Concealed semantic and episodic autobiographical memory electrified

Abstract

Electrophysiology-based concealed information tests (CIT) try to determine whether somebody possesses concealed information about a crime-related item (probe) by comparing event-related potentials (ERPs) between this item and comparison items (irrelevants). Although the broader field is sometimes referred to as "memory detection," little attention has been paid to the precise type of underlying memory involved. This study begins addressing this issue by examining the key distinction between semantic and episodic memory in the autobiographical domain within a CIT paradigm. This study also addresses the issue of whether multiple repetitions of the items over the course of the session habituate the brain responses. Participants were tested in a 3-stimulus CIT with semantic autobiographical probes (their own date of birth) and episodic autobiographical probes (a secret date learned just before the study). Results dissociated these two memory conditions on several ERP components. Semantic probes elicited a smaller frontal N2 than episodic probes, consistent with the idea that the frontal N2 decreases with greater pre-existing knowledge about the item. Likewise, semantic probes elicited a smaller central N400 than episodic probes. Semantic probes also elicited a larger P3b than episodic probes because of their richer meaning. In contrast, episodic probes elicited a larger late positive complex (LPC) than semantic probes, because of the recent episodic memory associated with them. All these ERPs showed a difference between probes and irrelevants in both memory conditions, except for the N400, which showed a difference only in the semantic condition. Finally, although repetition affected the ERPs, it did not reduce the difference between probes and irrelevants. These findings show that the type of memory associated with a probe has both theoretical and practical importance for CIT research.

Keywords: ERPs (event-related potentials); concealed information; deception; deception detection; episodic memory; semantic memory.

Figure 1

Schematic of the experimental paradigm. Participants were tested in two memory conditions in separate blocks: semantic autobiographical and episodic autobiographical. In both conditions, they saw four irrelevant dates, randomly intermixed with a target date and a probe date. In the semantic autobiographical condition, the probe was the participant's date of birth. In the episodic autobiographical condition, it was a secret date in an envelope each participant opened just before the study. Participants reported whether they possessed associated memories for any of the dates, responding honestly to both the irrelevant dates (by pressing the “no” key) and the target date (by pressing the “yes” key), but lying about their birth date or secret date (by pressing the “no” key). Note: Item type labels in the figure shown for illustration only and did not appear on the stimuli.

Figure 2

Behavioral results. Top, average response times (RTs) to irrelevants, probes, and targets in the semantic (red bars) and episodic (gray bars) autobiographical conditions during the first (light bars) and second (dark bars) repetition. Bottom, accuracy for the same conditions. Error bars depict 1 SEM.

Figure 3

Grand average ERPs elicited by irrelevants (thin solid lines) and probes (thick solid lines) in the semantic (black lines) and episodic (red lines) autobiographical conditions. ERPs are plotted between-100 and 900 ms (at all scalp recording sites). ERPs are shown negative up and referenced to the average of the left and right mastoids. A diagram with the location of the recording sites is shown on the bottom right.

Figure 4

Topographic maps of the ERP difference between probes and irrelevants for (top) the N2 (250–350 ms), (middle) P3b (400–600 ms), and (bottom) LPC (750–900 ms) in the semantic (left column) and episodic (right column) autobiographical conditions. An N400 map is not shown because there was no CIT effect in the episodic condition, and the P3b map for the semantic condition captures the N400 as a positive difference at Cz (28); thus, the centroparietal distribution in the P3b time period of the semantic condition reflects the combination of the overlapping central maximum of the N400 CIT effect and the parietal maximum of the P3b CIT effect. Note, the voltage scale is not the same for all topographic maps.

Figure 5

The left side of each panel shows the ERP time course for episodic probes (thin orange line), semantic probes (thin black line), and difference between episodic and semantic probes (thick blue line). The right side of each panel shows a topographic map for the difference wave shown on the left: (A) N2; (B) N400; (C) P3b and LPC.

Figure 6

Grand average ERPs elicited by irrelevants (thin solid lines), probes (thick solid lines) in the semantic (black lines) and episodic (red lines) autobiographical conditions in the first half of trials. ERPs are plotted between 100 and 900 ms (at all scalp recording sites). ERPs are shown negative up and referenced to the average of the left and right mastoids. A diagram with the location of the recording sites is shown on the bottom right.

Figure 7

Grand average ERPs elicited by irrelevants (thin solid lines), probes (thick solid lines) in the semantic (black lines) and episodic (red lines) autobiographical conditions in the second half of trials. ERPs are plotted between 100 and 900 ms (at all scalp recording sites). ERPs are shown negative up and referenced to the average of the left and right mastoids. A diagram with the location of the recording sites is shown on the bottom right.