Investigating the functional roles of occipital face area and lateral occipital cortex with transcranial magnetic stimulation

Silvia Bona

Research output: ThesisDoctoral Thesis

Abstract

This thesis investigates the causal role of two extra-striate visual regions, the lateral occipital (LO) cortex and the occipital face area (OFA), in certain visual processes. Firstly, I examined whether these areas are causally implicated in the perception of bilateral visual symmetry. Despite the ubiquitous presence of this feature in the external world, the neural basis underlying its detection is not fully known.

In Studies I and II,this issue was explored by disrupting the activity of LO and OFA with fMRI-guided transcranial magnetic stimulation (TMS) while participants discriminated between symmetric and nonsymmetric dot configurations and between perfectly symmetric and normal (i.e. somewhat non symmetric) faces. The results showed that rightOFA plays a causal role in detection of symmetry in both configurations of dots and faces whereas LO exclusively in the former, with the rightLO showing greater involvement relative to the homologous region in the left hemisphere.

As symmetry is extracted in a holistic manner (i.e. through a parallel global analysis of the stimulusrather than via a serial point-by-point comparisonof the local elements), Study III examined whether rightOFA is involved, more generally, in visual detection based on holistic encoding and, if so, whether its role is restricted to faces or extends also to non-face stimuli. To examine this issue, rightOFA and rightLO were stimulated with fMRI-guided TMS meanwhile participants were asked to detect Mooney faces and non-face images, a class of stimuli which are known to be perceived through holistic processes. The results showed that rightOFA is causally involved in detection of both Mooney faces and objects.

Taken together, this thesis sheds new light on the functions of LO and OFA in visual perception. Firstly, it demonstrates that both of these regions are causally involved in holistic processes, including detection of symmetry. Secondly, it is shownthat OFA s role in holistic processing extends to both face and non-face stimuli, suggesting that this region is not strictly face-selective.
Original languageEnglish
Place of PublicationHelsinki
Publisher
Print ISBNs978-951-51-2402-9
Electronic ISBNs978-951-51-2403-6
Publication statusPublished - 2016
MoE publication typeG5 Doctoral dissertation (article)

Fields of Science

  • 515 Psychology
  • 3112 Neurosciences

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