Studying face individualization through event related potentials and steady state techniques in healthy and prosopagnosic individuals
(2011)
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- Authors
- Supervisors
- Rossion, Bruno
- Abstract
- (en) Discriminating the identity of a person by the facial appearance is a ubiq- uitous facet of daily life supported by a distributed network of brain areas. This neural network has been divided into two distinct subsystems: a core system, which supports the visual analysis of faces, and an extended system, concerned with the construal of person knowledge. It is widely accepted that three main anatomical structures compose the face perception core system: the occipital face area (OFA), the fusiform face area (FFA) and the posterior superior temporal sulcus (STS). However, the temporal activation course of these structures during face perception is not fully understood. Event Related Potential (ERP) studies of prosopagnosic patients can help to clarify this issue. In the first part of the current thesis (Study 1) this approach was adopted to: 1. characterize the electrophysiological profile of a well known case of prosopagnosia (patient PS); 2. determine whether the N170 face effect (the amplitude increase exhib- ited by the N170 component when faces are presented compared to other object categories) and the N170 face inversion effect (amplitude and latency increases of this component in response to inverted faces compared to upright faces) are present in this patient despite exten- sive damages in the territory of the right inferior occipital gyrus that encompasses the territory of the OFA; 3. determine whether the obtained outcome is replicable across tech- niques (i.e., studying Event Related Fields (ERF) by means of mag- netoencephalogram (MEG)). The results demonstrated that: 1. PS electrophysiological profile exhibits differences compared to healthy controls, which might be due to changes in brain volume conductive properties after the lesion; 2. despite these differences, she exhibits an N170 face effect and an N170 face inversion effect similar to that exhibited by healthy controls; 3. all results can be replicated using MEG. While the first result is of usefulness to future EEG/MEG studies of patient PS, the second result helps to clarify the timing of the face selective FFA activations observed in this patient using functional Magnetic Resonance Imaging (fMRI). It also brings support to non-hierarchical models of face perception and sheds light on the debate about the neural sources of the face selective component N170 and its magnetic counterpart, the M170. Motivated by result # 1 obtained in Study 1, the second part of this the- sis, Studies 2 to 4, focused on the introduction of the Steady State Visual Evoked Potentials (SSVEP) technique in the study of face perception in healthy and prosopagnosic individuals. In contrast to ERPs, SSVEPs have a higher signal to noise ratio and can be objectively quantified. As a result, SSVEP measures are less influenced by possible changes to brain volume conductive properties. Study 2 presents an experiment aimed at: 1. demonstrating that the SSVEP sensitivity to facial identity appears despite variations in several dimensions of the stimuli such as face gender, skin color and presence of hair. Study 3 presents another experiment aimed at: 1. determining the range of stimulation frequencies for which the SSVEP sensitivity to facial identity is highest. The results demonstrated that: 1. the sensitivity of the SSVEP to facial identity can be observed despite the modifications introduced to the facial stimuli; 2. those modifications can produce subtle changes in the efficiency of face individualization processes, which can be captured by the SSVEP; 3. the stimulation frequency at which the SSVEP sensitivity to facial identity is highest ranges between 4 and 9.09 Hz (the optimal frequency is 5.88 Hz). These results have important methodological implications for future SSVEP studies of face perception as well as for current theories about the temporal dynamics of brain processes. Going a step further, Study 4 presents two experiments aimed at: 1. demonstrating that the optimal testing conditions identified in Study 2 and 3 can be extrapolated to patient PS. This study demonstrated that indeed, patient PS can be tested under the same conditions as healthy individuals. Additionally, it gives further sup- port to the demonstration that the SSVEP technique is sensitive to changes in the efficiency of face perception processes. Summarizing, this thesis brings further theoretical knowledge about the functional organization of the face perception neuronal network. It also demonstrates that ERPs and especially SSVEPs, are useful measures to study how the brain processes facial identity and provides important method- ological guidelines for future research in this field.
- Affiliations
Citations
Alonso Prieto, E. (2011). Studying face individualization through event related potentials and steady state techniques in healthy and prosopagnosic individuals. https://hdl.handle.net/2078.5/156194