Anglia Ruskin University

Visual short-term memory and its clinical application in patients with impaired memory functions.

Collaboration between Myopia and Visual Function group, Department of Computing and Technology, Brain and Cognition group, Department of Psychology, Department of Vision and Hearing Sciences.

Professor Shahina Pardhan, Dr Ian van der Linde, Dr Peter Bright, Keisha Notice and Raju Sapkota.

Current activities:

• To investigate how visual short-term memory is influenced by various parameters including central/peripheral visual field and stimulus type.
• To identify factors that influence vision loss in normal ageing and in visual impairment.

Outcomes:
Our researchers have helped resolve the key question of whether visual loss in normal ageing is primarily due to neural or optical processes. Neural effects are largely due to loss of neuronal substrate and impaired conduction of visual information in the visual system and the brain. Optical causes are mostly due to a decrease in pupil size, lenticular absorption and changes in optical aberrations. We show that both optical and neural processes are important, the relative influence of each is governed by the viewing conditions as well as by the specific aspect of the visual function being tested.

Our work on visual short-term memory for unfamiliar objects has shown how this memory is affected when deprived of support from visual long-term memory, and how factors such the position of the image in the scene affects it. We are the first to demonstrate how relatively few (less than 2) unfamiliar, nonverbal stimuli can be held in visual short-term memory compared to the commonly cited 4-6 items for familiar stimuli. We have shown how prior knowledge of the position of the image and whether we use central or peripheral retinal viewing affects visual short-term memory.

Our research on semantic dementia has challenged the widely held position that this is a condition which solely affects the semantic memory system. Over time, other cognitive functions become compromised as the disease spreads laterally and posteriorally in the brain. Our studies of patients with organic amnesia (secondary to herpes simplex encephalitis and alcoholic Korsakoff syndrome) offer a more complex picture of the role of the hippocampi (and the wider medial temporal cortex) in memory storage and forgetting. Functional and structural neuroimaging investigations of visual object processing in normal and brain damaged individuals have provided strong evidence for a hierarchical system in which low level visual features are processed in more posterior occipito-temporal cortex culminating in complex conjunctions of features represented in more anterior regions. This system is thought to provide the neural substrate for fine-grained visual and conceptual level understanding of our environment (and the objects within it).