A hallmark of human cognition is the ability to rapidly assign meaning to sensory stimuli. In the domain of vision, it is generally thought that this fast object categorization ability is accomplished by a cortical processing hierarchy beginning with selectivity to oriented edges in primary visual cortex (V1), extending along intermediate visual areas V2 and V4, and culminating in lateral occipital and ventral temporal regions that are selective for complex natural objects such as faces, words and cars. These high-level visual areas are then hypothesized to provide input to task-relevant circuits in downstream regions including prefrontal cortex (PFC). The hierarchical architecture of the ventral visual stream and its downstream projections present attractive theoretical properties for cognition, in particular for efficient transfer of learning of trained representations for novel tasks. However, key questions related to the temporal dynamics of information flow in this processing hierarchy remain unanswered. The latencies and direction of information flow involved in visual object categorization are still unclear, and the mechanisms supporting dynamic reorganization of the processing hierarchy are not known. To elucidate answers to these key questions, we performed a series of EEG experiments based on the core cognitive operation of object categorization. We find evidence supporting the proposition that perceptual categorization is accomplished by the brain within a quarter second through a largely feedforward process culminating in frontal areas, followed by later category-selective signals in posterior regions. Observed changes in functional connectivity for stimulus repetition suggest that a plausible neural mechanism underlying behavioral enhancements associated with stimulus repetition are increases in phase locking between relevant nodes of the network processing those stimuli. Finally, we observed functional connectivity between the network node used for a previous task and neural signals of stimulus familiarity, providing evidence that a neural signal indexing stimulus familiarity may be driven by feedback from anterior brain regions. Taken together, these results provide new insights into the temporal dynamics of visual object categorization in the human brain and demonstrate how neural networks are dynamically modified in support of changing behavioral goals.A hallmark of human cognition is the ability to rapidly assign meaning to sensory stimuli.
|Title||:||EEG Investigations of the Temporal Dynamics of Visual Object Categorization in Human Brain|
|Author||:||Clara Andersen Scholl|