Appendix 1—table 2. Summary of criteria used to define ‘non-responders’ across records included in the systematic literature search.
Fifteen records, reporting a total of 17 studies, were identified.
| Record | % excluded participants (‘non-responders’) |
Cut-off (in µS) for a valid SCR | Valid responses in at least % of trials | Stimulus type (also referred to as ‘trial’) on which the exclusion is based | Additional criteria/notes |
|---|---|---|---|---|---|
| Baeuchl et al., 2019 | 10% | >0.01 | ≥66% | CXT+ | |
| Tuominen et al., 2019 | 12% | >0.05 | ≥13% | CS+ and CS– | |
| Gruss and Keil, 2019 | 11% | visual inspectiona | CS+, CS–and US | ||
| Sjouwerman and Lonsdorf, 2019 | 14% | ≥0.02 | US:≥67% CS: no valid response in each CS modality |
CS+, CS– and US | |
| Grégoire and Greening, 2019 | 8% | >0.02 | ≥25%b | CS+ and CS–c | |
| Hu et al., 2018 | 3% | ≥0.02 | 100% | CS+ and CS–c | ‘non-responders’ discontinued after day 1 of the experiment |
| Oyarzún et al., 2019, Exp. 1 | 0% | ≥0.02 | ≥25% | CS+d and CS–c | |
| Oyarzún et al., 2019, Exp. 2 | 9% | ||||
| Tani et al., 2019 | 10% | >0.03e | 100% | CS+ | |
| Marin et al., 2019 | 0%f | ≥0.03 | ≥10% | US | |
| Taylor et al., 2018 | 5% | NA | 100% | motor testg | |
| Morriss et al., 2018 | 6% | >0.03 | ≥90% | CS+d and CS–c | only applicable if true across all phases/days of the experiment |
| Schiller et al., 2018; Schiller et al., 2010, Exp. 1 | 48%h | ≥0.02 | ≥25% | CS+d and CS– | |
| Schiller et al., 2018; Schiller et al., 2010, Exp 2 | 74%h | ||||
| Morriss and van Reekum, 2019, Exp. 1 | 2% | >0.03 | >90% | CS+d and CS– | |
| Morriss and van Reekum, 2019, Exp. 2 | 2% | ||||
| Hartley et al., 2019 | 6% | <0.05i | ≥33 %i | CS+ and CS–c | |
| Hu et al., 2019 | 4% k | ≥0.02 | 100% k | US | |
| Leuchs et al., 2019 | 4% | NA | ≥33% | CS+ and CS–c | only applicable if true across both days of the experiment |
aPersonal communication with L. Forest Gruss (29.4.2019): “the determination of non-responders was done, this was done on visual inspection by me through all trials of all individuals. I verified after determining who the lowest, i.e. non-responders were, in the same fashion as the startle non-responders in summing responding over the entire experiment, and this responding falling below a threshold of overall response (~<10%) AND one individual due to lack of response at the end of the trial to the UCS specifically".
bPersonal communication with S.G. Greening (24.4.2019): “non-responders if more than 75% of data were missing (i.e., SCR <0.02 μS) during the training phase. So, that means, if a participant had at least six trials (out of 24) with measurable SCRs (whatever the condition), we kept them (if the other acquisition criteria were OK, see below). If they had five trials or fewer with measurable GSR, we considered them a non-responder and removed them".
cPersonal communications that ‘trial’ or this statement refers to CS+ and CS– trials: S. Greening (24.4.2019), D. Schiller (1.5.2019), J. Oyarzun (21.5.2019), J. Morriss (15.4.2019), C. Hartley (2.5.2019), V. Spoormaker (18.4.2019).
d CS+ unpaired.
ePersonal communication with H. Tani (2.5.2019): only CS+ trials were considered (here as response to the sound or the intrapersonal stimulus).
fPersonal communication with M.-F. Marin (23.4.2019): exclusion criteria were defined, but no participant met these criteria and hence none was excluded.
gPersonal communication with V. Taylor (6.6.2019): clarified that "non-responders’ were identified in a “motor test of SCR responding during the preliminary session. Essentially, they had to compress a ball with the right hand with maximal physical force for a few seconds on about 10 trials, which typically elicits quite large SCRs in subjects. Failure to respond to an SCR to all of these trials was considered a non-responder".
hPercentages for ‘non-learners’, ‘non-extinguishers’ and ‘non-responders’ reported together.
iPersonal communication with C. Hartley (2.5.2019): clarified that “participants were considered non-responder if they had SCR values of 0 for more than 8 of the 12 trials in acquisition (<4 responsive trials)”.
k The percentage of ‘non-responders’ and ‘non-learners’ was reported together without percentages for each category; personal communication with D. Schiller (21.5.2019): in the paper, it is reported that five individuals ‘were excluded due to equipment malfunction (N = 2) or had non-measurable skin conductance response (SCR) to the shock (N = 3)”. It was confirmed that these individuals excluded for non-measurable SCR did not show any responses to any stimulus.