Abstract thesis; Neurosciences; Autobiographical memory; Visual mental imagery; Eye movements
Our research explores the relationship between eye movements and autobiographical memory in the elderly, comparing them to young subjects. Memories of our personal lives are stored by the autobiographical memory theorized by Conway in 2005. This memory is divided into a semantic component and an episodic component. The semantic component allows us to remember events in our lives without any associated details, such as a dinner out with relatives on our birthday. The episodic component allows us to relive the event with specific details, it allows us to remember the joy we felt when we saw our loved ones at the restaurant, the place and the precise date, and the taste of the food we ate that day.
Several studies have shown that our personal episodic memories are represented to us in the form of visual mental images. A mental image is a representation of perceptual or sensory information generated in the absence of direct perception in the external environment. A study with a person with amnesia specific to old memories showed that recall of his old personal memories was associated with lower visual imagery compared to recall of recent memories (El Haj et al., 2021). Furthermore, lesions in the occipital lobe, a crucial area in the generation of visual images, are associated with impairment of the episodic component of autobiographical memory while the semantic component is preserved.
Moreover, this visual imagery process during the recall of personal memories is also revealed by the existence of specific eye movements. Several studies with young healthy adults have varied the visual mental imagery processes with a “wall fixation” control condition and a “free visual exploration” condition. According to the results, the adults autobiographical memory performance is better when visual exploration is possible than in the fixation condition. The detailed analysis of these eye movements also revealed some specificities. The recall of personal memories is associated with a significantly higher amplitude, duration and number of saccades. Conversely, a lower number of fixations and a reduction in their duration. Interestingly, data collected using an eye-tracking system show a similarity between eye movement patterns played during perception and patterns played during recall.
With advancing age, changes in the brain are known to cause a weakening of autobiographical memory. However, age does not affect the two components of autobiographical memory in the same way. Normal aging is associated with a preservation of the semantic component of autobiographical memory and, conversely, with a deterioration of its episodic component. A study by De Beni et al (2007) was specifically interested in the effects of age on the different processes involved in the generation of visual mental images. They measured three processes : the ability to generate, maintain and modify visual mental images. The authors also varied the typology of these mental images. They asked each participant to generate general, specific, contextual and autobiographical mental images. The results of this study showed that the time required to generate visual mental images was globally higher in the elderly than in the young subjects. Furthermore, for both groups of subjects, the generation of general mental images was shorter than for other types of mental images. However, the generation as well as the maintenance of autobiographical mental images was higher only for the group of elderly subjects. Thus, age is associated with an increase in the time required to generate mental images. Visual mental images are less rich and developed as one ages.
The weakening of eye movements with age is an explanatory factor for this decrease in visual mental imagery. Aging also affects certain physiological processes related to visual exploration. In particular, advancing age is characterized by a significant decrease in the number of saccades (Sparks, 2002). However, aging is also associated with a preservation of ocular fixations. A study by Wynn et al. (2018) investigated eye movement patterns during a visuo-spatial recall task among young and elderly. In this study, arrays of abstract objects were presented in front of a gray background on a screen. The presentation of these objects lasted 2 seconds and then the screen was obscured for 500ms. Afterwards, subjects were allowed to freely explore visually the screen that had returned to gray for a relatively short or long period of time, ranging from 750 ms to 6000 ms. The subjects were then assigned to a recognition task in two modalities : the objects were arranged in the same position; one of the objects was in a different position. In this task, the authors gave subjects 5 seconds to decide whether the array of objects was identical to the one initially presented. The results show that young adults reactivate more of their eye movement patterns and therefore perform better on the recognition task compared to the elderly. Interestingly, when the visual exploration time is “short”, older subjects have a better reactivation of their fixations than younger subjects. Moreover, this reactivation of ocular fixations favors the performance of elderly subjects in the recognition task. The authors suggest that elderly subjects spontaneously use fixation to compensate for their deficit of cognitive resources during the memory task. Conversely, young adults would prefer this fixation mechanism only when their cognitive resources are threatened by the task, when the visual exploration time is “long”. In a task that calls on memory processes, the reactivation of fixations seems to constitute a compensatory mechanism for deficits in older subjects.
Our results only partially confirmed our hypotheses. Our first hypothesis was the following one : we expect to observe a weakening of visual exploration in elderly adults compared to young adults during autobiographical recall. In contradiction with our hypothesis, elderly show a higher number and duration of saccades than young adults during autobiographical recall. Our second hypothesis was : we assume that older adults will have more eye fixations than younger adults during autobiographical recall. This second hypothesis is validated. Moreover, the fixations of elderly adults are also more longer than those of young adults in the autobiographical recall modality.
Further research on the subject is needed to test these hypotheses. From a clinical perspective, this could allow in the future to set up cognitive stimulation or autobiographical memory rehabilitation exercises based on eye movements and ocular fixations.
Elisa Louf, Loïse Mollaret, Rania Ouarzazi
Bibliography
Conway, M. A. (2005). Memory and the self. Journal of Memory and Language, 53(4), 594-628. https://doi.org/10.1016/j.jml.2005.08.005
De Beni, R., Beni, R. D., Pazzaglia, F., & Gardini, S. (2007). The generation and maintenance of visual mental images : Evidence from image type and aging. Brain and Cognition, 63(3), 271-278.
El Haj, M., Lamy, E., Janssen, S. M. J., & Boutoleau-Bretonnière, C. (2021). Amnesia in your pupils : Decreased pupil size during autobiographical retrieval in a case of retrograde amnesia. Neurocase, 27(2), 155-159. https://doi.org/10.1080/13554794.2021.1902539
Sparks, D. L. (2002). The brainstem control of saccadic eye movements. Nature Reviews Neuroscience, 3(12), 952–964. https://doi.org/10.1038/nrn986
Wynn, J. S., Olsen, R. K., Binns, M. A., Buchsbaum, B. R., & Ryan, J. D. (2018). Fixation reinstatement supports visuospatial memory in older adults. Journal of Experimental Psychology. Human Perception and Performance, 44(7), 1119-1127. https://doi.org/10.1037/xhp0000522