Neuropsychology and neuroimaging in diffuse brain damage : a study of visual event perception
The aims of this project were (1) to investigate two forms of event perception: perception of movement and perception of sudden appearance, (2) to develop event perception procedures which could be applied to testing clinical populations, and (3) to relate event perception to abnormalities shown by neuroimaging. In addition issues relevant to each of the particular clinical populations involved were addressed. Event perception tasks used stimuli consisting of a background of randomly selected dots of light. In one task a dot was added to the display (appearance), in the other a dot started to move (movement onset). Four laboratory experiments were conducted examining the ability to detect and locate these events under varying conditions in healthy controls. Results indicated that neuronal coding strategies were different for appearances and movement onset. Laboratory tasks were adapted for clinical application and administered to groups of patients with different neurological conditions. Five studies were conducted to assess sensitivity and specificity of the Event Perception tasks in clinical settings. The groups studied were chronic solvent abusers, detoxified alcoholics, patients suffering from optic neuritis, and patients with traumatic brain injury. Event Perception tasks were found to be differentially sensitive to neurological conditions and showed dissociations and double dissociations both within and between neurological conditions. Relationships with Magnetic Resonance Imaging (MRI) and Single Photon Emission Computed Tomography (SPECT) were investigated in patients with head injury. Patterns of brain damage differed significantly for patients with impaired performance on the movement task. It is concluded that Event Perception tasks are of value in the assessment of neurological patients: They allow assessment of functions which are not usually evaluated in neuropsychological examinations, facilitate detection of subtle deficits and deficits which may present at an early stage, and offer greater specificity and sensitivity than many traditional neuropsychological test procedures. Event Perception tasks are easy to administer and do not suffer from training effects on repeated administration to the same degree as many traditional measures. It is also argued that tests with a theoretical basis are better suited to clinical research in neuropsychology than many traditional tasks because they potentially allow a more precise explanation and assessment of the abnormal processes under investigation.