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Genevieve Quek, Bruno Rossion; Predictability does not generate or modulate category-selective processes in fast periodic visual stimulation streams. Journal of Vision 2016;16(12):723. doi: 10.1167/16.12.723.
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© 2017 Association for Research in Vision and Ophthalmology.
Fast periodic visual stimulation (FPVS) combined with electrophysiological measures of brain activity can fundamentally advance the study of visual perception (Rossion, 2014). Where traditional visual stimulation paradigms use temporally isolated stimuli, this approach presents stimuli at a rapid periodic rate (e.g., 12Hz), providing a continuous flow of information in which each forward/backward-masked stimulus is visible for just a single glance. An electrophysiological response to this stimulation can be found at the exact frequency of presentation (i.e., 12Hz) (Norcia et al., 2015). By embedding critical stimuli at fixed intervals within the sequence (e.g., a face every 5 variable nonface objects), we can observe the response to the critical stimulus category at an objectively defined frequency (e.g., 12Hz/5 = 2.4Hz), and thereby directly quantify the visual system's specific response to this stimulus type. An important issue that we address here is how visual periodicity – which implies predictability - may modulate/generate the response to a critical stimulus. In 18 observers, we compared EEG responses in both the frequency and time-domain for faces appearing periodically or nonperiodically in a fast sequence of natural object images. The robust face-selective response, comprised of four distinct spatio-temporal components over the occipito-temporal cortex, is indistinguishable at the global level for periodic and randomly appearing faces. In a second experiment carried out on 13 observers, following a period of entrainment, rare omissions (10%) of periodic faces do not generate any face-selective response. Thus, overall, we find no evidence of "pre-coding" for faces that are highly temporally predictable: periodicity itself does not generate or drastically alter the profile of face-selective responses – showing that these responses cannot be generated by purely top-down processes.
Meeting abstract presented at VSS 2016
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