Institute of Clinical Sciences, Imperial College London
Doi
Abstract
This thesis investigated the role of the left ventral occipitotemporal (vOT)
cortex and how damage to this area causes peripheral reading disorders.
Functional magnetic resonance imaging (fMRI) studies in volunteers
demonstrated that the left vOT is activated by written words over numbers
or perceptually-matched baselines, irrespective of the word’s location on the
visual field. Mixed results were observed for the comparison of words versus
false font stimuli. This response profile suggests that the left vOT is
preferentially activated by words or word-like stimuli, due to either: (1)
bottom-up specialisation for processing familiar word-forms; (2) top-down
task-dependent modulation, or (3) a combination of the two. Further studies
are proposed to discriminate between these possibilities.
Thirteen patients with left occipitotemporal damage participated in the
rehabilitation and fMRI studies. The patients were impaired on word, text and
letter reading. A structural analysis showed that damage to the left
occipitotemporal white matter, in the vicinity of the inferior longitudinal
fasciculus, was associated with slow word reading speed. The fMRI study
showed that the patients had reduced activation of the bilateral posterior
superior temporal sulci relative to controls. Activity in this area correlated
with reading speed.
The efficacy of intensive whole-word recognition training was tested.
Immediately after the training, trained words were read faster than
untrained words, but the effects did not persist until the follow-up
assessment. Hence, damage to the left vOT white matter impairs rapid
whole-word recognition and is resistant to rehabilitation.
The final study investigated the role of spatial frequency (SF) in the
lateralisation of vOT function. Lateralisation of high and low SF processing
was demonstrated, concordant with the lateralisation for words and faces to
the left and right vOT respectively. A perceptual basis for the organisation of
vOT cortex might explain why left vOT damage is resistant to treatment