The results of a doctoral thesis developed at the Iscte-University Institute of Lisbon demonstrate the interdependence of two memory systems, usually considered independent.
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"There are several memory systems, among which we can highlight semantic memory, dedicated to more abstract and generic representations of facts and concepts (for example, knowing what a chair is); and episodic memory, responsible for contextual and vivid representations (for example, knowing where we had lunch yesterday)," explains researcher Cristiane Souza, of the Center for Psychological Research and Social Intervention (CIS-Iscte) and author of this work. These two types of memory have been considered and studied as independent, but recently there has been an interest in understanding their interdependence, which motivated Cristiane's work.
This work produced seven scientific articles, most of which have already been published in scientific journals. The strategy adopted throughout the research consisted of presenting images of objects, people, or places, evaluating the accuracy of the participants' memory and, in some cases, how vivid those memories were.
In a first line of research, the influence of semantic representations on episodic memories was assessed. Participants saw images of different categories (e.g., "mammals") with typical (dog) and atypical (dolphin) items and responded either about prior semantic knowledge (e.g., "Is this a mammal?"), or focusing on visual perception, independent of previous knowledge ("How complex is the object?"). After a short interval, the participants' memory for the previously presented images was tested. The typical items generated more generic memories. However, the atypical items led to better memory, especially in the categorical learning condition. In other words, the information of the atypicality of the item, because it does not entirely fit into the schematic and abstract memories already stored, also calls for the involvement of the episodic system and is therefore beneficial. The researcher explains that
"Overall, the results of this research indicate that the interaction between the two types of memory seems to be dependent on the type of information being processed and the memory systems required.”
In the same line of research, Cristiane used groups of people with alleged difficulties in episodic memory, namely people with autism spectrum disorders and older adults. The goal was to test, using the same task, whether these difficulties would impair the interaction between the two memory systems. The results show that, compared to healthy young people, the two groups do not show the same benefit from processing atypical items. Notably, the elderly participants used the accumulated abstract knowledge (the categories) to overcome the losses in more detailed retrieval of experiences, that is, episodic memory.
In a second line of research, the influence of episodic representations on semantic memories was assessed. Adult participants, young and older, were asked to name items from semantic classes of proper nouns, such as familiar people and places, and common nouns (chair, apple, scooter), also using neuroimaging techniques (electroencephalography). The results, overall, indicated that the proper noun items, especially the names of people, are more challenging to remember. Again, the elderly created retrieval strategies based on accumulated prior knowledge. Neurophysiological data obtained through brain frequency oscillations (a study currently under peer review) indicated reliance on the episodic memory system in a purely semantic task, particularly for place naming, corroborating the coexistence and interchange between the two memory systems.
In addition to theoretical contributions to models of human memory, the results of this research may help develop psychoeducational strategies and clinical practices in memory assessment and rehabilitation. "There is a need for an earlier, more differential, and comprehensive assessment that includes the various memory systems, especially in the elderly. The detailed knowledge of these processes will allow the development of stimulation strategies to explore the interaction between these memories through compensation mechanisms", concludes Cristiane Souza.
In the scope of this research, a database of images of real objects, the RealPic, was also validated for the Portuguese population, as well as a database of proper nouns for people and places, which may be used in future research. Cristiane Souza’s Ph.D. work was publicly defended in March 2023 and was supervised by Margarida Vaz Garrido (CIS-Iscte), and Joana Costa do Carmo (Lusófona University).