This thesis investigates the relationship between eye movements, memory and thinking in five studies based on eye tracking experiments. The studies draw on the human ability to spatially index multimodal events as demonstrated by people’s gaze reverting back to emptied spatial locations when retrieving information that was associated with this location during a preceding encoding phase – the so called “looking-at-nothing” phenomenon. The first part of this thesis aimed at gaining a better understanding of the relationship between eye movements and memory in relation to verbal information. The second part of this thesis investigated what could be learned about the memory processes involved in reasoning and decision-making by studying eye movements to blank spaces.
The first study presented in this thesis clarified the role of eye movements for the retrieval of verbal information from memory. More precisely, it questioned if eye movements to nothing are functionally related to memory retrieval for verbal information, i.e. auditorily presented linguistic information. Eye movements were analyzed following correct and incorrect retrievals of previously presented auditory statements concerning artificial places that were probed during a subsequent retrieval phase. Additionally, eye movements were manipulated as the independent variable with the aid of a spatial cue that either guided the eyes towards or away from associated spatial locations. Using verbal materials elicited eye movements to associated but emptied spatial locations, thereby replicating previous findings on eye movements to nothing. This behaviour was more pronounced for correct in comparison to incorrect retrievals. Retrieval performance was higher when the eyes were guided towards in comparison to being guided away from associated spatial locations. In sum, eye movements play a functional role for the retrieval of verbal materials.
The second study tested if the looking-at-nothing behaviour can also diminish; for example, does its effect diminish if people gain enough practice in a retrieval task? The same paradigm was employed as in the first study. Participants listened to four different sentences. Each sentence was associated with one of four areas on the screen and was presented 12 times. After every presentation, participants heard a statement probing one sentence, while the computer screen remained blank. More fixations were found to be located in areas associated with the probed sentence than in other locations. Moreover, the more trials participants completed, the less frequently they exhibited the looking-at-nothing behaviour. Looking-at-nothing behaviour can in this way be seen to indeed diminish when knowledge becomes strongly represented in memory.
In the third and fourth study eye movements were utilized as a tool to investigate memory search during rule- versus similarity-based decision-making. In both studies participants first memorized multiple pieces of information relating to job candidates (exemplars). In subsequent test trials they judged the suitability of new candidates that varied in their similarity to the previously learned exemplars. Results showed that when using similarity, but not when using a rule, participants fixated longer on the previous location of exemplars that were similar to the new candidates than on the location of dissimilar exemplars. This suggests that people using similarity retrieve previously learned exemplars, whereas people using a rule do not.
Eye movements were used yet again as a tool in the fifth study. On this occasion, eye movements were investigated during memory-based diagnostic reasoning. The study tested the effects of symptom order and diversity with symptom sequences that supported two or three contending hypotheses, and which were ambiguous throughout the symptom sequence. Participants first learned information about causes and symptoms presented in spatial frames. Gaze allocation on emptied spatial frames during symptom processing and during the diagnostic response reflected the subjective status of hypotheses held in memory and the preferred interpretation of ambiguous symptoms. Gaze data showed how the diagnostic decision develops and revealed instances of hypothesis change and biases in symptom processing.
The results of this thesis demonstrate in very different scenarios the tight interplay between eye movements, memory and thinking. They show that eye movements are not automatically directed to spatial locations. Instead, they reflect the dynamic updating of internal, multimodal memory representations. Eye movements can be used as a direct behavioural correlate of memory processes involved in similarity- versus rule-based decision-making, and they reveal rich time-course information about the process of diagnostic reasoning. The results of this thesis are discussed in light of the current theoretical debates on cognitive processes that guide eye movements, memory and thinking. This thesis concludes by outlining a list of recommendations for using eye movements to investigate thinking processes, an outlook for future research and possible applications for the research findings.