title: Interpreting local visual features as a global shape requires awareness.
abstract: How the brain constructs a coherent representation of the environment from noisy visual input remains poorly understood. Here, we explored whether awareness of the stimulus plays a role in the integration of local features into a representation of global shape. Participants were primed with a shape defined either by position or orientation cues, and performed a shape-discrimination task on a subsequently presented probe shape. Crucially, the probe could either be defined by the same or different cues as the prime, which allowed us to distinguish the effect of priming by local features and global shape. We found a robust priming benefit for visible primes, with response times being faster when the probe and prime were the same shape, regardless of the defining cue. However, rendering the prime invisible uncovered a dissociation: position-defined primes produced behavioural benefit only for probes of the same cue type. Surprisingly, orientation-defined primes afforded an enhancement only for probes of the opposite cue. In further experiments, we showed that the effect of priming was confined to retinotopic coordinates and that there was no priming effect by invisible orientation cues in an orientation-discrimination task. This explains the absence of priming by the same cue in our shape-discrimination task. In summary, our findings show that while in the absence of awareness orientation signals can recruit retinotopic circuits (e.g. intrinsic lateral connections), conscious processing is necessary to interpret local features as global shape.
authors.affiliation: UCL Institute of Cognitive Neuroscience, 17 Queen Square, London WC1N 3AR, UK. s.schwarzkopf@fil.ion.ucl.ac.uk
authors.forename: D Samuel
authors.initials: DS
authors.lastname: Schwarzkopf
authors.forename: Geraint
authors.initials: G
authors.lastname: Rees
mesh_terms: D001364:Awareness; D003463:Cues; D006801:Humans; D010775:Photic Stimulation; D011930:Reaction Time; D014796:Visual Perception