Processing of subliminal visual stimuli outside the focus of attention

Starting date
January 30, 2006
Duration (months)
Neurosciences, Biomedicine and Movement Sciences, Human Sciences
Managers or local contacts
Berlucchi Giovanni
Consciousness , Attention , Inhibition of Return , Visually guided behavior , Reaction times (RTS)

The relationships between consciousness and attention in goal directed behavior are relevant to psychology as well as to physiology. It is commonly thought that
attention is an obligatory requirement for complex behaviors that occur outside of consciousness. Recently the validity of this notion has been questioned. The aim of the present research project is to utilize a well known experimental paradigm, known as inhibition of return (Posner, Rafal, Choate e Vaughan, 1985), in order to examine possible facilitatory and inhibitory behavioral effects of weak visual stimuli that are unable to access consciousness as well as to engage attention. In
particular, the main aims of the project are: 1) to show that visual stimuli subliminal for consciousness can be processed without attention in order to emit relatively complex goal directed behaviors; and 2) to propose a revision of a currently popular model of the automatic orienting of visuospatial attention. The orienting of visual attention can occur under voluntary (or endogenous or top-down) control, indipendent of the presence or absence of external stimuli, or under the exogenous(or automatic or bottom-up) guidance of external stimuli. Here the exogenous orienting of visuospatial attention will be studied accordino to a paradigm whereby the presumed effects of attention are measured as changes in reaction time to lateralized targets preceded by similarly lateralized cues. The novelty of the approach lies in the use of cues with such a low luminance that they can neither reach consciousness nor attract attention. Subliminal visual inputs can facilitate or inhibit motor outputs, and inhibition is especially useful for suppressing prepotent response tendencies that are in conflict with the present voluntary motor goal. The expected results can reveal such influence of subliminal stimuli, as well as provide information useful to confirm the present attentional explanation of the inhibition-of-return phenomenon, or to correct it by pointing to the importance of sensory rather than attentional mechanisms in its origin. If, as suggested by preliminary results, the subliminal cues will prove apt to modulate the time of voluntary reactions to subsequent visible targets, the conclusion will be reached that behaviors more complex than reflexes can be influenced or driven by visual stimuli that are neither seen nor attended. Further, if the inhibitory effects of the cues will prove independent of any previous facilitation, it will be possible to confute the present influential attentional interpretation of inhibition of return phenomenon by attributing a major weight to sensory mechanisms in the generation of the phenomenon. Finally, the expected results can lend themselves to further investigations on the relationships between attention and ocular movements, and their neural bases may be studied with electrophysiological and neuroimaging methods.


Ministero dell'Istruzione dell'Università e della Ricerca
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