Postersession 1
Poster #: 49
Topic: Diagnostics and inter-individual differences
Wednesday, Sep 9, 2015
1st floor

Objective and rapid quantification of high-level visual impairment with fast periodic oddball stimulation in acquired prosopagnosia

Joan Liu-Shuang1, Katrien Torfs, & Bruno Rossion

1Face Categorization Lab, University of Louvain, Louvain-la-Neuve, Belgium

Perceptual deficits are common in many neurological conditions, but their assessment can be hindered by many unrelated factors (e.g. attention, comprehension, motor impairments…). Hence, a method allowing for an objective, sensitive, and efficient quantification of perception would be highly valuable. In the recently developed fast periodic oddball paradigm, base stimuli appear at a fixed rate (F Hz) with oddball stimuli, differing on a dimension of interest, inserted at regular intervals (every nth stimulus, or F/n Hz; Liu-Shuang et al., 2014, Neuropsychologia). Periodic EEG responses at the F/n Hz oddball frequency and harmonics (2F/n Hz, 3F/n Hz…) reflect the perceived mismatch between base and oddball stimuli. We tested this approach with PS, a well-described brain-damaged patient impaired at face individualisation. PS was first presented with sequences of base “object” stimuli at 6 Hz with periodically interleaved oddball “face” stimuli at 1.2 Hz (every 5th stimulus). In line with her preserved ability to detect faces, PS showed periodic oddball EEG responses within normal range. However, when “different” oddball face identities (B, C…) were inserted in sequences containing a repeated “same” base face identity (A; sequence structure: AAAABAAAACAA…, Liu-Shuang et al., 2014), significant oddball responses were found in all control (young & age-matched) participants but were absent for patient PS. These observations were obtained within 8-12 min of recording. Overall, our findings underline the value of the fast periodic oddball paradigm as a diagnostic tool for rapid and objective characterisation of visual discrimination in neuropsychology.