Human face processing : recurrent interactions across the visual system
(2023)
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- Authors
- Supervisors
- Goffaux, Valérie
- Abstract
- This thesis examines the role of recurrent processing in the human visual system, with a special emphasis on the perception of complex stimuli, notably faces. It draws inspiration from theories proposing that recurrent processing operates in a coarse-to-fine manner, where initial processing of coarse/low spatial frequencies (LSFs) guides subsequent processing of finer/high spatial frequencies (HSFs). Additionally, the need for recurrent processes increases when stimuli are degraded. The thesis is structured around three primary research questions. The first study (Chapter 2) investigated the role of the primary visual cortex (V1) in coarse-to-fine processing. Leaning on the conception of V1 as an ’active blackboard’ that integrates visual information in a coarse-to-fine manner. The study employed fMRI and applied backward masking over time and of different spatial frequency (SF) ranges in facial stimuli to interrupt LSF or HSF processing. Results showed strong disruptions in LSF processing as a result of early masking, reducing over time, whereas HSF processing was affected more at later stages. These effects were not only observed in V1 but also in ventral, dorsal, and orbitofrontal brain regions. The findings were in line with existing coarse-to-fine processing theories. The second thread of inquiry (Chapter 3) examined the behavioural outcomes of disrupting coarse-to-fine processing. While the results affirmed that later masking proves less disruptive for identity recognition, no effects from the SF manipulation of the mask were detected. This finding suggests the possibility of a transient coarse-to-fine processing window, potentially too brief for observable behavioural responses. The third study (Chapter 4), focussing on the relationship between stimulus degradation and recurrent processing, showed that noisy stimuli necessitate more recurrent processing. In V1/V2, the impact of masking was reduced with time, regardless of the stimulus degradation level, indicating that extended recurrent processes allows for more suppressive feedback from higher-level areas. Moreover, backward masking effects were more prominent with degraded stimuli, which naturally demand increased recurrent processing. Higher-order face-selective regions showed increased responses with prolonged stimulus exposure and clear face stimuli. The latter is in line with the regions’ tendency to respond more robustly to apparent faces. In summary, this research provides insights into the mechanics and role of recurrent processing in perception of complex stimuli. It underscores the function of coarse-to-fine processing in V1 during shaping visual perception and the impact of varying stimulus degradation levels on recurrent processes. By consolidating findings from diverse brain regions and behavioural outcomes, this study enhances the understanding of real-world visual perception mechanisms.
- Affiliations
UCLouvain SSH/IPSY - Psychological Sciences Research Institute
Citations
Schuurmans, J. (2023). Human face processing : recurrent interactions across the visual system. https://hdl.handle.net/2078.5/26579