title: The effect of parametric stimulus size variation on individual face discrimination indexed by fast periodic visual stimulation.
abstract: BACKGROUND
  The human brain is frequently exposed to individual faces across a wide range of different apparent sizes, often seen simultaneously (e.g., when facing a crowd). Here we used a sensitive and objective fast periodic visual stimulation approach while recording scalp electroencephalogram (EEG) to test the effect of size variation on neural responses reflecting individual face discrimination.
  
  
  METHODS
  EEG was recorded in ten observers presented with the same face identity at a fixed rate (5.88 Hz, frequency F) and different oddball face identities appearing every five faces (F/5, i.e., 1.18 Hz). Stimulus size was either constant (6.5 × 4 degrees of visual angle) or changed randomly at each stimulation cycle, by 2:1 ratio increasing values from 10% to 80% size variation in four conditions. Absolute stimulus size remained constant across conditions.
  
  
  RESULTS
  The base rate 5.88 Hz EEG response increased with image size variation, particularly over the right occipito-temporal cortex. In contrast, size variation decreased the oddball response marking individual face discrimination over the right occipito-temporal cortex. At constant stimulus size, the F/5 change of identity generated an early (about 100 ms) oddball response reflecting individual face discrimination based on image-based cues. This early component disappeared with a relatively small size variation (i.e., 20%), leaving a robust high-level index of individual face discrimination.
  
  
  CONCLUSIONS
  Stimulus size variation is an important manipulation to isolate the contribution of high-level visual processes to individual face discrimination. Nevertheless, even for relatively small stimuli, high-level individual face discrimination processes in the right occipito-temporal cortex remain sensitive to stimulus size variation.
authors.forename: Milena
authors.initials: M
authors.lastname: Dzhelyova
authors.affiliation: Psychological Sciences Research Institute and Institute of Neuroscience, University of Louvain, Louvain, Belgium. bruno.rossion@uclouvain.be.
authors.forename: Bruno
authors.initials: B
authors.lastname: Rossion
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology*; D004569:Electroencephalography; D005145:Face; D005260:Female; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D055815:Young Adult