Rescuing unseen stimuli through alerting retro-cues

Can we rescue a percept that would otherwise be processed non-consciously? While pre-stimulus alerting is known to facilitate conscious access, the effects of retro-cues remain ambiguous due to methodological confounds in existing literature. Specifically, most studies finding retro-cue benefits have relied on spatial features (such as lateralized targets or cues) which confound alerting with spatial selection. Our design addresses this gap by employing central visual targets and non-lateralized auditory cues, thereby isolating the temporal boost of phasic alerting from spatial orienting. Across four experiments, participants reported the presence and orientation of a central Gabor patch presented at near-threshold ([~]50% detection) or higher visibility ([~]75% detection) levels. An auditory alerting tone was presented prior, simultaneously or after the Gabor, at various short and long stimulus onset asynchronies, with both short and long temporal ranges. Results consistently showed that pre-stimulus and simultaneous cues significantly enhanced conscious perception, increasing both seen rates and (in some experiments) perceptual sensitivity. Crucially, the effectiveness of retro-cues strictly depended on stimulus visibility. While retro-cues provided no benefit under near-threshold conditions, an alerting cue presented 200 ms after target offset significantly increased the proportion of seen targets when target visibility was higher. This suggests that a sufficiently robust sensory trace can be retrospectively rescued or promoted into awareness by a late alerting boost, and that pure alerting retro-cues are able to modulate conscious perception even when no spatial features are involved. These findings demonstrate a decoupling of stimulus onset from the timing of conscious access, providing a behavioural platform to arbitrate between competing models of consciousness such as the Global Neuronal Workspace Theory and the phenomenal/access distinction of consciousness.