Scanning, biases, and inhibition to visual stimuli in healthy and right hemisphere lesioned adults

[摘要] This thesis explores right hemisphere involvement in perceptual biases tochimeric faces and posterior right hemisphere involvement in responseinhibition through an examination of the role of eye movements.Studies of patients with focal brain lesions and neuroimaging researchindicate that face processing is predominantly based on right hemispherefunction. Additionally, experiments using chimeric faces, where the left andthe right hand side of the face are different, have shown that observers tend tobias their responses toward the information on the left. A series ofexperiments were conducted using lifelike gender based chimeric faces (Burtand Perrett, 1997) to explore the relationship between eye movements andperceptual biases.A left perceptual bias was observed in experiment 1, in that subjectsbased their gender decision significantly more frequently on the left side of thechimeric faces. Additionally, analysis of the eye movement patterns indicateda strong tendency to first fixate on the left side of the image and subsequentlya relationship between perceptual biases and eye movements.Experiment 2 examined the issue of inversion of such facial stimuli andprovided evidence that the right hemisphere may still be more influential indetermining gender from inverted chimeric stimuli, as a significant leftperceptual bias was demonstrated to these types of stimuli. It is proposedthat the chimeric bias effects found in this experiment argue against the ideathat inversion destroys the right hemisphere superiority for faces.Whilst experiments 1 and 2 provided evidence for right hemispheredominance in the processing of chimeric faces, experiments 3 and 4investigated the influence of eye movements and exposure duration in modulating the bias. Experiment 3 and 4 demonstrate that in younger adultsbut not older adults that a reliable leftward bias can be obtained when stimuliare exposed for brief durations only. However, evidence is provided thatindicates that the perceptual bias is enhanced in the presence of eyemovements. Additionally, experiment 4 shows that the perceptual bias isdemonstrably diminished in older adults, possible mechanisms for this findingare discussed.Experiment 5 reviews evidence related to dysfunction in visual search inpatients with right hemisphere lesions, however what is less well understoodis how well such patients are able to inhibit a response in an otherwise simplesearch task. Experiments 5 and 6 explore oculomotor capture in suchpatients. Patients were asked to search for a colour target amongst distractersand to signal target location with a saccade. On each trial an additionaldistracter was presented which could be either similar or dissimilar to thetarget and appear either with or without a sudden onset. Patients weredemonstrated to have higher oculomotor capture rates by the additionaldistracter, and to be more susceptible to the distracting influence of suddenonsets.Experiment 7 employed an antisaccade task and a fixation task anddemonstrated in the same group of patients further impairments in responseinhibition. In both tasks patients were demonstrated to have significantdifficulty in inhibiting an eye movement to a peripheral distracter (relative toage matched controls). Results of experiments 5-7 indicate that patients withright hemisphere lesions that spare the frontal lobe have demonstrableimpairments in inhibiting responses to suddenly appearing peripheral stimuli,implicating a role for posterior brain structures in this type of inhibition.

[发布机构] University:University of Glasgow;Department:School of Psychology

[关键词] BF Psychology