title: The amodal system for conscious word and picture identification in the absence of a semantic task.
abstract: Previous studies using explicit semantic tasks, such as category or similarity judgments, have revealed considerable neuroanatomical overlap between processing of the meaning of words and pictures. This result may have been influenced by the semantic executive control required by such tasks. We examined the degree of overlap while minimizing semantic executive demands. In a first fMRI experiment (n=28), we titrated word (35.3 ms, SD=9.6) and picture presentation duration (50.7 ms, SD=15.8) such that conscious stimulus identification became a stochastic process, with a 50% chance of success. Subjects had to indicate by key press whether or not they had been able to identify the stimulus. In a second fMRI experiment (n=19), the identification runs were followed by a surprise forced-choice recognition task and events were sorted on the basis of subsequent memory retrieval success rather than a subjective consciousness report. For both words and pictures, when stimulus processing exceeded the conscious identification threshold, the left occipitotemporal sulcus (OTS), intraparietal sulcus, inferior frontal junction, and middle third of the inferior frontal sulcus (IFS) were more active than when subjects had been unable to identify the stimulus. For both words and pictures, activity in two of these regions, IFS and OTS, predicted subsequent memory retrieval success. A Bayesian comparison revealed that the effective connectivity between IFS and the word- or picture-specific systems was mainly mediated via its connections with OTS. The amodal nature of left OTS and IFS involvement in word and picture processing extends to tasks with minimal semantic executive demands.
authors.affiliation: Cognitive Neurology Laboratory, Experimental Neurology Section, K.U. Leuven, Belgium.
authors.forename: Leen
authors.initials: L
authors.lastname: Van Doren
authors.forename: Patrick
authors.initials: P
authors.lastname: Dupont
authors.forename: Sophie
authors.initials: S
authors.lastname: De Grauwe
authors.forename: Ronald
authors.initials: R
authors.lastname: Peeters
authors.forename: Rik
authors.initials: R
authors.lastname: Vandenberghe
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D003243:Consciousness / Q000502:physiology; D003463:Cues; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D011932:Reading; D012660:Semantics; D055815:Young Adult