CS+ during extinction.
As seen in , this was the case for US expectancy ratings to the CS+: the 1-min group showed a significant decrease during extinction, whereas the 2- and 4-min group did not show a significant change; the Group × Duration (48 s, 108 s, 168 s, and 228 s) interaction was significant, F(6,132) = 4.3, p = .001, η2 = .16. Also, whereas the 2- and 4-min groups continued to display differential conditioning after 168 s of exposure to both CS+ and CS−, both F(1,46) > 10.6, p < .002, η2 > .19, the 1-min group did not, F(1,46) = 3.1, p = .08. Data for the CS− is not provided in for clarity of presentation, but is available upon request from the first author. As can be seen in , the reduction in fear responding to the CS+ during extinction appeared to be largest for the 1-min group as compared to the 2- and 4-min groups. However, the Group × CS-Type × Phase interaction did not reach the level of significance for subjective fear, SRs, or SCRs (all F < 2.7, p < .12). It is possible that significant differences among the groups exist, but the present sample size was underpowered to detect them. In fact, when examining simple effects, almost the same pattern of results was seen for SCRs and SRs as US expectancy. The 1-min group showed a significant reduction in responding during extinction for SRs, F(1,40) = 5.1, p = .03, η2 = .11, and nearly showed one for SCRs, F(1,20) = 3.7, p = .07, η2 =0.15, whereas neither the 2- nor 4-min groups showed significant changes in SRs or SCRs during extinction (all F < 3, p > .10).
Figure 4 Extinction CS+ dependent variable means and standard errors presented separately by Group (1-, 2-, and 4-min). 4a: US expectancy ratings (0 = ‘certain no stimulation’, 5 = ‘uncertain’, and 10 = ‘certain stimulation’) (more ...)
Next, US expectancy and SRs were evaluated to determine if the temporal expectation of the US acquired during Day 1 persisted to Day 2, and whether or not US delivery was timed from CS+ onset regardless of whether or not the CS+ continued to be displayed. If the temporal expectation of US delivery persisted from Day 1 to Day 2, then the temporal pattern of fear responding to the CS+ should not change for the 2-min group from the end of acquisition to the start of extinction. In support of retention of temporal expectation of US delivery from Day 1 to Day 2, the 2-min group did not display a significant Trial (acquisition trial 4 and extinction trial 1) × Time (48, 108, and 168 s post CS+ onset) interaction for either CS+ US expectancy or SRs, both F < 1.0, p > .05. As seen when comparing for the 2-min group, there was no change in temporal expectation of the US from Day 1 to Day 2: US expectancy increased significantly from 48 to 108 s post CS+ onset and then decreased significantly from 108 to 168 s post CS+ onset. In other words, as the CS+ was onscreen and the time of US delivery (117 s) neared, participants’ expectancy of receiving the US increased, whereas it decreased after the CS+ was removed from the screen.
Figure 5 US expectancy rating (0 = ‘certain no stimulation’, 5 = ‘uncertain’, and 10 = ‘certain stimulation’) means and standard errors presented separately by Group (1-, 2-, and 4-min) for the CS+. Ratings provided (more ...)
If expectancy of US delivery is timed from CS+ onset (regardless of whether or not the CS+ is displayed onscreen), both the 1- and 4-min Groups should also show the same temporal pattern of responding in extinction as they did in acquisition. However, this was not the case as can be seen when comparing for both the 1- and 4-min groups. Both the 1- and 4-min groups display significant Trial (acquisition trial 4 and extinction trial 1) × Time interactions, both F > 15.8, p < .001, η2 > .64. For the 1-min group, US expectancy increases significantly from 48 to 108 s post CS+ onset when the CS+ was onscreen during acquisition (), F(1,10) = 14.7, p = .003, η2 = .59, but decreased significantly from 48 to 108 s post CS+ onset when the CS+ was removed during this period for extinction (), F(1,10) = 5.4, p = .04, η2 = .35. The pattern of SR means was similar to that of US expectancy ratings for the 1-min group, but the Trial × Time interaction was not significant, F(1,9) = 1.1, p = .33. For the 4-min group, there was a significant decrease from 108 to 168 s post CS+ when the CS+ was removed from the screen during this period for acquisition (), F(1,9) = 27.7, p < .001, η2 = .75, but there was no significant change when the CS+ remained onscreen for this entire period during extinction, F(1,9) = 0.4, p = .56 (). For the 4-min group, the Trial × Time interaction for CS+ SRs was also significant, F(2,12) = 6.8, p = .01, η2 = .53. As with US expectancy, there was a significant decrease in SRs from 108 to 168 s post CS+ onset for acquisition, F(1,6) = 14.3, p = .009, η2 = .71, but not for extinction, F(1,6) = 2.2, p = .19.
Based on the temporal cue specificity model, it was hypothesized that the reduction in differential fear conditioning from acquisition to extinction re-test would be larger for the 2-min group than either the 1- or 4-min groups. There was no support for this hypothesis as Group × CS-Type × Time × Trial (acquisition trial 4 and re-test trial 1) ANOVAs revealed that there were no significant Group main or interactive effects for US expectancy, SRs, or SCRs, all F
< 1.9, p
> .16 (see )1
. The only significant effect of Group was seen for subjective fear ratings. A Group × CS-type × Phase (post-acquisition, extinction re-test) repeated-measures ANOVA for subjective fear ratings revealed a significant Group × Phase interaction, F
(2,48) = 3.3, p
= .04, η2
= .12. Although subjective fear reduced significantly to both the CS+ and CS− for all three groups, the reduction for the 4-min group was slightly (yet significantly) larger than that of the 1- or 2-min groups when collapsing across CS-type. Given that the 4-min group had larger post-acquisition fear ratings, it is possible that this difference in combination with floor effects at re-test contributed to the observed interaction.
Figure 6 Acquisition trial 4 and re-test dependent variable means and standard errors presented separately by Group (1-, 2-, and 4-min). 6a: US expectancy ratings (0 = ‘certain no stimulation’, 5 = ‘uncertain’, and 10 = ‘certain (more ...)
Next, US expectancy and SRs were evaluated to determine if the temporal expectation of the US acquired during acquisition persisted to extinction re-test and whether or not Day 2 extinction resulted in a decrease in fear responding at Day 3 re-test. A Group × CS-type × Time × Trial (acquisition trial 4 and re-test trial 1) ANOVA for US expectancy revealed a significant CS-type × Time × Trial interaction, F(1,44) = 28.7, p < .001, η2 = .40. This interaction can be seen in : the temporal expectation of the US during the CS+ is demonstrated by US expectancy significantly increasing from the early to late time point at both the end of acquisition, F(1,44) = 62.6, p < .001, η2 = .59, and the beginning of re-test, F(1,44) = 15.7, p < .001, η2 = .26. However, the magnitude of this increase is significantly smaller at follow-up, F(1,44) = 33.8, p < .001, η2 = .43, indicating a reduction in CS+ responding at re-test. The three-way interaction arises because unlike the CS+, there is no significant Time × Trial interaction for the CS− (see ), F(1,44) = 0.8, p = .37. A Group × CS-type × Time × Trial ANOVA for SRs also revealed a CS-type × Time × Trial interaction, F(1,32) = 5.7, p = .02, η2 = .15. As with US expectancy, this involved a significant Time × Trial interaction for the CS+, F(1,32) = 5.1, p = .03, η2 = .14, but not for the CS−, F(1,32) = 0.4, p = .51 (see ).
Subjective fear and SCRs were examined to determine if extinction resulted in a decrease in differential fear responding from acquisition to extinction re-test. It was hypothesized that such a reduction would be observed. As seen in , this was the case for subjective fear ratings; there was a significant Phase × CS-type interaction, F(1,48) = 39.7, p < .001, η2 = .45. While subjective fear ratings decreased significantly from post-acquisition to extinction re-test for both the CS+, F(1,48) = 73.0, p < .001, η2 = .60, and the CS−, F(1,48) = 32.2, p < .001, η2 = .40, this decrease was significantly greater for the CS+. A similar pattern was seen for SCRs: there was a significant difference between CS+ and CS- SCRs at the end of acquisition, F(1,33) = 9.0, p = .005, η2 = .21, but not at re-test trial 1, F(1,33) = .3, p = .62 (see ). However, the CS-type × Trial interaction did not reach significance, F(1,33) = 1.1, p = .30.