Episodic Memory and Conscious Experience

The project investigates the dependence of episodic memory on direct experience of the remembered event. We have an episodic memory of an event in the past (e.g., a friend`s birthday party) if we can say: "I remember that party," in distinction to mere knowledge of the past: "I know who was at the party, and what happened there", as dry facts without having a real memory of it which I can re-experience. This difference can be explicated in terms of mental representation: Knowledge of the past just requires a mental representation of what happened in the past, while an episodic memory of the past requires an additional representation of our experience of that event. Consequently we can only have true episodic memories of events, which we directly experienced (we were at the party) and not events of which we have learned indirectly through testimony (our friend told us about what happened at the party). In the project we use very simple events: putting cards into a box and trying to remember the picture on the cards. In a direct experience condition the person sees the picture on the card. In an indirect knowledge condition the person can`t see the pictures on the cards but later sees a video of the pictures on each card. Now the person knows which picture she put inside the box, e.g., a flower; yet she can`t claim that she "remembers putting the card with the flower into the box." This distinction has previously been investigated only in direct experience conditions but asking people to make a "know-remember judgement" (R-K) for each item. Also different brain activity (electrophysiological correlates) has been found for these types of judgments. We now investigate the validity of R-K judgments by testing whether R-judgements are given only after direct experience and not in the indirect knowledge condition, and whether the electrophysiological correlates also obey this constraint. A third part of the project investigates whether episodic memories emerge in development around 4 to 6 years when children acquire the conceptual means to distinguish between direct experience and indirect knowledge.

According to Tulving (1985), there are two means of accessing the past: remembering (episodic memory) and knowing (semantic memory). Remembering is associated with mental time travel into the past and the possibility of re-experiencing past events, whereas knowing stands for the simple knowledge of past events without this possibility. The common way of testing the difference between episodic vs. semantic memory in adult participants is the usage of the Remember-Know-Recognition paradigm. Participants in a recognition test of a list of words are asked first whether each word had appeared in the study list. For "old" words they have to judge additionally whether they remember (R-judgments) or merely know that the word was on the list. Episodic memory is commonly attributed to items judged as remembered. Because the terminology of the word remember is not as straightforward as it seems. Remember judgments can either reflect re-experience or mark retrieval effort. To help decide between these possibilities we developed a completely new manipulation. Participants witness an event directly or get to know indirectly what had happened. Obviously there can be no re-experiencing of the event if it has not been experienced in the first place. Hence, any Remember-judgments in the indirect condition give us an estimate of how often participants use "remember" to convey retrieval or encoding effort. Only if the event has been actually experienced can a Remember-judgment reflect the recollective experience of re-experiencing the original event. Therefore the difference between Remember-judgments for directly experienced events minus Remember-judgments for indirectly conveyed events provides an estimate of how many events are being re-experienced. By using this method of difference we could show in various experiments that Remember-judgments were due to re-experience, but only to some degree. We also used this direct-indirect method with preschool children. Our experiments indicate that episodic memory develops in the preschool years. The growth of episodic memory was related to theory of mind development. In particular, episodic memory development seems to be specifically linked to the growing ability to introspect an ongoing experience and interpret it as representing an actual past event. Furthermore, episodic memory was specifically related to children`s ability to make use of mental images as required in mental rotation paradigms.