ABSTRACT
Human vision is sensitive enough to detect a single photon, but the minimal exposure required to extract meaning from stimulation – arguably the visual system’s function – remains unknown. This requirement cannot be characterised in terms of stimulus energy, because the system is differentially sensitive to attributes that are distinguished by stimulus configuration rather than physical amplitude. Observers can extract large amounts of information from brief displays; but for given display durations, certain types of information are discerned more readily than others, suggesting that visual pathways prioritise certain stimulus properties. Determining the minimal exposure durations required for processing various aspects of a visual stimulus can thus shed light on the system’s priorities. Technical limitations have so far prevented measurement of such minima; here, we used a novel technique enabling arbitrarily brief displays with microsecond-level precision to establish the minimal durations required for processing human faces, a stimulus category whose perception is associated with several well-characterised behavioural and neural markers. We found that neural and psychophysical measures converged to reveal a sequence of distinct minimal exposures required for object-level detection (1-2 ms), face-specific processing (3-4 ms), and emotion-specific processing (4-5 ms). Our findings resolve debates about factors that may facilitate processing: Face orientation affected minimal exposure, but emotional expression did not. Awareness emerged with detection; we found no evidence of subliminal perception. These findings critically inform theories of visual processing and awareness by elucidating the information to which the visual system is attuned.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
↵† Shared senior authorship.
Additions: - Extended Data Figures. - Supplementary Figures. - References
