Comparing Scanpaths During Scene Encoding and Recognition: A Multi-Dimensional Approach

Complex stimuli and tasks elicit particular eye movement sequences. Previous research has focused on comparing between these scanpaths, particularly in memory and imagery research where it has been proposed that observers reproduce their eye movements when recognizing or imagining a stimulus. However, it is not clear whether scanpath similarity is related to memory performance and which particular aspects of the eye movements recur. We therefore compared eye movements in a picture memory task, using a recently proposed comparison method, MultiMatch, which quantifies scanpath similarity across multiple dimensions including shape and fixation duration. Scanpaths were more similar when the same participant?s eye movements were compared from two viewings of the same image than between different images or different participants viewing the same image. In addition, fixation durations were similar within a participant and this similarity was associated with memory performance

Shifting Attention within Memory Representations Involves Early Visual Areas

Prior studies have shown that spatial attention modulates early visual cortex retinotopically, resulting in enhanced processing of external perceptual representations. However, it is not clear whether the same visual areas are modulated when attention is focused on, and shifted within a working memory representation. In the current fMRI study participants were asked to memorize an array containing four stimuli. After a delay, participants were presented with a verbal cue instructing them to actively maintain the location of one of the stimuli in working memory. Additionally, on a number of trials a second verbal cue instructed participants to switch attention to the location of another stimulus within the memorized representation. Results of the study showed that changes in the BOLD pattern closely followed the locus of attention within the working memory representation. A decrease in BOLD-activity (V1–V3) was observed at ROIs coding a memory location when participants switched away from this location, whereas an increase was observed when participants switched towards this location. Continuous increased activity was obtained at the memorized location when participants did not switch. This study shows that shifting attention within memory representations activates the earliest parts of visual cortex (including V1) in a retinotopic fashion. We conclude that even in the absence of visual stimulation, early visual areas support shifting of attention within memorized representations, similar to when attention is shifted in the outside world. The relationship between visual working memory and visual mental imagery is discussed in light of the current findings

Source Memory Revealed Through Eye Movements and Pupil Dilation

abstract: Current theoretical debate, crossing the bounds of memory theory and mental imagery, surrounds the role of eye movements in successful encoding and retrieval. Although the eyes have been shown to revisit previously-viewed locations during retrieval, the functional role of these saccades is not known. Understanding the potential role of eye movements may help address classic questions in recognition memory. Specifically, are episodic traces rich and detailed, characterized by a single strength-driven recognition process, or are they better described by two separate processes, one for vague information and one for the retrieval of detail? Three experiments are reported, in which participants encoded audio-visual information while completing controlled patterns of eye movements. By presenting information in four sources (i.e., voices), assessments of specific and partial source memory were measured at retrieval. Across experiments, participants' eye movements at test were manipulated. Experiment 1 allowed free viewing, Experiment 2 required externally-cued fixations to previously-relevant (or irrelevant) screen locations, and Experiment 3 required externally-cued new or familiar oculomotor patterns to multiple screen locations in succession. Although eye movements were spontaneously reinstated when gaze was unconstrained during retrieval (Experiment 1), externally-cueing participants to re-engage in fixations or oculomotor patterns from encoding (Experiments 2 and 3) did not enhance retrieval. Across all experiments, participants' memories were well-described by signal-detection models of memory. Source retrieval was characterized by a continuous process, with evidence that source retrieval occurred following item memory failures, and additional evidence that participants partially recollected source, in the absence of specific item retrieval. Pupillometry provided an unbiased metric by which to compute receiver operating characteristic (ROC) curves, which were consistently curvilinear (but linear in z-space), supporting signal-detection predictions over those from dual-process theories. Implications for theoretical views of memory representations are discussed.Dissertation/ThesisPh.D. Psychology 201

Exploring aspects of memory in healthy ageing and following stroke

Memory is critical for everyday functioning. Remembering an event with rich detail requires the ability to remember the temporal order of occurrences within the event and spatial locations associated with it. But it remains unclear whether it also requires memory for the perspective from which we encoded the event, whether these three aspects of memory are affected following stroke, and which are the key brain regions upon which they rely. These questions are explored in this thesis. In the first study presented here, I examined young and elderly healthy subjects with an autobiographical memory interview and a 2D spatial memory task assessing self-perspective, and found no correlation between performance on these tasks. In the second experimental study, by assessing stroke patients on a 3D spatio-temporal memory task, I found that damage to the right intraparietal sulcus was associated with poorer memory for temporal order. However, voxelwise analyses detected no association between parietal lobe regions and accuracy in the egocentric condition of this task, or between medial temporal lobe regions and accuracy in the allocentric condition, one possible reason being that performance was near ceiling. In the third experimental study, by assessing a considerably larger group of stroke patients on a spatial memory task, I found that, as a group, patients performed worse than healthy controls, and performance was correlated with an activities of daily living scale. A spatial memory network was identified in right (but not left) hemisphere stroke patients. These findings provide evidence that spatial memory impairment is common after stroke, highlight its potential functional relevance, and increase our understanding of which regions are critical for remembering temporal order and spatial information. Furthermore, they suggest a dissociation between the mechanisms underpinning recall of 2D scenes over relatively short intervals versus remembering of real-life events across periods of many years.Open Acces