General experimental design

The general design was identical in all three experiments. In this section, a brief overview over the common “time line” (Figure 11) and the commonalities in the experimental design of the three experiments will be given. A more detailed description of the experimental design of the different experiments is included in chapter 5 (Manuscript).

Figure 11. The presented “time line” was identical in all experiments.

In each experiment, participants started with the time-series for encoding after they had been instructed and placed in the MR-scanner. About four minutes after the

time-ENCODING

series for encoding, the time-series for retrieval took place. Following the retrieval task, participants underwent a step by step debriefing while still lying in the MR scanner. After debriefing, the visual presentation threshold was tested in a further run to ascertain that the subliminal stimuli had been presented below the objective awareness threshold (see Figure 11). During the time series for encoding and retrieval fMRI data was collected. No fMRI data was measured during the visual presentation threshold.

The same block design was used for the encoding and the retrieval time series in all four experiments. The duration of each block was 24s. During one block always four stimuli were presented within 6s. The general block design of the encoding and the retrieval time series will be explained below. For details about the task instructions and the stimuli used in the control experiment see chapter 5.

Each encoding time series consisted of blocks of six different conditions (see Figure 12). The six conditions were a masked baseline condition (Figure 12, A; identical in all experiments), implicit encoding of the experimental condition (Figure 12, B;

different stimuli used for the different experiments), explicit encoding of the experimental condition (Figure 12, C; identical stimuli used for the different experiments), unmasked baseline (Figure 12, D, identical in all experiments), implicit encoding of the neutral condition (Figure 12, E; identical in all experiments), explicit encoding of the neutral condition (Figure 12, F; identical in all experiments).

A block of four supraliminal face-profession pairs (C or F) was always preceded by a block of masked presentations of the same four faces (B or E). For the implicit encoding in the experimental condition (B) these masked faces were either combined with new professions that were semantically incongruent to the supraliminal professions (Experiment 1, incongruent; shown in Figure 12 lower panel), semantically congruent (Experiment 2, congruent) or with the same professions (Experiment 3, identical). For implicit encoding in the neutral condition (E) the masked faces were combined with nonwords in all experiments (see Figure 12 lower panel). During all blocks in which the stimuli were presented with masks, the same masking method was used (Figure 7).

Figure 12. Design of encoding time series.

The instructed strategy for explicit learning (C, F) was to imagine the presented person in a typical scene of the indicated profession. In the masked baseline condition (A) a single head contour was repeatedly presented. Participants were instructed to engage in an attention task during all blocks with masked presentation (A, B, D). In the unmasked baseline condition (D) a series of different head contours was presented for subjects to decide whether the left or right ear of each head contour was larger. There were three blocks, i.e. 12 stimuli per condition. Instruction slides with the letter “i” (imagining a scene) “a” (attentional task) or “e” (ear size) were presented for 2s before each block, to indicate which task has to be perfomed in the following block of 24 s.

A B C D E F

masked baseline implicit encoding exp. condition explicit encoding exp. condition unmasked baseline Implicit encoding neutr. condition explicit encoding neutr. condition

A

masked baseline implicit encoding exp. condition explicit encoding exp. condition unmasked baseline Implicit encoding neutr. condition explicit encoding neutr. condition

A

The design of the retrieval fMRI time-series was the same in all three experiments.

Each retrieval time series consisted of blocks of three different conditions (see Figure 13). The three conditions were a baseline task, retrieval of the experimental condition, and retrieval of the neutral condition. The explicitly learned faces from the experimental and neutral conditions of the encoding scans were presented again as retrieval cues (without professions), four per block, for the subjects to remember the explicitly learned professions. Subjects indicated by button press what professional category each retrieved profession belonged to (academic or artist?). The baseline condition was identical to the unmasked baseline condition used during the encoding scans. There were three blocks, i.e. 12 stimuli, per condition. Instruction slides with the letter “r” (retrieve the profession) or “e” (ear size) were presented for 2s before each block, to indicate which task has to be perfomed in the following block of 24 s.

Figure 13. Design of retrieval time series.

A B

unmasked baseline neutral condition retrieval experimental condition retrieval

A

unmasked baseline neutral condition retrieval experimental condition retrieval

A

B

C

Following the retrieval task in all experiments an additional task was done, to test whether the subliminal stimuli had been presented below the objective awareness threshold. For this purpose participants remained situated in the dark scanner. They were exposed to another 30 subliminal face-profession pairs. The masked presentation of each face-profession pair was immediately followed by two forced choice-tasks. One forced-choice task was between the target and a distracter face (“Which face had been subliminally presented?”) and the other was between the two professional categories “academic” and “artist” (“Which professional category did the subliminal profession belong to?”; Figure 14). Participants had to answer each of the two forced-choice tasks within 3s by button press.

Figure 14. Design of the task that was used to test whether the subliminal stimuli had been presented below the objectively defined awareness threshold. Shown is one trial. In total participants were presented with thirty different target faces and performed two forced choice tasks for each of them. In total 60 new different faces (30 target faces and 30 distracter faces) that never had been presented during the encoding and the retrieval time series had been used.

6 3 3

masked presentation

Academic artist?

presentation time s

physicist physicist

Forced choice task 1: Which face had been presented? Forced choice task 2: Professional category?

6 3 3

masked presentation

Academic artist?

presentation time s

physicist physicist

Forced choice task 1: Which face had been presented? Forced choice task 2: Professional category?