Many emotional signals are processed without being consciously perceived.
Non-conscious perception of emotional stimuli is present in both healthy observers, as a consequence of experimental manipulation, and in neurological conditions resulting from focal brain damage, such as hemispatial neglect and cortical blindness.
An emotional stimulus can be perceived non-consciously because it falls outside the focus of attention (a phenomenon referred to as attentional unawareness) or because its sensory analysis is hampered (a phenomenon referred to as sensory unawareness). Although both phenomena render the observer unaware of the stimulus, they involve different neural processes.
Non-conscious perception of emotional stimuli involves a neural system that is composed of subcortical structures, such as the superior colliculus, the visual pulvinar and the amygdala. This neural system receives visual information directly from the retina — thus bypassing the visual cortex — and has an old evolutionary origin, being present in other species like birds, rats and monkeys.
The function of this subcortical system is to provide a rapid, but coarse, analysis of the visual stimuli in order to provide reflex-like responses to emotional signals in the environment. Neurophysiological changes and expressive reactions associated with non-conscious perception of emotional stimuli are consistently more rapid and more intense than responses associated with conscious perception of the same stimuli.
The subcortical system for emotion processing influences cortical activity in several direct and indirect ways. The extent of this cortico–subcortical integration is a crucial factor in affecting visual awareness.
Many emotional stimuli are processed without being consciously perceived. Recent evidence indicates that subcortical structures have a substantial role in this processing. These structures are part of a phylogenetically ancient pathway that has specific functional properties and that interacts with cortical processes. There is now increasing evidence that non-consciously perceived emotional stimuli induce distinct neurophysiological changes and influence behaviour towards the consciously perceived world. Understanding the neural bases of the non-conscious perception of emotional signals will clarify the phylogenetic continuity of emotion systems across species and the integration of cortical and subcortical activity in the human brain.
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We gratefully acknowledge valuable comments from P. Whalen and two anonymous referees. M.T. was supported by a Veni grant (451–07-032) from the Netherlands Organization for Scientific Research (NWO) and also partly supported by the Fondazione Carlo Molo, Turin, Italy and by a Bando Scienze Umane e Sociali 2008 grant from the Regione Piemonte, Italy, for the project Grammatica Invisibile delle Relazioni Sociali (GIRS) (grant number 4). B.d.G. was supported by an Future and Emerging Technologies (FET) Open Scheme grant (ICT-2009-C) from the European Union for the Emotional Interaction Grounded in Realistic Context (also known as TANGO) Project (249858) and by a Lagrange Fellow visiting professorship to the University of Torino, Turin, Italy funded by the Cassa di Risparmio di Torino (CRT) Foundation.
The authors declare no competing financial interests.
- Magnocellular pathway
A system of visually responsive neurons that originates from retinal ganglion cells with large receptive fields and that is characterized by low spatial resolution and rapid transmission of nerve impulses.
- Parvocellular pathway
A system of visually responsive neurons that originates from retinal ganglion cells with small receptive fields and that is characterized by high spatial resolution and slow transmission of nerve impulses.
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Tamietto, M., de Gelder, B. Neural bases of the non-conscious perception of emotional signals. Nat Rev Neurosci 11, 697–709 (2010). https://doi.org/10.1038/nrn2889
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